Conference Agenda

Polymer gels are noncrystalline, disordered, and soft materials, consisting of infinite polymer networks and solvent. About 30 years have passed since small-angle neutron scattering (SANS) technique was applied to structure investigations of polymer gels,¹ which was about 15 years later than its first applications to polymeric systems.² Because of random cross-linking of the gel network, the structure of a gel is inhomogeneous over a wide spatial range from a few nanometers (the mesh size) to submicrons (large clusters). This is one of the reasons why scattering studies on gels started much later. Polymer gels are inherently much complicated systems than other polymeric systems. the gel network has various types of defects, entanglements, and a broad distribution of inter-crosslink chain length. As a result, structure investigations of polymer gels with SANS were far from quantitative level, even though SANS had been contributed to advances in polymer gel science, namely, deformation,³ swelling, polyelectrolytes,⁴ volume phase transition,⁵ etc. Though it was a dream for polymer chemists to fabricate “ideal” polymer networks, consisting of uniform mesh without defects, its realization had been unsuccessful. This lecture presents an overview of the history of fabrication and characterization of inhomogeneity-free polymer gels investigated by SANS, small-angle X-ray scattering, and light scattering.

A homogeneous gel consisting of monodisperse mesh size without negligible defects, named as tetra-PEG gel, was fabricated by cross-end-coupling of tetra-arm poly(ethylene glycol) (tetra-PEG) carrying complementary end groups.⁶ The network homogeneity was confirmed by SANS and by mechanical testing.^7-9 This methodology has brought a paradigm shift in synthesis, physics, and materials science of polymer gels, and various types of gels were prepared, e.g., ion gels,¹⁰ critical cluster gels,¹¹¹²

Owing to the development of gel fabrication, it is now possible to make a tailor-made multi-component polymer network gel with unimodal mesh size, such as 2x4 gels,¹³ and DNA-cross-linked physical gels.¹⁴ This has necessitated advancement of scattering theories for polymer gels. We have developed a scattering theory for multi-component polymer networks based on random phase approximation¹⁵¹⁶ and applied it to structural analyses of DNA-cross-linked physical gels¹⁴ and deuterated/hydrogenous hetero-polymer network gels¹⁷

[1] Baumgartner, A. Picot, C. E., Ed. (1989). Molecular Basis of Polymer Networks. 42 Berlin: Springer.

[2] Ballard, D. G. H. Schelten, J.. Wignall, G. D. (1973). Eur. Polym. J. 9, 965.

[3] Mendes, E. J. Lindner, P. Buzier, M. Boue, F. Bastide, J., (1991). Phys. Rev. Lett. 66, 1595.

[4] Moussaid, A. Schosseler, F. Munch, J. P. Candau, S. J. (1993). J. Phys. II France 3, 573.

[5] Shibayama, M. Tanaka, T. Han, C. C. (1992). J. Chem. Phys. 97, 6829.

[6] Sakai, T. Matsunaga, T. Yamamoto, Y. Ito, C. Yoshida, R. Suzuki, S. (2008). Macromolecules. 41, 5379.

[7] Matsunaga, T. Sakai, T. Akagi, Y. Chung, U. Shibayama, M. (2009). Macromolecules 42, 1344.

[8] Matsunaga, T. Sakai, T. Akagi, Y. Chung, U.. Shibayama, M. (2009). Macromolecules 42, 6245.

[9] Sakai, T. Akagi, Y. Matsunaga, T. Kurakazu, M. Chung, U. Shibayama, M. (2010). Macromolecular Rapid

Communications. 31, 1954.

[10] Asai, H. Fujii, K. Ueki, T. Sakai, T. Chung, U. Watanabe, M. Han, Y. S. Kim, T. H. (2012). Macromolecules, 45,

3902.

[11] Li, X. Hirosawa, K. Sakai, T. Gilbert, E. P. Shibayama, M., (2017). Macromolecules 50, 3655.

[12] Hayashi, K. Okamoto, F. Hoshi, S. Katashima, T. Zujur, D. C.. Li, X. Shibayama, M. Gilbert, E. P. Chung, U. Ohba, S.

Oshika, T. Sakai, T., (2017). Nat. Biomed. Eng. 1, 0044.

[13] Tsuji, Y. Li, X.. Shibayama, M., (2018) Gels, 4, 50.

[14] Li, X. Ohira, M. Naito, M. Shibayama, M. (2020). in preparation.

[15] Ijichi, Y. Hashimoto, T. (1988), Polym. Comm. 29, 135.

[16] Mortensen, K. Borger, A. L. Kirkensgaard, J. J. K. Garvey, C. J. Almdal, K. Dorokhin, A. Huang, Q. Hassager, O.

(2018). Phys. Rev. Lett. 120, 207801.

[17] Ohira, M. Tsuji, Y. Watanabe, N. Morishima, K. Gilbert, E. P. Li, X.. Shibayama, M. (2019). submitted.

Over the past 40 years, the use of group representation theory has transformed the study of phase transitions in crystalline materials. From my own perspective, I will present the history and development of the innovative methods and computational infrastructure that have supported this transformation. Highlights will include (1) the tabulation of irreducible representations for crystallographic space groups and their superspace extensions, (2) the determination of isotropy subgroups, (3) the projection and parameterization of symmetry modes, (4) the tabulation of superspace symmetry groups, (5) and the development of the online ISOTROPY Software Suite, which makes all of these advances and data sources immediately and freely accessible to the international research community.

The ‘Open Science’ model is based on open access to published scientific results and on sharing scientific data according to the FAIR (Findable, Accessible, Interoperable and Re-usable) principles. The importance of archiving raw data underpinning crystallographic research is well appreciated in recent years as demonstrated and emphasized by the report of the IUCr working group Diffraction Data Deposition Working Group (DDDWG) [1] and has now become feasible as the technology of disk storage has advanced enormously [2]. Crystallography as a research community has always been at the forefront of data sharing, firstly with atomic coordinates (derived data) and secondly with processed diffraction data. The next step, archiving of raw data, has the challenge of providing adequate metadata and the need for community agreed checks, similar to the checkCIF approach, to ensure adherence to the FAIR principles. Several generic and specific to crystallography raw data archives are available. IUCr Journals are now encouraging authors to provide a doi for their deposited original raw diffraction data when they submit an article describing a new structure or a new method tested on unpublished diffraction data. The Protein Data Bank (PDB) also asks for the DOI (digital object identifier), when available, for raw data and metadata for raw data during a deposition. Additionally, the Protein Data Bank Japan has set up the X-ray Diffraction Archive XRD-Arc where authors can submit their raw diffraction data corresponding to PDB entries. The current situation with respect to metadata, important for the future (re-)use of raw diffraction data, will be scrutinised in the light of the FAIR principles. A recent notable effort is the HDRMX community has agreed on a Gold Standard specification for high-rate diffraction data [3]. A leap forward in checking the completeness and validity of metadata by a CheckCIF approach will be discussed.

[1] Final report of the DDDWG https://forums.iucr.org/viewtopic.php?f=21&t=396

[2] L.M.J. Kroon-Batenburg, J.R. Helliwell, B. McMahon, T.C. Terwilliger, IUCrJ (2017). 4, 87–99, https://doi.org/10.1107/S2052252516018315

[3] H. J. Bernstein, A. Förster, A. Bhowmick, A. S. Brewster, S. Brockhauser, L. Gelisio, D. R. Hall, F. Leonarski, V. Mariani, G. Santoni, C. Vonrhein and G. Winter, IUCrJ (2020). 7, 784–792, https://doi.org/10.1107/S2052252520008672

TBD

We have previously described FragLites, a library of small molecules that incorporate an anomalous scatterer for ready detection in X-ray crystallographic fragment screening. Here I will describe our findings as we have assessed their the potential of Fraglites for use in phase determination and to map protein structures for interaction hotspots.

Crystal harvesting remains the bottleneck in protein crystallography experiments and is the rate-limiting step for many structure determination, high-throughput screening and femtosecond crystallography studies. Huge progress has been made towards the automation of high-throughput crystallization, even for membrane proteins. Moreover, free electron lasers and fourth generation synchrotrons support extraordinarily rapid rates of data acquisitions and put further pressure on the crystal-harvesting step. Here [1], a simple solution is reported in which crystals can be acoustically harvested from slightly modified MiTeGen In Situ-1 crystallization plates. Acoustic harvesting uses the automated and keyboard driven acoustic droplet ejection (ADE) technology, in which an acoustic pulse ejects each crystal out of its crystallization well, through a short air column and directly onto a micro-mesh. Crystals can be individually harvested or can be serially combined with a chemical library such as a fragment library.

As crystallization plates are used in most automated high-throughput crystallization robots, ejecting crystals directly from their crystallization wells eliminates the laborious and time-consuming manual harvesting of fragile protein crystals. We here made it possible with a very simple modification of the MiTeGen In Situ-1 crystallization plate, that consists in a light sanding of their edge pedestal (Figure 1a). This is enough to make the plate acoustically compatible with the Echo 550 liquid handler (Labcyte Inc.) and would not be needed if the plates were designed with acoustically compatible plastic. An acoustic compatible plate enables multiple acoustic harvests of crystals from different wells, directly to the X-ray diffraction data collection media (micro-meshes), (Figure 1b). Each harvested aliquot can then be combined with distinct chemicals, making combinatorial crystallography an obvious application. Our results demonstrate that acoustic harvesting is not merely a viable and gentle crystal harvesting technique, but it also makes protein crystal harvesting remarkably more efficient.

In recent years, serial crystallography has emerged as promising method for structural studies of integral membrane proteins. The possibility of collecting data from very small crystals at room temperature, with reduced radiation damage, has opened new opportunities to the membrane protein structural biology community. In particular in the field of time-resolved studies. However, one of the technical bottlenecks of the method is the production of large amounts of tiny optimized crystals in mesophases. Here, we present a simple and fast method to prepare hundreds of microliters of high-density microcrystals in lipidic cubic phase (LCP) for serial crystallography including time resolved measurements. This approach not only eliminates the need for large quantities of expensive gas-tight syringes, but also may be used as a high-throughput tool when screening conditions for the growth of high density well-diffracting crystals.

We also demonstrate, with practical examples, that this new approach is of great advantage to fragment drug discovery since it facilitates in situ crystal soaking with minimal disturbance to the crystals in LCP.

Finally, the method is economical and easily implemented in any standard crystallisation laboratory.

Antibiotic resistance is growing to dangerously high levels and poses a serious threat to global public health. The emergence and spread of resistance mechanisms to all antibiotics introduced into the clinic jeopardize the effectiveness of current treatments. Traditionally, antibiotics have been designed to inhibit bacterial viability or impair their growth; these mechanisms induce a strong selection pressure for resistance development. To overcome this problem, an alternate approach is to disarm bacterial virulence without killing them, which potentially reduces selection pressure and delays the emergence of resistance.

In this project, we target the thiol-disulfide oxidoreductase enzyme DsbA which catalyzes disulfide bond formation in the periplasm of Gram-negative bacteria. DsbA facilitates folding of multiple virulent factors and acts as a major regulator of bacterial virulence. Bacteria lacking a functional DsbA display reduced virulence, increased sensitivity to antibiotics and diminished capacity to cause infection in many Gram-negative pathogens [1].

We carried out a fragment screening campaign against Escherichia coli DsbA and identified the first small molecule inhibitors that bind to the catalytic site of DsbA and inhibit DsbA activity in vitro and cell-based assays [2,3,4]. By exploiting an array of biophysical/biochemical tools (NMR, SPR, X-ray crystallography and in vitro assays), we aim to optimize these DsbA inhibitors from fragment hits to high-affinity leads. Herein we report our established drug discovery pipeline and current efforts in developing DsbA inhibitors. The goal of this work is to develop a new generation of antimicrobials with a novel mode of action that could be used alone or in combination with existing drugs to treat multi-drug resistant infections.

Crystallographic fragment screening (CFS) is an established method in academia and the pharmaceutical industry thanks to dedicated workflows established and optimized at several synchrotron sites. Apart from the hit identity, this technique also provides the structural 3D-information of the fragment hits on the protein surface and therefore fosters rational tool compound development and drug discovery.
At Helmholtz-Zentrum Berlin (HZB), a dedicated CFS-workflow is available that enables stream-lined experiments and data analysis [1]. The outcome of such a workflow depends to a large extend on the quality of the fragment library employed. Higher count and chemical diversity of the resulting fragment hits increases the chances for successful design of follow-up compounds. To this end, in collaborative effort with the drug design group at Marburg University, we designed libraries that are highly diverse in terms of their 3D‑pharmacophores and representative for the chemical space of fragments. The resulting F2X‑Universal Library of 1103 compounds and its representative sub-selection of 96 compounds - the F2X‑Entry Screen - are now the libraries of choice for CFS user campaigns at our facility due to their high performance [2]. Validation campaigns and several user campaigns were performed and showed hit rates of usually 15-25%, reaching 30% in exceptional cases. Another advantage of the libraries is their physical presentation as ready-to-use 96-well plates with dried-in compounds which also enables CFS for sensitive crystals without DMSO tolerance.
Apart from the exceptional library, a dedicated tool was developed at HZB to ease handling of large amounts of crystals - the EasyAccess Frame [3]. By supplying the users with such and other tools, as well as the dried-in libraries we can provide CFS campaigns as “fragment screening to go”, i.e., campaigns can be conducted inside our facility or in the user’s home laboratory. Furthermore, the robot assisted, and remotely controllable beamlines BL 14.1 and BL 14.2 are a key part of the HZB workflow and deliver high-quality diffraction data. Subsequently, processing of the data up to the identification of even weakly bound fragments is highly automated and provided via FragMAXapp, a user friendly, web-based tool developed in collaboration with the FragMAX facility at MAX IV [4]. Several CFS campaigns have been conducted successfully using the described workflow at HZB. As part of the EU-funded iNEXT Discovery project, application for access to the facility is straightforward and convenient for users from academia and industry.

[1] Wollenhaupt, J., Barthel, T., Lima, G.M.A., Metz, A., Wallacher, D., Jagudin, E., Huschmann, F.U., Hauß, T., Feiler, C.G., Gerlach, M., Hellmig, H., Förster, R., Steffien, M., Heine, A., Klebe, G., Mueller, U. & Weiss, M.S. (2021). J. Vis. Exp. 169, e62208
[2] Wollenhaupt, J., Metz, A., Barthel, T., Lima, G.M.A., Heine, A., Mueller, U., Klebe, G. & Weiss, M.S. (2020). Structure. 28, 694.
[3] Barthel, T., Huschmann, F.U., Wallacher, D., Feiler, C.G., Klebe, G., Weiss, M.S. & Wollenhaupt, J., (2021). J. Appl. Cryst. 54, 376.
[4] Lima, G.M.A., Jagudin, E., Talibov, V.O., Benz, L.S., Costantino, M., Barthel, T., Wollenhaupt, J., Weiss, M.S. & Mueller, U. (2021). Acta Cryst. D. accepted.

Organic crystal structures, solved and refined from powder data, may be fully wrong, even if they are chemically sensible and give a good fit to the powder patterns.

Two examples are shown.

In both cases, the atomic positions and the molecular packing were completely wrong.

Example 1:

The crystal structure of the commercial organic hydrazone Pigment Red 52:1, Ca²⁺(C₁₈H₁₁ClN₂O₆S)^2-*H₂O was determined from powder data in the usual way by indexing, structure solution by real-space methods, and Rietveld refinement. The resulting structure was chemically sensible and gave a good fit to the powder data. By chance, a single-crystal of poor quality was obtained, and the correct structure was determined by a combination of single-crystal structure analysis and Rietveld refinement. The structure initially determined from powder data turned out to be completely wrong. The correct and the wrong structures differ in the position and coordination of the Ca²⁺ ions, as well as the position and mutual arrangement of the anions (see Figure).

Example 2:

The crystal structure of 4,11-difluoroquinacridone, C₂₀H₁₀F₂N₂O₂, was solved from unindexed powder data by a global fit of millions of random structures to the powder pattern using the FIDEL method [1,2], which uses cross-correlation functions for the comparison of experimental and simulated powder patterns. The structures were subsequently refined by the Rietveld method. Four completely different structures (different space groups, different molecular packings, different H bond topolgies) were obtained. All four structures were chemically sensible, had a good fit to the powder data, gave a good fit to the pair-distribution function and good lattice energies. One is correct, the other were wrong [3].

[1] S. Habermehl, P. Mörschel, P. Eisenbrandt, S.M. Hammer, M.U. Schmidt, Acta Cryst. B70 (2014), 347-359.

[2] S. Habermehl, C. Schlesinger, M.U. Schmidt, in preparation.

[3] C. Schlesinger, A. Fitterer, C. Buchsbaum, S. Habermehl, M.U. Schmidt, in preparation.

Next generation materials of nearly every kind rely on chemical, electronic, and/or magnetic heterogeneity for creating, harnessing, and controlling functionality. Exploration of these phenomena increasingly involve multiple length-scale scattering probes and require sophisticated modeling approaches to characterize and understand them. Total scattering methods, including both Bragg and diffuse scattering signals, are providing key insights into how long-range, nanoscale, and local atomic structure motifs differ in materials and cooperate to deliver their unique properties. The nuances of capturing nanoscale heterogeneities, including correlated defects, chemical short-range order, and stacking fault distributions, represent a modern frontier in the field of crystallography. We will explore this theme through detailed investigation of two distinct materials classes. First, we will present the operando study of nanostructured fluorite catalysts. We will specifically follow the nature of correlated oxygen vacancies at elevated temperatures, including their behavior under acid-gas exposure. Second, we will present structure-property characteristics of new pyrochlore and perovskite high entropy oxides (HEOs). HEOs exhibit a single-phase crystal structure containing five or more different metal cations of the same amount on single crystallographic lattice sites; their compositional and configurational disorder and associated structural diversity offer great potential for unique material characteristics. We will highlight contemporary challenges and opportunities in the quest to extract crystal structure models from experimental data with the detail needed to guide and validate solid state theories, and design new and improved functional materials.

Most of the natural or fabricated fibrous materials exhibit multiscale structures, which critically influence their mechanical, optical, and electronic properties. Therefore, knowing the structure is important to steer the properties or design novel fibrous material. This requires multiscale structural characterization to enrich their structure-properties relationship. State-of-the-art small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques are extremely powerful to characterize such materials from the nanometer to the Ångström scale [1].

In this contribution, multiscale structural insights of different fibrous materials such as electrospun nanofiber scaffolds [1], thermal protective fabrics [2], and fibrous biocomposite tissues would be presented with emphasis on their structure-properties relationship primarily using SAXS and WAXD methods. The schematic of the multiscale structure of the electrospun nanofiber scaffolds is shown in figure 1 as an example. Furthermore, the application of gained structural knowledge to steer the properties of polymeric nanofibers and the design of novel humid responsive nanofibrous scaffolds would be discussed.

[1] A.K. Maurya, L. Weidenbacher, F. Spano, G. Fortunato, R.M. Rossi, M. Frenz, A. Dommann, A. Neels, A. Sadeghpour, Structural insights into semicrystalline states of electrospun nanofibers: a multiscale analytical approach, Nanoscale 11(15) (2019) 7176-7187.

[2] A.K. Maurya, S. Mandal, D.E. Wheeldon, J. Schoeller, M. Schmid, S. Annaheim, M. Camenzind, G. Fortunato, A. Dommann, A. Neels, A. Sadeghpour, R.M. Rossi, Effect of radiant heat exposure on structure and mechanical properties of thermal protective fabrics, Polymer 222 (2021) 123634.

Orientation and conformation in nanoscale amorphous regions often dominate the properties of soft materials such as composites and semicrystalline polymers. Robust correlations between between structure in these amorphous regions and important properties are not well developed due to a lack of measurements with high spatial resolution and a sensitivity to molecular orientation. I will describe our approach to solving this issue using polarized resonant soft X-ray scattering (P-RSoXS), which combines principles of soft X-ray spectroscopy, small-angle scattering, real-space imaging, and molecular simulation to produce a molecular scale structure measurement for soft materials and complex fluids.

Because P-RSoXS is relatively new to the scattering community, I will first cover the basics of the measurement. The fundamental principles of P-RSoXS and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, the spectroscopic basis for P-RSoXS, will be reviewed. The P-RSoXS experiment will be discussed including sample preparation and constraints, which differ considerably from analogous scattering techniques such as conventional small-angle X-ray scattering (SAXS) and small angle neutron scattering (SANS). I will also cover approaches for including gases or liquids in the experiment, and describe available measurement facilities. Data collection best practices will be reviewed.

I will then describe polarized resonant soft X-ray scattering (P-RSoXS) measurements of model systems including polymer-grafted nanoparticles. Analysis will focus on quantitative extraction of orientation details from nanoscale glassy regions. This work is now accelerated by a powerful analysis framework using parallel computation across graphics processing units (GPUs) for the forward-simulation of P-RSoXS patterns. In polymer-grafted nanoparticles, we can apply this framework to fit quantitative and detailed descriptions of amorphous chain orientation with ≈ 2 nm resolution.

Characterising the supramolecular organisation of macromolecules in the presence of varying degrees of disorder remains one of the challenges of structural research. Discotic liquid crystals (DLCs) are an ideal model system for understanding the role of disorder on multiple length scales. Consisting of rigid aromatic cores with flexible alkyl fringes, they can be considered as one-dimensional fluids along the stacking direction and they have attracted attention as molecular wires in organic electronic components and photovoltaic devices [1].

With its roots in single-particle imaging, fluctuation x-ray scattering (FXS) [2] is a method that breaks free of the requirement for periodic order. However, the interpretation of FXS data has been limited by difficulties in analysing intensity correlations in reciprocal space [3]. Recent work has shown that these correlations can be translated into a three-and four-body distribution in real space called the pair-angle distribution function (PADF) – an extension of the familiar pair distribution function into a three-dimensional volume [4]. The analytical power of this technique has already been demonstrated in studies of disordered porous carbons and self-assembled lipid phases [5,6].

Here we report on the investigation of order-disorder transitions in liquid crystal materials utilising the PADF technique and the development of facilities for FXS measurements at the Australian Synchrotron

X-Ray Free Electron Lasers provide a means of conducting crystallography experiments with remarkable time and spatial resolution. These methods can directly recover the electron density of materials. However, there are stringent requirements such as crystal size, number density per exposure, and the crystal order which are required for reconstruction. Membrane proteins, which do not readily crystallise or meet these requirements [1], are particularly interesting to study as they comprise up to 50% of drug targets [2], but less than 10% of the protein structures in the Protein Data Bank [3].

The Pair Angle Distribution Function (PADF) describes the three and four body correlations of the electron density in a sample, and can be recovered from X-ray cross-correlation analysis (XCCA) [4]. Although PADF analysis does not recover the electron density directly, it still contains significant information about the local three dimensional structure of the material. PADF analysis also has the potential to relax the stringent crystal requirements of current single crystal experiments.

We discuss the sensitivity of the PADF to different protein structures [5], and the correlations generated at different length scales; from atomic bonding to tertiary structure. Our aim is to further develop PADF analysis to recover crystal structure factors using X-ray cross-correlation analysis.

[1] Johansson, L.C.; Arnlund, D.; White, T.A.; Katona, G.; DePonte, D.P.; Weierstall, U.; Doak, R.B.; 
Shoeman, R.L.; Lomb, L.; Malmerberg, E.; et al. Lipidic phase membrane protein serial femtosecond 
crystallography. Nat. Methods 2012, 9, 263–265.

[2] Cournia, Z.; Allen, T.W.; Andricioaei, I.; Antonny, B.; Baum, D.; Brannigan, G.; Buchete, N.V.; Deckman, J.T.; Delemotte, L.; del Val, C.; et al. Membrane protein structure, function, and dynamics: A perspective from experiments and theory. J. Membr. Biol. 2015, 248, 611–640.


[3] Berman, H.M.; Battistuz, T.; Bhat, T.N.; Bluhm, W.F.; Bourne, P.E.; Burkhardt, K.; Feng, Z.; Gilliland, G.L.; Iype, L.; Jain, S.; et al. The Protein Data Bank. Acta Crystallogr. Sect. D Biol. Crystallogr. 2002, 58, 899–907.

[4] Martin, A.V. Orientational order of liquids and glasses via fluctuation diffraction. IUCrJ 2017, 4, 24–36.

[5] Adams, Patrick, et al. "The Sensitivity of the Pair-Angle Distribution Function to Protein Structure." Crystals 10.9 (2020): 724.


Polymer crystallization, particularly near the glass transition, exhibits strong nonlinearities and prolonged metastability that enable fabrication of devices with complex hierarchal structure from nm to mm. A fascinating example arises in the production of bioresorbable scaffolds (BRS) from poly(L-lactide) (PLLA), in which a sequence of processes (extrusion, stretch-blow molding and crimping) create diverse semicrystalline morphologies, side-by-side within a span of a hundred microns (Figure 1). To discover how these structures form, we need to examine transient structure under conditions that mimic manufacturing processes. An apparatus that enables scattering measurements during the stretch-blow molding step, called “tube expansion” imposes a nearly constant-width elongation as it converts an extruded “preform” into an “expanded tube”.

To increase the range of accessible properties of PLLA-based BRS, we use this apparatus to examine inorganic nanotubes as potential reinforcing agents that also enhance radiopacity, relevant to clinical applications. Understanding how their microstructure develops during processing is relevant to increasing strength to enable thinner devices and improving radiopacity to enable imaging during implantation. Consistent with the premise of this MS, in-situ X-ray scattering reveals unanticipated phenomena in the transient microstructure of PLLA/WS₂NTs nanocomposites during “tube expansion” (Figure 2).

Surprisingly, the WS₂NT orientation hardly changes from that produced during extrusion of the preform (z-dir., defined Fig. 1A), despite significant strain in the transverse direction (at inner diameter, 500% strain in q-dir.). Although WS₂NTs promote PLLA nucleation, the NTs do not modify the orientation of crystallization (c-axis along q, just as observed in tube expansion of neat PLLA). The striking independence of the orientations of the NT and polymer crystals stems may arise from the favorable interaction between PLLA and WS₂NTs: facile and stable dispersion of WS₂NTs in PLLA enables strong NT orientation in shear (extrusion); NT that are orthogonal to the stretching direction do not reorient; remaining orthogonal to decouples WS₂NT orientation from that of PLLA crystals. Future directions include evaluating cross-reinforcement of the mutually orthogonal NT and PLLA crystals. Based on the surprising effects we have found, further discoveries likely lie ahead in the effects of WS₂NT on morphology development during crimping.

Polymeric nanoparticles are used in many fields, e.g. for drug delivery. Poly(N-isopropylacrylamide) in aqueous solution forms nanoparticles (“mesoglobules”) above its cloud point. The coexistence line of this system in the temperature-pressure frame is an ellipse with a maximum at ~60 MPa and 35 °C [1]. We investigate the formation and growth of mesoglobules as well as their disintegration after rapid pressure jumps across the coexistence line, both at low (below 20 MPa) and high pressures (above 101 MPa). Time-resolved small-angle neutron scattering at instrument D11 (ILL Grenoble) gives structural information on a large range of length scales and in a time range from 50 ms to ~1650 s after the jump [2,3].

Mesoglobule formation is found to be vastly different in the low- and the high-pressure regime. In the low-pressure regime, we find that, initially, growth of the mesoglobules proceeds via diffusion-limited coalescence, but this process is later slowed down by the appearance of a dense and rigid shell from dehydrated polymers. The deeper the target pressure in the two-phase region, i.e. the further away from the coexistence line, the earlier the slowing-down sets in and hinders further growth. In contrast, in the high-pressure regime, the chains stay hydrated and mobile, when the coexistence line is crossed towards the two-phase region, and the diffusion-limited coalescence proceeds without hindrance during the entire measuring time.

The disintegration of mesoglobules is studied by pressure jumps from the two-phase into the one-phase region, varying the target pressure. At a target pressure close to the coexistence line, the release of single polymers from the surface of the mesoglobules is the dominating mechanism, whereas for target pressures deeper in the one-phase regime, the swelling of the mesoglobules by water prevails. The disintegration time decreases with increasing jump depth. The results point to the importance of the osmotic pressure of water.

These findings are key for the tuning of the switching process in applications of responsive polymers for transport and release purposes. The comparatively simple polymer PNIPAM serves as a model system for more complex biological macromolecules, such as cellulose or proteins.

1. B. J. Niebuur, K.-L. Claude, S. Pinzek, C. Cariker, K. N. Raftopoulos, V. Pipich, M.-S. Appavou, A. Schulte, C. M. Papadakis, ACS Macro Lett. 6, 1180 (2017).
2. B.-J. Niebuur, L. Chiappisi, X. Zhang, F. Jung, A. Schulte, C. M. Papadakis, ACS Macro Lett. 7, 1155 (2018),
3. B.-J. Niebuur, L. Chiappisi, F. Jung, X. Zhang, A. Schulte, C. M. Papadakis, Macromolecules 52, 6416 (2019).

In general, when a polymer film becomes thinner, the aggregation states and physical properties will deviate from those in the corresponding bulk due to surface and interfacial effects. This is also the case for perfluorosulfonic acid polyelectrolytes such as Nafion, Aquivion, etc. We previously reported that the anisotropic conductivity of protons was induced by thinning of a Nafion film in water.[1] This could be explained in terms of the peculiar aggregation states of Nafion close to the solid interface. In this study, the impact of the solid interface on the proton conductivity in Nafion thin films under a humidity condition was examined by alternating current (AC) impedance measurements in conjunction with neutron reflectivity (NR) measurements.

Nafion films were prepared by a spin-coating method from Nafion alcohol dispersions onto the substrates and dried under vacuum at 413 K for 3 h. The films were kept under humidity condition for 5 h to reach an equilibrium swollen state. The AC impedance measurements were performed at room temperature by a two-point probe method with a Kelvin connection using an impedance analyzer combined with a micro-prober. The density profile of the Nafion film along the direction normal to the interface was examined by NR measurement under a D₂O vapor condition (RH86%) at BL-17 in J-PARC.

Figure 1 shows the thickness (h_w) dependence of in-plane proton conductivity (s) in Nafion thin films in water and under a humidity condition. While s increased with decreasing h_w in water, s decreased with decreasing h_w under the humidity condition. Since the interface-to-volume ratio increased with decreasing h_w, it was evident that the thinning-induced s variation was due to an interfacial effect.

Panel (a) of Figure 2 represents an NR curve of the 57 nm-thick Nafion thin film prepared on a quartz substrate under the D₂O vapor condition. A solid line denotes the best-fit calculated reflectivity to the experimental one based on the model scattering length density (b/V) profile shown in Figure 2(b). The model containing an interfacial segregation layer gave a better fitting for the experimental data. The interfacial layer having a lower (b/V) value than the internal region may correspond to the initially adsorbed H₂O-contained one. This was in contrast to the interfacial structure of Nafion in D₂O, showing multi-layers with a total thickness of ca. 5 nm [1]. These results make it clear that the aggregation states of Nafion at a substrate interface were strongly affected by the wet environment. Thus, it can be concluded that the presence or absence of the interfacial multi-layers, or the two-dimensional proton-conductive pathway, enhanced and suppressed the in-plane proton conductivity.

[1] Ogata, Y. Abe, T., Yonemori, S., Yamada, N. L., Kawaguchi, D., Tanaka, K. (2018). Langmuir, 34, 15483-15489.

Metal-organic frameworks (MOFs) are of great interest for applications such as energy storage and carbon capture[1] and have outstanding chemical tunability.[2] In particular, the isostructural Zr and Hf MOFs are particularly promising for real-world applications due to their stability.[3] We recently discovered that the formation during synthesis of Hf metal clusters with different nuclearities and geometries results in a dramatic change in the structure of the subsequent MOF. Selection between the resultant MOF phases can be controlled by tuning the synthesis conditions, including temperature and solvent system.[4,5,6] This finding raises the possibility of designing syntheses to obtain previously inaccessible MOF phases with new metal clusters and therefore different reactive properties. While recent studies have demonstrated the importance of understanding the formation of MOF frameworks,[7,8] the evolution of their formation, from individual clusters and their precursors through to the ordering of the full framework, during the reaction must be fully explored and understood in order to rationally synthesise new MOFs.

In our previous work, we have shown that X-ray Pair Distribution Function (XPDF) measurements are sensitive to the identity of the cluster in Zr MOFs, and can clearly distinguish between isolated Zr atoms, Zr₆ clusters, and Zr₁₂ clusters.[5] Here we show that XPDF measurements, taken in situ during reactions of both Hf precursor solutions and the full hcp UiO-66(Hf) MOF, can be used to identify critical intermediates in the materials,[9] improving our understanding of stages of growth of Hf metal-organic frameworks [Figure 1] and hence providing routes towards the efficient design of syntheses for new and unrealised members of this important MOF family.

[1] Schoedel, A., Ji, Z. & Yaghi, O. (2016). Nature Energy 1, 16034.

[2] Stock, N. & Biswas, S. (2012). Chem. Rev. 112, 933.

[3] Cavka, J.H., Jakobsen, S., Olsbye, U., Guillou, N., Lamberti, C., Bordiga, S. & Lillerud, K.P. (2008). J. Am. Chem. Soc. 130(42), 13850–13851.

[4] Cliffe, M.J., Castillo-Martínez, E., Wu, Y., Lee, J., Forse, A.C., Firth, F.C.N., Moghadam, P.Z., Fairen-Jimenez, D., Gaultois, M.W., Hill, J.A., Magdysyuk, O.V., Slater, B., Goodwin, A.L. & Grey, C.P. (2017). J. Am. Chem. Soc. 139, 5397.

[5] Firth, F.C.N., Cliffe, M.J., Vulpe, D., Aragones-Anglada, M., Moghadam, P. Z., Fairen-Jimenez, D., Slater, B., & Grey, C.P. (2019) J. Mater. Chem. A., 7, 7459.

[6] Cliffe, M.J., Wan, W., Zou, X., Chater, P.A., Kleppe, A.K., Tucker, M.G., Wilhelm, H., Funnell, N.P., Coudert, F.-X. & Goodwin, A.L. (2014) Nat. Commun., 5, 4176.

[7] Xu, H., Sommer, S., Broge, N.L., Gao, J. & Iversen, B.B. (2019) Chem. – A Eur. J., 25, 2051.

[8] Taddei, M., van Bokhoven, J.A. & Ranocchiari, M. (2020), Inorg. Chem., 59(11), 7860-7868.

[9] Firth, F.C.N., Wu, Y., Gaultois, M.W., Stratford, J., Keeble, D.S., Grey, C.P., Cliffe., M.J. (2021), ChemRxiv, https://doi.org/10.33774/chemrxiv-2021-ssr8z.

Keywords: in-situ; metal-organic frameworks; XPDF; crystallisation; metal cluster

The picture of the phase separation constitutes a continuing source of inspiration for the development of multicomponent functional materials [1]. A key point of many applications is to precisely control the size and the connectivity of the phase-separated domain to achieve the desired structure and properties. However, the region of the forming the interconnected domains does not coincide with the spinodal curve, as often supposed, but that its region is actually much narrower, instead a densely packed droplet structure forms, i.e., the so-called "droplet spinodal decomposition (DSD)" [2]. A richness of kinetic phenomena was observed in the DSD, especially the hydrodynamic motion and collision of the droplets which are different from the pure diffusion in the NG and also deserve particular attention in the theoretical investigation. Obviously, an effective control of the DSD structure is much more complicated, because, in addition to some relevant material and thermophysical parameters, we also need to know the structural details, such as the droplet size, their size distribution, and the spatial correlation between them, at any instant of the evolution.

In this work, since the scatterers are known to be a collection of spherical droplets, our aim is to construct a suitable scattering function for the DSD structure and then to solve the droplet size distribution in real space by the indirect Fourier transformation (IFT) method [3]. Furthermore, unlike the most commonly used a priori strategies, we adopt a posteriori judgment to solve the IFT problems and yield quantitatively accurate descriptions of the transient domain structure in the bulk, especially in the droplet-size distribution, the well-defined short-range order, and the stress-optical phenomenon. Furthermore, the microscopic observation shows that at high droplet densities, the droplet collision and coalescence trigger a series of chain collisions which looks like a "ripple" propagating. The IFT results of the scattering by bulk specimen also support the observation. It is interesting that this new hydrodynamic phenomenon seems to be a nonequilibrium self-organization process and can occur only if the size of the coalescing droplets is greater than a threshold value.

Liposomes have attracted increasingly higher attention due to its wide applications in bioengineering and drug transport. To prolong the circulation time of liposomes, it is advantageous to graft poly(ethylene glycol) (PEG) at the liposomal surface for so-called PEGylated liposomes. The grafted PEG layer increases the miscibility of the drug-carrier liposomes in blood, and reduces changes of being targeted by opsonins. In this study, EGylated liposome solutions, of tens of nanometers, prepared with the different surface-modified phospholipids, are studied using synchrotron small-angle X-ray scattering (SAXS). A 5-layer model is developed for the SAXS data analysis, to resolve the nanostructures of the complex vesicles of PEGylated phospholipids. The proposed model employs five Gaussian functions to represent: one central layer of the lipid-tail zone in the liposome vesicles, which is sandwiched by two layers of phosphate head groups of the lipids, and further capped by two outermost layers of PEG of the unilamellar vesicle bilayer of the liposomes. The 5-layer model could fit decently the SAXS data, and reveal the thickness and electron-density of each sublayer of the PEG-grafted vesicle bilayer of the liposome. The structural changes observed are further correlated to the drug releasing efficiency observed, providing a structural basis for the design of controlled drug delivery.

Mobile genetic elements (MGEs) drive evolution and adaptation throughout the tree of life. In bacteria, MGEs frequently transfer antibiotic resistance gene (ARGs) and are major drivers of resistance spreading. Their movements have been linked to the emergence of multidrug-resistant pathogens, including VRE, MRSA and ESBL, which present major public health challenges world-wide. Transposase enzymes that catalyze MGE movement, are the most abundant and most ubiquitous proteins in nature. Yet, their structure and biochemical mechanisms are poorly understood [1].

In this talk, I will present our recent discoveries on a group of transposases, which can effectively transfer ARG-carrying MGEs between diverse bacterial species in microbial communities. We have mapped the most wide-spread transposases in bacterial genomes [2] and reconstituted their molecular mechanisms [3, unpublished data]. We further characterized the biochemical steps of these MGEs and determined high-resolution crystal and cryo-EM structures of the protein-DNA assemblies involved in their transposition [4, unpublished data]. The results shed new light on the molecular strategies of transposase enzymes and elucidate how specific DNA structures enable these proteins to insert into diverse genomic sites, thus expanding ARG transfer. These insights open new possibilities for future strategies to block or prevent transposition and thus help control the spread of antibiotic resistance.

[1] Arinkin, V., Smyshlyaev, G. & Barabas, O. (2019) Curr Opin Struct Biol. 59, 168-177.

[2] Smyshlyaev, G., Bateman A. & Barabas O. (2021) Mol Syst Biol. e9880

[3] Lambertsen, L., Rubio-Cosials, A., Patil, K.R. & Barabas, O. (2018) Mol Microbiol. 107, 639-658.

[4] Rubio-Cosials, A., Schulz, E.C., Lambertsen, L., Smyshlyaev, G., Rojas-Cordova, C., Forslund, K., Karaca, E., Bebel, A., Bork, P. & Barabas, O. (2018) Cell 173, 208-220.

Recognition of DNA by proteins, both sequence and structure specific, is important in the functioning of the cell, such as in the processes of replication, transcription, and DNA repair. Twenty-five years after base flipping, a phenomenon whereby a base in normal B-DNA is swung completely out of the helix into an extrahelical position, was first observed in HhaI methyltransferase, we are still learning from and surprised by structures of protein-DNA complexes. The novel structures of the bacterium Caulobacter crescentus cell cycle-regulated DNA adenine methyltransferase (CcrM), as well as the newly discovered CamA enzyme (named for Clostridioides difficile adenine methyltransferase A) in complexes with double-stranded DNA containing their recognition sequence, will be discussed. Each of these enzymes affect their DNA substrate in a unique number of ways that are critical for their level of discrimination of their recognition DNA sequence.

CcrM in C.crescentus is responsible for maintenance methylation immediately after replication and methylates the adenine of hemimethylated GANTC. CcrM contains an N-terminal methyltransferase domain and a C-terminal nonspecific DNA-binding domain. CcrM is a dimer, with each monomer contacting primarily one DNA strand: the methyltransferase domain of one molecule binds the target strand, recognizes the target sequence, and catalyzes methyl transfer, while the C-terminal domain of the second molecule binds the non-target strand. The DNA contacts at the five base pair recognition site results in dramatic DNA distortions including bending, unwinding and base flipping. The two DNA strands are pulled apart, creating a bubble comprising four recognized base pairs. The five bases of the target strand are recognized meticulously by stacking contacts, van der Waals interactions and specific Watson–Crick polar hydrogen bonds to ensure high enzymatic specificity.

In the developed world, C. difficile is one of the leading causes of hospital-acquired infections. CamA-mediated methylation of the last adenine in CAAAAA is required for normal sporulation and biofilm production by this bacterium, a key step in disease transmission. Thus, selective inhibition of CamA has great therapeutic potential. CamA contains an N-terminal methyltransferase domain as well as a C-terminal DNA recognition domain. Major and minor groove DNA contacts in the recognition site involve base-specific hydrogen bonds, van der Waals contacts and the Watson-Crick pairing of a rearranged A:T base pair. These interactions provide sufficient sequence discrimination to ensure high specificity. In addition, this DNA methyltransferase has unusual features that may aide in discovery of a new selective antibiotic to combat C. difficile infection.

Knowledge acquired from these structures may also relate to other projects in our laboratory relating to mammalian epigenetics.

Enzymes with a protein kinase fold transfer phosphate from adenosine 5′-triphosphate (ATP) to substrates in a process known as phosphorylation. Here, we show that the Legionella meta-effector SidJ adopts a protein kinase fold, yet unexpectedly catalyzes protein polyglutamylation. SidJ is activated by host-cell calmodulin to polyglutamylate the SidE family of ubiquitin (Ub) ligases. Crystal structures of the SidJ-calmodulin complex reveal a protein kinase fold that catalyzes ATP-dependent isopeptide bond formation between the amino group of free glutamate and the gamma-carboxyl group of an active-site glutamate in SidE. We show that SidJ polyglutamylation of SidE, and the consequent inactivation of Ub ligase activity, is required for successful Legionella replication in a viable eukaryotic host cell. [1]

Here we also present cryo-EM reconstructions of SidJ:CaM:SidE reaction intermediate complexes. We show that the kinase-like active site of SidJ adenylates an active site Glu in SidE resulting in the formation of a stable reaction intermediate complex. An insertion in the catalytic loop of the kinase domain positions the donor Glu near the acyl-adenylate for peptide bond formation. Our structural analysis led us to discover that the SidJ paralog SdjA is a glutamylase that differentially regulates the SidE-ligases during Legionella infection. Our results uncover the structural and mechanistic basis in which the kinase fold catalyzes non-ribosomal amino acid ligations and reveal an unappreciated level of SidE-family regulation. [2]

[1] Black, M. H., Osinski, A., Gradowski, M., Servage, K. A., Pawłowski, K., Tomchick, D. R., Tagliabracci, V. S. (2019). Science 364, 787-792.

