Room-temperature superconductivity has been a century long-held dream of mankind and a focus of intensive research. Recent progress on findings of room-temperature superconductors among superhydrides stabilized at high pressure conditions is remarkable. Focus is placed on a class of clathrate superhydrides, the best ever-known family of superconductors, that exhibit extraordinarily high-T_c superconductivity (e.g., T_c = 260 K for LaH₁₀ [1-4]).

The first-ever clathrate structure in superhydride is proposed in CaH₆ [5] by my group that shows a potential of high-T_c superconductivity at about 235 K. This clathrate structure accepts the emergence of unusual H cages, in which H atoms are weakly covalently bonded to one another, with Ca atoms occupying the centers of the cages. The high-T_c superconductivity is arising from the peculiar H clathrate structure.

We recently found a common rule of the formation of superconducting clathrate structures in rare earth (RE, e.g., Sc, Y, La, Ce, Pr., etc) superhydrides accompanying the occurrence of three different stoichiometries of REH₆, REH₉, and REH₁₀, some of which exhibit extraordinarily high-T_c superconductivity [1]. Subsequent experiments [3,4,6,7] indeed synthesized the as-predicted clathrate superhydrides YH₆, YH₉, and LaH₁₀ with measured T_c values at 224, 243, and 260 K, respectively, setting up new T_c records among known superconductors. These discoveries open the door of achieving superconductors that could work at room temperature (300 K) in superhydrides.

In the talk, I will give an overview on the status of research progress on superconductive superhydrides, and then discuss the design principle for achieving room-temperature superconductor. Our prediction on a hot superconductor (T_c at ~400 K) in a clathrate superhydride Li₂MgH₁₆ [8] together with future research direction will be discussed.

References:

[1] Peng et al., PRL 119, 107001 (2017).

[2] Liu et al., PNAS 114, 6990 (2017).

[3] Somayazulu et al., PRL 122, 027001 (2019).

[4] Drozdov et al., Nature 569, 528 (2019).

[5] Wang et al., PNAS 109, 6463 (2012).

[6] Kong et al., arXiv 1909.10482 (2019) ; Snider et al., PRL 126, 117003 (2021).

[7] Troyan et al., Adv. Mater. 33, 2006832 (2021).

[8] Sun et al., PRL 123, 097001 (2019).

Biomineralization is the fascinating capability of living organisms to produce hard tissue. It integrates complex physical and chemical processes controlled by the organisms through ionic concentration regulation and organic molecules production. The ability to tune, from ambient conditions crystallisation, the structural, optical and mechanical properties of these hard tissues motivates extensive research to develop and transfer biomimetic approaches into material science studies. In paleoclimatology, where marine biomineral tests are used as paleo-tracers, understanding the biomineralization mechanisms is a key factor for improving the accuracy of thermal records. All these urge a detailed description of the underlying processes at play in biomineralisation.

Remarkably, most crystalline biominerals presents a sub-micrometric organo-mineral granular organization associated to crystallization kinetics, which involve different mineral polymorphs. While these features clearly point towards biomineralisation mechanisms escaping from the classical crystallisation theory (i.e., described as the addition of individual ions or molecules from a solution to a final bulk crystal), the specific pathways are however still subject to intense debates [1]. Providing a full description of the biomineralization pathways requires a multidisciplinary approach at the interface between biology, chemistry and physics, in order to identify not only the different minerals and organic molecules involved along the mineralization process, but also characterize the morphology of these constituents, the successively appearing polymorph phases and the nature of the different phase transitions. In this presentation, I will focus on this last aspect, making use of two crystalline microscopy approaches we have developed, optical vectorial ptychography [2] and x-ray Bragg ptychography [3].

Optical vectorial ptychography is a microscopy approach sensitive to the optical anisotropy of materials, among which birefringence. In the context of biomineralisation, it was used to characterize extended 2D crystals and evaluate their crystalline properties (orientation distribution, disorder, etc…), thanks to a lab-based experimental set-up. X-ray Bragg ptychography requires the use of a nano-diffraction set-up at a synchrotron source (such as ID13 - ESRF) and delivers 3D maps of crystalline properties, including strain, tilts and crystalline coherence. With these crystalline microscopy approaches, we were able to shed new light on the characteristics of early-mineralized units from calcareous mineralizing specie, the Pinctada margarita mollusc shell. The confrontation of the observed crystalline properties with the ones obtained on well-defined synthetic model films allowed us to discuss the nature of the amorphous to crystalline transition in biominerals.

[1] J. J. De Yoreo, et al., Science 349, aaa6760 (2015).

[2] P. Ferrand, et al., Optics Letters 43, 763 (2018).[3] F. Mastropietro, et al., Nature Materials 16, 946 (2017). S. O. Hruszkewycz, et al., Nature Materials 16, 244 (2017).

This project has received funding from the European Research Council (ERC) under the European Union’s Horizon H2020 research and innovation program grant agreement No 724881. The author thanks all collaborators from Fresnel Institute, CEA-NIMBE, Ifremer and ESRF for their participation to this work.