[2] Osinski, A., Black, M. H., Pawłowski, K., Chen, Z., Li, Y., Tagliabracci, V. S. (2021). bioRxiv doi: https://doi.org/10.1101/2021.04.13.439722

Results shown in this report are derived from work performed at the Structural Biology Center, Advanced Photon Source, Argonne National Laboratory. A portion of this research was supported by NIH grant U24GM129547 and performed at the Pacific Northwest Center for Cryo-EM at OHSU and accessed through EMSL (grid.436923.9), a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research. We thank the Structural Biology Laboratory and the Cryo Electron Microscopy Facility at UT Southwestern Medical Center which are partially supported by grant RP170644 from the Cancer Prevention & Research Institute of Texas (CPRIT) for cryo-EM studies.

Tick-borne encephalitis virus is the cause of tick-borne encephalitis, an important arboviral disease affecting population within European and north-eastern Asian countries. There is currently no specific treatment available although it is preventable by vaccination [1, 2]. The lack of specific antiviral together with low vaccination coverage allowed the expansion of the virus within the Europe in recent years.

In the lifecycle of TBEV, NS3 helicase domain plays an essential role in viral genome replication. This domain carries out three enzymatic activities: RNA 5’-triphosphatase, RNA helicase and ATP hydrolysis. The latter activity is coupled to and provides energy for the RNA helicase activity during unwinding of the double-stranded RNA replication intermediate [3]. To understand the coupling between ATP hydrolysis and NS3 helicase activity, we determined several crystal structures of NS3 helicase, either the apo form or in complex with non-hydrolyzable ATP-analogue (AMPPNP), ADP or ADP-Pi (post-hydrolysis state). These represent structural snapshots of the key stages in ATP hydrolysis and nucleotide exchange. We also demonstrated that the ATP hydrolysis is stimulated in the presence of ssRNA but not ssDNA, both of which bind but the latter acts as a competitive inhibitor. Thus, RNA selectivity is not due to specific binding but is encoded in the coupling mechanism.

The obtained structures served as basis for molecular dynamics simulations of NS3 helicase in complex with ssRNA. RNA binding in the post-hydrolysis state leads to an allosteric change which forces opening of the ATP binding site and allows release of the resulting inorganic phosphate ion, P_i. The allosteric change is commensurate with movement of ssRNA, suggesting that this step plays a key role in the tight coupling between helicase and ATPase activities.

Quinole-dependent nitric oxide reductases (qNORs), that use Nitric oxide (NO) to generate Nitrous oxide (N₂O) as the enzymatic product in agricultural and pathogenic conditions are of major importance to food production, environment and human health. These membrane-bound enzymes strongly contribute to environmental problem at the global level (N₂O is an ozone-depleting and greenhouse gas some 300-fold more potent than CO₂) and play significant roles in survival of pathogens (qNOR from human pathogenic bacterium, Neisseria meningitidis is responsible for detoxification of NO produced to combat immune response of the host). We have determined high-resolution cryo-EM structure of active quinol-dependent nitric oxide reductases (qNOR) from Neisseria meningitidis (Nm) and Alcaligenes xylosoxidans (Ax) at 3.06Å and 3.2Å, respectively [1,2]. For NmqNOR, we have also determined the crystallographic structure at 3.15Å. All of the crystallographic structures including that of NmqNOR are monomeric [3] while both cryoEM structures showed clear dimeric arrangement. We have identified a number of factors that may trigger destabilisation of helices necessary for preserving the integrity of dimer including the use of zinc in crystallisation. Activity assay of both NmqNOR and AxqNOR in the presence of ZnCl₂ or ZnSO₄ abolished the activity. A closer examination of the NmqNOR crystallographic and cryoEM structures revealed a significant movement of TMII where one of the Zn (called Zn1) is present in the crystallographic structure and the other was at Glu498 which is pulled away from binding to Fe_B in order to ligate the second Zn (called Zn2). It is unclear if the loss of activity is due to the binding of Zn1 located near TMII or is a consequence of the removal Glu498 from the coordination of Fe_B. The mutation of Glu to Ala led to an inactive enzyme with the size exclusion chromatography indicating the major species to be a monomer. We were able to determine the cryoEM structure of this monomer (~85kD) showing that the mutation, in addition to TMII movement, causes destabilisation of additional helices (TMIX and TMX). These results and their wider implications for structure determination of membrane proteins would be discussed in the context of enzyme mechanism.

Since resolution of the first macromolecular structure, the goal of structural biology has been to link structure to function. It is now widely accepted that the latter emerges from the structural dynamics animating the macromolecule, making characterization of intermediate (and sometime excited) states of high interest to further understand molecular processes and possibly control them. With the advent of serial crystallography at X-ray free electron lasers and synchrotrons, time-resolved crystallography, performed following a specific perturbation of the crystalline system (laser excitation, substrate soak, etc), is on the verge of becoming feasible on virtually all systems opening avenues to characterize such excited and/or intermediates states. Because crystallography is an ensemble-averaged method, however, an inherent limitation is that the occupancy of intermediate states must be high enough for the “probed state” under investigation to become visible in the electron density. This is generally not the case, with “perturbed” crystals rather existing as mixtures of initial and/or final state(s) with the “probed” state. Differences in structure factor amplitudes between the reference and “perturbed” dataset can allow calculation of Fourier difference maps (F_{obs,perturbed}-F_{obs,unperturbed}), in which only the differences between the states are depicted. An even more powerful approach is to generate extrapolated structure factor amplitudes (F_{extr,perturbed}) solely describing the intermediate state and and to use these to refine its structure using conventional refinement tools. Such data processing has in the past been performed by a handful of well-experienced crystallographers with strong knowledge of existing software but still remains out of reach for a wide audience.

Here, we will present a user-friendly program, Xtrapol8, written in python and exploiting the cctbx toolbox modules, that allows the calculation of high-quality Fourier difference maps, estimation of the occupancy of the intermediate state(s) in the crystals, and generation of extrapolated structure factor amplitudes. Briefly, the program uses Bayesian statistics to weight structure factor amplitude differences [1] which are then used to generate extrapolated structure factor amplitudes for a range of possible intermediate state occupancies, with distinct weighting schemes [2, 3] (Figure 1). Based on the comparison between experimental and calculated differences, i.e. solely on experimental observations, the correct occupancy of the intermediate state is determined and its structure refined, shedding light on conformational changes not visible before. With various user-controllable parameters of which defaults are carefully chosen, the program is adapted to be used by a wide audience of structural biologists, ranging from well-experienced crystallographers to newcomers in the field. We anticipate that this program will ease and accelerate the handling of time resolved structural data, and thereby the understanding of molecular processes underlying function in a variety of proteins.

[1] Ursby, T. & Bourgeois, D. (1997), Acta Crystallogr. Sect. A, 53, 564-575.

[2] Genick, U. .,Borgstahl, G. E., Ng, K., Ren, Z., Pradervand, C., Burke, P. M., Srajer, V., Teng, T. Y., Schildkamp, W., McRee, D. E., Moffat, K. & Getzoff, E. D. (1997), Science, 275, 1471-1475.

[3] Coquelle, N., Sliwa, M., Woodhouse, J., and others, Colletier, J.-P., Schlichting, I. & Weik, M. (2018), Nature chemistry, 10, 31–37.

The last decade has witnessed significant growth in our understanding on intermolecular interactions [1]. Experimental and computational approaches have resulted in obtaining quantitative insights into the underlying nature of different interactions [2]. Non-covalent interactions involving halogens have attracted significant attention. Interactions involving the heavier halogen bromine are ubiquitous and hence an investigation into the electronic features of such interactions is of interest. The existence of the s- hole in bromine-centered interactions have been quantitatively investigated via high resolution electron density analysis in crystals of an ebselen derivative (I). It has been observed that in addition to formation of s-hole centered linear interaction involving bromine, the lone pairs on bromine also interact with the electron deficient region on the π-ring (Fig. 1a) [3]. Thus bromine is associated with both electron donor and acceptor characteristics. Furthermore, this approach has also been utilized to understand carbon-centered π-hole directed O=C...O=C interactions in crystalline fluoroanil (II) and chloranil [4]. The topological characteristics in terms of the MESP, and the electronic features of the interacting atoms will be discussed (Fig. 1b). Such studies establish the subtle yet pivotal role of weak intermolecular interactions in the crystal packing of organic molecules.

Counterions are ubiquitous in solution but the role they play in species formation, stability, and reactivity is not well understood. Inspired by recent work that has shown that consideration of counterions may be important for understanding phase formation and the overall chemical behavior of a metal ion, our group has sought to examine the impact of nonbonding interactions on actinide (An) complex formation and precipitation. Our efforts have focused on the solution and solid‐state structural chemistry of An‐Cl complexes formed from acidic aqueous chloride solutions in the presence of protonated N‐heterocycles. Within this context, a series of seven unique Th^IV compounds that were precipitated from aqueous solution will be presented. The compounds consist of Th^IV metal centers that adopt 8- or 9-coordinate complexes with the general formulas [Th(H₂O)_xCl_8–x]^x–4 (x=2, 4) and [Th(H₂O)_xCl_9–x]^x-5 (x=5–7). While all of the complexes are heteroleptic, bound to Cl^- and H₂O ligand, the structural units vary in composition, charge, and coordination geometry. The complexes range from chloride rich to chloride deficient, with the number of bound chlorides and hence charge on the structural unit showing some dependence on the counterion present in the outer coordination sphere. Our experimental and computational efforts to understand phase formation, the effects of noncovalent interactions, and the energetics that drive the formation of this series of structurally related Th^IV–aquo–chloro compounds will be discussed.

Stacking interactions of aromatic fragments are ubiquitous in many chemical and biological systems [1]. Benzene dimer, as a prototype, has stacking energy of -2.73 kcal/mol, in the most stable parallel-displaced geometry [2]. However, stacking interactions can also be formed by non-aromatic fragments, most notably by metal-chelate rings [3].

Stacking interactions between chelate and aromatic rings were described in crystal structures deposited in the Cambridge Structural Database [3], and were shown to have parallel-displaced geometries (Fig. 1), similar to stacking of aromatic molecules. The study of crystal structures with stacking interactions between aromatic rings and systems that have chelate ring fused with aromatic ring showed that aromatic ring is dominantly closer to chelate than to aromatic ring of the fused system, indicating that chelate-aryl stacking is stronger than aryl-aryl stacking [3]. Calculated CCSD(T)/CBS and DFT interaction energies confirmed this; stacking of benzene with nickel chelate of acac type has the energy of ‑5.52 kcal/mol, while stacking of benzene with zinc chelate of acac type is even stronger, -7.56 kcal/mol [4].

Stacking interactions can be formed between two chelate rings as well. This type of stacking was also described by studying the CSD crystal structures [3]. Geometries of chelate-chelate stacking interactions are mostly parallel-displaced, but there are examples of face-to-face geometries (Fig. 1). Chelate-chelate stacking is even stronger than aryl-aryl and chelate-aryl stacking. Stacking energy between two acac type chelates of nickel is -9.47 kcal/mol [4], while stacking between two dithiolene chelates of nickel is -10.34 kcal/mol [5].

Chelate-aryl and chelate-chelate stacking interactions are much stronger than aryl-aryl stacking due to much stronger electrostatic interactions caused by the presence of metals [4]. Stacking geometries and relative strengths of interactions can be rationalized by observing electrostatic potentials of the complexes that contain metal-chelate rings.

[1] Salonen, L. M., Ellermann, M., Diederich, F. (2011). Angew. Chem. Int. Ed. 50, 4808.

[2] Lee, E. C., Kim, D., Jurečka, P., Tarakeshwar, P., Hobza, P., Kim, K. S. (2007). J. Phys. Chem. A 111, 3446.

[3] Malenov, D. P., Janjić, G. V., Medaković, V. B., Hall, M. B., Zarić, S. D. (2017). Coord. Chem. Rev. 345, 318.

[4] Malenov, D. P., Zarić, S. D. (2019). Dalton. Trans. 48, 6328.

[5] Malenov, D. P., Veljković, D. Ž., Hall, M. B., Brothers, E. N., Zarić, S. D. (2019). Phys. Chem. Chem. Phys. 21, 1198.

In the category of sigma-hole interactions, chalcogen bonding is an interaction between the electropositive surface of a chalcogen atom acting as a chalcogen bond donor and a Lewis-base acting as chalcogen bond acceptor.^[1-2] In today’s date, hydrogen bonding and halogen bonding interactions have been extensively exploited in the field of supramolecular chemistry and crystal engineering owing to the great strength of the interaction, strong directionality, predictability, and profound understanding, whereas the world of chalcogen bonding, in spite of being known for many decades, still struggles to make a mark due to the relatively weaker directionality or predictability and underdeveloped synthetic chemistry of chalcogen compared to the halogens.^[3-4]

Below is a figure demonstrating that when Iodine is attached to acetylene, it generates a strong sigma-hole in the prolongation of the acetylene--I bond which allows this moiety to easily interact with a given nucleophile through halogen bonds. However, what happens when we have a chalcogen (Se/Te) next to acetylene, can we similarly anticipate a strong sigma-hole activation that can favor this moiety to interact with a nucleophile through chalcogen bonds? Herein, we describe the synthesis and solid-state assembly of (methyl Se/Te)ethynyl-substituted derivatives acting as directional chalcogen bond donors in crystal engineering. Directional chalcogen-chalcogen contacts in this series of derivatives allow for a unique molecular helical arrangement in the solid-state assembly of monomer alone. Co-crystallization with various Lewis-bases, fabricate 1D chain motifs with short chalcogen bonds, quite comparable in strength to halogen bond observed with the analogous iodo derivatives.

[1] Aakeroy, C. B., Bryce, D. L., Desiraju, G. R., Frontera, A., Legon, A. C., Nicotra, F., Rissanen, K., Scheiner, S., Terraneo, G., Metrangolo, P., Resnati, G. Definition of the chalcogen bond (IUPAC Recommendation 2019). (2019). Pure Appl. Chem., 91, 1889-1892. [2] Vogel, L., Wonner, P., Huber, S. M. (2019). Angew. Chem. Int. Ed., 58, 1880-1891. [3] Huynh, H.-T., Jeannin, O., Fourmigue, M. (2017). Chem. Commun. 53, 8467. [4] Werz, D. B., Rominger, F., Gleiter, R. (2002). J. Am. Chem. Soc. 124, 10638-10639.

Alcohols and amines can be considered as excellent cocrystal forming agents, due to the compatibility of intermolecular interactions where both compounds act as hydrogen bond donor and acceptor. In such structures different motifs as isolated oligomers (0D), ribbons (1D), layers (2D), etc. can be expected. The main trust of the research was the crystallization and structure determination of cocrystals of allylamine and alcohols followed by the analyses of hydrogen bond architectures, using computational methods.

The examined mixtures are liquid at ambient conditions, therefore, an IR laser-assisted in situ crystallization method has been used directly on the goniometer of the single crystal diffractometer [1]. The X-Ray measurements were complement by DFT periodic calculation in CRYSTAL17.

Among obtained cocrystals, those with three simplest alcohols (methanol, ethanol, and 1-propanol) contain molecules arranged in layers with L4(4)8(8) motif [2] of hydrogen bonds. Further elongation of the aliphatic chain of the alcohol moiety leads to change in hydrogen bonds architecture from 2D to 1D. In consequence, all cocrystals containing C₄ to C₇ alcohols infinite ribbons reveal the T4(2) topology [2]. Further modification appears for 1-octanol cocrystal, where the molecules interact via hydrogen bonds forming layers of the L6(6) type [2]. Thus different topology than for C₁-C₃ alcohols is observed. This structural motif is preserved for cocrystals with C₉ and C₁₀ alcohols.

In the analyzed structures three types of hydrogen bonds motifs occur, depending on the aliphatic chain length of the alcohol molecule. Furthermore, all the systems were analyzed according the binding energy between structural units (ribbons or layers) present in the structures. In addition, the calculations were also performed for simulated structural units (e.g. applying 1D motif for methanol and 2D motif in case of butanol) to show a potential reason for specific architecture type formation in analyzed cocrystals.

The research shows that for ten allylamine – alcohol cocrystals three of structural motifs may exist. Elongation of the aliphatic chain of the alcohol impacts on the change of the motif in a systematic way. This alteration can be used for the rational design of similar systems.

Computational methods for predicting the crystal structures [1] of organic compounds have evolved over the past three decades to the point where they are now used in major pharmaceutical companies to support the solid-form development of new active pharmaceutical ingredients (APIs). More broadly, knowledge of the crystal structure of a compound is fundamental to understanding the mechanical response, charge carrying capacity and porosity of the material. Most crystal structure prediction (CSP) studies produce a static crystal energy landscape (CEL) which depicts the possible polymorphs as a function of lattice energy and crystal density. Although some promising results have recently been reported [2], the challenge of extracting the set of molecular and crystal descriptors from the CEL that will support the targeted crystallization of one polymorph over the many dozens of artefacts on the CEL remains a major unresolved challenge within the CSP community.

Whilst there have been many reports of the application of computational methods to support the discovery of binary cocrystals, very little is known about the accuracy of CSP methods for supporting the discovery of periodic multicomponent crystals that contain > 2 distinct chemical fragments in the crystallographic asymmetric unit. The discovery of such higher-order cocrystals widens the crystal form landscape and allows drug developers to choose the optimal solid dosage form for a particular API. We demonstrate [3] that CSP methods can be adapted to support the discovery of ternary molecular ionic cocrystals comprising many competing intermolecular hydrogen bonding interactions in the crystal. Beyond periodic cocrystals, eutectic composites are an example of aperiodic solid forms, whose discovery is associated with a depression in the melting point of the API. The extent of melting point depression is correlated with a commensurate increase in the solubility of the API. Since a large fraction of pharmaceutical lead compounds are abandoned due to poor solubility profiles, a computational model that can accurately predict eutectic formation is of significant value to the pharmaceutical industry. We demonstrate that the computed mixing energies and binding modes of candidate molecular pairs leads to temperature-dependent interaction parameters that can accurately predict the formation of eutectic composite materials of molecular compounds. Rather than relying on the traditional solid forms of salts, cocrystals, polymorphs or solvates to support the optimization of the solid-state properties of molecular compounds, our results demonstrate that the range of solid forms that may be developed to enhance one or more physicochemical properties of molecular compounds is wider than previously thought. Computational methods remain indispensable in supporting the discovery of new functional crystalline forms of organic compounds.

[1] Reilly, A. M. et al. (2016). Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 72, 439-459. [2] Pulido, A. et al. (2017). Nature 543, 657-664. [3] Shunnar, A. F., Dhokale, B., Karothu, D. P., Bowskill, D. H., Sugden, I. J., Hernandez, H. H., Naumov, P. & Mohamed, S. (2020). Chemistry – A European Journal 26, 4752-4765.

Discrete polyoxometalates: from geochemistry via crystal engineering to functional materials

U. Kortz

Jacobs University, Department of Life Sciences and Chemistry, Campus Ring 1, 28759 Bremen, Germany u.kortz@jacobs-university.de

Polyoxometalates (POMs) are a class of discrete, anionic metal-oxides with an enormous structural diversity and a multitude of interesting properties leading to potential applications in different areas including catalysis, nanotechnology and medicine [1]. Noble metal-containing POMs are in particular attractive for homogeneous and heterogeneous catalytic applications. However, the number of well characterized noble-metal POMs is rather small [2]. POMs based exclusively on Pd²⁺ addenda (polyoxopalladates, POPs) were discovered in 2008 [3]. The area of POP chemistry has developed rapidly ever since, due to the fundamentally novel structural and compositional features of POPs, resulting in unprecedented electronic, spectroscopic, magnetic, and catalytic properties [4]. In terms of POP structural types, the symmetrical 12-palladate nanocube {MPd₁₂L₈} and the 15-palladate nanostar {MPd₁₅L₁₀} are the most abundant. Especially for the {MPd₁₂L₈} nanocube, many derivatives with various central guests including d and f block metal ions and various capping groups are known [4]. We demonstrated the use of {MPd₁₂L₈} as discrete molecular precursors for the formation of supported palladium metal nanoparticles as hydrogenation catalysts, and we discovered an important dependence of the catalytic properties on the type of internal metal guest and external capping group [5]. We also managed to construct 3D coordination networks using externally functionalized POPs, resulting in metal-organic framework (MOF)-type assemblies (POP-MOFs) with interesting sorption and catalytic (C-C coupling) properties [6].

[1] Pope, M. T. (1983). Heteropoly and isopoly oxometalates. Springer Verlag.

[2] Izarova, N. V.; Pope, M. T.; Kortz, U. (2012). Angew. Chem. Int. Ed. 51, 9492.

[3] Chubarova, E. V.; Dickman, M. H.; Keita, B.; Nadjo, L.; Mifsud, M.; Arends, I. W. C. E.; Kortz, U. (2008). Angew. Chem. Int. Ed. 47, 9542.

[4] Yang, P.; Kortz, U. (2018). Acc. Chem. Res. 51, 1599.

[5] Ayass, W. W.; Miñambres, J. F.; Yang, P.; Ma, T.; Lin, Z.; Meyer, R.; Jaensch, H.; Bons, A.-J.; Kortz, U. (2019). Inorg. Chem. 58, 5576.

[6] Bhattacharya, S.; Ayass, W. W.; Taffa, D. H.; Schneemann, A.; Semrau, A. L.; Wannapaiboon, S.; Altmann, P. J.; Pöthig, A.; Nisar, T.; Balster, T.; Burtch, N. C.; Wagner, V.; Fischer, R. A.; Wark, M.; Kortz, U. (2019). J. Am. Chem. Soc. 141, 3385.

Titan, the largest moon of Saturn, has been revealed by the Cassini-Huygens mission to be a fascinating and quite Earth-like world. Among the parallels to Earth, which includes the lakes, seas, fluvial and pluvial features on its surface, is an inventory of organic minerals [1]. However, where on Earth these organic minerals are only found in niche environments, on Titan they are likely to be the dominant surface-shaping materials. Titan’s organic minerals are formed primarily from photochemistry induced by UV radiation and charged particles from Saturn’s magnetosphere, which cause molecular nitrogen and methane (the primary components of the upper atmosphere) to generate into various CHN-containing species that deposit onto the surface [2].

Despite the ubiquity of these organic minerals upon the surface, it is difficult to understand their influence on the landscape and as, in some cases, even their crystal structure is unknown let alone wider physical properties[3]. Hence we have undertaken an experimental program to address this, and are currently focusing on the missing crystal structure and physical property understanding of a number of molecular solids and co-crystals that are likely to be organic minerals upon Titan. Using a combination of neutron diffraction, X-ray diffraction and Raman scattering we have studied molecular solids including ethane, acrylonitrile, acetonitrile, butadiene and propyne, and explored what co-crystal form from the inventory of Titan’s molecules. This contribution will report highlights from these investigations.

[1] Lopes, R.M., Malaska, M.J., Schoenfeld, A.M., Solomonidou, A., Birch, S.P.D., Florence, M., Hayes, A.G., Williams, D.A., Radebaugh, J., Verlander, T. and Turtle, E.P. (2020) Nature Astronomy 4(3) pp.228-233. [2] Hörst, S. M. (2017). Journal of Geophysical Research: Planets 122 (3), 432-482 [3] Maynard-Casely, H.E., Cable, M.L., Malaska, M.J., Vu, T.H., Choukroun, M. and Hodyss, R. (2018) 103(3), pp.343-349 [4] Balzar, D. & Popa, N. C. (2004). Diffraction Analysis of the Microstructure of Materials, edited by E. J. Mittemeijer & P. Scardi, pp. 125-145. Berlin: Springer.

Over the last decade, crystal flask that converts one chemical species to another one in single-crystal-to-single-crystal (SCSC) manner has attracted much attention in crystal engineering. An important key for the construction of crystal flask is a porous space which can induce a chemical from outside of a crystal.¹ To design such a porous space, our group has intensively studied the metalloligand approach in which a pre‐prepared homometallic complex with coordination donor sites is reacted stepwise with secondary metal ions.² We established the construction of a variety of metalloarchitectures by the metalloligand approach with using thiolato groups derived from amino acids and phosphine ligands. Recently, our group has successfully prepared a microporous material of a nanometer-sized Au^ICd^II 116-nuclear cage-of-cage structure (1_CdNa) from the reaction of the tripodal-type trigold(I) metalloligand, [Au^I₃(tdme)(D-Hpen)₃] (tdme = 1,1,1-tris(diphenylphosphinomethyl)ethane, D-H₂pen = d-penicillamine), with Cd^II(NO₃)₂.³ The cage-of-cage structure was constructed from 12 building units of Au^I₆Cd^II₃ cage complex through hierarchical aggregation. Interestingly, 1_CdNa has large interstices connected by 3D channels which allow the easy incorporation and accommodation of guest molecules. Therefore, it was found that 1_CdNa underwent the stepwise SCSC transmetallation reactions to form Au^ICu^II metallocage (1_Cu). Furthermore, we found that the crystals of 1_Cu have the ability to accommodate MoO₄^2– ions (2_Mo1) and condense them to form Mo₇O₂₄^6– (2_Mo7) and β-Mo₈O₂₆^4– (2_Mo8) by the addition of protons in the solid state. These results show the availability of the large crystal interstices in 1_Cu as crystal flask, which serves as a reaction field for accommodated chemical species in crystal. Such a crystal flask reaction of polyoxomolybdate will give an important insight for not only material science but also biosynthesis in Mo-storage protein (MoSto) which contains Mo₈, Mo_5-7 and Mo₃ clusters. The detail will be discussed in the presentation.

[1] Inokuma, Y., Kawano, M. & Fujita, M. (2011). Nat. Chem. 3, 349. [2] Yoshinari, N. & Konno, T. (2016). Chem. Rec. 16, 1647. [3] Imanishi, K., Wahyudianto, B., Kojima, T., Yoshinari, N. & Konno, T. (2020). Chem. Eur. J. 26, 1827. [4] Kowalewski, B., Poppe, J., Demmer, U., Warkentin, E., Dierks, T., Ermler, U. & Schneider, K. (2012). J. Am. Chem. Soc. 134, 9768.

Stress-accumulated electrical charge to close wounds in living tissue, yet to-date this piezoelectric effect has not been realised in self-repairing synthetic materials which are typically soft amorphous materials requiring external stimuli, prolonged physical contact and long healing times (often >24h). Here we overcome many of these challenges using piezoelectric organic crystals, which upon mechanical fracture, instantly recombine without any external direction, autonomously self-healing in milliseconds with remarkable crystallographic precision (Figure 1). Atomic-resolution structural studies reveal that a 3D hydrogen bonding network, with ability to store stress, facilitates generation of stress-induced electrical charges on the fractured crystals, creating an electrostatically-driven precise recombination of the pieces via a diffusionless instant self-healing, as supported by spatially-resolved birefringence experiments. Perfect, instant self-healing creates new opportunities for deployment of molecular crystals using crystal engineering principles in robust miniaturised devices, and may also spur development of new molecular level repair mechanisms in complex biomaterials [1].

References:

[1] Bhunia S, Chandel, S., Karan, SK., Dey, S., Tiwari, A., Das, S., Kumar, N., Chowdhury, R., Mondal, S., Ghosh, I., Mondal, A., Khatua, BB., Ghosh, N., Reddy, C. M. Autonomous self-repair in piezoelectric molecular crystals. (2021) Science. 373 , 321-327

The crystalline sponge method^[1],[2] allows the absolute structural determination of non-crystalline compounds such as powder, amorphous solid, liquid, volatile matter or oily state. In this method, metal-organic frameworks (MOFs) are used as ‘crystalline sponges’ which can absorb target sample (guest) molecules from their solution into the pores and allow them to arrange themselves in a regular pattern with the help of specific interactions between MOF pores and the guests, such as π-π, CH-π, and charge-transfer interactions. This technique was first introduced in 2013^[1] and since then has grown rapidly and proved helpful in the structure elucidation of liquids and other volatile compounds.

In this work, the crystalline sponge [{(ZnI₂)₃(tris(4-pyridyl)-1,3,5- triazine)₂·x(solvent)_n] (1) was used to produce three novel encapsulation complexes of terpenes, such as geraniol-monoterpenoid, farnesol-sesquiterpenoid and β-damascone-tetraterpenoids.^[3] Along with the structure determination of the terpenoids, non-bonding CH-π, π-π interactions were identified in the host-guest complexes shown in Figure 1, which were responsible for holding the guests in the specific position with respect to the framework. Since pores of sponge 1 were hydrophobic, no hydrogen bonding between host and guest was observed.

In addition, new crystalline sponges were explored {[Co₂(bis-(3,5-dicarboxy-phenyl) terephthalamide)(H₂O)₃]·solvent_x}^[4] (2) and [Cd₇(4,4’,4’’-[1,3,5-benzenetriyltris(carbonylimino)]trisbenzoic acid)(H₂O)]·solvent _x]^[5] (3). With sponge 2 two novel inclusion complexes with 3-Phenyl-1-propanol and 2-Phenylethanol were obtained. Sponge 2 has three coordinated water molecules indicating the hydrophilic nature, which was further observed in the inclusion complexes where the hydroxyl group of guest molecules were found to form hydrogen bonds with the framework of 2. Further, 3 shows great potential to act as a crystalline sponge because of larger pore size than 1 and the hydrophilic nature which will allow a wide range of guest molecule for encapsulation and their structure elucidation.

The first developments on metal-organic frameworks, or MOFs, were made approximately four decades ago, marking the discovery of a novel class of porous materials. Initially thought to be ordered and truly crystalline, there is now an increasing realisation that defects and disorder are prevalent in MOFs, and that nontrivial arrangements can be important in physical properties [1]. Though, disorder in MOFs does not necessarily imply randomness. In fact, depending on the interactions between components, MOF structures can exhibit short-range order and long-range disorder simultaneously. This is what we refer to as correlated disorder [2]. Thorough understanding is achieved through investigation of the interactions involved in causing these states, with the aim of controlling physical properties via their manipulation.

Generally, there are three types of disorder observed in MOFs: vacancy defects, compositional disorder, and orientational/conformational disorder [3]. The latter forms the focus of this project. A key factor is the distinction between molecular point symmetry (i.e. the local structure) and that of the corresponding position in the lattice (i.e. the average structure). Namely, molecular components are arranged on a lattice of which the geometry is determined by that of the MOF, giving control over the molecular orientational degrees of freedom [4]. Since MOF geometry is often highly symmetric, lowering the symmetry of nodes and/or linkers can enable targeted design of correlated conformational disorder (Fig. 1).

In this work, correlated disorder is introduced to the highly symmetric (hypothetical) parent framework ZnO₄(BTC) (BTC = benzene tricarboxylic acid) by reducing the linker symmetry from D_3h to C_2v, giving ZnO₄(1,3-BDC) (BDC = benzene dicarboxylic acid) (Fig. 1). The resulting linker disorder is characterised via diffuse scattering observed in single crystal X-ray diffraction (SCXRD) patterns, 3DΔ-pair distribution functions (3DΔ-PDFs), and Monte Carlo code. Ultimately, we want to understand how to control defective structures in MOFs to optimise their properties, enabling utilisation in real-life applications.

[1] Bennett, T. D., Cheetham, A. K., Fuchs, A. H., Coudert, F.-X. (2017). Nat. Chem. 9, 11.[2] Keen, D. A. and Goodwin, A. L. (2015). Nat. 521, 303.[3] Meekel, E.G. and Goodwin, A.L. (2021). CrystEngComm.[4] Simonov, A. and Goodwin, A. L. (2020). Nat. Rev. Chem.

The structural dynamics of chemical systems can be investigated by in situ or operando X-ray experiments. Advanced and fast computational methods are needed to cope with the huge amount of data collected, and to extract precious information hidden in data through a model-free analysis. Data analysis approaches based on multivariate analysis are particularly suited to this aim, as they are able to efficiently process in a probe-independent way multiple measurements, by considering them as a whole data matrix [1].

We have developed a fully automatic and big-data set of computing procedures based on principal component analysis, which is able to process with the same algorithms in situ/operando X-ray diffraction and XAFS data to extract qualitative and quantitative information. The multivariate approach has been adapted to treat crystallographic data, by optimizing the directions of the principal components [2], or by including kinetic models in the extraction of the reaction coordinate [3]. The procedure includes several pre-processing strategies that can be applied on crystallographic and XAFS data; among them a peak-shift correction to disentangling lattice variations from changes of the atomic parameters [4]. The procedures have been implemented in the computer program RootProf [5], available from www.ic.cnr.it/ic4/en/software/. It can be also used for fast on-site analysis while running in situ experiments (Fig.1).

Here we show how in situ experiments coupled with new data analysis methods can disclose the structural mechanism underlying: i) the thermal adsorption of gas in zeolites [4]; ii) the non-isothermal solid-state synthesis of materials based on poly-aromatic molecular complexes [6]; iii) the temperature-induced transitions of metal halide perovskites [7].

Figure 1. The RootProf program processes data from in situ experiments to locate atoms responding to an external stimulus.

[1] Guccione, P., Lopresti, M., Milanesio, M., Caliandro R. Crystals 11, 12.

[2] Caliandro, R., Guccione, P., Nico, G., Tutuncu, G., Hanson, J.C. (2015). J. Appl. Cryst. 48, 1679.

[3] Guccione, P., Palin, L., Belviso, B. D., Milanesio, M., Caliandro R. (2018). Phys. Chem. Chem. Phys. 20, 19560.

[4] Guccione, P. Palin, L., Milanesio, M., Belviso B.D., Caliandro, R. (2018). Phys. Chem. Chem. Phys. 20, 2175.

[5] Caliandro, R., Belviso, B. D., (2014). J. Appl. Cryst. 47, 1087.

[6] Palin, L., Conterosito, E., Caliandro, R., Boccaleri, E., Croce, G., Kumar, S., van Beek, W., Milanesio M. (2016). CrystEngComm 18, 5930.

[7] Caliandro, R., Altamura, D., Belviso, B. D., Rizzo, A., Masi, S., Giannini. C. (2019). J. Appl. Cryst. 52, 1104.

In the last years a growing number of studies have been devoted, both experimentally and theoretically, to understanding the structural properties of disorder systems and chemical processes occurring in solution and more clear pictures are emerging. This was possible by the improvements of the experimental techniques and the development of more sophisticated and reliable theoretical models. As we will detail in this presentation, experimentally in the last years X-ray absorption spectroscopy (XAS) played a major role in unravelling many structural aspects of disordered systems and it was exploited to gain unprecedent information on chemical reactions occurring in solution. This was possible by coupling experiments with theoretical simulations and multivariate analysis, and by better exploiting the X-ray absorption near edge spectroscopy (XANES) that is very sensitive to three-dimensional structures. Here, we will show specific applications to several liquid systems and chemical reaction occurring in the ms time scale. Aqueous solutions containing lanthanoid and actinoid ions are analysed with the aim of providing a unified description of the hydration properties of these series. We will show how the combined approach using XAS and molecular dynamics simulations can be applied to the study of complex systems such as ionic liquids and deep eutectic solvents, that represent an innovative research field. Lastly, we will show how it is possible to shed light into mechanistic properties of bimolecular reactions in solution by combining XANES, UV-Vis with multivariate data analysis.

Tektites and impactites are mainly amorphous silicate glass bodies of impact genesis. The conditions, such as pressure (P), temperature (T), oxygen fugacity (fO₂), that existed during glass formation process influence the cation coordination. One of the common elements in impact glasses is iron, so it a useful probe of atmospheric parameters and collision conditions in geological history of Earth. X-ray absorption spectroscopy (XAS) is a direct probe of the local atomic structure around specific element applicable to liquids, single molecules or amorphous solids. Recent developments in theoretical interpretation of the X-ray absorption fine structure along with machine learning (ML) methods opened a new perspective for quantitative structural analysis of complex systems [1,2]. In this work we extend ML-driven fitting procedure to the amorphous structures of tektites, where several inequivalent sites with different coordination numbers can coexist. The analysis was performed in PyFitIt software [3]. For each possible coordination number N = 2…6 we constructed a fragment of silica where Fe ion was coordinated by several (SiO₄) tetrahedral units. Structural parameters of Fe(SiO4)_N cluster were varied to simulate possible bond length variation in amorphous silica both for Fe²⁺ and Fe³⁺ ions, e.g. all Fe-O distances were varied in the range [1.8…2.3 Å].

Figure 1 shows geometry parameters for the three-coordinated Fe ions: distance to the nearest oxygen, distance to the rest two oxygens, bending angle (distortions are marked with overlay of two structures for each of three deformations). In the space of structural parameters we selected a set of 700 points where XANES spectra were calculated by means of finite difference approach implemented within FDMNES software. These spectra were used as training set for machine learning method which established the relation between spectrum and structural parameters. The best quality of approximation was achieved for Radial Basis Functions method. After algorithm was trained the PyFitIt software allows user to predict structural parameters for a given spectrum in the input (so called direct method) or predict spectrum for a given set of structural parameters (so called indirect method, the analogue of multidimensional interpolation). Figure 2 shows the analysis of the Muong-Nong tektite spectrum. The two best fits are shown as red and blue lines and use a combination of 6-coordinated iron ions either with 4-coordinated or 3-coordinated species. The resulting parameters of two fits provided average coordination number <CN>=5.4±0.2 and average Fe-O distance <R>=1.96±0.04 Å which are in a good agreement with classical EXAFS analysis.

Copper molybdate (CuMoO₄) is a thermochromic and piezochromic material, which exhibits structural phase transitions under the influence of pressure and/or temperature that make this material perspective in chromic-related applications starting from the user-friendly temperature and pressure indicators to "smart" inorganic pigments.

Since the functional properties of CuMoO₄ are directly connected with its local structure, X-ray absorption spectroscopy (XAS) is an obvious choice to probe structural changes during temperature variation including the phase transition. However, the interpretation of extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) spectra is not straightforward and often requires the use of advanced simulation tools. Treatment of thermal fluctuations and static disorder in XAS is a complex task, which can be successfully addressed by reverse Monte-Carlo (RMC) method [1, 2].

In this study, we used XAS at the Cu and Mo K-edges to probe the temperature-induced evolution of the local structure of CuMoO₄ in the range from 10 to 973 K (Fig. 1). At low temperatures, the thermochromic phase transition between α-CuMoO₄ and γ-CuMoO₄ with a hysteretic behaviour was observed [3] while at temperatures above 400 K, the thermochromic properties of α-CuMoO₄ were related to temperature-induced changes in the O²⁻ → Cu²⁺ charge transfer processes [4].

The structural information encoded in the EXAFS spectra was extracted by RMC simulations based on an evolutionary algorithm (EA) implemented in the EvAX code [1]. This method allows one to obtain a structural model of such complex material as copper molybdate accounting for multiple-scattering effects as well as structural and thermal disorder contributions in the experimental EXAFS data. The structural models obtained by RMC were used to simulate the Cu K-edge XANES spectra at a high-temperature range, in which the temperature effect is the most pronounced. The simulated XANES spectra are in good agreement with the experiment and reproduce the main temperature-dependent XANES features.

[1] J. Timoshenko, A. Kuzmin, and J Purans, (2014) J. Phys.: Condens. Matter 26, 055401.

[2] I. Jonane, A. Anspoks, and A. Kuzmin, (2018) Model. Simul. Mater. Sci. Eng. 26, 025004.

[3] I. Jonane, A. Cintins, A. Kalinko, R. Chernikov, and A. Kuzmin, (2020) Rad. Phys. Chem. 175, 108411.

[4] I. Jonane, A. Anspoks, G. Aquilanti, and A. Kuzmin, (2019) Acta Mater. 179, 1901132.

Developments over the last two decades have achieved accuracies in attenuation coefficient and X-ray absorption fine structure of below 0.2%. This generally requires careful sample characterisation, monochromator and detector characterisation and additional experimental components to measure and correct for a range of systematics. More recently similar levels of accuracy have been obtained in fluorescence measurement. These techniques, XERT developed by Chantler, Barnea, Tran and group; and Hybrid, developed by Chantler, Tran, Best et al. offer accuracies and insight for disordered systems up to 100x more than previous work. To bring them to standard routine implementations for all users would strengthen hypothesis discrimination and testing for molecular and disordered structure and dynamics including for ideal crystals. In this they are complementary to XRD and ND investigations.

Over the past two years parts of this system have been implemented at the Australian Synchrotron with excellent precision and control of a range of systematics using XERT and Hybrid techniques in both transmission and fluorescence geometries.

Insight includes high accuracy of derived dynamical bond length, thermal parameters, consistency and inconsistency of energy offsets revealed from the data, and structural determination of nearby shells approaching an ab initio manner with XAS. It has allowed exploration of atomic form factors [1], XAFS dynamical bonding [2], electron inelastic mean free paths [3] and nanoroughness [4] appropriate for circuit quality control for microcomputers, with technological offshoots into detector and synchrotron diagnostics. As a consequence, the accurate characterization of fluorescence spectroscopy is developing [5], together with the accurate investigation of organometallic complexes. Further it has allowed investigation of several types of dynamic behaviour including the investigation of the reaction coordinate [6], thermal isotropy, and potentially Debye behaviour. The reaction coordinate investigations permit study of catalytic paths in Amyloid beta, and other electrochemical studies of ifficult or fragile organometallic systems in solid or solution form, at room temperature or in a cryostat.

Perhaps intriguingly, it has permitted the first X-ray measurements of electron inelastic mean free path [7]. This paper will explore the requirements for and applicability of higher accuracy in XAFS, the advantage of theory simultaneously fitting XANES and XAFS [8], and the opportunities for advanced dynamics and Debye studies, in addition to the potential for resolving challenges in catalytic and active centres.

The quality of XAFS data and the intrinsic information content can be outstanding, and its ability to determine bonding and dynamical modes can be unsurpassed. The talk will also look towards future opportunities not yet realised in advanced analysis and disorder measurement.

[1] de Jonge, MD et al., Measurement of the x-ray mass attenuation coefficient and determination of the imaginary component of the atomic form-factor of tin over the energy range of 29 keV – 60 keV, Phys. Rev. A75 032702 (2007)

[2] Glover, JL et al. Measurement of the X-ray mass-attenuation coefficients of gold, derived quantities between 14 keV and 21 keV and determination of the bond lengths of gold, J. Phys. B 43 085001 (2010)

[3] Chantler, CT, Bourke, JD, X-ray Spectroscopic Measurement of the Photoelectron Inelastic Mean Free Paths in Molybdenum, Journal of Physical Chemistry Letters 1 2422 (2010); Bourke, JD, Chantler, CT, Phys. Rev. Lett. 104, 206601 (2010)

[4] Glover, JL et al., Nano-roughness in gold revealed from X-ray signature, Phys. Lett. A373 1177 (2009)

[5] Chantler, CT, et al., Stereochemical analysis of Ferrocene and the uncertainty of fluorescence XAFS data, J Synch. Rad.19 145 (2012)

[6] Best, SP et al., Reinterpretation of Dynamic Vibrational Spectroscopy to Determine the Molecular Structure and Dynamics of Ferrocene, Chemistry - A European Journal, 22 18019-18026 (2016)

[7] Chantler, CT, Bourke, JD, Electron Inelastic Mean Free Path Theory and Density Functional Theory resolving low-Energy discrepancies for low-energy electrons in copper, Journal of Physical Chemistry A118 909-914 (2014)

[8] Bourke, JD et al., FDMX: Extended X-ray Absorption Fine Structure Calculations Using the Finite Difference Method, J Synchrotron Radiation 23 551-559 (2016)

Palladium nanocatalysts play significant role in wide range of reactions such as selective hydrogenation of alkynes. The information extracted during operando experiments on working catalysts allows us to consider various processes from a new point of view. In particular, X-ray absorption near edge structure (XANES) spectroscopy is a powerful tool widely applied for determining atomic and electronic properties of working catalysts [1]. In many cases, analysis of XANES data requires construction of theoretical models with a huge number of variable parameters. In this case, application of machine learning (ML) to in situ and operando XANES offers new horizons for structural characterization [2].

In this work, we discuss the construction of the theoretical models of palladium nanoparticles covering a big number of structural parameters. We investigate how the particle size, concentration of carbon impurities, which can be formed during hydrogenation of alkynes, and their distribution in the bulk and at the surface of palladium particles affect the Pd K-edge XANES features. We demonstrate step-by-step increasing similarity between the experimental difference spectra and theoretical model by increasing the complexity of the theoretical model, e.g. taking into account only interatomic distances (Fig. 1 dashed red), interatomic distances and carbon concentration (Fig. 1 dashed blue) and interatomic distances, carbon concentrations and particle size effects (Fig. 1 green line). Finally, we suggest a set of formal descriptors relevant to possible structural diversity and construct a library of theoretical spectra for ML-based analysis realized in PyFitit software [3].

Figure 1. Experimental difference Pd K-edge XANES for 2.8 nm Pd NPs in acetylene (solid black) and best fit results using theoretical spectra with interatomic distances only (dashed red), interatomic distances and carbon impurities in the bulk (dashed blue), and interatomic distances, carbon impurities in the bulk and surface (solid green) contribution as variable parameters. The best fit made by ML algorithm is represented by purple line [4].

[1] Bordiga, S., Groppo, E., Agostini, G., Bokhoven, J.A. & Carlo Lamberti, C. (2013). Chem. Rev. 113, 1736.

[2] Guda, A.A., Guda, S.A., Lomachenko, K.A., Soldatov, M.A., Pankin, I.A., Soldatov, A.V., Braglia, L., Bugaev A.L., Martini, A., Signorile, M., Groppo, E., Piovano, A., Borfecchia, E. & Lamberti, C. (2019). Catal. Today. 336, 3.

[3] Martini, A., Guda, S.A., Guda, A.A., Smolentsev, G., Algasov, A., Usoltsev, O., Soldatov, M.A., Bugaev, A., Rusalev, Yu., Lamberti, C. & Soldatov, A.V. (2019). Comput. Phys. Commun, 23, 107064.

[4] Usoltsev, O.A., Bugaev, A.L., Guda, A.A., Guda, S.A. & Soldatov, A.V. (2020) Top. Catal., in press.

Crystallography research in Latin America started with the pioneering work of Prof. Ernesto Galloni in Buenos Aires, Argentina, during the 1940s. The progress in several countries was very fast and, during the 1950s and 1960s, courses on crystallography were given regularly in Argentina, Brazil, Chile and Mexico. The first international crystallography course in Latin America was probably the “Latin American course on Pure and Applied Crystallography” held in Santiago, Chile, in 1959, which was the birth of the Ibero American Crystallographic Group. This group organized several meetings and courses during 35 years. Unfortunately, due to economic problems and the long distances among the countries involved, this group was finally dissolved. The Latin American Crystallographic Association (LACA) was founded in October 2013 in Córdoba, Argentina, and recognized as a Regional Association of the IUCr during the 22nd IUCr Congress and General Assembly (Montreal, Canada, August 2014). At present, this association has seven full members (Argentina, Brazil, Mexico, Chile, Costa Rica, Uruguay and Venezuela) and organizes several meetings, schools and OpenLabs. The International Year of Crystallography 2014 (IYCr2014) was an excellent opportunity to increase the work related to education and outreach throughout Latin America and several activities were carried out, including exhibitions, science fairs, art or photo contests, outreach talks, etc. In addition, very successful national crystal growing contests were organized in Argentina, Chile and Uruguay, which also involved short courses on crystallography and crystal growth for primary and secondary school teachers. Most of these activities were organized during several years with great success.

Nowadays, there are an important number of regular local, national or international courses in Latin America, covering all kind of topics: single crystal X-ray diffraction, powder diffraction, fundamental crystallography, protein crystallography, crystallization methods, synchrotron radiation techniques, neutronic techniques, small-angle X-ray scattering, X-ray absorption spectroscopies, etc. Many of them are organized by national crystallographic associations, while LACA has a regular regional Crystallography school. In most of the cases, the topics taught in these courses involve applications in a wide variety of areas, resulting in interdisciplinary activities that are enriching for all the participants.

The COVID-19 pandemic was a global challenge and many congresses, schools, courses and outreach activities in Latin America had to be postponed or cancelled. However, as 2020 progressed, some of these difficulties were overcome. For example, the 3rd LACA school on Small Molecule Crystallography, planned to be held in Mexico in March 2020, was postponed, but it was finally held in a virtual modality in November/December 2020 with great success. Many virtual courses were also organized and some of them, thanks to the online modality, reached new regions or countries. Such was the case of the short courses on crystallography and crystal growth organized by the Argentinian Association of Crystallography (AACr), that in 2020 had to be taught in a new virtual format. These courses received a large number of new participants not only from Argentinian cities not previously visited by AACr members, but also from all over Latin America.

Finally, it is worth to mention that the crystal growing contests organized in Argentina and Uruguay continued in 2020, this time proposing that students work from home with simple and inexpensive materials, without any danger. In the case of the contest organized by the AACr, bibliographic research works related to crystallography were also accepted in the 2020 edition, allowing the participation of students that could not grow crystals at home or school. Once again, both contests were highly successful and are planned to be continued in 2021.

African countries, especially Sub-Saharan Africa, suffers from a severe deficit of engineers and scientists and relies heavily on imported expertise for several reasons including poor quality of education, limited research facilities, and lack of practical experience among graduates. According to the UNESCO’s second engineering report, Africa continues to have the lowest number of engineering professionals per capita of all regions of the world [1]. Hence, developing inclusive high-tech education and research facilities is an efficient way to bridge this gap. That is the purpose of the X-TechLab.

X-TechLab is a regional training platform that aims to provide the region with skills and tools to use X-ray techniques for developing innovative solutions to critical issues in Africa. The initiative is the result of an interaction between the Lightsources for Africa, the Americas, Asia, Middle East, and the Pacific (LAAAMP) and the Sèmè City hub, one of Benin Government’s flagship projects, which aims to create a world-class knowledge and innovation centre in Africa. The goals are to: 1) provide hands-on experience with the use of cutting-edge X-ray equipment, 2) develop X-ray-based problem-solving skills targeting specific socioeconomic issues, 3) meet the requirement for Feeder Facilities that allow the preparation of samples to be studied at world advanced light sources and 4) contribute to the emergence of a community of experts who will be active users of the future African Synchrotron.

Learners participating in the X-TechLab are trained around 2 parallel, interrelated yet distinct, tracks: Crystallography and X-ray diffraction techniques, including both single and powder diffraction applied to structural studies; and Absorption and phase contrast X-ray imaging (Microtomography) using mathematical tools for research on sustainable and ecological materials. Started in 2019, X-TechLab training sessions gathered many scientists from several countries and scientific disciplines. As shown in the figure below, 84 participants with 1/3 of women from 12 African countries (Benin, Burkina Faso, Burundi, Cameroon, Congo-Brazzaville, Côte d’Ivoire, Democratic Republic of Congo, Ethiopia, Ghana, Nigeria, Senegal, Togo) have been trained [2]. About 20 Experts from several academic institutions worldwide (Africa, Europe, USA) are involved in the training sessions. This will emphasize the unique potential of X-ray techniques as a multidisciplinary tool for development in Africa.

Modern crystallography, as an umbrella of techniques and methods, reaches out to almost everyone interested in the basic question: how are atoms or molecules arranged in a material. This inherent interdisciplinarity of crystallography is further supported by availability of various schools for aspiring crystallographers. On one hand, a well-curated content, good choice of lecturers, and offered sponsorships, make it possible to reach out to students from various backgrounds, interests, regions and economic status. On the other, on-site presence and a good social program ensure interactions between lecturers, students and organizers. Having all this in mind, the success of these schools is not a coincidence. Their interdisciplinarity seems to rely on three factors: content, outreach and interactivity.

In the last year, COVID19 has forced many of crystallographic schools and initiatives to undergo a digital transformation. Emergence of virtual schools has removed many restraints imposed by physical presence in real space: costs, time and geographical limitations, and recruitment of lecturers and speakers. However, it also opened up new questions. What are the needs of a modern researcher/crystallographer? Can crystallography get more interdisciplinary by adopting new fields, such as didactics, communications and economics? Can modern technology be used to enforce interdisciplinarity by improving interactivity, outreach and content?

This presentation looks back to the past and then turns to the future in order to examine possible ways that could be taken to optimize content, outreach and interactivity in both real and virtual schools. Examples are focused on building and maintaining crystallographic communities and include use of social media, industry-academia collaborations, and online interaction tools.

chrome chrome

chrome chrome

From December 2010 till December 2020, I have been involved in over a dozen schools and short courses in different countries of Latin America where I -alone or as part of a group of Lecturers- have been teaching crystallographic symmetry and the International Tables for Crystallography Volume A: Space Group Symmetry (ITC-A). I was not new to teaching symmetry in 2010 since I have taught an undergraduate course of Crystallography for Chemists at my institution since 1995. However, the first of these international schools, and the one I have been involved in more times (the International School on Fundamental Crystallography with MaThCryst Commission [1]), has pushed me to teach symmetry in many other schools devoted to single crystals and/or powder X-rays and/or neutron diffraction, that have recently evolved to virtual schools (such as the 3^rd LACA School on Small Molecule Crystallography [2]). This lecturing has allowed me to meet all sorts of students/researchers of very different backgrounds from most of the countries of the region, as well as interacting with many colleagues working in different areas of crystallography, solid-state physics/chemistry, and materials science. With the aim of improving the learnings of students over the years, I have tried to make systematic observations of the background, difficulties, and outcomes of participants in the different kinds of schools. It is significantly different to evaluate the outcome of learning symmetry in very different course formats having a total time of symmetry lectures of 40, 15, or 4 hours. Moreover, it could be argued that nobody could learn any significant concept about crystallographic symmetry in 4 hours. However, the need of students and users/practitioners of crystallography coming from different disciplines, of having at least the minimal rudimentary tools to deal with symmetry in everyday work makes it worth it. Figure 1 shows two extracts of the many evaluation forms I have collected in the last decade. In this presentation, I will show the main conclusions of the evaluations regarding the fundamental part of the courses, and more specifically symmetry and the ITC-A, and share some of the strategies I have developed to give students with common or varied background the best tools I consider could make a difference for their understanding of symmetry, even in the very unfavourable conditions of teaching 2 hours of theoretical and 2 hours practical sessions. Luckily this will help other colleagues improve their teaching work, as well as giving me feedback for my next 10 years of teaching symmetry.

[1] https://www.crystallography.fr/mathcryst/meetings.php (scroll down to Schools in Latin America).

[2] https://www.iquimica.unam.mx/LACA/

I would like to acknowledge M.I. Aroyo and M. Nespolo from MaThCryst Commission and J. Ellena and H. Napolitano from LACA for pushing me to organize schools and Open-labs in Montevideo, Uruguay that have eventually made me specialize in teaching crystallographic symmetry in local and international schools in the Latin American region. I would also like to thank all the colleagues that have shared the heavy but rewarding task of organizing and Lecturing in the Schools I have been involved in over the years. I would finally want to dedicate this abstract to the memory of Prof. Dr. Graciela Punte from LANADI, Universidad Nacional de La Plata, Argentina for being an inspiring crystallographer and teacher and selflessly contributing to the current development of the Latin American and particularly the Uruguayan community of Crystallographers.

Resources to develop high impact skills in diffraction data collection and interpretation can be limited by facility access, expert availability, and the budgetary requirement to meet a critical mass of participants before it becomes practical to offer instruction. At the local level, shared resources between institutions, as well as curriculum approaches that incorporate scaffolding practices from first year general chemistry to senior undergraduate capstone courses, can be employed to equip trainees with skills in structural science.¹ Looking to the regional and (inter)national level, the Canadian National Committee for Crystallography (CNCC)¹ sponsors the annual Canadian Chemical Crystallography Workshop (CCCW) and the Canadian Powder Diffraction Workshop (CPDW), both which have now past their first decades of instruction. Several hundred trainees from Canada, and well beyond (for example, the US, UK, and Brazil) have participated in these opportunities.

As a university instructor, the organizer for CCCW2019 – 2021, and an administrative supporter of CPDW, this presentation will highlight (1) the diversity of experiences that attendees have, (2) logistical aspects of organizing and teaching in these various ventures, with a look at the transition to remote delivery for CCCW2020 and 2021, amid the current pandemic, and (3) I will share some insights and results from past trainees whose research practices have been transformed as a result of these learning opportunities.

1. Gražulis, S.; Sarjeant, A. A.; Moeck, P.; Stone-Sundberg, J.; Snyder, T. J.; Kaminsky, W.; Oliver, A. G.; Stern, C. L.; Dawe, L. N.; Rychkov, D. A.; Losev, E. A.; Boldyreva, E. V.; Tanski, J. M.; Bernstein, J.; Rabeh, W. M.; Kantardjieff, K. A. Crystallographic Education in the 21st Century. J. Appl. Crystallogr. 2015, 48, 1964–1975. https://doi.org/10.1107/S1600576715016830.

2. Canadian National Committee for Crystallography: https://xtallography.ca/

We are privileged in crystallography that every published crystal structure is shared through established databases and that scientists worldwide can gain new insights from these collections. The Cambridge Crystallographic Data Centre (CCDC) was set up to curate and distribute one of these databases, the Cambridge Structural Database (CSD), a resource containing over one million experimental crystal structures.

As a non-profit organisation sharing data from crystallographers worldwide the CCDC has always had a keen interest in developing material to help others to use structural data to teach both chemical concepts and crystallography. More recently we have realised that we also need to use our position in the scientific community to engage students and researchers to help promote interdisciplinarity in research.

This presentation will highlight some of our efforts to cultivate more interdisciplinarity in science from the establishment of new guidelines, partnerships, links and community initiatives. We will explore recent activities to engage scientists across research areas and ages through our involvement in a variety of schools, workshops and science festivals globally. We will also share our experiences in creating more virtual resources including a new series of CCDC virtual workshops and on-demand training courses through CSD University.

Finally, we will reflect on some of the challenges we have faced, what we have learnt from our experiences and look at what more could be done to increase interdisciplinarity in science.

Structure prediction, and the theoretical computation of reliable superconducting transition temperatures, have undoubtedly played a major role in the discovery of novel high temperature superconductivity in dense hydrides.[1] While the field has delivered room temperature superconductivity,[2] the technological relevance will be limited while the phenomenon is restricted to extremely high pressures. Furthermore, the number of experimental research groups that can study the properties of these compounds at megabar pressures is limited, restricting the potential scientific impact. Rightly, the field is focusing on identifying compounds that superconduct at high temperatures, but much lower pressures. But there are considerable obstacles to progress. The number of theoretical candidates far exceed those experimentally confirmed, suggesting more attention should be paid to predicting synthesisability. It is becoming clear that metastability favours high temperature superconductivity, but how should we choose from the multitude of metastable candidates? Experimentally determined structures are frequently not found to be dynamically stable in static calculations, but full dynamics is computationally expensive, and difficult to account for in high throughput searches. At the same time, it is not clear how to compute superconducting transition temperatures in highly dynamic systems. So far, most attention has been paid to perfect crystals. Doping and deviation from perfect stoichiometry, and well as defects (both point, and extended, such as grain boundaries and interfaces) are likely to be important to the detailed properties of these materials. Finally, as we turn to exploring a broader range of compounds, in the ternaries and beyond, structure prediction becomes more challenging, not least in terms of the management of the quantities of data generated, and the computation of large numbers of superconducting transition temperatures. I will show some recent results which go some way to addressing this.

[1] Pickard, Chris J., Ion Errea, and Mikhail I. Eremets. "Superconducting hydrides under pressure." Annual Review of Condensed Matter Physics 11 (2020): 57-76.

[2] Snider, Elliot, Nathan Dasenbrock-Gammon, Raymond McBride, Mathew Debessai, Hiranya Vindana, Kevin Vencatasamy, Keith V. Lawler, Ashkan Salamat, and Ranga P. Dias. "Room-temperature superconductivity in a carbonaceous sulfur hydride." Nature 586, no. 7829 (2020): 373-377.

The remarkable high-temperature superconducting behavior of H₃S (T_C=200 K, [1]) and LaH₁₀ (T_C=250 K [2]) at about 150 GPa catalyzed the search for superconductivity in compressed ternary hydrides. The highest critical temperature of 288 K at 275 GPa has been found recently in the C-S–H system [3]. High-temperature superconductivity in these compounds is due to the formation of metallic hydrogen sublattice, which is obtained by pulsed laser heating of various elements with hydrogen at extremely high pressures achieved during compression on diamond anvils. In this report we will present new results of studies of high-pressure chemistry, magnetic and superconducting properties of YH₆, UH₇, ThH₁₀, CeH_9-10, PrH₉, NdH₉, EuH₉ and BaH₁₂ binary and (La,Y)H₁₀ ternary polyhydrides discovered in the last 2 years by collaboration of IC RAS, LPI, Skoltech and Jilin University (China). Perspectives of design of light and magnetic sensors (SQIUDs) based on superhydrides synthesized in miniature diamond anvil cells will be discussed.

References:
[1] Drozdov A P, Eremets M I, Troyan I A, Ksenofontov V and Shylin S I, 2015, Nature, 525, 73–76.
[2] Drozdov A P, Kong P P, Minkov V S, Besedin S P, Kuzovnikov M A,Mozaffari S, Balicas L, Balakirev F F, Graf D E, Prakapenka V B,Greenberg E, Knyazev D A, Tkacz M and Eremets M I, 2019, Nature 569, 528–531.
[3] Snider E, Dasenbrock-Gammon N, McBride R, Debessai M, Vindana H, Vencatasamy K, Lawler K, Salamat A et al., 2020, Nature, 586, 373–377.

Artem R. Oganov

Skolkovo Institute of Science and Technology, 3 Nobel St., 121205 Moscow, Russia

Chemical behavior of the elements can be rationalized and anticipated based on a few properties, such as electronegativity, radius (atomic, ionic, van der Waals radii), polarizability, valence state. Among these, electronegativity plays perhaps the most important role – chemical reactivity of the elements, bond energies, directions and heats of reactions, and many properties of molecules and solids are related to electronegativities of the elements. The oldest and the most widely used is Pauling’s scale of electronegativity, developed in 1932 (see [1]) and based on bond energies. However, later it was found (e.g., [2]) that Pauling’s formula, relating bond energies with electronegativity differences, is very inaccurate for significantly ionic bonds. We have proposed [3] another formula, which works well for bonds with any degree of ionicity, and obtained a new thermochemical scale of electronegativities for all elements. New electronegativities better follow chemical intuition than traditional Pauling’s values (e.g. charge transfer in transition metal borides and hydrides is described qualitatively better, and so are oxyacids).
We have also studied another important concept – Mendeleev numbers, introduced in 1984 by Pettifor [4]. Pettifor showed that chemical behavior of the elements can be approximately characterized by just one number, which he called the Mendeleev number; he assigned these numbers to all elements, but the physical meaning of these remained unclear. We have shown [5] that Mendeleev number can be obtained by principal components analysis (PCA) or even a simple linear correlation applied to the set of points “atomic radius – electronegativity – polarizability” of all elements. This dimensionality reduction gives a single variable giving mathematically the best one-parameter description of the chemistry of the elements – the Mendeleev number. We have shown [5] that thus defined Mendeleev numbers perform better than those proposed by Pettifor [4]. Accurate representations of the chemical space require all key properties of the atoms to be explicitly used, but reduced-dimensionality representations (such as representation by Mendeleev numbers) allow easier visualization of big data.

This work is funded by Russian Science Foundation (grant 19-72-30043).

[1] Pauling, L. The Nature of the Chemical Bond 3rd edn (Cornell University Press, 1960).
[2] Matcha, R. L. (1983). Theory of the chemical bond. 6. Accurate relationship between bond energies and electronegativity differences. J. Am. Chem. Soc. 105, 4859–4862.
[3] Tantardini C., Oganov A.R. (2021). Thermochemical electronegativities of the elements. Nature Communications 12, 2087.
[4] Pettifor D.G. (1984). A chemical scale for crystal structure maps. Solid State Commun. 51, 31-34.
[5] Allahyari Z., Oganov A.R. (2020). Nonempirical definition of Mendeleev numbers: organizing the chemical space. J. Phys. Chem. C124, 23867-23878.

The hybrid inorganic–organic material [(CH₃)₂NH₂]₂NiCl₄ was reported to exhibit a remarkable thermochromism. [1] The color of this compound rapidly changes from deep red to deep blue upon heating at 383 K. Surprisingly, upon cooling to room temperature, the deep blue compound changes its color to dark, golden yellow. The so-produced yellow compound spontaneously transitions back to the starting deep red compound upon prolonged storage at ambient conditions. This color-change sequence can be cycled for a number of times without apparent degradation. Originally, it was believed that the color change originates from temperature-induced changes in the local geometry around the Ni⁺² cations in the structure. To shine light at these processes, we performed detailed studies using synchrotron X-ray powder diffraction, with diffraction data collected as a function of temperature. We discover that rather than undergoing thermochomic transitions, this compound is in fact a reacting system and the different color originate from different crystalline phases. The crystal structure and composition of these phases was solved and refined using the diffraction data. These structures were used to rationalize the color changes. This contribution emphasized the importance of powder X-ray diffraction, and crystallography in general, in the mechanistic studies of the stimuli-responsive crystalline compounds.

Molecules that change their colour, structure, and electronic properties in response to an external stimulus represent an emerging class of ‘smart’ material with potential applications in sensing, actuating and responsive technologies. The spin crossover (SCO) phenomenon leads to a redistribution of electrons within the d-orbitals of some transition metal complexes as a result of an external perturbation such as changes in temperature, pressure changes and light irradiation. The transition between high spin and low spin states involves a significant change in molecular volume and is often cooperative in crystalline materials, leading to dramatic changes in the optical, mechanical and magnetic properties.

We have demonstrated the use of mechanochemistry in the synthesis of SCO materials,¹ and have recently shown that they can be synthesised through contact of the reagents in the solid state without any applied mechanical force.² Recent work in our group has shown the significant promise of using supramolecular interactions to design new SCO materials with tunable thermally-responsive properties.³ This talk will focus on how various stimuli can affect the synthesis, structure and properties of these SCO materials in the solid state.

Rotors, motors and switches in the solid state find a favorable playground in porous materials, such as Metal Organic Frameworks (MOFs), thanks to their large free volume, which allows for fast dynamics. We fabricated MOFs with reorientable linkers and benchmark mobility also at very low temperature, to reduce the energy demand for motion-activation and light stimulus-response.

In particular, we have realized a fast molecular rotor in the solid state whose rotation speed approaches that of unhindered rotations in organic moieties even at very low temperatures (2 K). The rotors were hosted within the struts of a low-density porous crystalline MOF and energetically decoupled from their surroundings. A key point was the unusual crossed conformation adopted by the carboxylates around the pivotal bond on the rotor axle, generating geometrical frustration and very shallow wells along the circular trajectory. Continuos, unidirectional hyperfast rotation with an energy barrier of 6.2 cal/mol and a high frequency persistent for several turns is achieved (10 GHz below 2 K).[1]

Responsive porous switchable framework materials endowed with light-responsive overcrowded olefins, took advantage of both the quantitative photoisomerization in the solid state and the porosity of the framework to reversibly modulate the gas adsorption in response to light. [2]

Motors were inserted into metal-organic frameworks wherein two linkers with complementary absorption-emission properties were integrated into the same materials. Therefore, unidirectional motion was achieved by simple exposure to sun-light of the solid particles, which thus behave as autonomous nanodevices.[3]

MOF nanocrystals comprising high-Z linking nodes interacting with the ionizing radiation, arranged in an orderly fashion at a nanometric distance from diphenylanthracene ligand emitters showed ultrafast sensitization of the ligand fluorescence, thus supporting the development of new engineered scintillators.[4]

References

1. J. Perego, S. Bracco, M. Negroni, C. X. Bezuidenhout, G. Prando, P. Carretta, A. Comotti, P. Sozzani Nature Chem. 2020, 12, 845.

2. P. Sozzani, S. Bracco, S. J. Wezenberg, A. Comotti, B. L. Feringa et al. Nature Chem. 2020, 12, 595.

3. W. Danowski, F. Castiglioni, A. Comotti, B. L. Feringa et al. J. Am. Chem. Soc. 2020, 142, 9048.
4. J. Perego, F. Meinardi, S. Bracco, A. Comotti, A. Monguzzi et al. Nature Photonics 2021, doi 10.1038/s41566-021-00769-z.

Molecular crystals can be bent elastically by simultaneous expansion and contraction or plastically by delamination into slabs that glide along slip planes [1,2]. Here we describe a hitherto unreported mechanism of crystal bending in terephthalic acid crystal which undergoes pressure-induced phase transition upon bending where the two phases (form II and form I) coexist at ambient conditions. Scanning electron microscopy and microfocus XRD using synchrotron radiation provided direct evidence that upon bending, terephthalic acid crystals can undergo a mechanically induced phase transition without delamination and their overall crystal integrity is retained [3]. We report a distinctly different mechanism of plastic bending of molecular single crystals which have two phases and we provide the crystal structure of the bent section of such plastically bent crystal as direct evidence of the proposed mechanism. We also establish that this plastic deformation which effectively results in coexistence of two phases in the bent section of the crystal is the origin of unconventional properties such as shape-memory and self-restorative effects. Such plastically bent crystals act as bimorphs and their phase uniformity can be recovered thermally by taking the crystal over the phase transition temperature. This recovers the original straight shape and the crystal can be bent by a reverse thermal treatment, resulting in shape memory effects akin of those observed with some metal alloys and polymers. We anticipate that similar memory and restorative effects are common for other molecular crystals having metastable polymorphs.

[1] Ahmed, E., Karothu, D. P. & Naumov, P. (2018). Angew. Chem. Int. Ed. 57, 8837. [2] Naumov, P., Chizhik, S., Panda, M. K., Nath, N. K. & Boldyreva, E. (2015). Chem. Rev. 115, 12440. [3] Ahmed, E., Karothu, D. P., Warren, M. & Naumov. P (2019). Nat. Commun. 10, 3723.

Laser beam machining (LBM) of ceramics, polymers, or metals is usually performed using high-power femtosecond lasers (4–20 W). Using LBM, micro- or nano-sized patterns can be machined into surfaces of these materials to alter their properties for various applications. A drawback of such high-power techniques is the possibility of considerable chemical damage to the surface of the machined materials.

We now report the use of halogen bonding to generate new dye-based cocrystals with volatile cocrystal-forming molecules (coformers) that can be etched, cut, and punctured with micrometer-scale precision using low-powered laser beams (for example, between 0.5 and 20 mW).[1] This unique phenomenon, shown to be wavelength-tunable and power-dependent, can be utilized to machine molecular crystals by forming holes or cuts of controllable sizes. Using a microscope-guided low-power laser beam numerical control of this process can be achieved, enabling a variety of complex patterns to be inscribed onto the surface of molecular cocrystals. A mechanism is proposed with the volatile conformer acting as a leaving group, giving the ability to gently inscribe patterns using a low-power laser beam, without chemical decomposition of the cocrystals. This has not been previously reported in small molecule organic solids and appears to be a new emergent property achievable through crystal engineering by halogen bonding, opening a new type of materials to micrometer-scale shaping and machining applications.

[1] Borchers, T. H., Topić, F., Christopherson, J. -C., Bushuyev, O. S., Vainauskas, J., Titi, H. M., Friščić, T. & Barrett, C. J. (2021). ChemRxiv. https://doi.org/10.26434/chemrxiv.14398856.v1

Mechanical crystals are expected to be applicable for actuators and soft robots. Before the past decade, we have developed many mechanical crystals based on photoisomerization, and some based on phase transition and photothermal effect. In 2019, we have found a new kind of phase transitions, referred to as the photo-triggered phase transition. The photochromic crystal exhibiting a thermal, reversible single-crystal-to-single-crystal phase transition upon heating and cooling, transform to the identical phase upon light irradiation at temperatures lower than thermal phase transition temperature. A chiral salicylidnephenylethylamine [enol-(S)-1] crystal is known to undergo photoisomerization, and thermal phase transition. We have found that the enol-(S)-1 crystal exhibited the photo-triggered phase transition.

Upon heating, the enol-(S)-1 crystal in the α-phase (P2₁) transformed to the β-phase (P2₁2₁2₁) with the discontinuous β-angle change to 90° at 0 °C due to thermal phase transition from monoclinic to orthorhombic crystal system. Under UV light (365 nm) irradiation, the α-phase changed to the β-phase even at -30 °C. The mechanism was revealed that the photo-triggered phase transition is driven by the strain near the irradiated surface produced by the photoisomerization. A thick crystal in the α-phase deformed by the photo-triggered phase transition to the β-phase upon UV light irradiation; the surface temperature did not reach the thermal phase transition temperature. Furthermore, the thin plate-like crystal exhibited two-step bending motion by the photo-triggered phase transition and then the photoisomerization. Finally, by alternate irradiation of UV and visible light (488 nm) from the left, the plate-like crystal on the glass surface locomoted in the lower right direction. This finding leads to generalize the photo-triggered phase transition phenomenon and indicates that the photo-triggered phase transition enables to create various motions of crystals such as locomotion.

Over the recent decade, functional electronic materials design and discovery have shifted way from chemical-intuition-based towards data-driven synthesis and simulation. Numerous machine learning models have been developed to successfully predict materials properties and generate new crystal structures. Most existing approaches, however, rely much upon physical insights to construct handcrafted features (descriptors), which are not always readily available. For novel materials with sparse prior data and insufficient physical understanding, conventional machine learning models display limited predictability. In this talk, I will address this challenge by introducing an adaptive optimization engine for materials composition optimization, where feature engineering is not explicitly required. I then describe a use case where multi-objective Bayesian optimization with latent-variable Gaussian processes is utilized to accelerate the design of electronic metal-insulator transition compounds. Next, I will present a quantitative study on the structure-property relationship in crystal systems enabled by deep neural networks. The model which learns the structural genome could identify intrinsically similar structures in Fourier space. Finally I propose that these two methods could work harmoniously with each other towards an iterative exploration of novel functional materials.

That X-rays can affect the structure, and therefore functionality, of materials is well established. In macromolecular crystallography,

the phenomenology of ‘radiation damage’ is a mature and important field.[1] Conversely, discussions about radiation damage in small molecule crystallography are rarer and only starting to be identified.[2] X-ray-induced effects are somewhat less well studied in conventional inorganic systems, despite being implicated in a number of interesting phenomena. Examples include decomposition, conductivity enhancement, colour changes, spin-crossover, charge transfer, cell-parameter changes, crystallisation, and amorphisation.[3–5]

Cadmium cyanide, Cd(CN) ₂, is a flexible coordination polymer best studied for its strong and isotropic negative thermal expansion (NTE) effect. In this talk I will show that this NTE is actually X-ray exposure dependent: Cd(CN) ₂ contracts not only on heating but also on irradiation by X-rays.[6]

This behaviour contrasts that observed in other beam-sensitive materials, for which X-ray exposure drives lattice expansion. We call this effect ‘negative X-ray expansion’ (NXE) and suggest its origin involves an interaction between X-rays and cyanide ‘flips’; in particular, we rule out local heating as a possible mechanism.[7] Irradiation also affects the nature of a low-temperature phase

transition. Our analysis resolves discrepancies in NTE coefficients reported previously on the basis of X-ray diffraction measurements, and we establish the ‘true’ NTE behaviour of Cd(CN) ₂ across the temperature range 150–750 K. The interplay between irradiation and mechanical response in Cd(CN)₂ highlights the potential for exploiting X-ray exposure in the design of functional materials.

[1] E. F. Garman (2010) Acta Cryst. D 66, 339–351.

[2] J. Christensen, P. N. Horton, C. S. Bury, J. L. Dickerson, H. Taberman, E. F. Garman and S. J. Coles (2019) IUCrJ, 6, 703–713

[3] V. Kiryukhin, D. Casa, J. P. Hill, B. Keimer, A. Vigliante, Y. Tomioka and Y. Tokura (1997), Nature, 386, 813–815.

[4] H. Ishibashi, T. Y. Koo, Y. S. Hor, A. Borissov, P. G. Radaelli, Y. Horibe, S.-W. Cheong and V. Kiryukhin (2002), Phys. Rev. B

66, 144424

[5] M. Tu et al., (2021) Nat. Mater. 20, 93–99

[6] C. S. Coates, C. A. Murray, H. L. B. Boström, E. M. Reynolds and A. L. Goodwin (2021) Mater. Horiz.

The crystal chemistry of A^IB^IIXO₄ (A^I = Alkali ion, B^II = alkali-earth ion, X = P, V, As) is very rich and has been widely investigated, particularly the phosphate family [1]. In recent years, we have been investigated the crystal structures [2,3] and magnetic properties of some compositions within the A^IB^IIXO₄ series [4]. Besides the pure interest from a crystal chemistry point of view, the research activity related to this series of materials is driven mainly due to their ferroelectric, ferroelastic properties and possible applications as phosphors for LEDs [1, 5]. Within the rich A^IB^IIVO₄ sub-family (X = V), we have recently found a new structural type: the larnite structure with the composition NaSrVO₄ [3]. In this contribution, we are investigating its counter phosphate composition.

Despite its simple chemistry NaSrPO₄ has never been reported so far. Here, we present the synthesis, crystal structure and phase transitions of this phosphate. Surprisingly, this material exhibits a complex structure (31 atoms in the asymmetric unit-cell, Z = 10) at room temperature characterized by a strongly under bonded Na atom. This under-bonded atom is responsible for the complex and rich phase diagram as function of temperature as illustrated in Fig. 1. NaSrPO₄ exhibits 4 phase transitions between room temperature and 750°C. Besides its rich phase diagram, NaSrPO₄ exhibits a re-entrant phase transition slightly below 600°C before to reach a hexagonal paraelastic phase at high temperature. In addition, we show that the sequence of phase transitions is strongly driven by the history of the sample and several phases can be quenched at room temperature. Finally, the co-existence of Na channels within the structure with weakly bounded Na atoms makes this material a likely candidate for ionic conductivity.

[1] Isupov, V. A., (2002). Ferroelectrics 274, 203.

[2] Nénert, G., O’Meara, P. , Degen, T. (2017). Phys. Chem. Minerals 44, 455.

[3] Nénert, G., (2017). Z. Kristallogr. 232, 669.

[4] Nénert, G., et al. (2013). Inorg. Chem. 52, 9627.

[5] Choi, S., Yun, Y. J. , Kim, S. J., Jung, H.-K. (2013) Opt. Lett. 38, 1346.

Sr₂TiO₄, first member of the Ruddlesden-Popper series Sr_n+1Ti_nO_3n+1, has been long known to undergo a phase transition at 1550 °C. This transition makes the growth of single crystals of this material highly challenging, because it usually breaks the crystal into a periodic array of uneven lamellae. While the low temperature tetragonal phase is widely studied due to its close connection to the famous perovskite SrTiO₃, there is little information about the high temperature α-phase, except for an unindexed powder pattern by Drys&Trzebiatowski [1].

We stabilized the high-temperature α-Sr₂TiO₄ crystals by rapid cooling of the incongruent melt from above the liquidus temperature. The α-phase crystallizes in the orthorhombic Pna2₁ group with lattice parameters a=14.2901(5) Å b=5.8729(2) Å c=10.0872(3) Å and is isostructural to the orthorhombic forms of Sr₂VO₄ and Sr₂CrO₄ (which belong to the β-K₂SO₄ structure type). Its structure is formed by a complicated framework of large SrO_x polyhedra with tetrahedral cavities occupied by the transition metal. The tetrahedral coordination of Ti^IV makes the α-Sr₂TiO₄ quite a rare case among titanate compounds, the only other known example being the barium orthotitanate Ba₂TiO₄ [2].

However, whereas in Ba₂TiO₄ the coordination is tetrahedral in both high- and low-temperature polymorphs and the topotactic relation between the two is known, in the case of Sr₂TiO₄ a transition occurs to the layered Ruddlesden-Popper structure with octahedral titanium coordination.

In this work, we report for the first time the crystal structure of the high-temperature α-phase of Sr₂TiO₄. We elucidate the structural differences between the related compounds and discuss possible mechanism driving the structural transition.

[1] Drys, M., Trzebiatowski, W. (1957). Roczniki Chemii. 31, 489.

[2] Gunter, J., Jameson, G. (1984). Acta Cryst. C40, 207.

Magneto-caloric materials offer the possibility to design environmentally friendlier thermal management devices compared to the widely used gas-based systems [1]. These materials exhibit a change in entropy (ΔS_M) or a temperature change (ΔT_ad) when subjected to a magnetic field under isothermal or adiabatic conditions, respectively. The magnitude of change is largest about the materials Curie temperature (T_c) due to the order-disorder phase transition of the magnetic moments within the system. A suitable material must present a large magneto-caloric effect over a broad temperature span together with suitable secondary application parameters such as low heat capacity and high thermal conductivity. MnZnSb is derived from the PbFCl structure (in which the Mn sites are arranged within two-dimensional square nets), resulting in a pseudo 2D itinerant ferromagnetism which orders just above room temperature.

The first structural study reports that MnZnSb crystallises in the same anti-PbFCl-type structure as Mn₂Sb, with the tetragonal space group P4/nmm [2]. However, results from our experiments suggests that the true structure is more complex than this and has some aperiodic nature. Electron diffraction, in-house X-ray diffraction (Fig. 1(b)) and D20 neutron diffraction (Fig. 1(c)) data on powder samples all suggest that there is a small distortion of the tetragonal cell to a triclinic subgroup cell. As well as this, there appears to be incommensurate modulations in atomic positions and possibly Mn-Zn occupation (which is only seen in the neutron data). In the variable temperature neutron diffraction, we have also uncovered an unreported structural transition at ~130 K.

We have investigated the magneto-caloric properties of MnZnSb [3] using a combination of computational and experimental methods, including samples in which some Mn is substituted with Fe and Cr. Scaling analysis of the magnetic properties determines that they are second order phase transition ferromagnets and neutron diffraction has determined that the magnetic entropy change (Fig. 1(a)) is driven by the coupling of magneto-elastic strain in the square net through the magnetic transition. The primary and secondary application related properties have been measured experimentally, and the c/a parameter is identified as an accurate proxy to control the magnetic transition. Chemical substitution on the square net affords tuning of the Curie temperature over a broad temperature span between 252 and 322 K.

The epsilon phase of Fe₂O₃ (ε-Fe₂O₃, its least known polymorph) has gained considerable interest due to its intriguing properties and great application potentials. In the last few years this rare polymorph has received extraordinary attention due to its unique physical properties: it stands out for its huge coercive field (up to 2 T at room temperature), millimeter-wave ferromagnetic resonance, magneto-electric coupling, room temperature ferroelectricity, non-linear magneto-optical effect and photocatalytic activity [1-4].

ε-Fe₂O₃ presents a complex noncentrosymmetric structure (Pna2₁) with four distinct Fe sublattices: two positions in distorted octahedra (Fe1 and Fe2), one in regular octahedral environment (Fe3r), and one in distorted tetrahedral sites (Fe4t). This work examines the structural and magnetic phase transitions in ε-Fe₂O₃ nanoparticles (~20 nm) combining synchrotron X-ray and neutron diffraction measurements in the range 2-900 K. Complemented with X-ray absorption spectroscopy (XAS) and angle-dispersive X-ray diffraction under pressure up to 34 GPa.

The origin of the spin frustration was studied in the context of the rich magnetic phase diagram (with four different successive magnetic states) and its relationship with the magnetostructural transitions observed as a function of temperature. The successive magnetic transitions have been thoroughly studied in the whole temperature range, and have been fully described using the magnetic space groups approach. We have found that the spin frustration at the Fe³⁺ tetrahedral-site (Fe4t) not only is responsible for the unexpected different FIM1 (soft) and FIM2 (super-hard) commensurate ferrimagnetic phases [5], but also it is at the origin of the singular FIM2-to-ICM magnetic phase transition that disrupts the super-hard ferrimagnetic state of Pna'2₁' magnetic symmetry.

The structural evolution of ε-Fe₂O₃ is investigated across the magnetic transitions, putting the emphasis on the FIM1 (soft) to FIM2 (super-hard) phase transition. The observed coupling between structural and magnetic features explains the changes in the magnetic structures associated to the soft and super-hard phases. Puzzling changes are also observed between 150 and 100K, at the commensurate-incommensurate magnetic phase transition (FIM2-ICM) under cooling. The spiral magnetic structure previously proposed below 100 K does not match our neutron diffraction data. Incommensurate (ICM) collinear solutions compatible with neutron data are presented. This transition reduces the coercivity of ε-Fe₂O₃ (from 20 kOe to 0.8 kOe) and its ICM magnetic order (ground state) involves the formation of magnetic antiphase boundaries.

Finally, we report a polar-nonpolar structural phase transition under pressure associated to the volume collapse reported in [6]. The symmetry changes induced by pressure are fully described. The implications of this new centrosymmetric structure for understanding the mechanisms that allow the switching of the ferroelectric polarization in ε-Fe₂O₃ thin films are also analyzed.

[1] Namai, A.; Yoshikiyo, M.; Yamada, K.; Sakurai, S.; Goto, et al. (2012). Nature Commun. 3, 1035.

[2] Gich, M.; Fina, I.; Morelli, A.; Sánchez, F.; Alexe, M.; Gàzquez, J.; Fontcuberta, J.; Roig, A. (2014). Advanced Materials, 26, 4645.

[3] Xu, K.; Feng, J. S.; Liu, Z. P.; Xiang, H. J. (2018,). Physical Review Applied 9, 044011.

[4] X. Guan, L. Yao, K. Z. Rushchanskii, S. Inkinen, R. Yu, M. Ležaić, F. Sánchez, M. Gich, et al. (2020). Adv. Electron. Mater. 6, 1901134.

[5] García-Muñoz, J. L.; Romaguera, A.; Fauth, F.; Nogués, J. & Gich, M. (2017). Chemistry of Materials 29 (22), 9705.

[6] Sans, J. A., Monteseguro, V. et al. (2018). Nature Communications 9, 4554.

Keywords: ε-Fe₂O₃ , multiferroics, magnetic structures, magnetostructural coupling, nanoparticles

We acknowledge financial support from the European Research Council (ERC) under the EU Horizon 2020 programme (grant agreement No. [819623]). Also from the Spanish Ministerio de Ciencia, Innovación y Universidades (MINCIU), through Project No. RTI2018-098537-B-C21, cofunded by ERDF from EU, “Severo Ochoa” Programme for Centres of Excellence in R&D (FUNFUTURE (CEX2019-000917-S)) and MALTA Team network (RED2018-102612-T). We also acknowledge ILL and ALBA synchrotron for provision of beam time.

Simple solids such as TaS₂, NbSe₂, and CdI₂ show surprisingly complex polytypic behaviour where a number of crystalline structures can form whose unit cells differ only along their c-axis [1, 2]. This phenomena arises due to the differences in stacking sequences of the AB₂ layers along the c-axis. Although models have been developed to explain the complex phase behaviour, no model thus far has been able to account for all polytypes formed in practice [3, 4].

In this study we look at a new way of describing the structure of layered AB₂ compounds. Focusing on the layered dichalcogenides, we translate their structural degrees of freedom to a 1D model of coupled Ising chains to explain the polytypic behaviour. Our analysis suggests a family of ten ‘simplest’ ground states (Figure 1), seven of which have previously been reported. Using Monte Carlo simulations, we find that other phases identified in the literature but not expected by our model, are either describable as disordered states intermediate to our limiting phases, or mischaracterised. We proceed to show that the coupled 1D Ising chains encapsulate the behaviour of solid solutions of layered AB₂ systems, with a long term aim to link the properties of these materials to the interaction parameters relevant to the model. This phase control is an important result as it could lead to targeted design for specific properties, as structure is known to have a profound influence on materials’ properties.

We report discovery of new metallic and magnetic phases in the van-der-Waals antiferromagnets MPS3, where M = Transition Metal, form an ideal playground for tuning both low-dimensional magnetic and electronic properties[1-4]. These are layered honeycomb antiferromagnetic Mott insulators, long studied as near-ideal 2D magnetic systems with a rich variety of magnetic and electric properties across the family.

We will present magnetic, structural and electrical transport results and compare the behaviour of Fe-, V-, Mn- and NiPS3 as we tune them towards 3D structures – and Mott transitions from insulator to metal. I will show recent results on record high-pressure neutron scattering, which has unveiled an enigmatic form of short-range magnetic order in metallic FePS3.

We have mapped out the full phase diagram - a first in this crucial family of materials. We observe multiple transitions and new states, and an overall increase in dimensionality and associated changes in behaviour.

[1] G. Ouvrard et al., Mat. Res. Bull., 1985, 20, 1181.

[2] C.R.S. Haines et al., Phys. Rev. Lett. 2018, 121, 266801.

[3] M.J. Coak et al., J.Phys.:Cond. Mat. 2019, 32, 124003.

[4] M.J. Coak, et al., Phys. Rev. X, 11, 011024 (2021)

During last decades, the impact of high-pressure studies on fundamental physics, chemistry, and Earth and planetary sciences, has been enormous. Modern science and technology rely on the vital knowledge of matter which is provided by crystallographic investigations. The most reliable information about crystal structures of solids and their response to alterations of pressure and temperature is obtained from single-crystal diffraction experiments. Advances in diamond anvil cell (DAC) techniques, designs of double-stage DACs, and in modern X-ray instrumentation and synchrotron facilities have enabled structural research at multimegabar pressures.

We have developed a methodology for performing single-crystal X-ray diffraction experiments in double-side laser-heated DACs and demonstrated that it allows the crystal structure solution and refinement, as well as accurate determination of thermal equations of state above 200 GPa at temperatures of thousands of degrees. Application of this methodology resulted in discoveries of novel compounds with unusual chemical compositions and crystal structures, uncommon crystal chemistry and physical properties. Perspectives of materials synthesis and crystallography at extreme conditions will be outlined.

High pressure is a powerful tool to study experimentally the response of selected hydrogen bonds to mechanical stress. Cooling is an alternative method to compress a structure. A comparison of compression on cooling and increasing pressure gives an insight into intermolecular interactions. Guanine and its derivatives, as well as nucleic acids, in general, attract much attention because of their interesting properties. Crystals made of small RNA or DNA fragments can serve as models of the effect of pressure on nucleic acids and oligonucleotides, similar to how the crystals of amino acids are used to model proteins. Nucleobases are the structural elements of nucleic acids. They are widely used as components of some crystalline drugs and molecular materials. Guanine is remarkable for its unique ability to form assemblies. In particular, oligonucleotides enriched with guanine can form quadruplexes in the presence of alkali and earth-alkaline metals. Because of the extremely low solubility of guanine in water and most of the organic solvents at neutral pH, only a few guanine compounds are known. An additional challenge is to obtain single crystals. Crystal structures containing guanine, metal ions and water molecules can also be used, to shed more light on the interactions between the guanine anions, metal cations and water molecules. Potassium cations are of special biological importance because they form natural quadruplexes, which are present in telomeric parts of the chromosome. The hydrates of guanine metal salts are of interest in this respect. In this contribution, the approaches to the crystallization of salts of guanine and alkaline metals from aqueous, alcoholic and aqueous-alcoholic solutions. Two salts of guanine were investigated by single-crystal X-ray diffraction, namely, 2Na⁺·C₅H₃N5O²⁻·7H₂O and K⁺ ∙C₅H₄N₅O^- ∙H₂O. The crystals of K⁺∙C₅H₄N₅O^-∙H2O were obtained for the first time. The structure is quite different from that of the previously documented sodium salt hydrate (2Na⁺·C₅H₃N₅O²⁻·7H₂O) [1]. The crystal structures of both sodium and potassium salt hydrates have channels. However, the structure of the channels, the cation coordination, the tautomeric form of the guanine anions, as well as the role of water molecules in the crystal structure are different for the two salt hydrates. In the potassium salt hydrate, there are two tautomeric forms of guanine anions and two types of potassium ions with different coordination. It is interesting to note, that though no “true” guanine quadruplexes could be found in the crystal structure of the potassium salt of guanine hydrate the “quartets” of guanine connected via hydrogen bonds with each other and two water molecules are present in this crystal structure. The sodium salt hydrate (2Na⁺·C₅H₃N5O²⁻·7H₂O) was characterized by single-crystal X-ray diffraction in the pressure range of 1 atm- 2.5 GPa [2] as well as in the temperature range 100 K - 300 K. The potassium salt of guanine was characterized by single-crystal X-ray diffraction in the temperature range 100 K - 300 K. ThetaToTensor software was used to calculate the coefficients of thermal expansion tensor and create a graphical representation of the characteristic surface [3]. The anisotropy of strain on temperature variation was compared for the two salt hydrates, the similarities and the differences are discussed concerning the intermolecular interactions [4].

[1] Gur D., Shimon L. J. W. (2015) Acta Crystallographica Section E: Crystallographic Communications, 71 (3), 281-283.

[2] A.Gaydamaka et al. (2019) CrystEngComm , 21, 4484-92.

[3] Bubnova, R. S., V. A. Firsova, and S. K. Filatov. (2013) Glass Physics and Chemistry, 39.3, 347-350.

[4] Gaydamaka, A. A., Arkhipov, S. G., Boldyreva, E. V., 2021, Acta Crystallographica Section B, in preparation.

Keywords: IUCr2021; guanine, nucleobase, single crystal X-ray diffraction, XRD, vibrational spectroscopy, high pressure, low temperature, ionic channels.

The research was supported by project AAAA-A21-121011390011-4. The equipment of REC MDEST (NSU) was used.

Carbon dioxide, CO₂, is one of the most important compounds in nature and the second most abundant volatile in the Earth's interior. Its structure and properties at high pressures and temperatures pertaining to geoscience are crucial both to fundamental chemistry and solid state physics.

CO₂ has a very complex phase diagram consisting of a number of crystalline molecular phases below 40 GPa. On further compression it polymerizes forming at moderate temperatures (up to 680 K) amorphous glass with carbon in threefold and fourfold coordination [1], while the laser heating above 1800 K/40 GPa produces a polymeric covalent crystal phase (CO₂-V, space group
I-42d) that can be described as a network of fourfold coordinated carbon atoms interconnected by oxygen bridges resembling structurally β-cristobalite (SiO₂) [2].

The substantial kinetic barrier, reflecting dramatic changes in the bonding scheme on transition to the polymeric phase, led to numerous observations of metastable states in the stability field of CO₂-V, causing controversies. Hence, we have decided to investigate the chemical and phase stability of carbon dioxide at pressures up to 120 GPa [3] and temperatures reaching 6000 K [4], an unexplored range in all the previous reports.

High-pressure high-temperature in situ X-ray diffraction patterns, here reported for the first time, proved that CO₂-V is the only non-molecular form of CO₂ relevant to the Earth's deep interior. Moreover, contrary to the previous findings, no evidences for the decomposition of CO₂-V into the elements have been found. Variation of the Bragg peak distribution on Debye-Scherrer rings at temperatures >4000  K [4] may suggest a further possible extension of the stability field of this polymeric solid toward the pre-melting state. The presented findings play a pivotal role in understanding the behavior of hot dense carbon dioxide and provide a good basis for further experimental studies of CO₂ at extreme pressures and temperatures.

[1] Santoro, M., Gorelli, F.A., Bini, R., Ruocco, R., Scandolo, S. & Crichton, W.A. (2006). Nature 441, 857. [2] Santoro, M., Gorelli, F.A., Bini, R., Haines, J., Cambon, O., Levelut, C., Montoya, J.A. & Scandolo, S. (2012). Proc. Natl Acad. Sci. USA 109, 5176. [3] Dziubek, K.F., Ende, M., Scelta, D., Bini, R., Mezouar, M., Garbarino, G. & Miletich, R. (2018). Nat. Commun. 9, 3148. [4] Scelta, D., Dziubek, K.F., Ende, M., Miletich, R., Mezouar, M., Garbarino, G. & Bini, R. (2021). Phys. Rev. Lett. 126, 065701.

The authors thank the Deep Carbon Observatory initiative (Extreme Physics and Chemistry of Carbon: Forms, Transformations, and Movements in Planetary Interiors, from the Alfred P. Sloan Foundation) that supported this work and the ESRF for granting the beamtime.

The martensitic transformation is a fundamental physical phenomenon at the origin of important industrial applications. However, the underlying microscopic mechanism, which is of critical importance to explain the outstanding mechanical properties of martensitic materials, is still not fully understood. This is because for most martensitic materials the transformation is a fast process that makes in situ studies extremely challenging. Noble solids krypton and xenon undergo a progressive pressure induced fcc to hcp martensitic transition with a very wide coexistence domain. Here, we took advantage of this unique feature to study the detailed mechanism of the transformation by employing in situ X-ray diffraction and absorption. We evidenced a four stages mechanism where the lattice mismatch between the fcc and hcp forms plays a key role in the generation of strain. We also determined precisely the effect of the transformation on the compression behavior of these materials.

Water and soil pollution by heavy metals and other hazardous compounds is a global problem threatening the entire biosphere and affecting the life of many millions of people around the world. For instance, approximately two million tons of industrial, sewage and agriculture waste are discharged every day into water, causing serious health problems and the death of many thousands of people every day on a worldwide basis. Design and assessment of technologies for immobilization and removal of hazardous elements (HEs) is one of the highest priorities for environmental protection both in the industrialized and the developing countries.

The incorporation of HEs into crystalline and glassy silicate ceramics (the “harder” geomaterials) provides a perfect example to show that modelling the preferential distribution and the efficiency of immobilization of HEs in the crystal lattice and vitreous phase requires a detailed crystallographic knowledge at both the long- (XRD) and the short- (XAS) range.

Concerning the application of “softer” geomaterials, crystallographic knowledge of the zeolite structures proved successful for removal of heavy metals and VOCs from contaminated water and for the clean-up of water polluted with antibiotics. Simultaneous toxic metal uptake and bacteria disinfection from aqueous solution was achieved using well characterized nanocomposites of both the softer (zeolite) and the harder (e.g. Fe₃O₄) geomaterials.

Despite cadmium being a toxic element for environmental and human health, it is widely used in industries for fabrication of nickel-cadmium batteries, as anticorrosive agent, color pigment, etc. The most common and effective techniques for Cd removal from wastewater include filtration, chemical precipitation, bio-remediation and ion exchange [1]. Because of their microporous structure and extremely efficient cation exchange capacity, natural zeolites are good candidates for use as ionic filters. Moreover, heavy-metal exchanged zeolites show improved catalytic properties that can be exploited in post remediation processes [2,3]. Therefore, the chemical reactivity and stability of heavy-metal enriched zeolite is of paramount importance. Additionally, the nature of the metal species and their interaction with the zeolite framework play a fundamental role. Nevertheless, the correct determination of the aforementioned aspects can be compromised by the high disorder of the extraframework species, making difficult an unequivocal interpretation of the coordination chemistry of the metal cations. In this respect, the combination of X-ray diffraction (XRD) based techniques together with X-ray absorption spectroscopy (XAS) represents a valid tool to probe the long and short-range order of the species of interest.

In this contribution, we used a complementary experimental and theoretical approach to investigate in detail the structure of two Cd²⁺ -exchangedzeolites, levyne (LEV) and erionite (ERI). These two minerals are classified as small-pore zeolites (pore size between 0.35 and 40 nm) and, due to their structural similarity, they are often found as intergrown phase in nature [4]. In this study, experimental data from single crystal XRD and XAFS were coupled with Molecular Dynamics (MD) simulations to determine the distribution and coordination chemistry of Cd²⁺ in the two framework types (LEV and ERI). Our results showed that in Cd-LEV, Cd²⁺ ions have a fairly ordered distribution, resembling that characteristic of the pristine material [5]. In contrast, a strong disorder of the extraframework species (Cd²⁺ and H₂O) is detected in Cd-ERI pores, where the occupancy of the EF sites is lower than 20%. Such disorder was attributed to the presence of Cd⁺²(H₂O)₆ complexes, which are only partially coordinated to framework oxygen and, therefore, more mobile. To discriminate between the effect of thermal and structural disorder in the measured and theoretically calculated EXAFS spectra, we propose a theoretical approach based on a set of geometry optimizations performed starting from the uncorrelated atomic configuration of MD simulations [6]. Moreover, based on EXAFS analysis, the formation of metallic Cd within the pores of both zeolites could be ruled out.

Finally, we present the effect of Cd²⁺ incorporation on the thermal stability of Cd-LEV. The structural changes were monitored in situ from 25 to 400°C by single crystal X-ray diffraction. Our results demonstrated that, even if Cd had little influence on the room temperature structure, the dehydration behaviour drastically changes compared to that of the pristine material (natural levyne-Ca). The most relevant differences can be summarized by: i) a stronger volume contraction of the unit-cell volume (8% and 5% for Cd-LEV and levyne-Ca [5], respectively) in the investigated temperature range, and ii) the lack, at high temperatures, of the phase transformation to levyne B’ topology, characteristic of natural levyne-Ca.

[1] Rodriguez-Narvaez, O. M, Peralta-Hernandez, J. M., Goonetilleke, A., Bandala, E. R. (2017). Chem. Eng. J. 323, 361.

[2] Onyestyak, G., Kallo, D. (2003) Microporous and Mesoporous Mater. 61, 199.

[3] Zhang, Y., Qu, Y., Wang, D., Zeng, X. C., Wang, J. (2017) Ind. Eng. Chem. Res. 56, 12508.

[4] Passaglia, E., Galli, E., Rinaldi, R. (1974) Contrib. Mineral. Petrol. 43, 253.

[5] Cametti, G. (2018) Microporous and Mesoporous Mater. 265, 162.

[6] Cametti, G., Scheinost, A. C., Churakov, S. V. (2021) Microporous and Mesoporous Mater. 313, 110835.

In recent years, the occurrence and fate of perfluoroalkyl substances (PFAS) in the aquatic environment was recognized as one of the emerging issues in environmental chemistry. In particular, PFOA (C8HF15O2) and PFOS (C8HF17O3S) have recently become the targets of global concern due to their ubiquitous presence in the environment, persistence, and bioaccumulative properties. Strong carbon-fluorine (C–F) bonds make PFOA and PFOS extremely resistant to chemical, thermal and biological degradation, consequently, their removal from water is a crucial scientific and social challenge [1-2]. This work aims to investigate, for the first time, the structural modifications and the desorption kinetics during the thermal activation of FAU and Ag-exchanged FAU-type zeolites used for removal of PFOA and PFOS from water. The introduction of Ag in the framework confers them unique physical, chemical, and antibacterial properties along with strong absorption property, good stability and catalytic activity [3]. In situ high-temperature synchrotron X-ray powder diffraction and thermal analysis coupled with Elemental Analyzer – Isotope Ratio Mass Spectrometry (EA-IRMS) provided to: i) investigate high temperature structural modifications experienced after during PFOA and PFOS thermal desorption and to check the crystallinity preservation of the porous matrix; ii) monitor and evaluate the organics decomposition process upon heating; iii) estimate the influence of Ag active sites in working zeolites; iv) verify the best regeneration temperature in order to verify whether they can be re-used for PFAS removal from wastewater. This information was crucial for designing and optimizing the regeneration treatment of such zeolites, which are revealed to be highly effective in water-remediation technology. Powder diffraction data of each sample were collected at the synchrotron MCX beamline (Elettra, Trieste, Italy) and were subjected to the same heat treatment profile encompassing the heating ramp with a rate of 5°C/min from room temperature to 800 °C. The powder samples were loaded and packed into a 0.5 mm quartz capillary open at one end and heated in situ using a hot air stream. The analysis of the patterns collected using in situ synchrotron XRPD on zeolites showed no heat-induced symmetry change. Moreover, to carry out a comparison, structural data relating to bare zeolites are also reported in order to check the contribution of the loaded organic molecules. The differential thermal analysis (DTA) curve shows two DTA exothermic events between 300 and 600 ºC due to the PFAs degradation, in very good agreement with the EA-IRMS analyses. The complete thermal regeneration of selected materials was achieved at ~600 and 750 °C for PFOA and PFOS loaded samples, respectively. No relevant variations were observed in Ag-exchanged materials. This information is crucial to examine the efficiency of Ag-exchanged zeolites compared to same samples taken separately for the adsorption of PFOS and PFOA from water. The diffraction peaks were also accurately monitored to study in real-time their evolution (in terms of broadening, shift, changes of intensities) compared with the Y zeolites without any treatment, after silver activation and as well as after PFOS and PFOA adsorption. The XRD analysis demonstrated that the adsorption/desorption process occurred without significant loss of zeolite crystallinity, but with slight deformations in the channel apertures. The regenerated zeolites regain the unit-cell parameters of the bare materials almost perfectly, however. Only a slight memory effect in terms of structural deformations is registered in channel geometry thus demonstrating that the regenerated samples which could be able to re-adsorb similar amounts of PFOS.

[1] Ferreira, L., Fonseca, A.M., Botelho, G, Almeida-Aguiar, C, Neves, I.C. (2012). Antimicrobial activity of faujasite zeolites doped with silver. Microporous and Mesoporous Materials. 160, 126–132.

[2] Kucharzyk, K.H., Darlington, R., Benotti, M., Deeb, R., Hawley, E. (2017). Novel treatment technologies for PFAS compounds: A critical review. Journal of Environmental Management. 204, 757-764.

[3] Ziwen, D., Denga, S., Bei, Y., Huang, Q., Wang, B., Huang, J., Yua, G. (2014). Adsorption behavior and mechanism of perfluorinated compounds on various adsorbents—A review. Journal of Hazardous Materials. 274, 443–454.

Humans have used asbestos for about 5,000 years in various parts of the world [1] because of its outstanding properties. The massive use of asbestos turned out to be a global environmental problem when animal carcinogenicity tests and long-term epidemiological studies proved that inhalation of asbestos fibres may induce fatal lung diseases like asbestosis, carcinoma, malignant mesothelioma (MM) and many more after a latency period of decades [2].

Besides the morphological and chemical characterization conveyed by ESD-supported electron microscopy, X-ray diffraction is considered a reliable tool for the characterization of asbestos fibres. Due to problems of peak overlap in powder data, it is not possible though, to carry out a free refinement of these complex atomic structures in order to detect and measure subtle chemical changes to prove the biopersistence.

Since 2016, ID11 offered a new end station, called “nanoscope” where it is possible to focus the beam to the deep sub-micron scale. This is possible by using the in-line crossed silicon compound refractive lenses [3] and using a crossed pair of vertical and horizontal line foci. Combining the very small beam size with a diffractometer to align and maintain a sample in the beam during rotation is very promising for the crystallographic characterization of natural fibres. Here we report a proof of the in vivo biopersistence of asbestos fibres in human lung tissues (figure1) at the atomic scale using synchrotron micro-diffraction. We show that the atomic structure of an amosite fibre remained stable for about 40 years in the lungs of a subject diagnosed with malignant mesothelioma (MM) and originally exposed to a mixture of chrysotile, amosite and crocidolite [4].

Metal oxide aluminosilicate and aluminogermanate nanotubes, called imogolite nanotubes (INT), are nanotubes with well-controlled diameter and with different morphologies [1,2]. These nanotubes undergo major structural changes at high temperatures, including the transformation from one-dimensional nanochannels into a structure which is supposed to be lamellar [3,4].

Here, we report a complete analysis of the structural transformations of single and double-walled aluminogermanate nanotubes, up to 900°C. We applied an original approach combining (i) in-situ X-ray absorption spectroscopy measurements (LUCIA & DiffAbs beamlines, synchrotron SOLEIL), allowing us to investigate the evolution of both Al and Ge atoms coordination during the transformation process, and (ii) in-situ diffraction. It reveals that the dehydroxylation of nanotubes does not lead to a lamellar phase but to metastable intermediate states that we named “meta-imogolite” states by analogy with meta-kaolinite. A mechanism explaining the major structural reorganizations is proposed based on atomic jump processes. The understanding of these structural modifications represents a benchmark for further studies concerning the properties of transformed INT-based compounds.

[1] Paineau E. & Launois P. (2019) In. Nanomaterials from clay minerals. Amsterdam, Netherlands: Elsevier, pp. 257-284.

[2] Monet G., Amara M.S., Rouzière S., Paineau E., Chai Z., Elliott J.D., Poli E., Liu L.M., Teobaldi, G. & Launois P. (2018) Structural resolution of inorganic nanotubes with complex stoichiometry. Nat. Commun., 9, 2033.

[3] MacKenzie K.J.D., Bowden M.E., Brown I.W.M. & Meinhold R.H. (1989) Structure and thermal transformations of imogolite studied by ²⁹Si and ²⁷Al high resolution solid-state nuclear magnetic resonance. Clays Clay Miner., 37, 317-324.

[4] Zanzottera C., Vicente A., Armandi M., Fernandez C., Garrone E. & Bonelli B. (2012) Thermal collapse of single-walled alumino-silicate nanotubes: Transformation mechanisms and morphology of the resulting lamellar phases. J. Phys. Chem. C, 116, 23577-23584.

Naica's giant crystals caves have astonished scientists since their discovery in 2000. Their gypsum crystals have been the subject of extensive studies and reports, both on scientific aspects and general cultural news. This work reports a detailed investigation of the wall-crystal interface of a blocky type crystal pulled off the "Cueva de los Cristales" wall. At the interface, the zones that probably correspond to the nucleation and growth of the blocky were identified. Representative samples were extracted at different depths of the wall-crystal junction and studied by ICP-OES, light and electron microscopies, XRD, and synchrotron-based m-XRF and m-XANES methods. The interface layer, of an average thickness of about 30 to 60 mm, contains various crystalline and amorphous aggregates with diameters ranging from 1 to 30 mm. Calcite, silica, goethite, as well as several Pb, Mn, Cu, and Zn aggregates, have been identified as main components (Figure 1).

Figure 1.The wall-crystal interface of Cueva de los Cristales, with Fe and Zn μ-XRF and μ-XANES obtained from the sample.

The study of the shape and composition of these mineral aggregates, as well as the morphology of the wall-crystal interface, allowed deducing their transformation and role in crystal nucleation and growth. It has been concluded [1] that the nucleation and growth of the Naica giant crystals have occurred under conditions of a slightly supersaturated solution, almost in equilibrium, and stable over a long time. In addition, considering the non-classical theory of crystal nucleation [2] and the results presented here, we can formulate that the heterogeneous nucleation of the giant Naica crystals was initiated with the adsorption of nanocrystalline monomers. These clusters formed in the solution were successively physi- and chemisorbed on the cave walls and on the crystal surface, assembling the crystalline planes during the crystal growth.

The CONACYT (México), Projects 183706, 257912 and 270738, and Project MINECO(Spain) MAT2017-86168-R are acknowledged.

[1] Otalora, F. & Garcia-Ruiz, J. (2014). Chem. Soc. Rev. 43, 2013-2026.

[2] Van Driessche, A. E. S., Stawski, T. M. & Kellermeier, M. (2019). Chem. Geol. 530, 119274.μ

A painting is made up of complex mixtures of materials, carefully selected by an artist, usually to create a specific optical illusion or esthetic effect. Depending on its material composition and the environmental conditions that a painting is subjected to, various chemical reactions can take place which cause the paint layers to deteriorate over time. Therefore, collecting reliable chemical information from a work of art is essential to understand its composition, past and ongoing conservation issues and to develop preservation strategies. In this sense, X-ray powder diffraction is an important tool as it allows for the direct identification of crystalline phases within the complex mixtures present in a painting [1]. However, an important limitation of this method has been the amount of material that needed to be sampled [2]. In the past decade a new trend has been set towards the application of elemental and chemical imaging techniques, such as macroscopic X-ray fluorescence (MA-XRF) and reflectance imaging spectroscopy (RIS), for the study of painted artefacts as they provide valuable information on the heterogeneous composition within complete paintings [3-5].

Following this trend, the AXES research group has developed a macroscopic X-ray powder diffraction (MA-XRPD) imaging instrument that allows for the identification and visualization of the crystalline materials used in a painting in a non-invasive manner. This instrument uses a low power microfocus X-ray source (IµS, Incoatec) combined with multilayer mirrors to obtain a slightly focused and fairly monochromatic X-ray beam in combination with a large area detector (PILATUS 200K, Dectris). By moving the painting and the instrument relative to each other, a large set of diffraction images (typically >10000) is collected following a raster-scanning approach. Subsequently, this large powder diffraction dataset is azimuthally integrated after which the resulting one dimensional 2θ spectrum at each data point is individually fitted with the XRDUA software package [6] using a model comprising all identified crystalline phases. By plotting the scaling factors as grey-scale values individual images that correspond to the distribution of the crystalline materials can be created [7].

The MA-XRPD instrument can be used in a transmission geometry, suitable for underlaying and strongly absorbing paint layers, or in reflection geometry, which is more sensitive for the (thin) pictorial layers. The latter also has the added advantage that larger works of art can be investigated as the painting remains stationary while the scanning head is translated in three dimensions. Typically a (short) dwell time of 10 seconds is used with a step size of 1-2 mm over a maximum scanning range of 30 x 30 cm.

The MA-XRPD instrument has been used within several museums on well-known masterpieces, such as Van Gogh’s Sunflowers, Vermeer’s Girl with a Pearl Earring, the Ghent altarpiece by the brothers Van Eyck and The Night Watch by Rembrandt. On these works, next to the visualization of the original pigments employed by the artists and later additions or overpaint, also various chemical alteration products that have formed within/on top of the paint layers could be identified. In some cases, the data collected with the MA-XRPD instrument can be exploited to yield other types of highly-specific information, such as the buildup of the paint layer or the orientation of the crystals on the paint surface. Furthermore, the collection of large datasets allows a reliable quantification of various pigment mixtures and to track their differences within and between artworks/time periods.

[1] Artioli, G. (2013). Rendiconti Lincei-Scienze Fisiche E Naturali, 24, S55. [2] Madariaga, J. M. (2015). Anal. Methods, 7, 4848. [3] Alfeld, M., & Broekaert, J. A. C. (2013). Spectrochim. Acta, Part B, 88, 211. [4] Alfeld, M., & de Viguerie, L. (2017). Spectrochim. Acta, Part B, 136, 81. [5] Trentelman, K. (2017). Annu. Rev. Anal. Chem., 10, 247. [6] De Nolf, W., Vanmeert, F., & Janssens, K. (2014). J. Appl. Crystallogr., 47, 1107. [7] Vanmeert, F., De Nolf, W., De Meyer, S., Dik, J., & Janssens, K. (2018). Anal Chem, 90, 6436.

High-strength lightweight magnesium (Mg) alloys have substantial potential for reducing the weight of automobiles and other transportation systems and, thus, for improving fuel economy and reducing emissions. However, compared to other structural metals, the development of commercial Mg alloys and our understanding of Mg alloy physical metallurgy are less mature, and enabling the widespread use of Mg alloys requires significant improvement in strength, fatigue, and formability. The low formability of Mg alloy sheet is due to its strong basal texture in the rolling direction. The addition of Ca and rare earth elements can result in a desired weaker texture. However, despite numerous studies, the mechanisms by which this texture reduction occurs remains unknown, and it is likely that several different mechanisms occur simultaneously or sequentially. This is the topic of this research.

A Mg-3Zn-0.1Ca alloy was deformed under hot plane-strain compression and samples were subjected to annealing on ID3A on ID3A at the Cornell High Energy Syncrhotron Source (CHESS) and ID06 at the European Synchrotron Radiation Facility (ESRF). In-situ far-field and near-field high-energy diffraction microscopy (ff- and nf-HEDM) characterization was performed at CHESS, and in-situ partial intermediate-field HEDM (if-HEDM) and dark-field X-ray microscopy (DFXM) was performed on ID06 at the ESRF. By combining the different modalities, we were able to characterize the microstructure evolution during annealing on different length scales, from the subgrain morphology of individual grains (using DFXM) to the aggregate behavior of several thousands of grains (using HEDM).

The mechanical and functional properties of polycrystalline materials have significant contributions from the 3D interaction of grains that form their micro-structure. Such grain maps can be extracted from existing characterisation techniques that utilise X-rays or electrons. However, complimentary techniques using neutrons have not yet developed to maturity. Furthermore, neutrons provide distinct advantages where, due to their lower attenuation, larger materials can be analysed, such as real-world engineering materials.

Here, a novel 3D grain mapping methodology, known as Trindex, has been demonstrated to reveal the micro-structure of a prototypical cylindrical iron material. While there already exist several methods on grain mapping with neutron imaging, Trindex provides a robust and relatively straightforward approach. Trindex is a pixel-by-pixel neutron time-of-flight reconstruction method which extracts the morphology of grains throughout the sample, in addition to their pseudo-orientations.

Experiments were performed at the SENJU beamline of the Japan Proton Acceleration Research Complex (J-PARC). For the setup, an imaging detector was placed behind the sample with diffraction detectors simultaneously collecting the backscattering from the sample. Such diffraction will be used to confirm grain orientations. Details of the methodology and the resulting 3D grain maps of materials will be presented.

1. Cereser, A., et al. "Time-of-flight three dimensional neutron diffraction in transmission mode for mapping crystal grain structures." Scientific reports 7.1 (2017): 1-11.
2. Peetermans, S., et al. "Cold neutron diffraction contrast tomography of polycrystalline material." Analyst 139.22 (2014): 5765-5771.

The properties and behaviour of materials (metals, alloys, semiconductors, ceramics, polymers, drugs, biomaterials) are to a large extent determined by their phase composition, particle size, crystallinity, stress, defects and crystallographic orientation (texture). Two-dimensional (2D) X-ray diffraction is one of the most appealing techniques for users who are interested in extracting every bit of information about their samples. 2D X-ray diffraction patterns, collected using area detectors contain detailed information about all these important material characteristics. Furthermore, the high sensitivity and resolution of modern detectors (e.g. PIXcel^3D, GaliPIX^3D) make possible the collection of relevant structural information within seconds. This allows following in real time transformation processes of materials, like recrystallization, deformation or phase transitions. XRD2DScan is the Malvern Panalytical software for displaying, processing, and analyzing 2D X-ray diffraction data. The latest version of the software (version 7.0) offers new features such as orientation and crystallite size analysis, image comparison, as well as scripting for easy automation. The application of the software to the characterization of complex anisotropic materials (liquid crystals, polymers, bone, wood, ...) will be illustrated through several examples.

A material responds to its surroundings via residual changes in its structure that change its corresponding properties. The macroscopic structural evolution is instigated by the dynamics of statistical populations of defects that move, interact, and pattern – causing atomic-scale defects to create 3D networks of boundaries that comprise the heterogeneous “real-world” materials. While techniques exist to probe material defects, they are mainly limited to surface measurements or rastered scans that cannot measure the dynamics of irreversible or stochastic processes characteristic of defect dynamics. In this talk, I will introduce time-resolved dark-field X-ray microscopy (tr-DFXM) as a new tool to capture movies that visualize dislocation dynamics in single- and poly-crystals at the mesoscale. I will start by describing the infrastructure we have developed to build and align the microscope, then to interpret and quantify the information captured in our movies. With this new tool, I will then demonstrate how dislocation patterns evolve at high temperatures in aluminum (Fig. 1). Tr-DFXM holds important opportunities for future studies on mesoscale dynamics, as it can inform models that have previously been refined only by indirect measurements and multi-scale models.

This work was performed in part under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

The three-dimensional X-ray diffraction (3dxrd) technique provides a useful tool to investigate polycrystalline materials, grain-by-grain, in a non-destructive way. The approach of the scanning 3dxrd microscopy is to probe the sample by moving a pencil beam horizontally across it (y direction) with a resolution dependent on the beam size. For each step, the sample is rotated of 180° (or 360°, ω angle) in order to collect the diffraction spots of all the grains in the sample [1].

We used a combined approach of scanning 3dxrd and Phase Contrast Tomography (PCT) to investigate the hydration of a widespread hydraulic binder material, namely gypsum plaster. This material forms when the bassanite (calcium sulfate hemihydrate) reacts with water. In-situ 3dxrd measurements allowed to understand the crystallographic lattice, orientation and position of each grain in the sample during the hydration reaction (Figure 1 a,b).

The PCT reconstructions, instead, allowed the visualization of the shape of the crystals in the sample over time and a quantification of density and porosity (Figure 1 c,d).

Monitoring the evolution of the hydration reaction of gypsum plaster with both these techniques appears to be a promising tool to gain insights about the kinetics of the hydration reaction, the crystallization and growth of the hydrated phase and the shape of the final gypsum crystals that build the interlocked and porous gypsum plaster hardened mass.

The first few months of the SARS-CoV-2 pandemic illustrated, in many ways, the level of maturity and essential nature of modern structural biology. The outbreak was given official pandemic status on 11 Feb 2020 - six days after the release of the first crystal structure of the main protease; the first cryo-EM structure of the spike protein was released just two weeks later. These were the first of a flood of new structures - most, in a strong break with tradition, released well before the associated manuscripts. This, combined with the recent decision by the worldwide Protein Data Bank to allow re-versioning of submitted structures by the authors, allowed for an almost unprecedented scenario: while the experimentalists worked to get these critically important structures solved as quickly as possible, specialists in model building and refinement could check and (where necessary) improve their models, returning the results to the original authors often before their papers were ever published.

In this talk I will discuss some of my observations arising from inspecting and rebuilding some three dozen early SARS-CoV-2 and SARS-CoV-1 structures. In a great many respects, the remarkable improvement in the rate of modelling errors between SARS-CoV-1 and -2 structures shows just how far the field has come. However, the devil is in the details, and various classes of repeated errors in the modern structures point to the need for further improvement in model-building and validation methods.

The Protein Data Bank (PDB) [1] was established as the first open-access digital data resource in biology in 1971 with just seven X-ray crystallographic structures of proteins. Today, the single global archive houses more than 177,000 experimentally determined 3D structures of biological macromolecules that are made freely available to millions of users worldwide with no limitations on usage. This information facilitates basic and applied research and education across the sciences, impacting fundamental biology, biomedicine, biotechnology, bioengineering, and energy sciences. The PDB archive is managed jointly by the Worldwide Protein Data Bank [2-3] (wwPDB, wwpdb.org) which is committed to making PDB data Findable-Accessible-Interoperable–Reusable (FAIR) [4].

To ensure the highest quality structure data, the wwPDB OneDep system for structure deposition [5], validation [6], and biocuration [7] (deposit.wwpdb.org) provides enhanced validation reports. During 2019-2020, wwPDB implemented depositor-initiated coordinate versioning that enables the Depositor of Record (or Principal Investigator) to replace previously released x,y,z atomic coordinates without obsoleting the original PDB entry or changing the PDB ID. This feature was developed in response to feedback from PDB depositors, who were reluctant to update their structures because the newly issued PDB ID would differ from that reported in original structure publication. We thank all of many PDB depositors, who have proactively corrected their structures using the new versioning feature within OneDep. To date, more than 200 PDB structures have been updated with newly versioned atomic coordinates.

Since the early days of the COVID-19 pandemic, PDB data have informed our understanding of SARS-CoV-2 protein structure, function, and evolution, and facilitated structure-guided discovery and development of anti-coronaviral drugs, vaccines, and neutralizing monoclonal antibodies. More than 1,000 SARS-CoV-2 related protein structures are now freely available from the PDB, reflecting enormous efforts made by the structural biology community in fighting the pandemic. Occasionally, rapid PDB data deposition and publication of coronavirus structural studies driven by an understandable sense of urgency has resulted in public release of PDB structures containing minor errors. The wwPDB coordinate versioning feature described above has enabled rapid correction of SARS-CoV-2 related structures archived in the PDB.

The wwPDB strongly encourages PDB depositors to update structures as needed using OneDep. Doing so will improve the quality of data stored in the archive, while preserving original PDB IDs and maintaining connections to the scientific literature.

[1] Protein Data Bank. (1971). Crystallography: Protein Data Bank. Nature (London), New Biol. 233:223-223.

[2] Berman, H., Henrick, K., Nakamura, H. (2003). Announcing the worldwide protein data bank. Nat Struct Biol. 10:980.

[3] wwPDB consortium. (2019). Protein Data Bank: The single global archive for 3d macromolecular structure data. Nucleic Acids Res. 47:D520-D528.

[4] Wilkinson, MD, Dumontier, M, Aalbersberg, IJ, Appleton, G, Axton, M, Baak, A, Blomberg, N, Boiten, JW, da Silva Santos, LB, Bourne, PE, et al. (2016). The FAIR guiding principles for scientific data management and stewardship. Sci Data. 3:1-9

[5] Young, J. Y., Westbrook, J. D., Feng, Z., Sala, R., Peisach, E., Oldfield, T. J., Sen, S., Gutmanas, A., Armstrong, D. R., Berrisford, J. M., et al. (2017). OneDep: Unified wwpdb system for deposition, biocuration, and validation of macromolecular structures in the pdb archive. Structure. 25:536-545.

[6] Gore, S., Sanz Garcia, E., Hendrickx, P. M. S., Gutmanas, A., Westbrook, J. D., Yang, H., Feng, Z., Baskaran, K., Berrisford, J. M., Hudson, B. P., et al. (2017). Validation of structures in the protein data bank. Structure. 25:1916-1927.

[7] Young, J. Y., Westbrook, J. D., Feng, Z., Peisach, E., Persikova, I., Sala, R., Sen, S., Berrisford, J. M., Swaminathan, G. J., Oldfield, T. J., et al. (2018). Worldwide protein data bank biocuration supporting open access to high-quality 3d structural biology data. Database. 2018:bay002.

RCSB PDB is funded by the National Science Foundation (DBI-1832184), the US Department of Energy (DE-SC0019749), and the National Cancer Institute, National Institute of Allergy and Infectious Diseases, and National Institute of General Medical Sciences of the National Institutes of Health under grant R01GM133198.

COVID-19, caused by SARS-CoV-2, is a global health and economic catastrophe. The viral main protease (M^pro) is indispensable for SARS-CoV-2 replication and thus is an important target for small-molecule antivirals. Computer-assisted and structure-guided drug design strategies rely on atomic scale understanding of the target biomacromolecule traditionally derived from X-ray crystallographic data collected at cryogenic temperatures. Conventional protein X-ray crystallography is limited by possible cryo-artifacts and its inability to locate the functional hydrogen atoms crucial for understanding chemistry occurring in enzyme active sites. Neutrons are an ideal probe to observe the protonation states of ionizable amino acids at near-physiological temperature, directly determining their electric charges – crucial information for drug design. Our X-ray crystal structures of M^pro collected at near-physiological temperatures brought rapid insights into the reactivity of the catalytic cysteine, malleability of the active site, and binding modes with clinical protease inhibitors. The neutron crystal structures of ligand-free and inhibitor-bound M^pro were determined allowing the direct observation of protonation states of all residues in a coronavirus protein for the first time. At rest, the catalytic Cys-His dyad exists in the reactive zwitterionic state, with both Cys145 and His41 charged, instead of the anticipated neutral state. Covalent inhibitor binding results in modulation of the protonation states, retaining the overall electric charge of the M^pro active site cavity. In addition, high-throughput virtual screening in conjunction with in vitro assays identified a lead non-covalent compound with micromolar affinity, which is being used to design novel M^pro inhibitors. Our research is providing real-time data for atomistic design and discovery of M^pro inhibitors to combat the COVID-19 pandemic and prepare for future threats from pathogenic coronaviruses.

The COVID-19 pandemic, instigated by the SARS-CoV-2 coronavirus, continues to plague the globe. The SARS-CoV-2 main protease, or M^pro, is a promising target for development of novel antiviral therapeutics. Previous X-ray crystal structures of M^pro were obtained at cryogenic temperature or room temperature only. Here we report a series of high-resolution crystal structures of unliganded M^pro across multiple temperatures from cryogenic to physiological, and another at high humidity. We interrogate these datasets with parsimonious multiconformer models, multi-copy ensemble models, and isomorphous difference density maps. Our analysis reveals a temperature-dependent conformational landscape for M^pro, including a mobile water interleaved between the catalytic dyad, mercurial conformational heterogeneity in a key substrate-binding loop, and a far-reaching intramolecular network bridging the active site and dimer interface. Our results may inspire new strategies for antiviral drug development to counter-punch COVID-19 and combat future coronavirus pandemics.

Technological developments and growing interests in the study of cellular assemblies have led cryo-EM as a powerful technique to solve the three-dimensional structures of macromolecular complexes. More than 450 structures of molecular complexes from SARS-CoV-2 have been solved using cryo-EM and the structures have been crucial to understand molecular details behind the viral infection and development of drug molecules and vaccines. Given that majority of the cryo-EM reconstructions are solved at resolutions worse than 2.5Å and often the local resolution within the map varies considerably, atomic model validation is crucial to identify errors and less reliable areas of the model.

Here, we present the database CoVal, which is a repository of amino acid replacement mutations identified in the SARS-CoV-2 genome sequences, mapped onto protein structures from cryo-EM and X-ray crystallography. We provide information on the demographic distribution of these mutations, along with details on co-occuring mutations. CoVal gives easy access to mutation sites mapped to known structures with multiple metrics on the quality of the structure and agreement with experimental data. We also provide validation scores for the local quality of mutation site(s) and their structural neighbors. The database is freely accessible at: https://coval.ccpem.ac.uk. We also discuss tools for atomic model validation in the CCP-EM software suite [1] and results from the validation analysis of cryo-EM structures from SARS-CoV-2.

Semiconductor nanowires have mostly been synthesized from conventional three dimensional (3D) crystalline materials. Layered crystals, in which covalently bonded sheets are held together by weaker van der Waals forces, have emerged as a class of materials with extraordinary properties not found in 3D crystals. Shaping layered materials into nanowires could open up new, tunable structural, optoelectronic, and electronic transport/device characteristics.

Here, we discuss the realization of this vision, namely the synthesis and emerging properties of van der Waals nanowires of layered crystals, formed by combining the concepts of vapor-liquid-solid (VLS) growth and van der Waals epitaxy. We demonstrate the possibility of forming nanowires of germanium (II) sulfide (GeS), a 2D/layered chalcogenide semiconductorwith anisotropic structure [1], by a VLS process [2]. High-quality van der Waals nanowires crystallize with layering along the wire axis and show bright, size dependent band-edge luminescence [3], [4]. A strong propensity for forming screw dislocations, often found for layered crystals [4], introduces extraordinary properties without analogues in 3D-crystalline nanowires. Eshelby twist, induced by a torque on the ends of a cylindrical solid due to the stress field of an axial dislocation, causes a chiral structure of the layered nanowires and leads to spontaneous, size-tunable twist moiré patterns between the van der Waals layers along the wires. Using tailored growth protocols complex structures can be obtained that are impossible to realize in planar van der Waals stacks, including homojunctions between twisted (dislocated) and ordinary layered (dislocation-free) segments as well as continuously variable Eshelby twist translating into a seamless progression of helical moiré patterns [5]. Combined electron diffraction and local (nanometer-scale) optoelectronic measurements using cathodoluminescence and electron-energy loss spectroscopy show the correlation between the interlayer twist and locally excited light emission/optical absorption that is due to progressive changes in the lattice orientation and in the interlayer moiré registry along the nanowires. These findings demonstrate an avenue for the scalable fabrication of van der Waals structures with defined twist angles for the emerging field of twistronics, in which interlayer moiré patterns are realized along a helical path on a nanowire instead of a planar interface.

References

[1] E. Sutter, B. Zhang, M. Sun, P. Sutter, ACS Nano 13, 9352 (2019).

[2] E. Sutter, P. Sutter, ACS Applied Nano Materials 1, 1042 (2018).

[3] P. Sutter, C. Argyropoulos, E. Sutter, Nano Letters 18, 4576 (2018).

[4] P. Sutter, S. Wimer, E. Sutter, Nature 570, 354 (2019).

[5] P. Sutter, J.-C. Idrobo, and E. Sutter, Adv. Funct. Mater. 31, 2006412 (2021).

Over the last decade, the discovery of graphene has triggered a new paradigm of two-dimensional (2D) crystal materials. They are characterized by a periodic network structure and topographical thickness at the atomic/molecular level, enabling the investigation of fundamental exotic physical and chemical properties down to a single-layer nanosheet. Thereby, robust technologies and industrial applications, ranging from electronics and optoelectronics to energy storage, energy conversion, membranes, sensors, and biomedicine, have been inspired by the discovery and exploration of such new materials.

In contrast to the tremendous efforts dedicated to the exploration of graphene and inorganic 2D crystals such as metal dichalcogenides, boron nitride, black phosphorus, metal oxides, and nitrides, there has been much less development in organic 2D crystalline materials, including the bottom-up organic/polymer synthesis of graphene nanoribbons, 2D metal-organic frameworks, 2D polymers/supramolecular polymers, as well as the supramolecular approach to 2D organic nanostructures. One of the central chemical challenges is to realize a controlled polymerization in two distinct dimensions under thermodynamic/kinetic control in solution and at the surface/interface. In this talk, we will present our recent efforts in bottom-up synthetic approaches towards novel organic 2D crystals with structural control at the atomic/molecular level and beyond. We will introduce a surfactant-monolayer assisted interfacial synthesis (SMAIS) method that is highly efficient to promote supramolecular assembly of precursor monomers on the water surface and subsequent 2D polymerization in a controlled manner. 2D conjugated polymers and coordination polymers belong to such materials classes. The unique structures with possible tailoring of conjugated building blocks and conjugation lengths, tunable pore sizes and thicknesses, as well as impressive electronic structures, make them highly promising for a range of applications in electronics and spintronics. Other application potential of organic 2D crystals, such as in membranes, will also be discussed.

Single crystals of lead-free organic-inorganic 2D (BA)₂CsAgBiBr₇ with double perovskite structure (monoclinic, P2₁/m) exhibit a significant potential for X-ray sensing [1]. This stems from their heavy elements constituting the perovskite octahedral network that is in an alternating arrangement with the barrier layer of organic BA⁺ cations, consequently producing desirable electrical properties. In this study, several yellow-coloured single crystals of (BA)₂CsAgBiBr₇ were grown from a low-temperature solution [2]. All crystals are characterised by growth/dissolution features and defects (Figure 1). The phase purity and crystallinity of all samples have been verified from the powder XRD data. High ordering of Ag⁺ and Bi³⁺ octahedra cations is apparent from the XRD patterns for single crystals, which depict peaks arising from the {001} plane.

Results from electrical characterisation of the single crystals of (BA)₂CsAgBiBr₇ reveal high resistivity (10¹¹ Wcm) and low density of trap states (10¹¹-10¹² cm^-3), which are comparable to those published in literature [1]. This implies that the samples synthesised in this study also satisfy requirements for radiation sensors.

Figure 1. The top crystal surface of the sample (BA)₂CsAgBiBr₇_Exp1 (top right corner, 4 x 4 x 0.75 mm³) is characterised by irregular growth /dissolution features (image on the left made in reflected light, 100 mm scale bar) and defects such as twinning planes at 90^o (image on the right made in transmitted light).

[1] Xu, Z., Liu, X., Li, Y., Liu, X., Yang, T., Ji, C., Han, S., Xu, Y., Luo, J., & Sun, Z. (2019). Angew. Chem. Int. Ed. 58, 15757. [2] Connor, B. A., Leppert, L., Smith, M. D., Neaton, J.B., & Karunadasa, H. I. (2018). J. Am. Chem. Soc. 140, 5235.

Functional devices such as sensors, actuators or micro-electromechanical systems (MEMS) are obtained through a large variety of microfabrication processes, many of whom affect the structure and microstructure of materials because of the introduction of stress, strain, crystalline defects and volume-cracks. The materials degradation originated by these effects may translate into a lack of performance and reliability of the final devices. Indeed, in the frame of the microfabrication industry, controlling the structure of materials at the micrometer and nanometer scale represents a fundamental objective toward the optimization of the microfabrication process itself and achievement of improved devices' performance and lifetime.

In this work, we studied the influence of an innovative wafer bonding process, namely Impulse Current Bonding (ICB), in principle enabling low-temperature bonding between a wide class of materials, on the degradation of SCSi, SC-sapphire and borosilicate glass structures and crystallinity. A comprehensive frame of the microstructural deterioration at different size scales is obtained by a correlative approach between high-resolution X-ray diffraction (HRXRD) and X-ray micro-computed tomography (CT). In particular, micro CT revealed the formation of large cracks with thickness in the order of tens of microns generated to release the high stress at the bonding interface. In parallel, strain and tilt affecting the SCSi crystallinity due to the presence of defects at the nanoscale dimension are revealed by HRXRD methods, such as the mapping of the reciprocal space (RSM), radial scans (i.e., 2θ/θ) and angular scans (i.e., ω-scans or rocking curves) of symmetrical and asymmetrical reflections. The residual stress after the bonding process is also calculated from the in-plane and out-of-plane X-ray strain. The effectiveness and strength of the bonding are also assessed by our approach and compared to the conventional wafer bonding technologies, i.e., the anodic bonding.

We aim to present here a unique approach to the evaluation of the structural and crystalline degradation of materials involved in wafer bonding microfabrication processes. The combination of X-ray micro CT with HRXRD enables a holistic evaluation of the bonding between SCSi, sapphire and borosilicate glass wafers achieved exploiting an innovative low-temperature process, namely ICB. This allows the correlation between the micrometer scale and volumetric defect detection (voids and cracks) with atomic-level strain and defect analysis.

The interest in layered and multi-layered materials such as graphene and van der Waals crystals, e.g. the transition metal dichalcogenide crystal family, is constantly growing owing to their interesting properties and possible technological applications. The symmetry of single monolayers can be described by the so-called layer groups, which are three-dimensional crystallographic groups with two-dimensional translations. Due to the arising interest in these type of materials, new programs dedicated to the study of materials with layer and multilayer symmetry have been developed and implemented in the Bilbao Crystallographic Server (www.cryst.ehu.es) [1,2]. The server is in constant improvement and development, offering free of charge tools to study an increasingly number of crystallographic systems which now also includes the ones with layer symmetry.

The section dedicated to Subperiodic groups in the Bilbao Crystallographic Server gives access to the layer groups databases which contains the basic crystallographic information of the 80 layer groups (generators, general positions, Wyckoff positions and maximal subgroups) [3] and the Brillouin zone and k-vectors tables that form the background and classification of the irreducible representations of layer groups which can also be calculated with one of the programs available in the server. More sophisticated programs to identify the layer symmetry of periodic sections and to describe the electronic structure and surface states of crystals [4] are also available. The symmetry relations between the localized state (atomic displacements) and extended states (phonon, electrons) over the entire Brillouin zone can also be calculated. The utility of the available applications will be demonstrated by illustrative examples.

Glutathione peroxidase (GPX) [1] is a selenoenzyme containing multiple selenocysteine units in its active site. It catalyses the reduction of harmful peroxides, thus protecting cells from oxidative stress. High concentrations of active peroxides results in an alternative path of the catalytic cycle of GPX, where selenenic acid residues (R–SeOH) undergo oxidation to the corresponding seleninic (R–SeO₂H) and selenonic acids (R-SeO₃H). In general, synthetic seleninic acids and their sulfurated analogues sulfinic acids (R-SO₂H) have been reported as key component in redox regulation [2], exerting in some cases a surprising anticancer activity [3].

The reactivity of these moieties may be related to the electrophilic behaviour of selenium and, to a lesser extent, of sulphur. The propensity of an electron rich atom to act as an electrophile is related to the presence of regions of positive electrostatic potential (σ-holes) on its surface, located on the back-end of the covalent bonds formed by the considered atom. σ-hole interactions are named from the group of the periodic table to which the element behaving as an electrophile belongs; based on this, interactions given by atoms of group 16 are dubbed as Chalcogen Bonds (ChB) [4].

Here, we report the controlled oxidation of L-selenocystine (C₆H₁₂N₂O₄Se₂) in selenocysteine seleninic acid, which is a simple mimic of GPX activity. This compound was isolated and single crystals suitable for X-ray diffraction allowed to an insight at the atomic level of the electrophilic behaviour of selenium. This crystal structure suggests the possible involvement of ChB in the redox regulation activity of the seleninic acid moiety. A survey of the Cambridge Structural Database (CSD) and some computational studies on a small library of these class of compounds may confirm the propensity of seleninic (and sulfinic) acids to act as ChB donors.

The decomposition of the crystal contacts on the Hirshfeld surface between pairs of interacting chemical species enables to derive a contact enrichment ratio [1,2,3]. This descriptor yields information on the propensity of chemical species to interact with themselves and other species. The enrichment ratio is obtained by comparing the actual and equiprobable contacts. H∙∙∙N, H∙∙∙O and H∙∙∙S as well as weak H∙∙∙halogen hydrogen bonds appear generally more or less enriched, depending on the context. Larges series of molecules made of a set of chemical groups and retrieved from the Cambridge Structural Database can be investigated to find trends in the propensity of interactions to form.

The electrostatic energy of between atoms in contact was also computed using a multipolar atom model after electron density database transfer. The mean energy values of different contact types between multipolar pseudoatoms were compared statistically to the contact enrichment ratios.

The analyses suggest that hydrogen bonds are often the most enriched and attractive interactions and are therefore a driving force in the crystal packing formation for organic molecules. The methodology also enables to compare different types of hydrogen bonds which are in competition within a crystal packing. The behavior of weaker interactions such as halogen bonds is less contrasted. The methodology is a way to rank the occurrence of given synthons and the impact in crystal engineering will be discussed

The tenoxicam (4-hydroxy-2-methyl-N-2-pyridyl-2H-thieno(2,3-e)-1,2-thiazine-3-carboxamide 1,1-dioxide), is a non-steroidal anti-inflammatory drug (NSAID), member of oxicam family, widely used in the treatment of osteoporosis. Tenoxicam (TXM) could be present in the β-keto-enolic form (BKE) or β-diketone (BDK) and in a zwitterionic form (ZWC) (Figure 1). However, in solid form (more than 20 different compounds including polymorphic modifications, co-crystals, and solvates) [1 and present work] TXM has predominantly found in the zwitterionic form (ZWC). While in a dissolved form, keto-enolic equilibrium is observed since recorded by us experimental absorption and fluorescence spectra for various TXM solutions show presence two forms of TXM (called A and B) in solvents with high polarity and only A form of TNX in low polar solvents (cyclohexane, toluene, chloroform, dioxane). This led us to think about the possibility to obtain solid forms of tenoxicam contain it in BKE or BDK form.

A set of NMR measurements using various 1D- and 2D- techniques were used to assign which of TXM keto-enolic form (see Figure 1) belong to the A and B forms observed in a liquid environment. As a result, form A observed by optical methods assigns to BKE form and the form B – to ZWC. ¹H NMR spectra of tenoxicam in CDCl₃ detected at various temperatures from -55 to 25 °C show almost 100% TXM in form of BKE at 25 °C and almost 100% TXM in ZWC form at -55°C.

Taking into account optical and NMR data about the domination of BKE form in low polar solvents at room temperature, we tried to obtain solid forms of TNX containing TXM in BKE form by its crystallization from cyclohexane, toluene, dioxane, and chloroform. These experiments showed no crystal phase from cyclohexane and powder of TXM polymorph I from dioxane and toluene. Crystallization from chloroform gave single crystals of three different solvates so called TXM-CHCl₃-I (grow up at room temperature), TXM-CHCl₃-II (grow up at -18°C) and TXM-CHCl₃-III (grow up at -18°C). But in all these solvates TXM presents in ZWC form.

For understanding why TNX exists in BKE form in solution, but crystallize in ZWC form, DFT calculations in vacuo were made. It shows that BKE to be the most thermodynamically stable form, ZWC is less stable and BDK is the least stable (ΔG between BKE and these two forms of 2.20 kcal/mol and 12.49 kcal/mol, respectively). But BKE form is characterized by a large twist between A 2-pyridyl ring and TXM backbone with respect to almost flat ZWC form. Planarization of BKE form diminishes the energy difference between flatten BKE and ZWC forms almost to 0.15 kcal/mol that indicates a presence of another thin interaction within TXM molecule predisposing it to crystallization in ZWC form. This thin interaction was showed to be S-bond between thiophenil ring and carbonyl oxygen according to the analysis of intramolecular interactions within natural bond orbital theory [4]. This S-bond is significantly stronger for ZWC form as compared with flatten BKE form and it should be considered as the driving force of TXM crystallization

The authors would like to thank Dr. Anatoly A. Politov for useful discussion. SGA would like to thank Prof. Dr. Elena V. Boldyreva for her ongoing support. CT would like to thank his former supervisor Prof. Dr. Elena V. Boldyreva and his present supervisor Prof. Dr. Artem R. Oganov for their ongoing support.

SGA is indebted to Ministry of Science and Higher Education of the Russian Federation (project АААА-А19-119020890025-3).

PSS and ASK thank Ministry of Science and Higher Education of the Russian Federation for access to optical and NMR equipment (АААА-А16-116121510087-5).

Halogen bonding (XB) interactions are defined as those involving electrophilic sites (σ-holes) associated to a covalently bonded atom of group-17 with nucleophilic sites from either the same or a different molecule¹. These σ-hole regions are expected to exhibit along the extension of covalent bonds and can be finely tuned by the electronic nature of substituents in the molecule bearing the halogen atom.

In a previous study involving donor-acceptor complexes, we have succeeded to co-crystallize iodine substituted imide derivatives with pyridine derivatives. In these systems, we have pointed out a strong halogen bonding motif where the halogen atom is significantly shifted towards the acceptor moiety. For one of them, which is leading to an ionic crystal rather than a co-crystal², an electrostatic secondary interaction of C=O^δ-···I ^δ+ type has been discussed as one of the reasons behind such a halogen atom shift towards the acceptor. In our work, we are actually investigating the evolution of such XB interactions in an organic binary adduct composed of N-Iodosaccharin and Pyridine (NISac.Py) via X-ray diffraction experiments under pressure. These experiments were undertaken with a Membrane Diamond Anvil Cell (MDAC) under external pressure ranging from 0 GPa to 4.5 GPa, by using an in-house set-up (with the in-situ measurement of pressure from time to time) developed in our laboratory and adapted to the diffractometer (Bruker D8 venture) that was used to collect high-pressure X-ray diffraction data.

Aiming to analyse the influence of the molecular environment on the XB motif of NISac.Py, X-ray diffraction studies have permitted to follow the evolving behaviour of the N_sac-I···N’_py interactions as a function of pressure, which results in the shifting of the halogen atom position between donor and acceptor moieties. This trend might be linked to a potential change of state from co-crystal to ionic crystal form under pressure. The study also opens up an opportunity to understand the modification of secondary interactions as a function of pressure. Another interesting finding resulting from this work is the occurrence of a mechanical twinning and its behaviour as a function of pressure, which is analysed in detail. Periodic theoretical calculations were also carried out by applying isotropic external pressures. They were followed by the analyses of the Equation of State (EOS), molecular environments and non-covalent interactions, all of them showing good agreements with experimental results. In summary, this work illustrates the possibility of working with pressure as another thermodynamic variable that permits to alter weak intermolecular interactions and therefore to explore phase transformation or polymorphic phases in other donor-acceptor systems formed by similar interactions.

[1] Cavallo, G., Metrangolo, P., Milani, R., Pilati, T., Priimagi, A., Resnati, G. & Terraneo, G. (2016). Chem. Rev. 116, 2478–2601. [2] Makhotkina, O., Lieffrig, J., Jeannin, O., Fourmigué, M., Aubert, E. & Espinosa, E. (2015). Cryst. Growth Des. 15, 3464–3473.

Keywords: High-pressure X-ray diffraction; Membrane Diamond Anvil Cells; Halogen bonding; Mechanical Twinning

V.V.S. thanks the French ANR and the Region Grand-Est for a PhD fellowship. We thank PMD²X X-ray diffraction facility of the Institut Jean Barriol, Université de Lorraine, for X-ray diffraction measurements and ERDF for funding high-pressure experimental set-up. High-performance computing resources were partially provided by the EXPLOR center hosted by Université de Lorraine

Controlling supramolecular synthetic output, with the aim to achieve targeted macroscopic properties, is the main goal of crystal engineering.[1] Mechanical flexibility, as one of the highly desired properties of functional materials, has recently become a feature of a growing number of crystalline compounds.[2-5] Plastic deformation, together with elastic response, is frequently observed among organic molecular crystals,[3] but quite rarely noticed among crystalline metal-organic compounds.[4,5] Since the introduction of metal cations to organic systems allow us to achieve specific properties such as magnetic and electric ones, and therefore opens a wide range of possible applications, it is clear that there is a need for determining structural requirements that need to be fulfilled to equip metal-organic crystals with mechanical flexibility.Recently, it was shown that cadmium(II) coordination polymers equipped with halopyrazine ligands adaptably respond to applied external stimuli, displaying elastic flexibility.[5] It was observed that introducing a slight structural changes, simply by exchanging bridging halide anion or halogen atom on halopyrazine ligand, changes the extent of elastic response significantly, while the quantification of their mechanical behaviour clearly showed that they can be categorized into three main subgroups, highly, moderately and slightly elastic. To get an invaluable insight into the phenomenon, we decided to systematically examine similar classes of coordination polymers by introducing slight structural differences through the exchange of supramolecular functionalities only. Herein we opted for pyridine-based ligands decorated with cyano functionality to explore their impact on macroscopic mechanical output. It was determined that the position of cyano group on pyridine ring, as well as used bridging halide anion, dictate the nature and extent of mechanical response. For crystals that displayed elastic behaviour, the responses were quantified and correlated with structural features, primarily the strength and geometry of supramolecular interactions, and compared with the mechanical behaviour of similar metal-containing systems.

[1] Desiraju, G. R. (2007) Angew. Chem. Int. Ed. 46, 8342.

[2] Commins, P., Tilahun Desta, I., Prasad Karothu, D., Panda, M. K., Naumov, P. (2016) Chem. Commun. 52, 13941.

[3] Saha, S., Mishra, M. K., Reddy, C. M., Desiraju, G. R. (2017) Acc. Chem. Res. 51, 2957.

[4] Worthy, A., Grosjean, A., Pfrunder, M. C., Xu, Y., Yan, C., Edwards, G., Clegg, J. K., McMurtrie, J. C. (2018) Nat. Chem. 10, 65.

[5] Đaković, M., Borovina, M., Pisačić, M., Aakeröy, C. B., Soldin, Ž., Kukovec, B.-M., Kodrin, I. (2018) Angew. Chem. Int. Ed. 57, 14801.

This work has been fully supported by Croatian Science Foundation under the project IP-2019-04-1242.

Strong intermolecular interactions serve as vital tools in cocrystal assembly. Halogen bonding (XB) [1], a highly directional interaction, is most often observed between a halogen-atom donor and electron-rich acceptors, such as oxygen or nitrogen. However, XBs can also be used for the organization of arenes in the solid state through interactions with aromatic p-systems, as previously explored in the dichroic and pleochroic cocrystals of naphthalene or azulene, respectively. [2]

This presentation will outline our study of XB cocrystal structures containing various polycyclic aromatic hydrocarbons (PAHs), and evaluate the reliability of halogen bonding to carbon as an overlooked tool for crystal engineering.

[1] Christopherson, J. C.; Topić, F.; Barrett, C. J.; Friščić, T. (2018). Crystal Growth & Design, 18, 1245-1259.

[2] Vainauskas, J.; Topić, F.; Bushuyev, O. S.; Barrett, C. J.; Friščić, T. (2020) Chemical Communications 56, 15145-15148.

Almost all cellular processes depend on protein-protein interactions (PPI) which therefore are promising targets for drug design or tool compound development. PPIs as targets have the advantage that the interaction surfaces are highly specific and unique, meaning potent and selective compounds are less likely to cause side effects compared to targeting enzyme activities. However, targeting PPIs is usually challenging due to their large interaction surface and shallow pockets. It is important for such surfaces to find hotspots where compounds engage in strong interactions with the protein. Finding hotspots can be achieved by screening fragments (organic compounds < 300 Da), which form specific interactions with the target. These fragments can be used as starting points for compound development. In order to identify fragments bound to a protein, crystallographic fragment screening [1] is a great tool as it not only informs about the presence of a fragment, but also about its 3D position towards the protein. Thus, enabling structure-guided drug design or tool compound development for any target that can be crystallized reproducibly and gives diffraction data to sufficient resolution.

We chose the spliceosomal protein-protein complex of yeast Aar2 and Prp8^RNaseH (AR) [2], to screen our novel over 100-membered F2X-Universal Library [3]. The spliceosome is a large cellular machine that depends on dynamically changing PPIs throughout its functional cycle and thus is an ideal object of study for PPI compound development. Prp8 is highly conserved in the spliceosome and acts as a scaffolding protein. Prp8 is shuttled into the nucleus via a shuttling factor Aar2. Utilizing the complex for our screen has the advantage to identify fragments bound close to the interface of AR while also probing the surfaces of Prp8^RNaseH and Aar2 at the same time. That means information can be gathered to either develop an enhancer for the interaction of AR or inhibitors for other interactions Prp8^RNaseH is involved in or to find potentially interesting sites on Aar2. In previous work a representative subset of the F2X‑Universal Library, the F2X‑Entry Screen (96 fragments) was screened against AR, which already resulted in 20 unique hits that hinted towards possible hot spots [3]. However, in order to verify the found hotspots as such, to potentially find more hotspots and to confirm the found binding motifs of the fragments the full F2X‑Universal Library, i.e. 1013 compounds in total, were screened. For the automatic data analysis FragMAXapp [4] in combination with cluster4x [5] was utilized and this resulted in 278 unique hits scattered across the two proteins highlighting hotspots on their surfaces. This translates into a hit rate of 27,5%, which is the highest hit rate for such a large screen to the best of our knowledge and successfully validated the library. The additional hits found by screening the complete F2X‑Universal Library validated certain binding modes presented by the F2X‑Entry Screen and provided novel hotspots. This way we gained a large number of interesting starting points to develop potential modulators for several PPIs inside the spliceosome.

The hypoxia mediated prolyl-hydroxylase isoforms 1-3 (PHD1-3) are members of the Fe(II)-/2-oxoglutarate (2OG)-dependent oxygenase superfamily of enzymes. PHD1-3 catalyse the trans-4-prolyl-hydroxylation of the labile hypoxia-inducible factor-α subunit (HIFα) in the presence of cofactors; Fe(II), 2OG, ascorbic acid, and molecular dioxygen. The hydroxylation of the oxygen degradation domain (ODD) of the HIF1-3α substrates marks the transcription factor for degradation via the ubiquitin-E3 ligase-28S proteasome pathway. In hypoxic conditions, PHD1-3 are less active and the HIFα subunits translocate into the nucleus and form an α,β-heterodimer with the stabile HIFβ subunit that subsequently leads to the genetic cascade in response to hypoxia, e.g. upregulation of erythropoietin (EPO) and vascular endothelial growth factor (VEGF). The inhibition of the PHDs and specifically PHD2, the most commonly expressed isoform, have been the focus for small-molecule based therapies to treat individuals with blood disorders, such as anaemia and ischaemia-related disorders. Recently, several PHD inhibitors have been approved; Roxadustat (Japan, Chile, and China), Daprodustat (Japan), Molidustat (Japan), Enarodustat (Japan), and Vadadustat (Japan). Co-crystal structures of some of the clinical inhibitors have been challenging to obtain due to heterogeneity induced through ligand complexation. A clinical inhibitor complex structure with PHD2 has been obtained using a novel crystallisation system utilising succinate, co-product of the PHDs reaction, as a crystallisation tool to stabilise the active site during incubation with Molidustat, the related compound IOX4, and monodentate binding inhibitor Takeda-17. The novel crystal form was then further used for inhibitor soaking and scale-up of crystal growth (~500 crystals) for an XChem fragment-based screen (I04-1, Diamond Light Source) in search for allosteric binding sites. To date, the crystallisation system yielded 3 inhibitor co-crystal structures, 8 complex structures through soaking, and 5 hits from the fragment screen.

Fragment-based lead discovery (FBLD) is by now an established drug development strategy, which has so far delivered four novel drugs and more than 40 additional molecules in clinical trials. Starting points for FBLD are usually found by biophysical screening of fragment libraries with several hundred and up to a few thousand compounds. Crystal-based fragment screening has become increasingly popular over the last few years, facilitated by automation, improvements in beamline instrumentation and software development. The FragMAX facility provides a new user platform for crystallographic fragment screening at BioMAX, the first operational beamline for macromolecular crystallography at MAX IV Laboratory. This presentation will provide an overview of the different components of the FragMAX facility and describe the screening process. It will highlight different modes of access and outline planned developments.
The FragMAX platform started serving external users in 2019 and has since established an international user program that is open to academic and industrial research groups. The platform consists of three main components: (i) a crystal preparation facility, (ii) diffraction data collection at BioMAX and (iii) FragMAXapp, an intuitive web-based tool for large-scale data processing. The facility provides free access to several fragment libraries, notably, the in-house developed FragMAXlib. The screening processes have been adjusted throughout the COVID-19 pandemic and our aim is to further develop the platform so that users with different levels of experience can routinely achieve actionable screening hits for their targets.
While the facility was conceptualized for crystal-based fragment screening, its design is entirely generic. It can therefore be used for other applications that require large-scale crystal preparation and potential new applications will be discussed at the end of the presentation.

Carboxylated Pillar[5]arene (CPA5), first reported by Ogoshi in 2010 [1], is highly symmetrical pillar-shaped compound, composed of hydroquinone units linked by methylene bridges at the para-positions, modified by ten carboxylic acid groups. Its rigid hydrophobic, electron-rich cavity combined with its water solubility make it great candidate as host molecule for various electron-deficient guest or other neutral molecules. Moreover, carboxyl groups, that can take part in proton transfer, are located at the terminal positions of flexible aliphatic chains, so they can adjust to the size and shape of guests.

In 2015 Danylyuk described crystal self-assemby of CPA5 in its complex with ethanol molecules [2]. Authors described the chains of CPA5 molecules connected via cyclic carboxylic-carboxylic hydrogen bonds (HBs) as main supramolecular motif. Introduction of tertacaine guest reorganized the formation of HBs. Inspired by this result, we decided to investigate how guest molecules, decorated with different functional groups, affect on the self-assembly of the host.

Here we want to present our results on the X-ray structures of CPA5 in the form of its host-guest complexes with viologens, guanidine and amidine compounds. Our study on the CPA5-viologens complexes shows that the main chain motif is dictated by very strong carboxylic-carboxylate HBs [3]. Altering the guest into an amidine or guanidine molecules changes main synthon into amidinium-carboxyl/ate and guanidinium-carboxyl/ate HBs. In a broader perspective our results may have potential applications in drug delivery and molecular recognition systems.

[1] Ogoshi, T., Hashizume, M., Yamagishi, T., Nakamoto, Y. (2010). ChemComm, 21, 3708.

[2] Danylyuk, O., Sashuk, V. (2015). CrystEngComm, 17, 719.

[3] Butkiewicz, H., Kosiorek, S., Sashuk, V., Danylyuk, O. (2021). CrystEngComm, 23, 1075.

Supramolecular arrangements in the crystal structures and the interaction energy calculations of resonance-assisted hydrogen-bridged (RAHB) rings - RAHB/RAHB and RAHB/C₆-aromatic contacts

J. P. Blagojević Filipović¹, S. D. Zarić²

¹Innovation Centre of the Faculty of Chemistry, Studentski trg 12-16, Belgrade, Serbia, ²Faculty of Chemistry, University of Belgrade, Studentski trg 12-16, Belgrade, Serbia szaric@chem.bg.ac.rs

The Cambridge Structural Database (CSD) is searched for mutual contacts between six-membered resonance-assisted hydrogen-bridged rings (RAHB) (the example of a fragment is shown in Fig. 1a) [1] and for contacts between six-membered RAHB rings and C₆-aromatic rings (Fig. 1b). There is a quite large prevalence of parallel contacts in the set of RAHB/RAHB contacts, since 91% from totally 678 contacts found are parallel contacts, mostly with antiparallel orientation of the rings [1]. At the other side, the prevalence of parallel contacts in the set of RAHB/C₆-aromatic contacts is not so pronounced, since 59% from totally 677 contacts found are parallel contacts. The distances between the interacting ring planes are mostly between 3.0 and 4.0 Å, while horizontal displacements are mostly in the range 0.0-3.0 Å in both parallel RAHB/RAHB and RAHB/C₆-aromatic contacts.

Figure 1. The examples of fragments used in CSD search for a) six-membered RAHB/RAHB contacts; b) six-membered RAHB/C₆-aromatic contacts

The interaction energy calculations were performed on stacked dimer model systems based on abundance in the CSD. The strongest calculated RAHB/RAHB interaction is -4.7 kcal/mol, while the strongest calculated RAHB/benzene interaction is significantly weaker -3.7 kcal/mol. However, RAHB/RAHB stacking interactions can be stronger or weaker than the corresponding RAHB/benzene stacking interactions, depending on the RAHB ring system. The Symmetry Adopted Perturbation Theory (SAPT) calculations show that the dominant contribution in total RAHB/RAHB stacking interaction energy is the dispersion term, which can be mostly or completely cancelled by the exchange repulsion term, hence, the electrostatic term can be effectively dominant. Depending on the RAHB ring system, the electrostatic contribution can be practically equal to the net dispersion contribution (the sum of dispersion and exchange-repulsion terms) [1]. The electrostatic term is effectively dominant in all RAHB/benzene systems observed, due to the almost complete cancellation of the dispersion by the exchange-repulsion terms.

[1] Blagojević Filipović, J. P., Hall, M. B. & Zarić, S. D. (2019).Cryst. Growth Des. 19, 5619.

Keywords: stacking; RAHB; CSD

This work was supported by the Serbian Ministry of Education, Science and Technological Development (Grant number 172065).

Within the relevant field of metal-containing polymers and their applications in the biomedical context [1], a Silver(I) coordination polymer of formula [(bpy)Ag]OTf_∞ presenting polymorphism has been synthetized through reaction between the N^N ligand 2,2’-bipyridine (bpy) and Silver trifluoromethanesulfonate (AgOTf). By varying the stoichiometric ratios and the order of the addition of the reagents along the synthetic routine, two polymorphs have been synthesized and structurally characterized. The first polymorph of [(bpy)Ag]OTf_∞, the α-form, crystallized in the P3₁21 space group, is characterized by the alternance, along the polymeric chain, of Ag(I) ions with linear and tetrahedral geometry (Fig.1); this arrangement results in the generation of chiral helices [2]. In a second polymorph of [(bpy)Ag]OTf_∞, indicated as the β-form (P2₁/c space group), prepared by modifying the synthetic procedure adopted previously, all the Ag(I) ion adopts a slightly distorted linear geometry. The silver ions are coordinated to the nitrogen atoms of bridging bpy ligands, while the non-coordinated OTf anions are found weakly interacting with the metal centres (Fig.1). The β-polymorph presents a zig-zag conformation which, as already reported for 1D organic polymers [3], can generate pocket-like cavities able to accommodate organic molecules through non-covalent interactions, rising the role of inorganic-polymer co-former in the formation of biologically active co-crystals. Hence, the β-form of [(bpy)Ag]OTf_∞ was used for the preparation of an inorganic-polymer co-crystal by using curcumin (curc) as the organic bioactive molecule. The [(bpy)Ag]OTf_∞-curc co-crystal was obtained through a quick solution reaction and characterized through several techniques, including Powder X-Ray Diffraction (PXRD), Differential Scanning Calorimetry (DSC), ¹H-NMR, UV-visible and Infrared Spectroscopies. The instauration of weak intermolecular interactions between the keto-enolic function of curc and both the Ag(I) cationic chains and the triflate anions of the inorganic-polymer is the driving force for the formation of this multicomponent material. Considering the multiple biological functions of curc [4] and the well-known antimicrobial activity of silver compounds [5], the [(bpy)Ag]OTf_∞-curc co-crystal could represent a multi-functional supramolecular system. Moreover, embedding the [(bpy)Ag]OTf_∞-curc co-crystal into an ethylcellulose (EC) polymeric matrix, antimicrobial films with potential biomedical and food-packaging applications have been obtained and characterized.

[1] Yan, Y.; Zhang, Z.; Ren, L.; Chuanbing, T.; (2016) Chem. Soc. Rev., 45, 5232

[2] Bellusci, A.; Ghedini, M.; Giorgini, L.; Gozzo, F.; Szerb, E. I.; Crispini, A.; Pucci, D. (2009) Dalt. Trans. 36, 7381.

[3] Chappa, P.; Maruthapillai, A.; Voguri, R.; Dey, A.; Ghosal, S.; Basha, M. A. (2018) Cryst. Growth Des. 18, 7590.

[4] Gupta, N.; Verma, K.; Nalla, S.; Kulshreshtha, A.; Lall, R.; Prasad, S. (2020) Molecules, 25, 1. [5] Scarpelli F., Crispini A., Giorno E., Marchetti F., Pettinari R., Di Nicola C., De Santo M. P., Fuoco E., Berardi R., Alfano P., Caputo P., Policastro D., Oliviero Rossi C., Aiello I. (2020). ChemPlusChem 85, 426.

Crystal structures of diastereomeric salt pairs, as well as double salts are rare to find in the literature. Present work involves the crystallization and structural elucidation of two constitutional isomer double salts along with their related diastereomeric salt pairs. The investigated systems are 1-cyclohexylethylammonium 2-chloromandelate (S-S, R-S, SS-SR) and 1- cyclohexylethylammonium 4-chloromandelate (R-R, S-R, SS-SR). Alongside structural elucidation, the thermal properties of all diastereomers and double salts have been determined and compared. In the crystal of five of the six chiral salts, hydrogen bonded layers are formed with the participation of the ionic groups and the hydroxyl group of the mandelate anion. In one structure, the formation of one-dimensional hydrogen bonded columns is observed. Due to the different position of the chlorine substituent in the two compound families, the halogen interactions are oriented towards the inside of the hydrogen-bonded structures or positioned between the layers and establish a relatively strong connection between them. The two different halogen positions and every possible combination of configurations in the six investigated salts provide a quite detailed landscape of the effect of stereochemistry on the solid-state structure of the salts.

Knowledge on conformation and crystal structures (including crystal polymorphs and solvatomorphs) is important in the use and development of active pharmaceutical ingredients (API). Polymorphism plays a very important role in the bioavailability of a drug [1] as the physico-chemical properties (e.g. solubility, stability) of polymorphs can differ significantly [2]. Clopamide (4-chloro-N-2,6-dimethylpiperidin-1-yl)-3-sulfamoylbenzamide) drug is used worldwide in the treatment of hypertension and oedema and despite its medical application the crystal structure has not yet been investigated. It has also been shown that some diuretic may also cause urinary loss of certain trace elements or modify their levels in blood and may induce changes in the levels of copper in normal hypertensives [3]. According to the molecular structure it is noticeable that the carbonyl oxygen and the piperidine nitrogen of Clopamide are able to coordinate to metal centres, so the complexation of Clopamide with metal ions in the human body may be responsible for this side effect (Fig. 1). To gain a better insight into the structure and interaction of this drug molecule with metal ions, structural study of Clopamide compound and its coordination compounds with copper(II) have been studied under different crystallization conditions. The crystal structure of this drug and its copper(II) complexes were studied by screening different solvatomorph and polymorph crystals and the structures were determined by single-crystal X-ray diffraction. Our challenge was to detect the conformations and possible arrangements of the complexes induced by coordination bond and by different secondary interactions. These investigations enrich the knowledge on the aspects which contribute to the development of materials with specific properties. The crystal structures of anhydrous, and hemihydrate form of Clopamide have been determined. We present how the inclusion of water contributes to the crystal perfection of the drug crystals. The newly defined chalcogen bonds are recognised in the Clopamide anhydrate crystals being in competition with intramolecular halogen bonds. The bis-ligand copper(II) complex crystals were synthesized from the homolouges series of alcohols, with the inclusion of solvent molecules, resulting four isostructural [4] crystals with increasing size of void and unit cell volumes in the order of MeOH, EtOH, PrOH and iPrOH. From organic solvents, three solvent free polymorphs and a crystal containing dichloromethane was prepared. All Cu(II) compounds are of square-planar geometry, in which copper(II) centres are coordinated by piperidine-N and carbonyl-O donor atoms in a five-membered chelate ring with the two ligands in trans positions. The 2,6-dimethylpiperidine units of the molecule is perpendicular to the plane of the coordination sphere, preventing axial coordination of solvate molecules. The solution structure of the copper(II) complex have been investigated in DMSO by EPR spectroscopy.

Previously it was revealed very frequent occurrence of the specific ferrocene-ferrocene dimers in the ferrocene containing crystal structures [1]. Thus, the analysis of the Cambridge Structural Databank (CSD) showed that nearly 60% of monosubstituted ferrocene derivatives form robust ferrocene dimers composed of two Fc units in parallel orientation (see Figure below). Formation of the dimer is based on an excellent electrostatic complementarity between the Fc units (Figure below). A subsequent theoretical study [2] revealed the significant stabilization energy of −5.7 kcal/mol for this specific interaction with dispersion as the most important attractive contribution. In the present work, we have used the CSD to explore the same interaction between metallocene units but this time analyzed in all metallocene based crystal structures. We have found that all metallocenes equally as ferrocene derivatives are able to form the dimers with very similar geometrical parameters. In addition, we have investigated the supramolecular aggregation of the dimers into chains of different geometry.

[1] Bogdanović, G. A. & Novaković, S. B. (2011). CrystEngComm 13, 6930-6932.

[2] Vargas-Caamal, A. et al. (2016). Phys. Chem. Chem. Phys. 18, 550-556.

The identification of differences and similarities in non-covalent interactions of molecules in closely related solids (polymorphs, solvates, homologues, isostructural series, and others) is crucial for crystal engineering. However, crystalline environment also affects molecular reactivity within a "reaction cavity" or conformations of flexible molecules. Analysis of contributions of various types of non-covalent interactions to the molecular surface allows their comparison in different solid forms both in terms of molecular functional groups, and in the context of crystal field effect. The advantages of this approach include rapid calculations, consideration of 3D screening effect, and investigation of strong and week, hydrophobic and hydrophilic, rare and abundant interactions from unified positions. Particularly, the molecular Voronoi surfaces give qualitative, quantitative and visual representation of all types of intra- and intermolecular non-covalent interactions in crystals of inorganic, organic and macromolecular compounds (Fig. 1).

We applied the molecular Voronoi surfaces for analysis of non-covalent interactions in a number of bulky organic and organoelement molecular compounds. An approach to analyze conformation polymorphs was demonstrated on the example of photochromic N-salicylideneanilines, and (2',4'-dinitrobenzyl)pyridine derivatives. Interplay of hydrogen and halogen bonds was studied for polymorphs of alkylboron-capped iron(II) and cobalt(II) hexachloroclathrochelates, and for a series of polybromide salts. The effect of crystalline environment on molecular conformations of a flexible imatinib molecule, and on a photoinitiated solid-state reaction of eicosaborate isomerization were studied. Non-covalent interactions of imatinib, abirateron and bicalutamide in their polymorphs, solvates, salts and ligand-receptor complexes were compared. The molecular Voronoi surfaces were proved to be suitable for understanding of the interplay between intermolecular strong and weak interactions, effect of a particular contact on molecular and material properties, and were found to be applicable to a large number of objects.

Cocrystallization is becoming a more and more popular method to obtain new forms of drugs in the pharmaceutical industry. In this way, their physicochemical properties, like solubility, bioavailability, permeability through biological membranes, stability can be modified without affecting their pharmacological properties [1]. Cocrystals are homogeneous solids consisting of components in a neutral or ionic form, which are solids under ambient conditions, in a specific stoichiometric ratio. Such combinations of APIs (active pharmaceutical ingredients) with appropriately selected coformers are defined as pharmaceutical cocrystals [2].

The main goal of the study was to use purine alkaloids, such as theobromine, theophylline, and caffeine for cocrystallization with trimesic (TMSA) and hemimellitic acid (HMLA) [3]. Theobromine forms cocrystals TBR·TMSA and TBR·HMLA. Caffeine forms the cocrystal CAF·TMSA and the cocrystal hydrate CAF·HMLA·H₂O. Theophylline forms TPH·TMSA and TPH·HMLA cocrystals, the cocrystal hydrate TPH·TMSA·2H₂O and the salt hydrate (TPH)⁺·(HMLA)^-·2H₂O. The reactions were carried out in solution and by neat or liquid-assisted grinding in a ball mill. Powder analysis showed that 7 out of 8 solids were obtained by mechanochemical synthesis. All obtained multicomponent complexes were structurally characterized by the single-crystal X-ray diffraction method. The use of compounds with slight structural differences allowed the investigation of the complexity of specific non-covalent interactions formation. Selected coformers can form strong hydrogen bonds with the carboxyl groups participation, therefore 3 types of supramolecular synthons have been distinguished: alkaloid-alkaloid, alkaloid-acid and acid-acid synthons.

X-ray structural analysis showed the dominant role of alkaloid-acid and acid-acid interactions. These studies also show that it is sometimes possible to predict what non-covalent interactions will be responsible for the arrangement of molecules in the crystal lattice of the synthesized complex. However, the study of the self-assembly processes of molecules in systems with many functional groups is well-founded as the complexity of supramolecular synthons shows that the crystal structure design is often laborious.

Additionally, UV-Vis measurements determined the effect of the cocrystallization of purine alkaloids on their solubility in water.

[1] Kumar S., Nanda A. (2017), Pharmaceutical Cocrystals: An Overview, Indian J. Pharm. Sci., 79, 858-871.

[2] Duggirala N. K., Perry M. L., Almarsson Ö., Zaworotko M. J. (2016), Pharmaceutical cocrystals: along the path to improve medicines, Chem. Commun., 52, 640-655.

[3] Gołdyn M., Larowska D., Bartoszak-Adamska E. (2021), Novel Purine Alkaloid Cocrystals with Trimesic and Hemimellitic Acids as Coformers: Synthetic Approach and Supramolecular Analysis, Cryst. Growth Des., 21, 396-413.

Polymorphism is of significant interest owing to its potential to influence the physiochemical properties of pharmaceuticals and other materials. The high directionality and the intrinsic tunability of the intermolecular halogen bond make it a compelling design element in crystal engineering. In this work, we describe various polymorphs of halogen-bonded co-crystals constructed from 2,3,5,6-tetramethylpyrazine with different halogen bond donors (1,4-diiodotetrafluorobenzene, 1,3,5-trifluoro-2,4,6-triiodobenzene, and their bromo- and chloro-analogues). Polymorphic cocrystals are obtained from solution-based and solid-based methods. Solution-based methods are implemented by manipulating the solvent system mixture and the mixing temperature while solid-based cocrystals are obtained via co-sublimation and mechanochemical techniques. Co-crystal structures are characterized via single crystal X-ray diffraction and powder X-ray diffraction. 13C solid-state nuclear magnetic resonance spectroscopic investigations of cocrystals are used to validate and further probe the polymorphic structures. This study serves as a holistic approach in investigating polymorphism and demonstrates the unquenchable importance of halogen bonding in crystal engineering.

In this work, we report a single-crystal structure of a new organic-inorganic hybrid material base on two different mononuclear halogenidometallate complexes, in which hexachloridorhodate (III) ([RhCl₆]^3-), tetrachloridoferrate (III) ([FeCl₄]^-) and chloride ions (Cl^-) are combined with the organic cation 1,6-diammoniumhexane (C₆H₁₈N₂²⁺) to form a three-dimensional (3D) framework via non-covalent ‘intermolecular’ interactions. Tetrakis(1,6-diammoniumhexane) hexachloridorhodate(III) tetrachlorioferrate(III) tetrachloride has been hydrothermally synthesized in concentrated hydrochloric acid solution. Red single crystals of the compound with sufficient size for X-ray structure determination were grown by slow evaporation of the hydrochloric acid solution of the hydrothermally treated reactants. The crystal structure analysis indicates that the titled compound crystallizes in the tetragonal space group I4₁/a with unit cell dimensions a = 19.154(3) Å, c =14.363(3) Å, and Z = 4. The solid with the sum formula C₂₄H₇₂Cl₁₄FeN₈Rh is formed by three types of distinct anionic units, [RhCl₆]^3-, [FeCl₄]^- and Cl^-, which are chargsed balanced by cations [C₆H₁₈N₂]²⁺. The asymmetric unit consists of one Rh, one Fe and one chloride atom viz. atom Cl(4), on special positions (fourfold axes, glide plane), three chloride atoms viz. atom Cl(3), Cl(2) and Cl(1), and one complete all-transoid zigzag chain-like 1,6-diammoniumhexane dication is placed in general positions. Cl(4) and Cl(3) occupy the axial and equatorial positions, respectively, in the slightly distorted octahedral geometry around Rh with bond lengths Rh-Cl(4) = 2.344(3) Å and Rh-Cl(3) = 2.355(2) Å. Cl(2) fills the coordination sphere in the tetrahedral geometry around Fe with bond length Fe-Cl(2) = 2.166(4) Å. Figure 1 depicts the asymmetric unit with atom numbering and colour legend. [C₆H₁₈N₂]₄[RhCl₆][FeCl₄]Cl₄ is isomorphous with the organic-inorganic hybrid compound containing 1,6-diammoniumhexane, hexachloroferrate (III), tetrachloroferrate (III) and chloride ions [C₆H₁₈N₂]₄[FeCl₆][FeCl₄]Cl₄ [1,2]. The solid-state structure of [C₆H₁₈N₂]₄[RhCl₆][FeCl₄]Cl₄ features a three-dimensional network of N-H···Cl hydrogen bonds between the ionic components. The N-H···Cl hydrogen bonds donate from the protonated amino groups (NH₃⁺) at both ends of the organic ion to the chloride ligands of [RhCl₆]^3- and free chloride ions with NH···Cl distances ranging from 3.124(8) to 3.309(7) and are to be considered as week interactions. Inorganic layers are built up from [RhCl₆]^3- octahedral and [FeCl₄]^- tetrahedral which are arranged in line along the crystallographic c-axis and the distance between metal centers is long (7.181 Å); the organic cationic species along with the free chloride anions are located between the inorganic layers and bound to each other by further N-H···Cl hydrogen bonds. In contrast, [FeCl₄]^- does not participate in any hydrogen bonding of significant strengths. It seems, the free chloride and [RhCl₆]^3- ions have priority to interacting with [C₆H₁₈N₂]²⁺. The titled organic-inorganic hybrid compound was also characterized by Fourier-transform infrared spectroscopy (FT-IR), elemental and differential scanning calorimetry (DSC) analyses, and powder X-ray diffraction (XRD). To the best of our knowledge, it is the example of a mixed-metal organic-inorganic hybrid compound base on mononuclear transition metal halide complexes.

Amines can (co)crystallize with water fairly well. The crystals can be formed mostly because both components form hydrogen bonds. Depending on the stoichiometric ratios, amines can create several hydrates with different amount of water per amine molecule. An excellent example is a piperidine - an aliphatic, heterocyclic secondary amine with a six-membered ring. This system can form five different hydrates [1]: the lower ones (containing ½ or 2 water molecules per amine) which present features characteristic for well-defined structures of cocrystals, and the higher hydrates (8.1, 9¾, 11) which have the architecture more similar to clathrate hydrates with the organic molecules embedded in the cages [2].

Steric hindrance is an interesting factor influencing the formation of hydrates. The presence of the substituent group (like a methyl group) in close proximity of the NH group can reduce an access for the other molecules and hence may lead to significant structural changes. Piperidine can be easily substituted with methyl groups in 2nd and/or in the 6th position, what maximizes the steric hindrance effect. Consequently the number of possible 2,2,6,6-tetramethylpiperidine hydrates might be expected to be smaller than for the parent piperidine system. Another possible modification of piperidine moiety is a replacement of carbon in the 4th position with an oxygen atom giving morpholine. Interestingly, despite of similar shape and properties to piperidine, the morpholine hydrates have not been discovered up-to-date. Therefore an intriguing problem appears whether the 3,3,5,5-tetramethyated morpholine is willing to cocrystallize with water. If so, do these hydrates reveal a similar kind of architectures to piperidine analogue or not?

Because both 2,2,6,6-tetramethylpiperidine or 3,3,5,5-tetramethylmorpholine and water are liquid at RT, amines and their hydrates were crystalized on the diffractometer, using in situ crystallization technique with IR laser [3]. As a result of throughout analyses crystals of both amines, but also of four hydrates were obtained and their structures were determined. The amines form hemihydrates and dihydrates. Interestingly, while hemihydrates of the amines have very similar, but not identical, structural motifs, dihydrates are isostructural. Despite of numerous attempts no higher hydrates (clathrate-like systems) could be obtained. This is probably due to too large size of the whole molecules to fit to the cavities observed in the clathrate hydrates.

[1] Dobrzycki, Ł., Socha, P., Ciesielski, A., Boese, R., Cyrański, M.K., (2019). Cryst. Growth Des., 19, 2, 1005-1020

[2] Sloan, E. D. (1990) “Clathrate Hydrates of Natural Gases”, Marcel Dekker, New York, USA

[3] Boese, R. (2014). Z. Kristallogr. 229, 595.

σ-hole interaction properties of divalent sulfur
Albert S. Lundembaa, Dikima D. Bibelayia, Juliette Pradonb* and Zéphyrin G. Yava*
Abstract
Non-covalent interactions like hydrogen bonds, aromatic stacking contacts and even σ-hole interactions are commonly observed in biologic macromolecular compounds like proteins, polysaccharides, and nucleic acids. These rather weak interactions often play a significant role in determining the tertiary structure of macromolecules. Evidence of σ-hole interactions has been given by both theoretical and experimental studies reported in the literature. The present study explores the σ-hole interaction properties of divalent sulfur groups (R1-S-R2) using the Cambridge Structural Database (CSD) in conjunction with ab initio calculations. CSD analysis revealed that 7 095 structures contained a divalent sulfur atom that formed an intermolecular σ-hole contact within the sum of the van der Waals radii with N, O, F, P, S, Cl, As, Se, Br, Sb, Te or I as the acceptor atom. The structural fragments (C,C)-S, (C,S)-S, (N,S)-S, (C,N)-S, (N,N)-S, (S,S)-S, (C,Se)-S, (C,P)-S, (C,Te)-S and (C,As)-S were each observed to exhibit intermolecular contacts that are potentially σ-hole interactions. The geometric preferences of some of these contacts indicated that genuine σ-hole interactions were likely. That finding was confirmed by the geometries of the optimised complexes formed by the σ-hole donors CH3O-S-OCH3 (KUYRIF), FOC-S-CN (AMOREA), (CH3)2N-S-Cl (VAMPEF) and CN-S-CN (fragment of GOJZUC) derived from the CSD. Values of the binding energy (BE) calculated with B3LYP were markedly smaller than values calculated with MP2, the latter being close to those with B3LYPD3-G and B3LYPD3-BJ. This suggested that dispersion interactions were in addition to σ-hole interactions the main forces stabilizing the complexes. The energy of the σ-hole interaction was dependent on the environment of the sulfur atom. The dependence agreed well with molecular electrostatic potential surfaces of the donors and partial charges of the sulfur atom predicted by ab initio calculations. The positive charge of the sulfur atom was enhanced when increasing the electron withdrawing effect of the substituents R1 and R2 in the following sequence: F>CH3O> CN>Cl>Br.

Hypodiphosphoric acid (H₄P₂O₆) – the structural analogue of diphosphoric acid (H₄P₂O₇) – contains two phosphorus atoms at the +4 oxidation state, which are connected by a direct covalent bond. After its synthesis was described in the 19th century, the mainstream of scientific research focused on the synthesis and physicochemical properties of its inorganic salts [1, 2].

In recent years, research has been intensified on organic-inorganic hybrids, including organic hypodiphosphates [3-5]. The lack of an oxygen bridge in hypodiphosphates contributes to their slightly higher stability (compared to diphosphates) and makes the ions/molecules more rigid. At the same time they still have six oxygen atoms capable of participating in the formation of networks stabilized by strong O–H···O hydrogen bonds, composed exclusively of hypodiphosphate anions and/or acid molecules. This is confirmed by the known hypodiphosphate crystals characterized by the presence of such substructures, with different architectures and dimensions.

In the present poster, the effect of methyl or amino substitution of thiazole ring on the hydrogen bond patterns observed in eight thiazolium hypodiphosphate crystals will be analyzed. It was found that the presence of one-, two- or three-dimensional anionic substructures was related to the degree of anion ionization and the size of the cation used. Monoanions form 3D hypodiphosphate networks, while ionic cocrystals containing dianions and hypodiphosphoric acid molecules (depending on the cation type) – 1D or 2D substructures. The presence of water molecules in the crystal results in the formation of higher dimensional inorganic substructures.

[1] Salzer, T. (1987). Liebigs Ann. 187, 322.

[2] Kinzhybalo, V., Otręba, M., Ślepokura, K. & Lis, T. (2021). Wiad. Chem. 75, 423.

[3] Otręba, M., Budzikur, D., Górecki, Ł. & Ślepokura. K. (2018). Acta Cryst. C74, 571.

[4] Emami, M., Ślepokura, K. A., Trzebiatowska, M., Noshiranzadeh, N. & Kinzhybalo, V. (2018). CrystEngComm.. 20, 5207.

[5] Budzikur, D., Szklarz, P., Kinzhybalo, V. & Ślepokura. K. (2020). Acta Cryst. B76, 939.

The physicochemical properties of solvated crystals are greatly influenced by the interactions between the solvent and solute. Therefore, various properties of solvated crystals, such as stability, spectral properties, and solubility, are variable depending on the type of solvent molecules included in the lattice. The design of solvated crystallization has attracted great attention as a means of modifying the properties of organic solids, especially in the fields of pharmaceuticals and organic optoelectronic materials. [1][2] Solvates formation of organic compounds is also important in the separation process in chemical industries. [3]

Bisphenol A derivatives are applied as a raw material of polymers for various applications. Solvates formation is applied in the process of industrial production of several bisphenol A derivatives. The bisphenol A derivative 1 shown in Fig. 1 (a) was found to form solvates with branched alcohols, but it was difficult to form solvates with linear alcohols. To clarify the observed difference in its solvation behavior, X-ray structure analysis was performed on its solvates with isopropanol (IPA), 2-butanol (2-BuOH), iso-butanol (i-BuOH), and water.

The result showed that the four solvated crystals involve 1 and a solvent molecule in a 1:1 ratio. The four solvated crystals were also found to be isomorphous. One solvent molecule in the crystals is linked to two neighboring molecules of 1 by intermolecular hydrogen bonds along the a-axis and included in the void surrounded by the bisphenol moieties. There found no significant structural difference in the arrangement of 1 itself in the four solvates, whereas the space around the solvent molecules was dependent on the size of a solvent molecule. To compare the differences between the space for solvent molecules, the three interatomic distances X, Y, and Z shown in Fig. 1 (b) were examined. The structure of the solvated crystals was found to be expanded along the Y direction due to the solvent molecules, whereas there was no remarkable difference in the other two directions as listed in Table 1. This structural feature could be correlated with the crystallization behavior of these solvates and their stability.

The understanding and control of intermolecular forces allows for the creation of supramolecular architectures held together by relatively weak, flexible interactions. The exploitation of π-π stacking interactions can produce materials with dynamic properties such as crystal to crystal transitions.[1] Co-facial π-interactions are also important in the preparation of semiconducting organic materials,[2] however, face-to-face π-stacking is generally repulsive and often disfavoured.[3]

In our development of an S_NAr-based methodology for the synthesis of heteropentacene analogues 1a-c we synthesised a series of electronically biased 1,2,3,4-tetrasubstituted dibenzodioxin (2a-c) and phenoxazine (3a-c­) derivatives.[4] An examination of the crystal structures of 2a-c and 3a-c indicates that a combination of electronic bias and C−H substitution affords compounds which tend to π-stack in a co-facial, antiparallel manner. A search of the Cambridge Structural database for representative structures was also conducted. The results indicate such motifs could be valuable building blocks for supramolecular design of materials held together by co-facial π-π stacking interactions.

References

1. Reger, D. L.; Horger, J. J.; Smith, M. D.; Long, G. J.; Grandjean, F. Inorg. Chem. 2011, 50 (2), 686–704.
2. Anthony, J. E. Angew. Chem. Int. Ed. 2008, 47 (3), 452–483.
3. Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 112 (14), 5525–5534.
4. Hiscock, L. K.; Raycraft, B. M.; Wałęsa-Chorab, M.; Cambe, C.; Malinge, A.; Skene, W. G.; Taing, H.; Eichhorn, S. H.; Dawe, L. N.; Maly, K. E. Chem. Eur. J. 2019, 25 (4), 1018–1028.

Targeting the polyamine biosynthetic pathway by inhibiting ornithine decarboxylase (ODC) is a powerful approach in the fight against both viruses and cancers.

D,L-alpha-ifluoromethylornithine (also called DFMO, eflornithine, ornidyl) is the best-known inhibitor of ODC and a broad-spectrum, unique therapeutical agent. It is promising pan-drug against diverse cancers, such as leukemia, skin cancer, breast cancer, prostate cancer and pancreatic cancer, cervical, small-cell lung cancer and melanoma, gastric cancer, colorectal cancer, neuroblastoma, glial tumors, such as malignant gliomas, as well as antiviral pan-drug, against RNA and DNA viruses, inter alia against dengue virus, zika, chikungunya virus, hepatitis B virus, human cytomegalovirus, herpes simplex virus, coxsackievirus B3, ebola, hepatitis C virus, sindbis virus, Japanese encephalitis virus, yellow fever virus, enterovirus 71, polio, rift valley fever virus, vesicular stomatitis virus, rabies virus, la crosse virus, semliki forst virus, as well as Middle East respiratory syndrome coronavirus (MERS-CoV) and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Here, we present the first supramolecular study focusing on the structure of DFMO. We discuss qualitative and quantitative survey of non-covalent interactions via Hirshfeld surface, molecular electrostatic potential, enrichment ratio and energy frameworks analysis visualizing 3-D topology of interactions in order to understand the differences in the cooperativity of interactions involved in the formation of supramolecular synthons at the subsequent levels of well-organized supramolecular self-assembly, in comparison with the ornithine structure.

In the light of the drug discovery, supramolecular studies of amino acids, essential constituents of proteins, are of prime importance. In brief, the same amino-carboxy synthons are observed in the bio-system containing DFMO.

References

Bojarska J, New R, Borowiecki P, Remko M, Breza M, Madura ID, Fruzi ´nski A, Pietrzak A and Wolf WM (2021) The First Insight Into the Supramolecular System of D,L[1]α-Difluoromethylornithine: A New Antiviral Perspective. Front. Chem. 9:679776. doi: 10.3389/fchem.2021.679776

In the last decade, Hybrid Photon Counting (HPC) X-ray detectors [1] like the PILATUS have transformed synchrotron research. They provide noise-free detection and enable new data acquisition modes. The most current HPC detector family EIGER2 enables even more ambitious X-ray science. These detectors combine all advantages of previous generations while offering new acquisition features and improved performance: maximum count rates of 10⁷ photons/sec per pixel, small pixels of 75 µm × 75 µm, two energy-discriminating thresholds, and frame rates up to 2 kHz with zero dead time (<100 ns) between exposures.

EIGER2 detectors were designed and optimized for the demands of synchrotron applications, and they are available for the laboratory as well. Equipped with CdTe sensors they provide high quantum efficiency at energies up to 100 keV, making them ideal for hard x-ray diffraction applications. Two energy thresholds allow for reduction of high-energy background such as from cosmic radiation, higher harmonics, or unwanted sample fluorescence. These benefits advance established X-ray diffraction methods in general like crystallography including powder diffraction as well as scattering techniques. Fast and gated measurements become possible and empower new fields of research, by enabling e.g., time-resolved or pump-probe techniques such as in laser-heating or fast compression and decompression experiments [2].

We will demonstrate the advantages of the HPC CdTe technology for high-pressure X-ray research. We show results from characterization and application measurements carried out in the laboratory and at synchrotron beamlines (ESRF, DLS, BSRF, APS) using loan detectors and the recently installed EIGER2 CdTe systems.

[1] Förster, A. et al. (2019), Philos Trans R Soc Math Phys Eng Sci, 377, 20180241

[2] Shen, G et al. (2017), Rep. Prog. Phys. 80, 016101

Insufficient coverage of reciprocal space may impede space group determination [1, 2], render revealing a crystal structure impossible [3] and conceal or wrongly reveal fine details such as disorder or unusual charge density distribution. [4] Standardised quality checks demand the diffraction pattern to be complete up to a certain resolution, usually 0.6Å^-1, for a good reason. [5]

While in majority of X-ray diffraction experiments modern area detectors and multi-axis goniometers allow to quickly scan the reciprocal space, the signal will not be observed if the beam does not have access to sample altogether. [6] This can be caused by a presence of Diamond Anvil Cell (DAC) or any other device which absorbs the beam around the sample. Deficiencies of such kind can be usually fixed by the means of symmetry. [7] The problem stands firm in case of compounds growing in low-symmetry crystal systems. A necessity to collect at least half or quarter of the whole pattern discourages investigators from conducting diffraction experiments, as suggested by the Cambridge Structural Database (CSD) [8] statistics.

Here we would like to present a comprehensive set of statistics describing a completeness of data in high-pressure experiments. Presented values have been calculated using a series of numerical simulations performed in a custom software. An influence of internal symmetry, crystal orientation and diamond anvil cell geometry on a final data completeness is meticulously analysed. Examples of experimental strategies leading to e.g. complete dataset for monoclinic sample and incomplete dataset for cubic sample are presented. Experimental strategies aiming to increase obtained completeness in various conditions are suggested. While similar estimations have been already suggested, [9] to the best of out knowledge our work is the first comprehensive study of this kind.

[1] Arnold, H., Aroyo, M. I., Bertaut, E. F., Billiet, Y., Buerger, M. J., Burzlaff, H., Donnay, J. D. H., Fischer, W., Fokkema, D. S. et al. (2005). International Tables for Crystallography, Volume A, 5th Edition (reprint), Space-group symmetry, edited by T. Hahn. pp 44–54. Springer.

[2] Sheldrick, G. M. (2015) Acta Cryst A 71, 3.

[3] Yogavel, M., Gill, J., Mishra, P. C. & Sharma, A. (2007) Acta Cryst D 63, 931.

[4] Takata, M. & Sakata, M. (1996) Acta Cryst A 52, 287.

[5] Spek, A. L. (2020) Acta Crystallogr. Sect. E 76, 1.

[6] Merrill, L. & Bassett, W. A. (1974) Review of Scientific Instruments 45, 290.

[7] Binns, J., Kamenev, K. V., McIntyre, G. J., Moggach, S. A. & Parsons, S. (2016) IUCrJ 3, 168.

[8] Bruno, I. J., Cole, J. C., Edgington, P. R., Kessler, M., Macrae, C. F., McCabe, P., Pearson, J. & Taylor, R. (2002) Acta Cryst B 58, 389.

[9] Casati, N., Genoni, A., Meyer, B., Krawczuk, A. & Macchi, P. (2017) Acta Cryst B 73, 584.

Pressure dependence of crystal and molecular structure and NLO response of L-Arg homologue salts

Rejnhardt P. ¹, Zaręba J.K. ², Katrusiak A. ³, Daszkiewicz M. ^1
1Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Division of Structure Research, Wrocław, Poland
²Wrocław University of Science and Technology, Faculty of Chemistry, Wrocław, Poland
³Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, Poznań, 61-614, Poland

Second harmonic generation (SHG) in organic crystals is a subject of extensive investigation for years. The absence of an inversion centre in such crystalline materials is mandatory in order to observe second-order non-linear response, although many other features play an important role and must be taken into account for synthesis of non-linear materials. For example, an occurrence of delocalized π electrons and intramolecular donor-acceptor charge transfer between two molecular subparts (functional groups) is necessary and it leads to large hyper-polarizability β. So, this kind of materials are good candidates for second harmonic generation studies.

In light of the above, the burning question is – in which direction one should look for materials with great SHG response? In the author’s concept, conformation of molecules in crystals is a key factor to obtain high SHG signal. Generally, the most important parts of molecule in the SHG context are donor – acceptor groups. With this reason, L-arginine analogues were chosen in these studies. They have shorter carbon chain in comparison to the L-arginine. We observed that relative distance between functional groups have a key role for enhancement of the SHG signal. What is more, inorganic anions in salts have a great influence on conformation of carboxyl and guanidinium groups. Some of them make single hydrogen bond with cation, what leads to appear more degrees of freedom for donor-acceptor groups. It is possible, that more degrees of freedom for aforementioned groups causes more suitable alignment of intramolecular charge transfer vectors in the crystal, which gives higher non-linear response.

The goal of the study is to verify experimentally, how the high pressure can modulate SHG response in one phase to avoid SHG changes connected to phase transitions and juxtapose them to the results for L-arginine homologues. So, correlation of molecular conformation and crystal structure with SHG is shown. This knowledge give us opportunity to describe theoretically which conformation can give the highest SHG response for particular materials.

We present crystal and molecular structures of 7 new salts (2Cl^–, 2Br^–, 2I^–, 2NO₃^–, Cl^–, I^–, 4NO₃^–) of (S)-2-amino-3-guanidinopropanoic acid, which is an analogue of L-arginine. Crystal structures were determined by X-ray diffraction at room and low-temperature conditions (100 K). Since earlier studies have shown that external pressure can tune SHG signal, diamond anvil cell was used to investigate the pressure dependence of SHG response.

The result of SHG measurements revealed that monochloride salt of (S)-2-amino-3-guanidinopropanoic acid has better optical non-linear properties than L-arginine chloride, 3·I_KDPvs. 0.3·I_KDP. This fact can be associated with shorter carbon chain (S)-2-amino-3-guanidinopropanoic acid and thus closer intramolecular distance between p-electron rich carboxyl and guanidinium groups than in L-arginine. What is more, the SHG response is more than 2 times better in 2.8 GPa pressure than in standard pressure.

Ice VII is one of the crystalline ices that stably exist above 2 GPa at room temperature. Oxygens form a bcc-type lattice and each oxygen is bound to neighbouring oxygens via hydrogen bonds. Hydrogens are disordered among the four sites on the oxygen-centred tetrahedra with equivalent probability resulting in their occupancy of 0.5 shown in Fig. 1. This simple cubic structure model is widely adopted but the true structure of ice VII is yet to be known. Strictly speaking, the oxygen sublattice is not bcc, and two models with oxygen displacements along <100> [1] and along <111> [2] are postulated. We reinvestigated the site disorder of oxygens (and hydrogens) in ice VII by neutron diffraction using modern high-pressure apparatuses.

Single-crystal and powder neutron diffraction patterns were collected at the D9 at the ILL in France and at the BL11 (PLANET) at the MLF J-PARC in Japan, respectively. Both measurements were conducted at approximately 298 K and 2 GPa. The single-crystalline specimen were directly crystallised from an alcohol-water mixture (D₂O:MeOD:EtOD = 5:4:1 in vol. ratio) in a newly-developed diamond anvil cell [3]. Powder specimen were prepared from pure D₂O in situ using the MITO system [4]. Fine powder crystals were obtained through solid-solid phase transitions (ice I_h+III→II→VI→VIII→VII).

Single crystals of ice VII were obtained by cyclic heating and cooling at a pressure above 2 GPa. The collected diffraction patterns were analysed by the maximum entropy method. The obtained scattering length density map exhibited anisotropic distribution from the average site. A derived pair-distribution function resembles that calculated from the average structure model in the long-r region while it does not match in the short-r region. This inconsistency is considered to be caused by the correlation between local structures.

[1] Kuhs, W. F., Finney, J. L., Vettier, C. & Bliss, D. V. (1984). J. Chem. Phys. 81, 3612–3623.

[2] Nelmes, R. J., Loveday, J. S., Marshall, W. G., Hamel, G. & Besson, J. M. (1998). Phys. Rev. Lett. 81, 2719–2722.

[3] Yamashita, K., Komatsu, K., Klotz, S., Fernández-Díaz, M. T., Fabelo, O., Irifune, T., Sugiyama, K., Kawamata, T. & Kagi, H. (2020). High Press. Res. 40, 88–95.

[4] Komatsu, K., Moriyama, M., Koizumi, T., Nakayama, K., Kagi, H., Abe, J. & Harjo, S. (2013). High Press. Res. 33, 208–213.

Improvement to macroscopic features such as better conductivity, weather resistance, and improved capacity and speeds for digital storage is in high demand for the ever-growing electronic-device market. A key point in this development is to relate these features with the atomic and electronic structure of the material in interest, regardless of knowledge area (e.g. chemistry, physics, engineering). With this in mind, we intend to develop an infrastructure that supports both control and analysis of such structural properties based on uniaxial pressure and advanced synchrotron-based techniques. For this, a compact cell [1] allows a consistent uniaxial strain to sub-millimeter-sized samples over a temperature range between 0.3 and 325 K. Its clever design guarantees easy access to the sample, which also allows electrical contacts into it and provides a great solid angle for XRD experiments. In addition to it, the cell also supports magnetic fields up to 30 T. On the other hand, a code based on the xrayutilities [2] python package allows an efficient description of the material in interest via its composition, crystalline structure and, most essentially in our case, its elastic properties. Therefore, it plays an essential role in tracking or predicting the sample's structural changes depending on its orientation and the uniaxial strain direction, as is shown in Fig. 1, where a uniaxial stress sweep was applied to sapphire (Al₂O₃) to obtain its lattice parameters at each state.

Here, we exhibit the status of this uniaxial strain infrastructure present at the EMA beamline of Sirius [3], which can be used with other extreme thermodynamic conditions such as high magnetic field (up to 11T) and low temperatures (down to 0.5K). Particularly for XRD experiments, the uniaxial strain cell conveniently sits on top of a 6-circle (4S+2D) diffractometer (Fig. 2) that supports conventional single-crystal experiments and high-resolution Reciprocal Space Mapping (RSM), which are great tools to probe strain and crystal symmetry breaking. This approach will open a plethora of opportunities for fine-tuning of properties of advanced materials, such as the Heusler material Mn₃Ge, also shown here. Given its various crystalline structures with different magnetic ordering (cubic → ferrimagnetic, tetragonal → ferromagnetic with momenta along the c axis, hexagonal → non-collinear antiferromagnetic with Anomalous Hall Effect), it is a particularly interesting material, and it being theoretically possible to change between each structure using pressure in specific directions [4] offer a great potential of exploration.

The possibility to induce transformations in solid materials by grinding is known since ancient times [1]. While in those times only simple tools like mortar and pestle were available, laboratories nowadays use automatized milling instruments. Well-known examples for these tools are ball mills, for which shaker and planetary ball mills are the most widely used types [1, 2]. Since 2013, in situ X-ray powder diffraction (in situ XRPD) is applied to study processes taking place in shaker mills [3]. By using high-energy synchrotron radiation, it is possible to monitor transitions of crystalline compounds and the appearance of intermediate crystalline phases during grinding in real-time [3, 4]. Special adaptations of the grinding setup are necessary to fulfill the criteria for the successful performance of such in situ studies [3, 4]. Two aspects are especially important. On the one hand, the material composition and the wall thicknesses of the applied vessels determine the remaining intensity of the diffracted X-rays [5]. On the other hand, the used mill must provide a free pathway for the X-rays, which is not the case for conventional shaker mills [4]. The established way to ensure the fulfillment of both conditions is the use of vessels made from polymethyl methacrylate (PMMA) together with a modified shaker mill [4, 5]. This combination allowed for the successful in situ XRPD monitoring of the syntheses of soft materials by ball milling, like metal organic frameworks or organic co-crystals [3-5]. Recently, the utilization of an alternative vessel design was published for the successful in situ XRPD study of the mechanochemical synthesis of zinc sulfide from its elements [6]. In this case, the vessel was made of a material mix of stainless steel and PMMA. Despite these successful applications, the in situ monitoring of hard materials, which have a high demand towards the mechanical properties of the grinding tools, remain especially challenging. In this work, we present the first in situ XRPD data of the mechanochemically induced transformation of boehmite (γ-AlOOH) to corundum (α-Al₂O₃). So far, the transformation could only be shown by ex situ XRD data [7]. As one of the hardest materials, corundum is especially suited to explore the limits of a grinding system. We will discuss the specific demands, which arise for in situ XRPD of hard materials during ball milling and their technical solutions.

[1] Balaz, P., Achimovicova, M., Balaz, M., Billik, P., Cherkezova-Zheleva, Z., Criado, J. M., Delogu, F., Dutkova, E., Gaffet, E., Gotor, F. J., Kumar, R., Mitov, I., Rojac, T., Senna, M., Streletskii, A. & Wieczorek-Ciurowa, K. (2013). Chem. Soc. Rev. 42, 7571–7637.

[2] Friscic, T., Mottillo, C. & Titi, H. M. (2020). Angew. Chem., Int. Edit. 59, 1018-1029.

[3] Friscic, T., Halasz, I., Beldon, P. J., Belenguer, A. M., Adams, F., Kimber, S. A. J., Honkimaki, V. & Dinnebier, R. E. (2013). Nat. Chem., 5, 66-73.

[4] Halasz, I., Kimber, S. A. J., Beldon, P. J., Belenguer, A. M., Adams, F., Honkimaki, V., Nightingale, R. C., Dinnebier, R. E. & Friscic, T. (2013). Nat. Protoc., 8, 1718-1729.

[5] Halasz, I., Friscic, T., Kimber, S. A. J., Uzarevic, K., Puskaric, A., Mottillo, C., Julien, P., Strukil, V., Honkimaki, V. & Dinnebier, R. E. (2014). Faraday Discuss., 170, 203-221.

[6] Petersen, H., Reichle, S., Leiting, S., Losch, P., Kersten, W., Rathmann, T., Tseng, J., Etter, M., Schmidt, W. & Weidenthaler, C. (2021). Chem. Eur. J. 10.1002/chem.202101260

[7] Amrute, A. P., Lodziana, Z., Schreyer, H., Weidenthaler, C. & Schüth, F. (2019). Science, 366, 485-489.

Pressure has been used as an effective tool to tune the structure and property of materials. The near room temperature superconductive was achieved recently at extremely high pressure with great help from the crystal structure prediction via first principles calculation. But the superconducting mechanism in disordered systems has been less in focus. Superconductivity and Anderson localization represent two extreme behaviors of electrons in condensed matter system. Surprisingly, these two competitive behaviors can occur in the same quantum system, e.g., amorphous superconductor. Although disorder-driven quantum phase transition has attracted much attention, the structure origins remain unclear. Here, by applying high pressure to amorphous Sb₂Se₃, we discover an unambiguous correlation between superconductivity and density up to 65 GPa. Superconductivity first emerges in high density amorphous (HDA) phase above 23 GPa when the glass density reaches crystalline Sb₂Se₃, and then becomes more prominent in the body-center-cubic (BCC) phase above 50 GPa. Upon decompression, superconductivity persists until a sharp density drop where BCC phase transforms back to low density amorphous (LDA). Ab initio simulations reveal that the BCC-like local geometry motifs form in HDA by increasing fractions of short atomic rings, which could simultaneously transform the covalent bonds into “metavalent bonds”, a recent classification of chemical bonding coined in chalcogenide materials. Our results demonstrate that the intermediate amorphous state is responsible for the incipient superconductor prior to normal superconductive behavior.

The past few decades have witnessed mechanochemistry emerging at the forefront of solid-state chemical synthesis, driven by the search of new and cleaner synthetic methodologies. Mechanochemical synthesis utilizes high energy impact phenomenon to initiate chemical reactions. The peak impact pressures, which the individual sample particles experience, vary depending on the type of mill, milling speed, as well as size, shape, and density of the milling components, but can often exceed 10 GPa, while the temperature remains below 100 ^oC. Evolving beyond simply a solvent-free alternative, mechanochemistry offers significant sample quantities (grams) processed over a short period of time (minutes to hours). The design of the mill (e.g. tumbler, oscillatory, planetary) can also control the relative contributions of friction and impact during the milling process. In an effort to introduce mechanochemistry further into geoscience, the current presentation wishes to showcase the successful mechanochemical synthesis of compounds in the Mg-Co olivine solid solution series (e.g. Mg₂SiO₄, MgCoSiO₄, Co₂SiO₄) starting from simple oxide precursors such as MgO, CoO, and SiO₂ utilizing oscillating mill equipped with tungsten carbide (WC) jars/ balls as reaction vessels [1,2]. We further address on the contamination issue of the final synthesized product with debris shaved off from milling media (e.g. stainless steel, WC) and report on a successful development of method for converting WC to a water-soluble form [3]. Lastly, we report our investigations into pressure-induced phase transformation of anatase TiO₂ to rutile TiO₂, quartz-type α-GeO₂ to rutile GeO₂, and cubic Dy₂O₃ to monoclinic Dy₂O₃, processes that require pressure up to 7.7 GPa in a typical diamond anvil cell experiment [4]. Powder X-Ray Diffraction was employed as the main process characterization, with complete Rietveld refinements of the powder patterns of end products, where applicable.

This work was performed with the financial support provided by the Office of Naval Research, Department of Navy’s Historically Black Colleges and Universities/ Minority Institutions, the Materials for Thermal and Chemical Extreme program, grant number FOA N00014-19-S-F004.

[1] Nguyen, P. Q. H, Zhang, D., Rapp, R., Bradley, J. P., Dera, P. (2021). RSC Adv. 11, 20687.

[2] Nguyen, P. Q. H., McKenzie, W., Zhang, D., Xu, J.; Rapp, R., Bradley, J. P., Dera, P. submitted

[3] Nguyen, P. Q. H., McKenzie, W., Zhang, D., Xu, J., Dera, P. submitted

[4] Nguyen, P. Q. H., Dera, P. submitted

Alloys are important because of their superior physical properties and are extensively used in industries. Substitutional alloys are formed by randomly substituting one element by another. The formation of substitutional alloys made from metals are ruled by Hume Rothery rules. These rules say, that an alloy can be formed only if, the difference in atomic size of the solute and solvent is within 15%, the valency of solute and solvent is similar and the difference in electronegativity is small. Very few alloys have been synthesized from non-metallic elements. Well known examples, are the pnictogen chalcogenides (Bi₂Te₃, Sb₂Te₃, Sb₂Se₃, Bi₂Se₃) which form a disordered bcc substitutional alloy at high pressure[1-6].It is interesting to know that this is despite the fact that the atomic radii of Se is 26 % and 28 % smaller than Sb and Bi respectively. In order to understand if the presence of Pb will still lead to the formation of a substitutional alloy we have investigated the high pressure behaviour of this layered topological insulator, PbBi₄Te₇[6] consists of a seven-layer block Te-Bi-Te-Pb-Te-Bi-Te ,where the layers are linked by weak van der Waals forces.

Our x-ray diffraction studies show that PbBi₄Te₇ undergoes a phase transition at 6.15 GPa. However, beyond 10 GPa it transforms to a cubic bcc substitutional alloy despite the presence of Pb. Our ab-initio density functional theory based calculations show that at high pressure, there is a charge transfer from Bi and Pb atom to Te atom which makes the radii of these atoms approximately equal thus favouring the formation of a substitutional alloy. The covalent bonds become weaker with pressure as the ionicity increases. It was also observed that insertion of Pb enhances the charge transfer and thus lowers the pressure at which the substitutional alloy is formed in comparison to the parent compound Bi₂Te₃.

[1] I. Efthimiopoulos, C. Buchan, Y. Wang, Scientific Reports 6, 24246 (2016).

[2] A. Bera, et al. Phys. Rev. Lett. 110, 107401 (2013).

[3] A. Polian et al, Phys. Rev. B 83, 113106 (2011).

[4] S. M. Souza et al, arXiv preprint arXiv:1105.1097 (2011).

[5] D Pal et al, Materials Letters, 302, 130401, 2021

[6] Taichi Okuda et al., (2013). Phys. Rev. Lett. 111, 206803.

The current state-of-the-art synchrotron x-ray techniques combined with diamond anvil cell (DAC) and large volume press (LVP) techniques make phase transition studies one of most active, burgeoning fields in the high pressure community. The structural evolution of material under pressure is the long-term active research subject, which in fact strongly depends on the development of corresponding high pressure and synchrotron technologies. The selected research cases for various types of material, such as metallic glasses, melt, and crystalline materials under high pressure conditions, will be presented in this paper. The topics will include pressure-induced polyamorphization in several typical metallic glass systems, pressure-induced potential liquid-liquid in gallium melt, evaluation on novel characteristic method of fractional dimensionality for non-crystalline cases, pressure-induced phase transition consequence trend in metal dioxides at multiple 100 GPa conditions, etc. The contributions from the first principle calculations and synergetic effort in synchrotron sources will be discussed based on these scientific cases.

The development of many advanced synchrotron X-ray techniques provided great opportunity for the researches under high pressure conditions. Besides the most popular synchrotron X-ray diffraction technique to study the crystalline samples, we could use the high energy X-ray scattering technique combined with the Pair Distribution Function (PDF) method, to study structural evolution of non-crystalline samples in DAC or LVP. In addition, the densities of non-crystalline samples in DAC or LVP could be directly measured by synchrotron X-ray tomographic techniques. With instrumental developments in the collection of sparse scattering signals and to an increased flux and coherence of X-ray beams, X-ray photon correlation spectroscopy (XPCS) has recently emerged as a very powerful technique able to follow the evolution of the dynamics at the atomic length scale in crystalline and amorphous materials. Different from the conventional diffraction and scattering methods, which offer the information of average structures over the diffraction volume in sample, the XPCS could uncover the local order from time domain when the coherent beam size is equal to the illuminated sample volume, and exposure time is shorter than the onset time for the speckle dynamics. So the temporal relaxation procedure on the origin of amorphous state to another amorphous state transition process upon compression could be monitored. XPCS experiments under high pressure conditions were performed at room temperature, and results on selected typical metallic glass systems, will be presented by comparing with temperature effect using same XPCS techniques.

Crystalline molecular materials are usually brittle and are prone to break upon external mechanical force. This fragility poses challenges for their application in next-generation technologies, including sensors, synthetic tissues, and advanced opto-electronics. The recent discovery of mechanical flexibility in single crystals of molecular materials has solved this problem and enable the design of smart flexible device technologies.[1] Mechanical flexibility of organic crystals can be tuned by altering the weak interactions in the crystal structure, for example through polymorphism. Here we report 4-bromo-6-[(6-chloropyridin-2-ylimino)methyl]phenol (BCMPMP) as a promising candidate for future waveguide technologies. It turns out that BCMPMP has two different polymorphs with distinct optical and mechanical properties. Form I shows brittle behavior under mechanical stress and exhibits very weak emission at 605 nm (λ_ex = 425 nm) together with a low photoluminescence quantum yield (Φ = 0.4 %). In contrast, Form II has a large plastic (irreversible bending) regime and a bright emission at 585 nm (λ_ex = 425 nm; Φ = 8.7 %). Making use of favorable mechanical flexibility and optical properties, form II was explored as a bendable optical waveguide. Light was successfully propagated through a straight-shaped and mechanically deformed BCMPMP crystal. Depending on the light source, active or passive waveguiding could be achieved. So BCMPMP can also be used as a flexible wavelength filter.

[1] Annadhasan, M., Agrawal, A. R., Bhunia, S., Pradeep, V. V., Zade, S. S., Reddy, C. M. & R. Chandrasekar (2020), Angew Chem Int Ed, 59, 13852-13858.

Mechanical flexibility in single crystals of covalently bound materials is a fascinating and poorly understood phenomenon.[1-2] We present here the first example of a plastically flexible one-dimensional (1D) coordination polymer (CP). The compound [Zn(µ-Cl)2(3,5-Cl2Py)2]n (1), is flexible over two crystallographic faces.[3] Through the combination of microscopy, diffraction, and spectroscopic studies we probe the structural response of the crystal lattice to mechanical bending. Our results suggest that mechanical bending occurs by displacement of the coordination polymer chains. Based on experimental and theoretical evidence, we propose a new model for mechanical flexibility in 1D coordination polymers.[4] To understand the role of weak interactions on mechanical flexibility of CP crystals, we explored a family of metal halide-based CPs isomorphous with 1, based on combination of two different metals (Zn and Cd) and two halogens (Cl and Br). We demonstrate how these simple modifications can tune the mechanical flexibilities across a significant range from plastic to delaminating, and ultimately to elastic. We rationalized these remarkable changes of mechanical properties by ab initio simulations.

[1] Saha, S., Mishra, M. K., Reddy, C. M. & Desiraju G. R. (2018). Acc. Chem. Res. 51, 2957–2967. [2] Đaković, M., Borovina, M., Pisačić, M., Aakeröy, C. B., Soldin, Ž., Kukovec, B. M. & Kodrin, I. (2018). Angew. Chem. Int. Ed. 57, 14801–14805. [3] Bhattacharya, B., Michalchuk, A. A. L., Silbernagl, D., Rautenberg, M., Schmid, T., Feiler, T., Reimann, K., Ghalgaoui, A., Sturm, H., Paulus, B. & Emmerling, F. (2020). Angew. Chem. Int. Ed. 59, 5557–5561.

[4] X. Liu, AAL Michalchuk, B Bhattacharya, F Emmerling, and CR Pulham (2021) Nat. Commun. 12, 3871.

Single crystals of optoelectronic materials that respond to external stimuli, such as mechanical, light or heat are immensely attractive for next generation smart materials.^[1,2] Here we report single crystals of a green fluorescent protein (GFP) chromophore analogue with irreversible mechanical bending and associated unusual enhancement of the fluorescence owing to the suppression of aggregation-induced quenching by aromatic stacked molecules in the perturbed structure.^[3] Such fluorescence intensity modulations, which were observed in high-pressure studies earlier,^[4] are now shown to occur as function of bending under ambient pressure, hence the study has potential implications for the design of technologically relevant tunable fluorescent materials.^[5]

Ductility, which is a common phenomenon in many metals, is difficult to achieve in molecular crystals. Organic crystals have been recently shown to bend plastically on one or two face specific directions, but they fracture when stressed in any other arbitrary directions.[1] Here, we present an exceptional metal-like ductility and malleability in the isomorphous crystals of two globular molecules, BH3NMe3 and BF3NMe3, with characteristic tensile stretching, compression, twisting and thinning (increase of width over 500%).[2] Surprisingly, the mechanically deformed samples, which transition to lower symmetry phases, not only retain good long range order, but also allow structure determination by single crystal X-ray diffraction. Molecules in these high symmetry crystals interact predominantly via electrostatic forces (B–-N+) and form columnar structures, thus forming multiple slip planes with weak dispersive forces among columns. While the former interactions hold molecules together, the latter facilitate exceptional ductility. On the other hand, the limited number of facile slip planes and strong dihydrogen bonding in BH3NHMe2 negates ductility. The structureproperty correlation established in these aminoboranes with exceptional ductility and ability to retain crystalline order may enable designing highly modular, easy-to-cast crystalline functional organics, for applications in solid-state electrolytes, adaptable
electronics[3] (soft ferro/piezo/pyro-electrics), barocalorimetry (solid coolants),[4] soft-robotics etc.[5]

Protein crystallization is a key step in enabling structural studies using crystallographic methods. Despite much research and experimental progress in this area, there is still no clear model to explain the mechanisms and physicochemical principles for all of the stages of crystallization. Studying the mechanisms of crystallization at the earliest possible stage of the procedure, including rapid characterization of the solution and protein solubility, would greatly enhance the prediction of potential crystal formation.

The process of the protein cluster formation was discussed and the attempts to observe it were made, but the structure of the formed clusters remained unknown. Recently, we have proposed the hypothesis that there is a pre-crystallization phase in solution composed of protein oligomers, where these oligomers are the elements of the resulting crystal structure. On the base of crystal structure of tetragonal lysozyme crystals octomer cluster was selected as a possible element of crystal growth [1]. These octamers were found in crystallization solutions by small-angle X-ray and neutron scattering methods (SAXS and SANS). The results show noticeable presence of lysozyme dimers and octamers under crystal growth conditions and total absense of oligomers under conditions when crystal growth is impossible. The influence of the precipitant cation type in a series of chlorides (NaCl, KCl, LiCl, NiCl2, CuCl₂, CoCl₂) on the structure of lysozyme solutions was also investigated [2]. The bonds between lysozyme molecules and precipitant ions in single crystals grown with chlorides of these metals are analysed on the basis of crystal structure data [3].

The relationship between various parameters of crystallization solutions and the possibility of protein oligomers formation under selected conditions could be useful for ordered films formation. The formation of the Langmuir films from crystallization solutions were studied by grazing-incidence X-ray standing waves [4]. Studying the formation of these monolayers by GIXSW showed that the thickness of the resulting protein layer was twice the diameter of an individual lysozyme molecule and matched the diameter of the octamer. Thin layers of precipitant ions (K and Cl) formed directly under the protein monolayer.

[1] Kovalchuk M. V., Blagov A.E., Dyakova Y.A., Gruzinov A.Y., Marchenkova M.A., Peters G.S., Pisarevsky Y. V., Timofeev V.I., Volkov V. V. (2016). Crystal Growth & Design 16 (4), 1792.
[2] Dyakova Y.A., Boikova A.S., Ilina K.B., Konarev P. V., Marchenkova M.A., Pisarevsky Y. V., Timofeev V.I., Kovalchuk M. V. (2019). Crystallography Reports 64 (1), 11.
[3] Marchenkova M.A., Kuranova I.P., Timofeev V.I., Boikova A.S., Dorovatovskii P. V., Dyakova Y.A., Ilina K.B., Pisarevskiy Y. V., Kovalchuk M. V. (2019). Journal of Biomolecular Structure and Dynamics in press, 1.
[4] Kovalchuk M. V., Boikova A.S., Dyakova Y.A., Ilina K.B., Konarev P. V., Marchenkova M.A., Pisarevskiy Y. V., Prosekov P.A., Rogachev A. V., Seregin A.Y. (2019). Thin Solid Films 677 (February), 13.

This study was supported in part by the Ministry of Science and Higher Education within the State assignment FSRC «Crystallography and Photonics» RAS and by the Russian Foundation for Basic Research (project number 18-32-20070 mol_a_ved).

The formation of structured oligomers in protein solutions during crystallization by SAXS and SANS methods are shown. The experimental SAXS and SANS data are processed using models of oligomers extracted from the crystal structure. Octamers and dimers are formed in a crystallization solution during growth of tetragonal lysozyme crystals with the addition of precipitant NaCl [1]. The volume fraction of octamers increases with the protein concentration increase and the temperature decrease. Addition of (NH₄)₂SO₄ or NaNO₃ as precipitants is shown to induce the formation of a significant fraction of protein dimers in proteinase K solution during the growth of tetragonal crystals [2]. Hexamers are formed in crystallization solution during hexagonal crystal growth of thermolysin [3]. The hexameric volume fraction increases when the supersaturation conditions are met, i.e. when the temperature decreases and the precipitant ((NH₄)₂SO₄) concentration increases. The formation of transaminase dodecamers is shown in crystallization solution with addition of precipitant NaCl [4]. Protein crystal and its oligomers are presented in the figure 1-a. Oligomers may act as building blocks in the growth of proteins single crystals. Also, the influence of solvent type (Н₂О and D₂O) on structure crystallization solution was investigated [5]. The dimer and octamer formation in crystallization solution in Н₂О and D₂O is shown.

The volume fraction of octamers increases with a decrease in temperature in both type of solvent (figure 1-b). Concentration of octamer is higher in crystallization solution in D₂O then in H₂O.

[1] Boikova, A.S., Dyakova, Y.A., Ilina, K.B. et all. (2017) Acta Crystallographica Section D: Structural Biology, 73 (7), 591
[2] Boikova, A.S., D’yakova, Y.A., Il’ina, K.B. et all.Crystallography Reports, 63 (6), 865
[3] Kovalchuk, M.V., Boikova, A.S., Dyakova, Yu.A. et all. (2019) Journal of Biomolecular Structure and Dynamics, 37 (12), 3058
[4] Marchenkova, M.A., Konarev, P.V., Rakitina, T.V. et all. (2019) Journal of Biomolecular Structure and Dynamics, in press
[5] Boikova, A.S., D’yakova, Y.A., Il’ina, K.B. et all. (2017) Crystallography Reports, 62 (6), 837

This study was supported in part by the Ministry of Science and Higher Education within the State assignment FSRC «Crystallography and Photonics» RAS and by the Russian Foundation for Basic Research (project number 18-32-20070 mol_a_ved).

Using the molecular dynamics simulation method, the stability of lysozyme octamer and two types of dimer (A and B) formed in solution under conditions of crystallization of tetragonal syngony was studied. In order to investigate the influence of NaCl precipitant ions bound to the protein in the crystal, various combinations of sodium and chloride ions associated with lysozyme molecule were probed: 1) with Na and Cl ions, 2) only with Na ions, and 3) without any ions. Using the GROMACS program, 100-ns molecular dynamics trajectories of the oligomers in the presence and absence of precipitant in water were calculated at different temperatures from 278 to 318 K.

To evaluate the stability of oligomers, RMSF (Root Mean Square Fluctuations) graphs were plotted at every simulated temperature.

As a result, flexibilities of octamer and dimer A have regularly increased with the temperature growth only in the case of considering precipitant ions embedded in the crystal structure. The RMSF values of dimer B are approximately the same at temperatures from 283 to 313 K and become higher at 318 K for all simulations whether they were performed with bound precipitant ions or not.

Thus, the importance of Na and Cl ions associated with the lysozyme is shown as only results of simulating oligomer models containing precipitant ions are consistent with the ones obtained by small-angle x-ray scattering experiments on crystallization lysozyme solutions [1-2].

[1] Kovalchuk, M. V., Blagov, A.E., Dyakova, Y.A., Gruzinov, A.Y., Marchenkova, M.A., Peters, G.S., Pisarevsky, Y. V., Timofeev, V.I., Volkov, V. V. (2016). Crystal Growth & Design 16 (4), 1792.
[2] Boikova, A. S., Dyakova, Y. A., Ilina, K. B., Konarev, P. V., Kryukova, A. E., Kuklin, A. I., Marchenkova, M. A., Nabatov, B. V., Blagov, A. E., Pisarevsky, Y. V. & Kovalchuk, M. V. (2017). Acta Cryst. D73, pp. 591-599

Poly(N-isopropylacrylamide) (PNIPAM) is a representative thermoresponsive polymer, and its aqueous solution becomes phase separated at a temperature higher than the cloud point (T_cp). To further promote the use of PNIPAM as a functional material, its phase behavior should be understood as a first benchmark. Previously, it was pointed out that the viscosity of a PNIPAM aqueous solution with a relatively higher concentration dramatically increased with temperature near to the T_cp. Although the origin of the peculiar viscosity increase just below the T_cp is a key to understanding the phase behavior, it remains unclear at the moment. Thus, it is necessary to examine the structure and physical properties of the PNIPAM solution a temperature just below the T_cp on various length scales. In this study, we report on the structure and physical properties examined by small-angle X-ray scattering (SAXS) measurement in conjunction with a particle tracking, in which the thermal motion of probe particles in the solution was tracked.

An aqueous solution with a concentration of 10 wt% was prepared from atactic PNIPAM with a number-average molecular weight of 193k and a polydispersity index of 2.2. The T_cp of the PNIPAM solution was determined by monitoring the light transmittance at a wavelength of 633 nm passing through the solution, as a function of temperature. A temperature (T_cp’), at which the transmittance started to decrease upon heating, was collected at different heating rates (n). By extrapolating the T_cp’ value to n = 0, the T_cp value was determined to be 304 K. SAXS experiments were performed at the BL03XU in SPring-8, Japan.

Fig. 1(a) shows photographic images of the time-variation in the physical state of the PNIPAM-water mixtures. When the PNIPAM-water mixture was aged for 3 h at 302 K, which was just below the T_cp, it turned into a transparent gel without any loss of transparency. Such a gelation was not observed at 294 K. Fig. 1(b) shows SAXS profiles for the mixtures that were aged for 3 h at 302 and 294 K. The contribution of water to the scattering for the sample was subtracted. In general, a scattering from the polymer chains in semi-dilute solution, where the polymer concentration is above the overlap concentration, can be described by the Ornstein−Zernike (OZ) function. In fact, the experimental data obtained for the mixture aged at 294 K could be reproduced by the OZ function, as drawn by solid lines in the panel (b). The value of x, which corresponded to the average size of blobs consisting of polymer segments, was 2.6 nm. On the other hand, the data for 302 K could not be fitted by the OZ function. The scattering intensity in the range smaller than 0.6 nm⁻¹ was intensified. To express the data in the small q region, the scattering function based on the Guinier model, which was used for an aqueous solution of isotactic PNIPAM, was included as an additional term [1]. The x, and R_g values obtained by the curve fitting were 5.9 and 7.5 nm, respectively. According to the previous result, the R_g value should correspond to the size of the clusters formed by intermolecular association of segments, as shown in Fig. 1(c). In the presentation, the results of the particle tracking will be also given to discuss a possible mechanism for the gelation [2].

The phase separation relationship between polymer and fullerene have been treated as a major influence that impact the operation of bulk heterojunction solar cells. In this research, we investigate the intercalation behavior between PBTTT-C14(PBTTT (Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene])) and PCBM ([6,6]-Phenyl C71 butyric acid methyl ester, PC71BM) to unveil the phase separation relationship in this system.

Temperature dominates the competition between the intercalation of PCBM into PBTTT-C14 order phase and self-crystallization of PCBM. At lower temperature, PCBM tends to intercalate into the cavity among PBTTT-C14 side chain. However, at higher temperature PCBM tends to crystallization.

In the other hand, PCBM are not able to intercalate into PBTTT-C14 domain once the side chain regularity is reduced by partially soluble solvent on PBTTT-C14. No self-assembling relationship are found between PBTTT-C14 and PCBM either at high or low temperature.

In the Cu-Sb-O ternary system, CuSb₂O₆ is the most intensively studied compound, owing to its unusual structural and magnetic behaviour. Jahn-Teller distortions from the Cu²⁺ cause an axial elongation of the Cu-O octahedra to give rise to a monoclinic structure (s.g. P2₁/n)[1,2]. At high temperatures, this material undergoes a second order phase transition to the tetragonal phase (s.g. P4₂/mnm), isostructural to room temperature structures of CoSb₂O6 and NiSb₂O₆[3]. This modification may only be possible through an intermediate orthorhombic modification in Pnmm as defined through systematic symmetry reduction [4]. Through the doping of CuSb₂O₆ with Co and Ni, this structural transition can be investigated.

Neutron, lab X-ray and synchrotron single crystal and powder diffraction have been used to study phase transitions in both solid state solutions. In the Cu_1-xCo_xSb₂O₆ system, it was found that two phases exist between compositions x = 0.2 and 0.5, with a Cu-rich monoclinic phase and a Co-rich tetragonal phase⁴. By contrast, the Cu_1-xNi_xSb₂O₆ system exhibits a single-phase region from x = 0.4, where only the tetragonal phase remains. A phase transition can be observed in the solid solution where the monoclinic phase becomes tetragonal at high temperature. The orthorhombic intermediate can only be observed through Synchrotron powder diffraction.

X-ray absorption spectroscopy indicates that there has been partial reduction of Cu²⁺ to Cu¹⁺ in the higher doping concentrations of Cu_1-xNi_xSb₂O₆ with neutron diffraction on these materials confirming a net oxygen deficiency in the materials. Compounds with similar structures have also been investigated, including NiSb_2-xSn_xO₆ and ZnSb_2-xSn_xO₆, which also show a net oxygen deficiency in the structure. At higher temperatures, these materials also indicate a mixed occupation of Ni and Sb on the 2a and 4f sites, that suggest the material is undergoing a high temperature phase transition to the rutile phase.

Over the past 25 years, the field of negative thermal expansion (NTE) materials has grown from a scientific curiosity observed in a small number of oxide families to a vibrant field encompassing numerous different compositions, structures and mechanisms. Successful prediction and synthesis of new compositions that may show NTE by substituting atoms in known structure types has significantly expanded the number of materials that display this property. However, control of expansion and phase transition behavior as a function of temperature and pressure remains a challenge in many families of NTE materials.

This talk will focus on materials in the scandium tungstate (A₂M₃O₁₂) family, in which the M-site generally contains Mo or W, while the A-site can be substituted by trivalent cations ranging in size from Al³⁺ to the smaller lanthanides. Compositions in which the A and/or M-site are substituted by aliovalent cations have also been reported, which may adopt cation ordered structures. In this family, NTE is observed in an orthorhombic structure, but many compounds show a reversible phase transition to a structurally related denser monoclinic polymorph with positive expansion upon cooling or when pressure is applied. We recently found that strategic choice of A-site cations can be used to suppress undesired phase transitions to lower temperatures and higher pressures.

The CeT₂X₂ (T: transition element, X: p-element) intermetallics are intensively studied for their magnetic properties and exotic ground states. Determination of crystal structure is usually the basic characterisation for further research, but this is not the case in CePt₂Al₂ and selected homolog compounds, which are structurally unstable at low temperatures. This structural instability influences then the magnetic and electronic properties and plays the key role.

CePt₂Al₂ is a new member of this family, therefore we focused on structural properties in broad temperature interval 3 – 500 K. At room temperature the single-crystal X-ray diffraction study shows that the crystal structure is orthorhombic and modulated (Cmme(a00)000, with q⃗= (0.481, 0, 0)). This is uncommon in this family of compounds, which are usually tetragonal at room temperature. The high temperature X-ray powder diffraction was used for structure determination above room temperature and reveals structural transition to a tetragonal structure, which could be presumably described by CaBe₂Ge₂ structural type. This transition exhibits 50 K hysteresis and creates a domain structure in the sample. During the transition both tetragonal and orthorhombic phases coexist and their ratio is dependent on cooling rate.

The structural phase transition study is complemented by measurement of physical properties such as a specific heat, magnetization, and transport measurements in the temperature range between 0.5 and 300 K. Specific heat and magnetic susceptibility show an antiferromagnetic order below 2 K. On the basis of electrical resistivity and other bulk measurements, CePt₂Al₂ can be considered as a Kondo lattice material, for which the reduction of free magnetic Ce³⁺ moment is typical. The presence of a modulated crystal structure opens the possibility of a charge density wave state in CePt₂Al₂ as observed in (Re)Pt₂Si₂.

In cuprate materials, copper-oxide based perovskites, high-temperature superconductivity microscopically intertwines [1] with the pseudogap phase [2,3], charge-density-wave (CDW) order [4-5], as well as electronic nematic phases [6]. The mechanisms underlying the emergence of superconductivity, the nature of the pseudogap phase and the symmetry properties of the density-wave states remain to be clarified.

In the La-Sr-Cu-O system the ubiquitous presence of twin domains [7] prevents to unambiguously establish the true nature of CDW order. Under these conditions, in fact, the diffraction signatures of a uniaxial stripe CDW order [4] are indistinguishable from those of biaxial structures in which the charge density is simultaneously modulated along two perpendicular directions.

Here we report on our high-energy (100 keV) X-ray diffraction experiments carried at the P21.1 beamline at PETRA III (DESY) showing that applying uniaxial pressure to La_1.88Sr_0.12CuO₄ (LSCO) it is possible to resolve the domain degeneracy and thereby uncover the underlying charge stripe structure. We find that the resulting charge stripe ordering vector is perpendicular to the uniaxial stress direction. We discuss the average symmetry transition from the high temperature tetragonal (HTT) to the low-temperature orthorhombic (LTO) showing signatures of a possible breaking of the lattice centering and its link to the symmetry of the CDW order. Using a first-of-its kind dataset of CDW peaks, collected with a 2D single-photon counting detector, we attempt to resolve the underlying structure modulation in terms of in-plane and out-of-plane ionic displacements and discuss our finding within the bounding limits imposed by the evidence of an extended stacking-type disorder along the c-axis.

[1] Fradkin E., Kivelson S. A., Tranquada J. M., (2015) Rev. Mod. Phys. 87, 457–482.[2] Norman M. R., Pines D., Kallin C., (2005) Advances in Physics 54, 715–733.

[3] Daou R., Chang J., LeBoeuf D., Cyr-Choinière O., Laliberté F., Doiron-Leyraud N., Ramshaw B. J., Liang R., Bonn D. A., Hardy W. N., Taillefer L., (2010) Nature 463, 519–522.

[4] Tranquada J. M., Sternlieb B. J., Axe J. D., Nakamura Y., Uchida S., (1995), Nature 375, 561–563.[5] Wu T., Mayaffre H., Krämer S., Horvatic M., Berthier C., Hardy W. N., Liang R., Bonn D. A., Julien M., (2011), Nature 477, 19.

[6] Murayama H., Sato Y., Kurihara R., Kasahara S., Mizukami Y., Kasahara Y., Uchiyama H., Yamamoto A., Moon E. G., Cai J., Freyermuth J., Greven M., Shibauchi T., Matsuda Y., (2019) Nature Communications 10, 3282.

[7] Braden M., Heger G., Schweiss P., Fisk Z., Gamayunov K., Tanaka I., Kojima H., (1992) Physica C 191, 455.

The charge-density wave (CDW) is a modulation of the density of conduction electrons in metals, which is coupled to displacements of the atoms according to a wave with the same wave length (same wave vector) as the modulation of the conduction band [1]. The classical CDW is the stable state of quasi-1-dimensional (1D) metallic crystals at low temperatures. The latter possess crystal structures with obvious 1D features, like chains of atoms supporting 1D electron bands, and these materials display a highly anisotropic electrical resistance, with the low resistance in the direction of the 1D atomic chains. The mechanism is Fermi-surface nesting (FSN), where a single wave vector q connects to each other different parts of the Fermi surface. A modulation of the atomic positions according to a wave with this wave vector q leads to a lowering of the electronic energy. The accompanying elastic strain then leads to an optimal magnitude of the atomic displacements, the latter which can be measured by x-ray diffraction (XRD).

More recently, CDWs have been found in metals whose crystal structures and physical properties lack obvious 1D features [2, 3]. Mechanisms have been put forward, that provide alternative explanations for the formation of CDWs. In particular this includes q-dependent electron-phonon coupling (EPC). The EPC peaks at a particular wave vector q. A static modulation with this wave vector then leads to a lowering of the energy of the system, which is not purely electronic, but should be attributed to the EPC terms.

Here, we present comprehensive studies towards CDWs in the materials La₃Co₄Sn₁₃, CuV₂S₄ and Er₂Ir₃Si₅ with strong electron correlations [4–6]. Temperature-dependent transport and thermodynamic properties are correlated with temperature dependent diffraction studies. First-order and second-order CDW phase transitions are identified. Crystal structures of the CDW phases are determined, while considering changes of the symmetry along with the development of twinned crystals at the phase transitions. Crystal structures are successfully used to identify the atomic mechanisms of CDW formation and to explain peculiar electronic and magnetic properties. La₃Co₄Sn₁₃: Pm-3n (No. 223) to I2₁3 (No. 199; 8-fold supercell); CuV₂S₄: Fd-3m (No. 227) to Imm2(s 0 0) (No. 44.1.12.4) and Er₂Ir₃Si₅: Ibam (No. 72) to I-1(s₁ s₂ s₃) (No. 2.1.1.1).

[1] Monceau, P. (2012). Electronic crystals: an experimental overview. Adv. Phys. 61, 325-581. Doi: 10.1080/00018732.2012.719674

[2] Chen, C.-W., Choe, J. & Morosan, E. (2016). Charge density waves in strongly correlated electron systems. Rep. Prog. Phys. 79, 084505.

[3] Ramakrishnan, S. & van Smaalen, S. (2017). Unusual ground states in R₅T₄X₁₀ (R = rare earth; T = Rh, Ir; and X = Si, Ge, Sn): a review. Rep. Prog. Phys. 80, 116501. Doi: 10.1088/1361-6633/aa7d5f.

[4] Ramakrishnan, S., Schönleber, A., Hübschle, C. B., Eisele, C., Schaller, A. M., Rekis, T., Bui, Ng. Hai An, Feulner, F., van Smaalen, S. Bag, B., Ramakrishnan, S., Tolkiehn, M. & Paulmann, C. (2019). Charge density wave and lock-in transitions of CuV₂S₄. Phys. Rev. B 99, 195140. Doi: 10.1103/PhysRevB.99.195140

[5] Welsch, J., Ramakrishnan, S., Eisele, C., van Well, N., Schönleber, A., van Smaalen, S., Matteppanavar, S., Thamizhavel, A., Tolkiehn, M., Paulmann, C. & Ramakrishnan, S. (2019). Second order structural and CDW transitions in single crystals of La₃Co₄Sn₁₃. Phys. Rev. Mater. 3, 125003. Doi: 10.1103/PhysRevMaterials.3.125003

[6] Ramakrishnan, S., Schönleber, A., Rekis, T., van Well, N., Noohinejad, L., van Smaalen, S., Tolkiehn, M., Paulmann, C., Bag, B., Thamizhavel, A., Pal, D. & Ramakrishnan, S. (2020). Unusual charge density wave transition and absence of magnetic ordering in Er₂Ir₃Si₅. Phys. Rev. B 101, 060101(R). Doi: 10.1103/PhysRevB.101.060101

Lead titanate (PbTiO₃) is a prototype ferroelectric material. At high temperatures, it presents the ideal centrosymmetric cubic perovskite structure with Pm-3m symmetry. Cooling down to 770K, a first-order phase transition from the paraelectric phase to the non-centrosymmetric tetragonal P4mm is observed[1]. Its high para-ferroelectric phase transition temperature would be promising for its technological application. However, the high anisotropy (6% c/a at room temperature) combined with its positive thermal expansion in cooling, makes it impossible to produce this ceramic in the form of bulk. Doping the Pb or Ti site of the perovskite are options to decrease the anisotropy only enough to makes possible bulk production[2]. In this work, we study the effect of isovalent substitution of Pb⁺² by Ca⁺² in paraelectric to ferroelectric phase transition by structural, dielectric and ferroelectric properties.

The bulk ceramics with stoichiometry Pb_0.6Ca_0.4TiO₃ were synthesized by solid-state reaction, uniaxially and hydrostatically pressured and sintered by the conventional method. The electric permittivity as a function of frequency and temperature was carried out in an impedance analyzer (Agilent - 4294A) from 20K up to 600K with the sample in Linkan furnace and APD cryostat. The ferroelectric polarization versus electric field loops were carried out using a Sawyer-Tower circuit and APD cryostat. To perform the Synchrotron X-ray diffraction (SXRD) patterns collection a piece of the bulk was crushed into thin powder and annealed at 600K for 5 hours to remove the residual strain. The patterns were collected at XPD and XRD1 beamlines at the Brazilian Synchrotron Laboratory. The high-temperature piece of experiment was performed in reflection geometry using Arara’s furnace, while the low-temperature piece of experiment was performed in transmission mode using Oxford Cryoject.

The structural analyses were performed by Rietveld Refinement method using GSASII and the model P4mm from the pristine PbTiO₃ compound. Heating up, the linear expansion of the a lattice parameter is observed while c contracts until 360K, then an abrupt change happens and c presents a linear expansion. This structural anomaly temperature is relatively close to the paraelectric-ferroelectric phase transition is observed at ~390K by ferroelectric and dielectric properties [3]. However, differently to the pristine PbTiO₃ compound, this phase transition happens from a tetragonal non-centrosymmetric to another tetragonal but centrosymmetric (therefore paraelectric) symmetry – which can be the same phase of CaTiO₃-high temperature (I4/mcm)[4].

Moreover, uniaxial anisotropy was observed in the ferroelectric phase, in the direction (001). This anisotropy became isometric at the paraelectric phase.

To conclude, from 40% of Ca-doping in PbTiO₃ ceramic, we characterized a tetragonal ferroelectric to a tetragonal paraelectric phase transition in which the crystallite anisotropy (or strain) was an important feature to characterize the polar transition. This was also the first report of tetragonal-paraelectric phase in Ca-modifield PbTiO₃ ceramics.

[1] B. Jaffe, W.R. Cook, H. Jaffe, Nom-metallic Solids: Piezoelectric Ceramics, 1971.

[2] J. Zhao, et al., A combinatory ferroelectric compound bridging simple ABO3 and A-site-ordered quadruple perovskite, Nat. Commun. 12 (2021) 1–9.

[3] F. Regina Estrada, M. Henrique Lente, D. Garcia, The normal to diffuse phase transition crossover from thermal expansion analysis in calcium modified lead titanate, Ferroelectrics. 534 (2018) 50–55.

[4] M. Yashima, R. Ali, Structural phase transition and octahedral tilting in the calcium titanate, Solid State Ionics. 180 (2009) 120–126.

Valence tautomers are characterized by different distributions of electron density, where metal-to-ligand electron transfer accomplishes interconversion between tautomers [1]. These compounds are unique model systems that can help to study electron transfer mechanisms and find applications as sensors and displays or storage and fast optical switching devices. Wherein, the valence tautomeric interconversion can be thermally, magnetically or radiatively driven. Among transition metal complexes cobalt complexes with redox-active ligands have been shown to undergo a valence tautomeric interconversion between high-spin and low-spin forms [2, 3].

This study is devoted to optical and x-ray structure characterization of novel (N-cyclohexyl-2-iminopyridine)(3,6-di-tert-butyl-o-benzosemiquinonato)(3,6-di-tert-butyl-catecholato) (Co2) cobalt complex. We have monitored the transition induced both by temperature and laser stimuli. Complexes were dissolved in toluene. X-ray pump-probe study was performed at the Super-XAS beamline of the Swiss Light Source, Villigen, PSI. Green nanosecond laser with 532 nm wavelength was operated at 150 kHz repetition mode. For each energy point we accumulated an X-ray fluorescence signal for different delays after laser excitation pulse with 20 ns time resolution. Then principal component analysis was applied for the whole data set.

Figure 1. (a) Co K-edge XANES measured for Co2 sample at 213K and 293K in a solution, (b) transient difference signal after laser excitation for Co2 and (c) temperature dependence of UV-Vis spectrum for the Co2 sample in toluene.

Fig. 1 shows XANES and optical results for one of the studied cobalt complexes. According to XANES, change in the oxidation and spin state of cobalt can be observed when temperature decreases below 240 K (Fig.1(a)). Time-resolved transient difference shown in figure 1b can be compared to the static difference obtained at low and high temperatures (Fig.1b). Kinetics of the transient signal decay for 213 K can be approximated by a monotonic exponential decay with characteristic time 490 ns. Low-temperature UV-Vis spectra show intensity decreasing of broad band at 800 nm and increase of bands at 600 nm and 395 nm (Fig.1(c)). The band at 700 – 850 nm shows the transition in the high spin Co^II tautomer and has likely a metal-to-ligand charge transfer nature. The peak at ~600 nm characterise the low spin Co^III tautomer and caused by the ligand-to-metal charge transfer. The appearance of isosbestic points during cooling is strong evidence that only two different species are present in solution [2]. Obtained results confirm the presence of a valence tautomeric transition in the cobalt complex under study. Our measurements indicate that where Co^II is transformed into Co^III under temperature decrease while reverse transition can be induced both under the influence of temperatures and laser radiation.

[1] Pierpont, C. G. (2001). Coord. Chem. Rev. 216, 99.

[2] Adams D.M., Hendrickson D.N. (1996). J. Am. Chem. Soc. 118, 11515.

[3] Ash R., Zhang K., Vura-Weis J. (2019) J. Chem. Phys. 151, 104201.

Rare-earth iron borate RFe₃(BO₃)₄ crystals are studied worldwide lately owing to their perspective magnetoelectric and multiferroic properties [1]. A major part of these single crystals was grown by flux method using Bi₂Mo₃O₁₂ as a solvent [2, 3]. In this work temperature-dependent structural behavior of RFe₃(BO₃)₄ (R = Ho, Y, Sm, Nd) single crystals were studied by X-ray structure analysis. The chemical composition was verified by X-ray energy-dispersive elemental analysis. Additional structure information was obtained by Mössbauer spectroscopy on ⁵⁷Fe nuclei.

Bi atoms entered the composition of all the crystals during the growth process and the final compositions of single crystals studied are Ho_0.96Bi_0.04Fe₃(BO₃)₄, Y_0.95Bi_0.05Fe₃(BO₃)₄, Sm_0.93Bi_0.07Fe₃(BO₃)₄, and Nd_0.91Bi_0.09Fe₃(BO₃)₄.

Unit cell parameters for R = Ho, Y, Nd were measured over 30–500 K. Parameters a,b of the crystals with R = Ho, Y are descending with temperature lowering, whereas a,b parameters of Nd-crystal do not change strongly. A sharp jump of a,b for R = Ho and Y was registered demonstrating presence of structural phase transition. At the same time, c (T) dependence has the similar character for all three crystals (R = Ho, Y, Nd) – c parameter decreases with lowering temperature to 80–100 K and then grows smoothly down to 30 K.

Structure of Ho_0.96Bi_0.04Fe₃(BO₃)₄, Y_0.95Bi_0.05Fe₃(BO₃)₄, Sm_0.93Bi_0.07Fe₃(BO₃)₄, and Nd_0.91Bi_0.09Fe₃(BO₃)₄ was determined at several temperatures in 90–500 K temperature range to study temperature-dependent structure peculiarities, in particular, changes during the structural phase transition for R = Ho, Y. The temperature of the phase transition T_str= 365 К for R = Ho and T_str= 370 К for R = Y was stated on the basis of systematic absences analysis and temperature dependence of a,b parameters. Inclusion of Bi atoms with a larger ionic radius leads to T_str lowering in comparison with powder samples without Bi [4]. The structure of the compounds with R = Ho, Y was refined in sp. gr. R32 above T_str and in sp. gr. P3₁21 below it. Structure of crystals with R = Sm, Nd belongs to sp. gr. R32 at all temperatures studied. There is a slight steady decrease of specific distanced in (R,Bi)O₆ trigonal prisms, FeO₆ octahedra, BO₃ triangles, and Fe–Fe helicoidal chains with temperature lowering in sp. gr. R32. When going to lower-symmetry sp. gr. P3₁21 (for R = Ho, Y) and with further temperature decreasing non-uniform changes in the bond lengths are observed. Equivalent atomic displacement parameters U_eq decrease with temperature lowering. However, U_eq of oxygen atoms O1 and O2 as well as ones of boron atoms B2 and B3 (sp. gr. P3₁21 labels) are highly sensitive to a structural phase transition, demonstrating fluctuations around T_str.

Debye (T_D) and Einstein (T_E) characteristic temperatures for cations in the crystals with R = Ho, Y, Sm, Nd were calculated. Both T_D and T_E values are close for the same type of cations. T_D and T_E for R and Fe atoms in sp. gr. R32 are close to the corresponding values in sp. gr. P3₁21, and there is a significant change in T_D, T_E values for B atoms after a phase transition.

Gamma-resonance measurements on ⁵⁷Fe nuclei showed that the hyperfine parameters of the Mössbauer spectra correspond to Fe³⁺ ions in an octahedral oxygen environment. Quadrupole splitting Δ temperature dependence demonstrates complex behaviour and is in good agreement with X-ray diffraction results.

[1] Kadomtseva, A.M., Popov, Yu F., Vorob'ev, G.P. et. al. (2010) Low Temp. Phys. 36. 511.

[2] Bezmaternykh, L. N., Kharlamova, S. A. & Temerov, V. L. (2004) Crystallogr. Rep. 49 (5). 855.

[3] Gudim, I.A., Eremin, E.V., Temerov, V.L. (2010) J. Cryst. Growth. 312. 2427.

[4] Hinatsu, Y., Doi, Y., Ito, K., Wakeshima, M. & Alemi, A. (2003) J. Solid State Chem. 172, 438.

While polynomial coefficients cannot explain the physical parameters associated, the Debye-Einstein-Anharmonicity (DEA) model [1, 2] adequately describes the temperature-dependent vibrational energy in the Grüneisen first-order approximation for lattice thermal expansion of a crystalline solid. In the DEA model, the Grüneisen parameter accounts for the isothermal and the anharmonicity parameter for the isochoric anharmonicity. Beside such advantages in DEA that concomitantly holds both quasi-harmonic and low-perturbed anharmonic [3] terms, this model is limited to explain metric thermal expansions close to phase transitions. For instance, framework material |Na₈I₂|[AlSiO₄]₆ sodalite [4] shows Landau-type tri-critical phase transition at 1080(6) K driven by tilt mechanism. The DEA model strikingly departs from the evolution of lattice parameters from 820(10) K up to the T_c. The kentrolite-type Pb₂In₂Si₂O₉ exhibits a second order phase transition at 778(5) K due to group-subgroup driven coordinate changes; again, the thermal expansion between 580(10) K and T_c cannot be modeled using DEA. Starting from the Landau theory for phase transitions [5-7], we propose a model that considers additional energy contributions integrated into the DEA, leading to metric parameter calculations close to phase transition. Adding the gliding (G) function to the temperature-dependent changes of internal energy essentially extends the general description as DEA+G. Thus, for the temperature-dependent metric parameter (M_i(T)) the Grüneisen first-order approximation can be expressed as:

?? (?) = ?0,? + ?????(?) + ??? (?) (1)

with M_0,i as the zero-point metric parameter of the i^th phase and be the contributed by DEA energy. is expressed as:

??? (?) = ?_? ?? = ?_? ?_? 3? ?_? ? ?^−?(??−?)? (2)

where N is the number of atoms, κ_G (1/K_o) the compressibility, a_G the isochoric anharmonicity parameter, k_B the Boltzmann constant, T_C the phase-transition temperature, λ the purview parameter, and n the transition exponent. While κ_G could be calculated from the bulk moduli associated with the Debye- and Einstein-thermoelastic terms, the only variable parameter is the isochoric anharmonicity in the range of a_G ~ 10^-5 K^-1 [3]. The function keeps the properties that describe the abrupt change of the metric parameters of a given material close to phase transition. The new approach (DEA+G) shows excellent fits for thermal expansion of both |Na₈I₂|[AlSiO₄]₆ and Pb₂In₂Si₂O₉ (Figure 1), and the model can be further justified using more relevant cases.

Chirality is a property that real images are non-superimposable on their mirror images. The importance of chirality has commonly been known through drug incidents of thalidomide all over the world ₁ ^1, ₂ ². Chirality exists not only molecules, crystals, membranes and other objects in nature. Crystal chirality is derived from not only molecular chirality but also helical arrangement of molecules in crystals. In the latter case, even if achiral molecules are put in a right-handed or a left-handed helical arrangement in crystals, the crystals occur chirality. It has already been known that the same amount of left-handed and right-handed crystals are obtained when chiral crystals composed of achiral molecules are grown ₃³. Among crystals composed of achiral molecules, about 8% of them are chiral crystals, so it is very important to grow chiral crystals that have particular chirality. However, it is extremely difficult to grow only right-handed or left-handed crystals from achiral molecules. In this study, we succeeded in growing right-handed or left-handed crystals from achiral molecules.

We have focused on Triglycine sulfate (TGS) crystals composed of glycine and sulfuric acid (Figure 1(a)). We found that TGS with particular chirality has grown by doping with L-, or D-alanine (Figure 1(b)). L-alanine-doped TGS (LATGS) crystals showed left-handedness, while D-alanine-doped TGS (DATGS) crystals showed right-handedness (Figure 2). This is an extremely interesting phenomenon. We discuss that this phenomenon is derived from polarity because TGS is ferroelectricity. The relationship between chirality and polarity helps the elucidation of the explicit mechanism of preferred chirality of TGS crystal by alanine.

HP research on Si started more than 50 years ago and since then several allotropes, displaying a wide variety of physical properties, have been reported. The narrow-bandgap semiconductorSi-III with BC8 structure (originally believed to be semimetal) can be obtained from the high-pressure tetragonal metallic phase, Si-II, formed during compression of common silicon according to Si-I→Si-II. Such a transformation during decompression can be either direct, Si-II→Si-III, or with an intermediate step Si-II→Si-XII→SiIII. Our in situ studies of pure Si in oxygen-free environment indicated that in the absence of pressure medium, Si-I remains metastable at least up to ~14 GPa, while the pressure medium allows reducing the onset pressure of transformation to ~10 GPa. Upon heating Si-III at ambient pressure a hexagonal structure, named Si-IV, was observed. This allotrope was believed to be a structural analogue of the hexagonal diamond found in meteorites (called also lonsdaleite) with the 2H polytypestructure. Calculations have predicted several hexagonal polytypes of Si and of other Group-IV elements to be metastable, such as 2H (AB), 4H (ABCB) and 6H (ABCACB). Exhaustive structural analysis, combining fine-powder X-ray and electron diffraction, afforded resolution of the crystal structure. We demonstrate that hexagonal Si obtained by high-pressure synthesis correspond to Si-4H polytype (ABCB stacking), in contrast with Si-2H (AB stacking) proposed previously. The sequence of transformations Si-III→Si-IV(4H)→Si-IV(6H) has been observed in situ by powder X-ray diffraction. This result agrees with prior calculations that predicted a higher stability of the 4H form over 2H form. Further physical characterization, combining experimental data and ab-initio calculations, have shown a good agreement with the established structure. Strong photoluminescence emission was observed in the visible region, for which we foresee optimistic perspectives for the use of this material in Si-based photovoltaics. The study of silicon allotropic transformation in Na-Si and K-Si systems at high pressure led to new open-framework allotrope of Si, Si24 with zeolite structure and promising optoelectronic properties.

Protic Ionic Liquids (PILs) are a class of tailorable solvents made up of fused salts with melting points below 100 °C, which are formed through a Brønsted acid-base reaction involving proton exchange[1]. These solvents have applications as lubricants, electrolytes, and many other uses[2]. Although they are quite similar to molten salts, their crystal structures have not been explored in-depth, with only ethylammonium nitrate (EAN) having a reported crystal structure[3, 4].
Ten alkylammonium-based protic ionic liquids at both neat (<1 wt% water) and 90 mol% PIL, 10 mol% water concentrations were selected. Diffraction patterns were collected at the Australian Synchrotron ANSTO while attempting to crystallise the samples by cooling to 120 K. Five samples crystallised (3 neat, 2 dilute), where the temperature of the system was then increased at a rate of 6 K/min to room temperature. From these patterns we have identified a number of crystal phases, identifying their stability ranges and lattice constant variation from 120 K to room temperature.

[1] Hallett, J.P. and Welton, T. (2011). Chemical Reviews. 111, 3508–3576.
[2] Greaves, T.L. and Drummond, C.J. (2008). Chemical Reviews. 108, 206–237.
[3] Abe, H. (2020). Journal of Molecular Liquids. 6.
[4] Henderson, W.A., et al. (2012). Physical Chemistry Chemical Physics. 14, 16041.

Hydrated sulfates are likely to be the dominant water reservoir in the equatorial region of Mars [1] forming massive, stratified deposits [2]. Hence their detailed mineralogical characterisation is critical in order to understand the aqueous history as well as the present-day equatorial water cycle of our neighbouring planet. Due to significant spectral similarities between sulfates of different chemical composition and degrees of hydration, attempts to constrain the exact nature of the polyhydrated sulfates from remote sensing data has proven to be challenging [3]. In-situ analysis by means of Raman spectroscopy and X-ray diffraction in Rover missions, however, appears to be a promising approach to provide insight on the mineralogy of these deposits. In order to facilitate such a phase analysis, there is a major interest in the thermal expansion and vibrational characteristics, and structural stability of candidate minerals at temperatures relevant to the martian surface.

To this end, we carried out a systematic study on various magnesium sulfate hydrates and related compounds and, notably for the first time, managed to synthesise cranswickite-type MgSO₄·4D₂O in the laboratory. Subsequently, we determined its thermal expansion at temperatures ranging from 340 to 20 K by means of time-of-flight neutron powder diffraction at the HRPD instrument (ISIS facility, UK) and from 300 to 80 K using high-resolution synchrotron X-ray powder diffraction at the I11 beamline (Diamond Light Source, UK).

The cranswickite samples studied revealed negative linear thermal expansion // c of approximately the same magnitude as the the positive linear thermal expansion // a, resulting in a net-zero thermal expansion in the ac plane over the entire temperature range under investigation. At 340 K cranswickite (space group C2/c) underwent a polymorphic phase transition to starkeyite (space group P2₁/n). The phase transition proceeded sluggishly and took several hours to complete. Most importantly, the cranswickite-to-starkeyite transition is accompanied by a volume reduction (ΔV ≈ -4.5 %), thus contradicting the general expectation that a less dense polymorph is formed at higher temperatures. To the best of our knowledge such interesting behaviour has so far just been observed for ThSiO₄ and isotypic PaSiO₄, albeitat substantially higher temperatures of approximately 1520 K [4].

[1] Feldman, W., Mellon, M., Maurice, S., Prettyman, T., Carey, B., Vaniman, D., Bish, D., Claire, F., Chipera, S., Kargel, J., Elphic, R., Funsten, H. (2004). Geophys. Res. Lett. 31, 10.1029/2004GL020181.

[2] Roach, L., Mustard, J., Swayze, G., Milliken, R., Bishop, J., Murchie, S., Lichtenberg, K. (2010). Icarus 206, 253-268. 10.1016/j.icarus.2009.09.003.

[3] Bishop, J. L., et al. (2009). J. Geophys. Res. 114, E00D09, 10.1029/2009JE003352.

[4] Keller, C., (1963). Nukleonik 5, 41-48

Spin crossover occurs in octahedral coordination compounds of the 3d⁴-3d⁷ electronic configuration of metal ions. The most spectacular changes are observed in Fe(II) complexes, where the HS→LS (HS – high spin, LS – low spin) transition is associated with shortening of Fe-N distance at about 0.2 Å. Although an ability to change of spin state is an intrinsic feature of the metal ion, the spin crossover properties of bulky, crystalline samples depend on the crystal structure of the coordination compound. Thus, different compositions of first coordination spheres of metal ions or presence in the crystal lattice crystallography unique molecules can result in the complex course of γ_HS(T) dependence (γ_HS(T) – the molecular ratio of molecules in HS form). Most often, a two-step spin crossover can be observed in such a situation. Our studies on iron(II) coordination polymers based on 1,4-di(1,2,3-triazol-1-yl)butane (bbtr) and its derivatives revealed a variety of spin crossover behaviours. [Fe(bbtr)₃](ClO₄)₂ exhibits abrupt spin crossover accompanied by hysteresis loop (T_1/2^¯ = 112 K, T_1/2^­ = 141 K)[1]. Importantly spin crossover in this complex is accompanied by structural phase transition P-3→P-1 depending on the shift of neighbouring polymeric layers. The structural phase transition has not been found in the tetrafluoroborate analogue, and the complex [Fe(bbtr)₃](BF₄)₂ remains in the HS form in the range 10-300 K[2]. The importance of structural changes on spin crossover properties showed our further studies using bbtr derivatives. An application of 1,4-di(5-ethyl-1,2,3-triazol-1-yl)butane (ebbtr) leads to the formation of two-dimensional coordination polymers exhibiting unique spin crossover: “double”[3] and “normal and reverse”[4] transitions. The occurrence of uncommon spin transitions in these complexes is associated with significant structural changes. An application of regioisomeric ligand bbtre leads to forming a three-dimensional coordination network in which the multi-way spin crossover is strongly related to conformational changes of the bridging ligands[5].

Studies of bbtr-based coordination polymers revealed the importance of counterion. Therefore, we have expanded our studies on the application of triflate derivatives. Synthesis performed between Fe(CF₃SO₃)₂·6H₂O and bbtr leads to forming a two-dimensional coordination polymer. The complex crystallizes in R-3 space group. The characteristic feature is the ordering of the half of bbtr bridging molecules and the presence of two crystallographically unique Fe(II) ions. Spin crossover is gradual and complete. Careful analysis of change of Fe-N distances revealed interesting phenomena. Namely, despite one-step spin crossover, both crystallographically unique Fe(II) ions change the spin state in different temperature ranges. Moreover, we have established the occurrence of very slow structural phase transition R-3→ P6₃. This structural transformation is associated with the vanishing of ligand disorder. Details concerning crystal structures of complexes before and after R-3→ P6₃ transformations on the poster.

[1] Bronisz, R. (2005). Inorg. Chem. 44, 4463.

[2] Kusz, J., Bronisz, R., Zubko, M. & Bednarek, G. (2011). Chem. Eur. J. 17, 6807.

[3] Weselski, M., Książek, M., Rokosz, D., Dreczko, A., Kusz, J. & Bronisz, R. (2018). Chem. Commun. 54, 3895.

[4] Weselski, M., Książek, M., Mess, P., Dreczko, A., Kusz, J. & Bronisz, R. (2019). Chem. Commun. 55, 7033.

[5] Książek, M., Weselski, M., Dreczko, A., Maliuzhenko, V., Kaźmierczak, M., Tołoczko, A., Kusz, J. & Bronisz, R. (2020). Dalton Trans. 49, 9811.

[Zn(ebtz)₃](BF₄)₂ (1,2-di(tetrazol-2-yl)ethane) was a first example of coordination polymer based of 2-substituted tetrazole as donor group [1]. Expanding studies on Fe(II) complexes showed that species of [Fe(tetrazol-2-yl)₆]-type core exhibit thermally induced spin crossover (SCO) [2]. Further researches revealed an ability of 2-substituted tetrazole to the formation of coordination compounds in which metal ion (Cu(II), Fe(II)) is surrounded by four tetrazole rings and two alcohol or nitrile molecules. The complexes of the type [Fe(tetrazol-2-yl)₄(RCN)₂] also exhibit SCO, which can be additionally affected by conformational changes of axially coordinated nitrile molecules [3]. It was established that the presence of a wide hysteresis loop in [Fe(ebtz)₂(C₂H₅CN)₂](ClO₄)₂ is related to the reorientation of coordinated propionitrile molecules coupled with significant changes of separation between supramolecular layers [4]. In order to explain the role of coordinated nitrile molecules on spin crossover properties, we have carried out detailed studies depending on systematic exchange of the ones in series of [Fe(ebtz)₂(RCN)₂](BF4₄)₂ [5]. We have focused on uncommon, very slow spin crossover observed in propionitrile derivatives. Measurements of the temperature dependence of magnetic susceptibility revealed thermal quenching of HS form after rapid cooling of the sample at 10 K. Measurements carried out at very slow scan rates showed an occurrence of hysteretic spin crossover (T_1/2^↓= 78 K, T_1/2^↑­=123 K). It allowed to perform isothermal (80 K) time-resolved single-crystal X-ray diffraction studies for the HS®LS transition. Initially, it occurs very slow shrinkage of polymeric chains associated with reduced cell volume at 77% (concerning the difference between cell volumes V_HS - V_LS) and only 16% of iron(II) ions adopt LS form. Then there starts fast and abrupt spin crossover associated with a significant increase of the distance between supramolecular layers, which occurs along the direction of the Fe–nitrile bonds. In this stage, there is a reorientation of propionitrile molecules connected with an increase of Fe-N-C(nitrile) angle from 143.6 to 161.6°. LIESST and r-LIESST studies performed at 14 K on single crystals confirmed that the contribution of switched Fe(II) ions strongly corresponds to the orientation of the nitrile molecule. These studies showed that stabilization of the spin form, produced by light irradiation, is dependent on the lattice-based effects. This property was utilized to manipulate spin crossover parameters by partial exchange of propionitrile by butyronitrile molecules. These studies showed that an increase in a fraction of butyronitrile molecules involves an increase of Fe-N-C(nitrile) angle resulting in a shift of SCO temperatures to higher values and in reduction of the width of the hysteresis loop.

[1] Bronisz, R. (2002). Inorg. Chim. Acta 340, 215.

[2] Bronisz, R. (2007). Inorg. Chem. 46, 6733.

[3] Książek, M., Kusz, J., Białońska, A., Bronisz, R. & Weselski, M. (2015). Dalton Trans. 44, 18563.

[4] Białońska, A. & Bronisz, R. (2012). Inorg. Chem. 51, 12630.

[5] Książek, M., Weselski, M., Każmierczak, M., Tołoczko, A., Siczek, M., Durlak, P., Wolny, J.A., Schünemann, V., Kusz, J. & Bronisz, R. (2020). Chem. Eur. J. 26, 14419.

The Li-ion battery technology completely revolutionized the portable electronic market and today it has become almost impossible to imagine a world without laptops, cell phones, etc.[1] This imposes a great challenge for the Li-ion battery industry, as demands for storing renewable energy and self-sufficiency in private homes are becoming more attractive.[2, 3] This will inevitably put pressure on the demand for both Li and Co, which are very limited resources.2 Despite elimination of toxic transition metals, like Co, has become a general aim for researchers and industry the Li extraction problem is yet to be solved.[4, 5] Here, Na-ion batteries are a great alternative to Li-ion batteries. Two types of materials are especially interesting, namely the O3 and P2 material, first discovered by Delmas and co-workers.[6, 7] Here O3-type has the highest capacity, as this material is synthesized with a higher Na content.[8]

From previous studies, the O3-type material is known to go through several phase transitions going from rhombohedral to monoclinic symmetry. In the beginning of 1980 Na intercalation was established for several O3-materials herein O3-NaCrO₂. The O3-NaCrO₂ is relatively, as great cycling stability and thermal stability has been shown, though upon complete charge, this material becomes disordered, and reversibility is lost.[9, 10] The material has been proposed to form Cr⁶⁺, via a disproportionation from the formation of Cr⁴⁺, during charge which migrates into the interslab forming a tetrahedral environment with oxygen. At end of charge, Cr⁴⁺ is reformed via a comproportionation which is suggested to arrange in a rock-salt structure.[11]

In this work, we set out to follow the structural behavior during charge and discharge in NaCrO₂. We have via operando PXRD confirmed that the material undergoes 3 phase transitions during charge, before the disorder is introduced in the material. Furthermore, we aim to trace the formation of tetrahedral Cr⁶⁺ with both ex situ and operando pair distribution function analysis (PDF) as this is directly linked to Cr-migration This is believed to be the source to the disordering of the material and the misfunctioning as positive electrode material in Na-ion batteries.

References

1. T. Nagaura and K. Tazawa, Lithium Ion Rechargeable Battery, Progress in Batteries Solar Cellsl, 1990.

2. C. Vaalma, D. Buchholz, M. Weil and S. Passerini, Nature Reviews Materials, 2018, 3, 18013.

3. T. M. Gür, Energy & Environmental Science, 2018, 11, 2696-2767.

4. Z.-Y. Li, J. Zhang, R. Gao, H. Zhang, L. Zheng, Z. Hu and X. Liu, Journal of Physical Chemistry C, 2016, 120, 9007-9016.

5. N. Zhang, N. Zaker, H. Li, A. Liu, J. Inglis, L. Jing, J. Li, Y. Li, G. A. Botton and J. R. Dahn, Chemistry of Materials, 2019, 31, 10150-10160.

6. C. Delmas, C. Fouassier and P. Hagenmuller, Physica B & C, 1980, 99, 81-85.

7. C. Delmas, J. J. Braconnier, C. Fouassier and P. Hagenmuller, Solid State Ionics, 1981, 3-4, 165-169.

8. P. F. Wang, Y. You, Y. X. Yin and Y. G. Guo, Advanced Energy Materials, 2018, 8, 1701912.

9. Y. N. Zhou, J. J. Ding, K. W. Nam, X. Q. Yu, S. M. Bak, E. Y. Hu, J. Liu, J. M. Bai, H. Li, Z. W. Fu and X. Q. Yang, Journal of Materials Chemistry A, 2013, 1, 11130-11134.

10. C. Y. Chen, K. Matsumoto, T. Nohira, R. Hagiwara, A. Fukunaga, S. Sakai, K. Nitta and S. Inazawa, Journal of Power Sources, 2013, 237, 52-57.

11. S.-H. Bo, X. Li, A. J. Toumar, G. Ceder and B. C. A. Lawrence Berkeley National Lab, Chemistry of Materials, 2016, 28, 1419-1429.

Traditionally, electrode materials for intercalation-type rechargeable batteries have been crystalline. For crystalline materials, the material structure on the atomic length scale may be probed through traditional diffraction experiments and structure-property relations may be revealed through operando experiments, where the battery is charged and discharged, while irradiated with a proper probe, e.g. intense high-energy synchrotron x-rays. However, when electrode materials disorder, either during battery operation or are disordered ab origine, the limited range of structural coherence diminishes the amount of structural information extractable through traditional diffraction experiments. To probe the material structure on a more local length scale, total scattering combined with pair distribution function (PDF) analysis may be applied to elucidate the atomic structure on a very local level, even under dynamic conditions through operando experiments. [1-2]

This poster presents selected examples on both irreversible and reversible order-disorder phase transitions, for TiO₂-rutile and Na_xFe_1.13(PO₄)(OH)_0.39(H₂O)_0.6, respectively. The phase transitions are induced electrochemically by ion-intercalation and ion-deintercalation during battery operation. Also, an example on an ab origine nanocrystalline material, TiO₂-bronze, is presented. Also for this nanocrystalline material, traditional diffraction methods fall short, when it comes to characterization of the material structure at the atomic length scale. In all three cases presented here, x-ray total scattering and PDF analysis provide unique structural information on the atomic length scale for otherwise crystallographically challenged materials.

Figure 1. Left: Operando X-ray diffraction of Na_xFe_1.13(PO₄)(OH)_0.39(H₂O)_0.6. In the upper part, an overview plot of the scattering data is shown, where the scattering angle in degrees and the time in hours are displayed on the axes. In the lower part, the electrochemical data is shown as the voltage as a function of state of charge (overall Na content). The time and state of charge axes are congruent. Bragg intensity fades during deep discharge but is recovered upon charge. Middle: Ex-situ x-ray diffraction data for the pristine (start), Na-rich (end of 1^st discharge), and Na-poor (end of 1^st charge) Na_xFe_1.13(PO₄)(OH)_0.39(H₂O)_0.6 materials. For the Na-rich material, Bragg intensities fade, and broadening is observed to a rather large extent. Right: Fitted reduced atomic pair distribution functions for the pristine (start), Na-rich (end of 1^st discharge), and Na-poor (end of 1^st charge) Na_xFe_1.13(PO₄)(OH)_0.39(H₂O)_0.6 materials. The experimental PDF is shown as blue circles, the calculated PDF as a red curve, and difference curve of the two is shown as a green curve. [3]

[1] Christensen C. K., Sørensen D. R., Hvam J. & Ravnsbæk D. B. (2019). Nanoscale. 31, 512-520.

[2] Christensen C. K., Mamakhel M. A. Balakrishna A. R., Iversen B. B., Chiang Y.-M. & Ravnsbæk D. B. (2019). Nanoscale, 11, 12347-12357.

[3] Henriksen C., Karlsen M. A., Jakobsen C. L. & Ravnsbæk D. B. (2020). Nanoscale. 12, 12824-12830.

Keywords: Batteries; Operando; Pair Distribution Function Analysis; Order-Disorder Phase Transitions

We acknowledge the Carlsberg Foundation, The Independent Research Fund Denmark, and the instrument center DanScatt for funding.

Methylammonium Tin Halide Perovskites CH3NH3SnX3 (MASnX3, X: halide) are candidates of lead-free light- absorbing materials for photovoltaic devices. They undergo successive phase transitions caused by tilting or distorting of the SnX6 octahedra and orientational ordering of the organic MA cation. The structures of low temperature phases are still controversial due to the difficulty of accurate determination for the orientation of organic cation. In this study, neutron diffraction measurements were performed on MASnX3 with X=I, Br to determine the structures at low temperature phases and elucidate the ordering mechanism of the organic cation through the phase transitions.

Time-of-flight neutron diffraction data were collected using single crystal diffractometer SENJU (BL18) and Super High Resolution Powder Diffractometer SuperHRPD (BL08) installed at Materials and Life Science Experimental Facility, J-PARC. Diffraction patterns observed at five phases of MASnBr3 are distinctly different from each other, showing that the crystal structure changes successively through the four phase transitions. The result requires reconsideration of the structures below 213K in which no perceptible structural changes have been observed between β - γ phases nor δ – ε phases. For MASnI3, three phases with different structures were recognized as previously reported. Structure of the lowest temperature g phase remains uncertain, but a drastic change of the diffraction pattern between β and γ phases indicates that the structural symmetry is reduced considerably from tetragonal to triclinic system. Single crystal structural analysis at the cubic a phase reveals that the center of mass of the MA molecule locates off-center of the cubic unit cell, and nuclear density of the molecule synthesized by the maximum-entropy method shows anisotropic distribution along cubic axis. These tendencies appear more remarkable in MASnBr3, indicating stronger effect of organic-inorganic interaction in the X=Br crystal.

A new cobalt phosphite templated by diprotonated ethylendiamine molecule (C₂N₂H₁₀)[Co(H₂O)₆](HPO₃)₂ has been prepared via slow evaporation method. The hybrid material crystallizes in the orthorhombic system, space group Pbca, with the cell parameters: a=11.1518(9), b=9.8014(8), c=13.3782(8) Å, V=1462.28(19) Å3, and Z=4. The compound exhibits a bidimensional crystal structure formed by an anionic layer with the formula [Co(H₂O)₆(HPO₃)₂]^2- along the a-axis. The ethylenediammonium cations are located within the anionic cavities, through establishing hydrogen bonds network. The layers are made upon isolated Co(H₂O)₆ octahedra and (HPO₃)^2- tetrahedral phosphite anions, which interact through hydrogen bonds. The Infrared spectroscopy presents the characteristic bands of the hydrogenophosphite anion, ethylenediammonium cation, and water molecule. Thermogravimetric analysis (TGA) and catalytic efficiency data for the hybrid compound are investigated and it was found to be very efficient as a catalyst.

Diffraction techniques has been employed to study the molecular reorganisation of three oligonuclear spin crossover (SCO) complexes of the form [Fe(II)_XL^R₄]BF₃·MeCN (X = 2,3,4; L =R-3,5-bis{6-(2,2’-bipyridyl)}pyrazole; R= H, CH3), with a grid-like arrangement [1-2]. A multi-temperature crystallographic investigation exhibits the gradual phase transition in all compounds and a cross-talk between strongly linked metal centres. A systematic comparison between metallogrids suggests that the intramolecular cooperativity results from the complex interplay between grid flexibility and nuclearity. The latter has also a key role in molecular geometry of the ephemeral species formed after light irradiation with a femto-second laser pulse, as observed by time-resolved crystallography. The metallogrid with two non-linked metal centres shows a single molecular rearrangement during the first nanosecond after excitation, while the tetranuclear grid has multiple structural arrangements during the same span of time. More in general, this work exhibits the structural modifications accompanying the thermal and ultra-fast photo-induced spin transition of three metallogrids complexes.

Beta titanium alloys possess several attractive properties for use in load-bearing biomedical implants of large body joints, in particular the high strength combined with low Young’s modulus, biocompatibility and corrosion resistance. Recently developed alloy Ti-35Nb-6Ta-7Zr-0.7O (wt.%) with high content of strengthening oxygen exhibits the high strength of 1000 MPa and the Young’s modulus of 80 GPa. By reducing the content of beta stabilizing elements (Nb, Ta), the high strength of 1000 MPa is preserved due to oxygen strengthening and the Young’s modulus is reduced, reaching value of approx. 60 GPa in Ti-29Nb-7Zr-0.7O (wt.%). The pure beta phase after solution treatment is retained even at these low Nb/Ta concentrations. On the other hand, the phase transformations during heating differ significantly. The ongoing phase transformations in this alloy were investigated by in-situ dilatometry and electrical resistance measurements as well as by ex-situ methods after linear and isothermal heating. The ex-situ methods include: scanning electron microscopy, microhardness measurements and x-ray diffraction. It was found, that the beta phase stability is reduced significantly by reducing the content of Nb/Ta.

The main findings of this complex experimental investigation of several Ti-Nb-(Ta)-Zr-0.7 wt%O may be summarized as follows:

- The yield strength exceeding 1000 MPa and the ductility of approx. 20% was achieved in these alloys.

- The decrease of the content of Nb and Ta resulted in the decrease of the Young’s modulus from 80 GPa at Ti-35Nb-6Ta-7Zr-0.7O to 60 GPa at Ti-29Nb-7Zr-0.7O alloy.

- In-situ dilatometry and electrical resistance measurements suggest ω phase formation in less stable alloys.

- The lower phase stability leads to more homogeneous alpha precipitation at higher temperatures (700°C).

- At lower temperatures (400°C), no phase transformation occurs in highly stabilized alloys while in the least stable alloy, very fine α lamellae and relatively large ω particles (tens of nm) are formed. This is also accompanied by a significant microhardness increase.

- The Ti-29Nb-7Zr-0.7O alloy seems to be a suitable material for orthopaedics and implantation surgery.

The recycling of critical elements has crucial importance to maintain sustainable use of raw materials. Phosphorus(P) is a sought-after limited natural resource due to its wide use in modern agriculture mainly as P-fertilizers. But it causes major problems for the environment such as eutrophication of ecosystems. In the future it could be depleted due to the high demand and declining natural phosphorite ore deposits. Therefore, the phosphorus recovery from mine and agricultural waste waters will be an important factor in preservation of the global consumption. The precipitation of M-struvite (NH₄MPO₄·6H₂O, M²⁺= Mg²⁺, Ni²⁺, Co²⁺) from waste waters is a promising P-recovery route. Besides avoidance of eutrophication due to extraction of excess phosphates and the restoration of the phosphorus resources the recovered M-struvites may be potentially be up-cycled for industrial applications e.g. Co and Ni-phosphate show excellent electrochemical properties for batteries or supercapacitors.

The precipitation process of M-struvites is strongly dependent on the degree of supersaturation, pH and on the exchange ions M²⁺.The influence of these precipitation parameters on the crystal morphology and size of transition metal struvite has been investigated only to a limited extent. An optimization of the reaction conditions could lead to more efficient M-struvite precipitation and significantly improved P-recovery method.

We reveal the effect of different reaction conditions on the crystal shape and crystallite size of M-struvites (NH₄MPO₄∙6H₂O, M = Mg²⁺, Ni²⁺, Co²⁺). Furthermore, we characterize the coordination environment of the crystalline end products and their related phases [Co-dittmarite (COD) NH₄CoPO₄∙H₂O and Co(II)phosphate octahydrate (CPO) Co₃(PO₄)₂∙8H₂O]. Due to the presence of various amorphous phases pH is changing significantly in the different systems. Mg- and Ni-struvite are stable in multiple concentrations of the educts and metal/phosphorus (M/P) ratios in contrast to Co-struvite which forms below M/P ratios of 0.4. A high M/P ratio with high concentrations of the educts decrease the crystallite size and idiomorphism of the crystals while low M/P ratios with low concentrations of the educts increase the crystallite size and the euhedral formation of the crystal planes. In the (Ni, Co)-solid solutions Ni and Co are homogenously distributed in the crystals with similar Ni# as in the aqueous solutions indicating no elemental fractionation in crystallization. Ni and Co-struvite exhibit a more centrosymmetric coordination environment compared to their related phases of COD and CPO determined by EXAFS. The CoO₆ octahedron expands slightly the ideal size of the struvite structure and decomposes to Co-dittmarite. From TEM analysis and pH measurements it is suggested that the crystallization of Ni- and Co-struvite follows a non-classical crystallization theory which consists of multiple nanophases, crystalline or amorphous, on the way to the final crystalline product.

Metastable β titanium alloys are widely used as construction materials in automotive and aerospace industry. These applications demand materials with superior properties, such as high specific strength, good ductility and excellent fatigue and corrosion resistance. The improvement of strength can be achieved through ageing treatment which results in the formation of small precipitates of thermodynamically stable α phase in the metastable β matrix. When the α precipitates are very fine and homogeneously distributed, the strength of the alloy increases without a significant deterioration of the ductility. This fine microstructure can be achieved by employing such heat treatment in which the α phase precipitation is preceded by ω phase formation. ω phase is a metastable phase occurring as nanometric-sized, homogeneously dispersed particles. ω-assisted α phase nucleation results in very fine α phase microstructure.
In this study, very small precipitates of the α phase were studied by scanning electron microscopy (SEM). This observation allowed us to investigate theorientation and spatial relationship between Alpha phase lamellae and Beta phase mattrix. The SEM study was supplemented by the measurement of small-angle x-ray scattering (SAXS) which provides precise information on crystallographic orientation between the β and α lattices and on the shape and size of α precipitates. In order to assess the relationship of microstructure and mechanical properties of the material, Vickers microhardness was measured.

Within the last 15 years, the Parameter Space Concept (PSC) was theoretically developed by Fischer, Kirfel and Zimmermann as an alternative approach to solve crystal structures from diffraction intensities without use of Fourier transforms [1-6]. Each experimentally determined reflection restricts the 3N-dim. parameter space of atomic coordinates for a crystal structure solution (N atoms) by a manifold of 3N-1 dimensions, equivalent to a unique isosurface, whereas the true solution vector will be the intersection of all isosurfaces. The method has already been tested on numerous, partly challenging problems of X-ray diffraction.

We present a study of the maximum resolution of the PSC. As an example, a split position of La and Sr with (0, 0, z=0.3584) has been investigated in the potential high-temperature super-conductor (La_0.5Sr_1.5)MnO₄, I4/mmm. A positional shift of the cations in the order of Δz≈0.001₅ (≈0.02 Å) has been suggested in literature [7]. Enhancing the scattering difference of La and Sr by f’_Sr, this split was later verified using the PSC within a rather conservative model test [8]. As a result a shift Δz=0.01₃ had been determined. We now add to the discussion an evaluation based on two additional model data sets, each with (00l) reflections (l = 2,4…20) and varied relative errors of up to 20%. A graphical representation of the parameter space revealed an improvement of resolution with a shift of Δz=0.01₂…0.01₆ (≈0.1₅…0.2₀ Å). Due to the difference in scattering power of La and Sr, a pseudosymmetric structure solution exists for approximately interchanged z-positions, which we discuss in conjunction with the accurate solution . The two solutions were defined by the intersection of isolines representing (00l) reflection intensities [9]. There is a non-vanishing variance of the pseudosymmetric structure solution, whereas the accurate solution does not vary. Depending on the relative error of the diffraction intensities, we present respective resolution limits for the split position.

Figure 1. Left: Model study of the real (0.362 | 0.349) and the (broken) pseudosymmetric structure solution (z*_La,z*_Sr) of the PSC model as a function of the relative scattering strength of the La and Sr atom. Inset: Variance of the (broken) pseudosymmetric structure solution ∆z*_La,Sr as a function of the relative scattering strength of the La and Sr atom. The real solution shows no variance. Right: Monte-Carlo-Study of the structure solution as a function including the single (2.3-times) trust region for 20% intensity error and equal scatterers.

[1,2] K.F. Fischer, A. Kirfel, H. Zimmermann, (2005) Z. Krist. 220, 643; (2008) Croatica Chemica Acta 81, 381.

[3,4] A. Kirfel, K.F. Fischer, H. Zimmermann, (2006) Z. Krist. 221, 673; H. Zimmermann, K.F. Fischer, (2009) Acta Cryst. A65, 443.

[5,6] A. Kirfel, K. F. Fischer, (2009) Z. Krist. 224, 325; (2010) Z. Krist. 225, 261.

[7,8] T. Lippmann et al., (2003) HASYLAB Jahresberichte 583; A. Kirfel, K. F. Fischer, (2004) Z. Krist. Suppl. 21, 101.

[9] M. Zschornak, M. Nentwich, D.C. Meyer, A. Kirfel, K. Fischer, (2020) 27^th Annual Meeting of the DGK, Wrocław, Poland.

In order to improve solubility and dissolution rate of pharmaceutical products in human body, the cocrystal formation has been focused on. The cocrystal allows to form the new crystal structure composed of active pharmaceutical ingredients (APIs) and additives called as coformer (CF). Most conventional methods require a treatment in organic solvent to form cocrystal, so they include disadvantages on the safety due to remaining the organic solvent. A hot melt extrusion, which is the cocrystal formation process using liquefied polymer, may include a thermal decomposition of APIs by heating process at high temperature to melt polymer. In this study, we focus on melting point depression of lipids by high pressure CO₂. In this research, we propose a cocrystallization process with liquefied lipid under high pressure CO₂.

In this study, we use theophylline (TPL) as API, nicotinamide (NA) as CF. In addition, stearic acid (SA), oleic acid (OA) and linoleic acid (LA) whose unsaturation is each 0, 1 and 2 are used as lipids. The carbon numbers of all the lipids are. For comparison, we conducted experiments without lipids and experiments using hydrocarbon with the same carbon number, octadecane (OD) and 1-octadecene (1-OD). We put TPL (0.1 mmol), NA (0.1 mmol) and lipid (0.04 g) in high-pressure vessel under 16.0 MPa at 50 ^oC (60 ^oC only SA) for 2 h. Moreover, the experiments were conducted in which TPL (1 mmol), NA (1 mmol) and lipid (0.4 g) were being stirred at 300 rpm for 2 h under same the temperature and pressure conditions. As the X-ray diffraction results, cocrystal formations are improved by liquified lipid compared with those formed in hydrocarbon or without lipids. Moreover, the conversion rate of cocrystal formation is evaluated from the peak intensity ratio of XRD between TPL and cocrystal by RIR method, which is a way to evaluate cocrystal’s purity using that the mass ratio in the mixture is proportional to the characteristic peak intensity ratio. As a result, it is found out that cocrystal formation is improved as the degree of lipid unsaturation increased. Similarly, in the cases with stirring, lipids with high unsaturation promotes cocrystallization than hydrocarbons. These results could be due to the facilitation of interactions between TPL or NA surfaces and lipid surfaces by carboxyl groups in lipids, which may cause the activation of each interface during cocrysallization. In addition, to explain the facilitation of interactions by lipids, we calculate the molecular interaction energy among TPL, NA and lipid by Conductor-like Screening Model (COSMO). As a result, the comparison between calculated and experimental results suggests that cocrystal formation is promoted by increasing molecular interactions. Therefore, we conclude that lipids with big interaction energy with API and CF help to form cocrystal under high pressure CO₂.

Grazing-incidence X-ray diffraction (GIXD) is a widely used technique for the crystallographic characterization of thin films. The identification of a specific phase or the discovery of an unknown polymorph always requires indexing of the associated diffraction pattern. However, despite the importance of this procedure, only few approaches have been developed so far. Recently, an advanced mathematical framework for indexing of these specific diffraction patterns has been developed [1, 2].

Here, the successful implementation of this framework in the form of an automated indexing software, named GIDInd, is introduced. GIDInd is based on the assumption of a triclinic unit cell with six lattice constants and a distinct contact plane parallel to the substrate surface. Two approaches are chosen: (i) using only diffraction peaks of the GIXD pattern and (ii) combining the GIXD pattern with a specular diffraction peak (see Figure 1). In the first approach the six unknown lattice parameters have to be determined by a single fitting procedure, while in the second approach two successive fitting procedures are used with three unknown parameters each. The output unit cells are reduced cells according to approved crystallographic conventions. Unit-cell solutions are additionally numerically optimized. The computational toolkit is compiled in the form of a MATLAB executable and presented within a user-friendly graphical user interface. The program is demonstrated by application on two independent examples of thin organic films.

[1] Simbrunner, J., Simbrunner, C., Schrode, B., Röthel, C., Bedoya-Martinez,N., Salzmann, I. & Resel, R. (2018). Acta Cryst. A74, 373.

[2] Simbrunner, J., Hofer, S., Schrode, B., Garmshausen, Y., Hecht, S., Resel, R. & Salzmann, I. (2019). J. Appl. Cryst. 52, 428.

Serial femtosecond crystallography (SFX) enables the retrieval of the molecular structure of protein molecules at the atomic level through the measurement of large numbers of small crystals intersecting intense X-ray pulses. The method of sample delivery for SFX has a very significant impact on the success (or otherwise) of the experiment since this can impact the signal-to-noise, resolution, and amount of data that can be obtained. In particular, highly efficient sample delivery is critical, since this minimizes the amount of X-ray Free Electron Laser (XFEL) beamtime required as well as reducing sample consumption and data volumes. Here we present the results from a series of liquid jet experiments performed at the European XFEL using gas-focused liquid injectors, gas virtual dynamic nozzle (GVDN), and double flow-focusing nozzles. Although these methods are well-established and used extensively at the European XFEL a major drawback of using these injectors is that over time the jet can become misaligned with the XFEL beam. At present, this requires regular manual monitoring in order to ensure that the relative drift of the jet with respect to the X-ray beam does not become so significant that the beam either ‘clips’ or misses the jet entirely. Manual adjustment of the liquid jet to ensure alignment with the X-ray beam costs the beamline staff time is prone to errors, and ultimately reduces the amount of useable data that is collected. In order to address the issue of jet misalignment, we present a novel approach to analyzing the liquid stream both with (‘hit’) and without (‘miss’) intersection by the X-ray beam using machine vision. Optical images from the side microscope currently used to monitor the jet are fed into our machine vision algorithm and used to classify the images as either a hit or miss. Currently, we are testing the efficacy of the algorithm with a variety of nozzles and jetting conditions. The algorithm will then be incorporated into the control system at the SFX/SPB beamline at the European XFEL where it will be used to generate an ‘alignment correction’ to the stepper motors controlling the location of the nozzle within the chamber. Via a continuous feedback loop, fine adjustments will be made to the position of the liquid jet ensuring that maximum X-ray beam/liquid jet overlap is achieved. Since this process is fully automated we anticipate that it will result in a larger volume of useful data being collected without requiring any manual intervention. By increasing the efficiency and reducing the per experiment operational cost of SFX at the European XFEL ultimately more experiments can be performed. In addition, via analysis of the feedback metrology, we anticipate that optimized nozzle designs and jetting conditions could be achieved further benefitting the end-user.

In case of grazing incidence X-ray diffraction (GIXD), as usually performed on fibre textured films, only two components (of the total three) of the reciprocal lattice vectors – namely an out-of plane component q_z and an in-plane component q_xy – are available for the indexing procedure. In previous work, we have presented an algorithm for indexing such diffraction patterns, where the additional presence of a specular diffraction peak is being explicitly taken into account [1]. In the present work, we now aim to formulate this indexing method for a number of GIXD patterns collected for samples at different azimuthal rotation angles account [2]. Thus, all three components of the scattering vector are obtained. Also in this case, the combination of the diffraction peaks obtained from GIXD with the specular diffraction peak(s) simplifies the indexation procedure, so that finally, different phases of epitaxially oriented films can be identified.

In theory, the parameters of the reduced unit cell and its orientation can simply be obtained from the matrix of three linearly independent reciprocal space vectors. However, if the sample exhibits unit cells in various alignements and/or with different lattice parameters, it is necessary to assign all experimentally obtained reflections to their associated individual origin. An effective algorithm is described to accomplish this task in order to determine the unit-cell parameters of low symmetry systems comprising different orientations and polymorphs. Our method is particularly advantageous if the number of reflections is relatively small or the sample consists of various crystal lattices or alignments, as it is commonly found for organic thin films grown on single crystalline substrates. For easy access to epitaxial relationships, the lattice constants of the involved unit cells and the parameters of the orientation matrix can be determined simultaneously.

Well-known (PTCDA, pentacene), as well as crystallographically less characterized samples (trans-DBPen, DCV4T-Et2) on various substrates were analyzed [3]. In all cases, crystallographic unit cells exhibiting specific contact planes with the substrate were obtained. Additionally, distinct 60° symmetries for the positive and negative orientations of the contact plane were found. In the particular case of DCV4T-Et2 grown on Ag(111), three new polymorphs with different contact planes and cell parameters were found (see Figure 1); when using graphene/SiC(0001) as substrate, however, only one of these polymorphs could be observed. Our work shows that indexing is possible even when different alignments of crystals occur within a thin film and also in the presence of several polymorphs.

[1] Simbrunner, J., Simbrunner, C., Schrode, B., Röthel, C., Bedoya-Martinez,N., Salzmann, I. & Resel, R. (2018). Acta Cryst. A74, 373.

[2] Simbrunner, J., Schrode, B., Domke, J., Fritz, T, Salzmann, I. & Resel,, R. (2020). Acta Cryst. A76, 345.

[3] Simbrunner, J., Schrode, B., Hofer, S., Domke, J., Fritz, T, Forker, R. & Resel,, R. (2021). J. Phys. Chem. C125: 618.

In the functional analysis of proteins, it is essential to know the crystal structure at the atomic level and its electronic and chemical changes. Spectroscopy is an effective technique for detecting the structural states of proteins, even within protein crystals. Therefore, spectroscopic methods such as Raman and UV-Visible absorption have been complementarily combined with X-ray diffraction studies to evaluate the structural states of proteins. To utilize the spectroscopic study at macromolecular crystallography beamline at the Photon Factory, the development of spectroscopic instrumentation for both offline and online has been started at beamline AR-NW12A. For the development of offline spectroscopic instrumentation, the laser booth has been built beside of control cabin of AR-NW12A. After the end of the construction of the laser booth, we have started to develop the offline UV-Visible absorption spectroscopic instrumentation and it has now been in general user operation. Herein, we describe the outline of the offline UV-Visible and Raman spectroscopic instrumentations. The continuing development of the online spectroscopic instrumentation is also outlined. In the future, macromolecular crystallographic beamline users will be able to not only determine the atomic structure of their samples but also to explore the electronic and vibrational characteristics of their sample, before, during, and after data collection.

High-throughput protein X-ray crystallography offers an unprecedented opportunity to facilitate drug discovery. The most reliable approach is to determine the three-dimensional (3D) structure of the protein-ligand complex by soaking the ligand in apo-crystals, but many lead compounds are not readily water-soluble. Such lead compounds must be dissolved in concentrated organic solvents such as DMSO. Therefore, to date, it has been impossible to produce crystals of protein-ligand complexes by soaking in apo-crystals, because protein crystals dissolve immediately upon soaking in concentrated organic solvents containing lead compounds. The problem arises from the influence of osmotic shock on crystal packing during soaking.

Protein crystals grown in hydrogel allow us to prevent serious damage to the crystals caused by soaking in high-concentration organic solvents, producing crystals of complexes between the target protein and poor water-soluble compounds by soaking in it. We previously reported the high-strength hydrogel method [1-4], but obstacles remain for general versatility. To overcome this difficulty, we devised an improved method for diffusing proteins into the pre-solidified hydrogel [5]. This study established a new crystallization method that prevents high-temperature damage to proteins. This method offers a technique to osmose the protein from the top of a hydrogel layer and recover its crystals with the precipitant on the bottom of the hydrogel layer by using a plate with a dialysis membrane. This study concentrated on the protein crystallization in hydrogels, but the results indicate that this method will be applicable to various proteins because it can always be operated at a low temperature.

For crystal structure analysis including light weight atoms such as hydrogen and lithium and magnetic structure analysis for strong correlation system, neutron single crystal diffraction is very powerful tool. Generally, A two-dimensional area detector by X-ray and neutron diffraction has huge reciprocal space data, so that it is necessary efficient analysis method. In the past decade, we developed the program package “Reciprocal Analyzer”, for a single crystal neutron diffractometer, using a curved two-dimensional position sensitive detector (C-2DPSD) installed at HANARO-ST3 and at T2-2 beam port in JRR-3M [1, 2]. This software was utilized by 32-bit OpenGL UI libraries "GLUI", and it realized cross-platform packages available used major operating systems. However, these user interfaces are old-fashion for present computers, so that it is essential to improve using recent libraries. Thus, we developed a new application based on three-dimensional reciprocal space mapping using latest C++17 languages, and it applied to TOF neutron data by neutron single crystal diffractometer "SENJU" installed at J-PARC/MLF shown in figure 1.

Moreover, we also developed UB matrix determination program based on probabilistic algorithm, which is bundled the reciprocal mapping software above mentioned. Some algebraic methods are well known as algorithms to calculate the UB matrix such as the two-reflection method and the vector minimum method. On the other hand, in many cases of samples brought to large neutron and Synchrotron experimental facilities, lattice parameters have already determined through preliminary experiments using laboratory X-ray equipment. Therefore, the determination of the UB matrix is often equivalent to the problem of finding the rotation matrix as U matrix. Because the rotations in each axis are continuous variables and the number of combinations is proportional to the cube of the discrete rotations, the round robin algorithm is not a realistic solution. The Monte Carlo method is one of estimation methods for the global optimal solution by a probabilistic algorithm in a broad sense. In this study, we developed a UB matrix estimation program that newly introduced probabilistic algorithms such as (1) Random Walk, (2) Simulated Annealing, (3) Generic Algorithm, and (4) Particle Swarm Optimization, the properties and costs of each algorithm are discussed. In the presentation, we report the details of each algorithm and the comparison of the calculation results.

See attached

Application of result of atoms and centrosymmetric cubic space groups for sharpening of Patterson function

P. S. Yuen

237 Des Voeux Road West, 5th Floor, HONG KONG

puisumyuen@netvigator.com

|F_obs|² is used in the Patterson function. All phases equal 0. The value of the function is non-negative. The Patterson peaks are broad. The result of atoms and centrosymmetric cubic space groups is that an approximate structure of the crystal is contained in the peaks of the calculated electron densities [1]. We apply this property to the crystal of the Patterson function, to sharpen the Patterson peaks. We use a hydrogen atom with random coordinates in the general position of the space group of the crystal of the Patterson function. Combine the phases with all |F_obs|². Some of these phases have signs -1. Therefore, some electron densities are negative, and some Patterson peaks are sharpened. We apply this method to Ba₃Y₂B₆O₁₅ [2]. Space group of the Patterson function is Im-3. Some results are presented in Table 1 and Fig.1.

Table 1. Some peaks in the sharpened Patterson function.

Label

x

y

z

Peak height

Half-width

Origin

0.000

0.000

0.000

14076

0.0361^s

Ba1 - Y1

0.344

0.000

0.251

3545

0.0253^s

Ba1 - O1

0.322

0.000

-0.077

12074^h

0.0421^s

Y1 - O1

-0.049

0.000

-0.321

14940^h

0.0517

^h higher peak height. ^s smaller half-width (Compare with peaks in the Patterson function)

Figure 1.Sharpened Patterson peak Ba1-O1

[1] Yuen, P. S. Result of using atoms and centrosymmetric cubic space groups. (Unpublished).

[2] Zhao, S., Yao, J., Zhang, G., Fu, P. & Wu, Y. (2011). Acta Cryst. C67, i39.

Keywords: IUCr2020; abstracts; atom; centrosymmetric cubic space group; sharpening.;

An attempt to find the use of atomic scattering factors and centrosymmetric cubic space groups; two choices of random phases in direct methods

P. S. Yuen

237 Des Voeux Road West, 5th Floor, HONG KONG

puisumyuen@netvigator.com

In [1], we have used one hydrogen atom with random coordinates in a general position of centrosymmetric cubic space groups to calculate the phases. An approximate structure of the crystal is contained in the peaks of the calculated electron densities. As atomic numbers and atomic scattering factors are not included, the electron densities of the peaks of the approximate structure of calculated electron densities do not follow the pattern of the atomic species. Procedures for identifying this approximate structure are presented in [1]. A simple new method for crystal structure determination is presented in [2]. This involves a large number of combinations of the peaks. If we can distinguish the different types of atoms, the procedures in [1] will be more efficient. The number of combinations in [2] will be significantly reduced. This leads to two fundamental and important questions in X-ray crystallography: What is the result of using atomic numbers and centrosymmetric cubic space groups? What is the result of using atomic scattering factors and centrosymmetric cubic space groups? If we can obtain an answer to one of these questions, the peaks in the calculated electron densities may then be classified into species of atoms. This is very useful for identification of the atoms of the approximate structure. As an attempt to answer the second question, in this article, we use the lightest and heaviest atom of the crystal, with random coordinates in general positions of the space group. As in [1], the result of using phases from these atoms is that an approximate structure of the crystal is embedded in the peaks of the calculated electron densities. The electron densities of the peaks of approximate structure do not follow the trend of atomic numbers. More investigation is needed.

Random initial phases have been employed in direct methods. Phases from one atom with random coordinates in a general position, and phases from the lightest and heaviest atom may be used as random phases. They are random in the sense that they are
phases from one or two atoms with random coordinates. They have the property of an approximate structure of the crystal contained in the peaks of the calculated electron densities. This may be useful when these are employed as random phases in direct methods.

[1] Yuen, P. S. Result of using atoms and centrosymmetric cubic space groups. (Unpublished).

[2] Yuen, P. S. Determination of structure of CoS₂ by the means of a simple new method; a solution to the phase problem for centrosymmetric cubic crystals. (Unpublished).

Keywords: IUCr2020; abstracts; initial phases; random phases; approximate structure;

X-ray Absorption Spectroscopy has been one of the most powerful tools for probing atomic and molecular structures of materials. However, the measured fine structures in the absorption domain do not have adequate dimensionalities to extract three-dimensional structural information of the material of interest. A technique that allows accurate measurements of atomic fine structure in both the absorption and phase domains will open exciting opportunities in a wide range of fundamental and applied research. In this presentation, we will describe a new technique for determining simultaneously the real and imaginary components of the complex atomic form factor. The technique used Fourier Transform Holography with an extended reference and applicable to both crystalline and amorphous samples. Details of an application of the technique in spectroscopy mode to obtain the X-ray Complex Fine Structure across the copper K-edge will be discussed.