In each human cell, only a subset of the genes is transcribed into RNA and translated into proteins, because gene expression is tightly regulated. The regulation of gene expression is a complex process involving several hierarchical stages, beginning in the nucleus with the control of transcription initiation by transcription factors. After maturation, mRNAs are translocated into the cytosol, where their stability, translation and, ultimately, degradation is under the control of RNA-binding proteins. The central event at all stages of gene expression regulation involves the recognition of DNA or RNA sequence motifs by transcription factors or RNA-binding proteins. Structural studies in my laboratory have highlighted crucial aspects of transcriptional and translational regulation. Transcriptional target gene recognition in bacteria (1) and eukaryotes (2,3) proceeds according to common principles, but differs in crucial aspects. Half-life and translation of mRNAs are controlled by proteins often binding to the 3’-untranslated regions of mRNAs. RNA-binding proteins studied in my laboratory promote mRNA degradation by recruiting nucleolytic degradation complexes (4,5) or through their intrinsic ribonuclease activity (6).

References

1. Khare, D. et al. (2004) Sequence-specific DNA binding determined by contacts outside the helix-turn-helix motif of the ParB homolog KorB. Nat. Struct. Mol. Biol. 11, 656-663
2. Schuetz, A. et al. (2011) The structure of the Klf4 DNA-binding domain links to self-renewal and macrophage differentiation. Cell. Mol. Life Sci. 68, 3121-3131
3. Ming, Q. et al. (2018) Structural basis of gene regulation by the Grainyhead/CP2 transcription factor family. Nucleic Acids Res. 46, 2082-2095
4. Mayr, F. et al. (2012) The Lin28 cold-shock domain remodels pre-let-7 microRNA. Nucleic Acids Res. 40, 7492-7506
5. Schuetz, A. et al. (2014) Roquin binding to target mRNAs involves a winged helix-turn-helix motif. Nat. Commun. 5:5701
6. Garg, A. et al. (2021) PIN and CCCH Zn-finger domains coordinate RNA targeting in ZC3H1 family endoribonucleases. Nucleic Acids Res. 49, 5369-5381

Superoxide dismutases (SODs) are the major regulators of oxidative stress and therefore the first line of defense to protect organisms against metabolic- and environmentally-induced reactive oxygen species (ROS). Human mitochondrial manganese SOD (MnSOD) expression is modulated to prevent ROS-based damage, promote redox homeostasis and maintain proper cell signaling. Our research goal is to understand the molecular basis of how MnSOD uses coupled proton-electron transfers to dismute superoxide. For this, the 3D arrangement of all atoms is needed, most importantly the position of protons. Our recent technical advancements with neutron crystallography at Oak Ridge National Laboratory have overcome the limitations of X-ray crystallography – revealing proton positions with high detail while also allowing control of the metal electronic state. In this research project, MnSOD neutron maps reveal the proton relays to the active site metal and the protonation states of metal-bound ligands. Our results demonstrate the transfer of protons to the bound active site solvent that is triggered by the reduction of the active site manganese. This proton transfer involves unusual active site amino acid pKas, at least five low barrier hydrogen bonds, glutamine tautomerization and a water bridge in the active site channel.

Copper-containing nitrite reductases (CuNiRs) that convert NO₂ to NO are of central importance in nitrogen-based energy metabolism [1]. These metalloenzymes, like all redox enzymes, are very susceptible to radiation damage from the intense synchrotron radiation by X-rays, that are used to obtain structures at high resolution. Understanding the chemistry that underpins the enzyme mechanisms in these systems usually requires atomic resolutions of better than 1.2 Å. The damage-free structure of the resting state of one of the most studied CuNiRs was obtained by X-ray free-electron laser (XFEL) and neutron crystallography, which allows direct comparison of neutron, XFEL structural data [2] and atomic resolution X-ray structural data used to obtain the most accurate (atomic resolution with unrestrained SHELX refinement) structure.

It was demonstrated that Asp_CAT (Asp₉₈) and His_CAT(His₂₅₅) are deprotonated in the resting state of CuNiRs at pH values close to the optimum for activity (Fig.1).

References

[1] Zumft, W. G. (1997). Microbiol. Mol. Biol. Rev. 61, 533

[2] Halsted, T.P., Yamashita, K., Gopalasingam, C. C., Shenoy, R.T, Hirata, K., Ago, H., Ueno, G., Blakeley, M.P., Eady, R R.; Antonyuk, S.V., Yamamoto, M., Hasnain, S. S. (2019). IUCrJ 6, 761

Acknowledgement; Moulin M.; Haertlain,M.; Blakeley, M.P.; Halsted, T.P.; Yamashita, K.; Gopalasingam, C,;. C.;Hirata, K; Ago, H.; Ueno, G.; Eady, R R.; Yamamoto, M. and Hasnain S.S

Hydrogen (H) atoms often play essential roles in enzymatic reactions as they are responsible for the reversible protonation of active site residues and for the organization of the solvent network. More generally, hydrogens are also necessary for the establishment of H-bonds which, in turn, stabilize interactions between macromolecules and between macromolecules and their ligands. Although H atoms represent a large fraction of the total atomic content of macromolecules their direct visualization is not straightforward. Even at (sub-) atomic resolution (<1.2 Å), X-ray macromolecular crystallography (MX), the most common technique for structural determination, affords the localization of only a small percentage of H atoms as their contribution to the total scattering is minimal owing to their low electron content. Differently from MX, neutron macromolecular crystallography (NMX) relies on the interaction between neutrons and atomic nuclei. With this technique the visualization of H atoms is possible even at modest resolution (2.0 - 2.5 Å). In fact, NMX maps indicate the nuclear positions of H atoms while MX maps show the positions of valence-electron density for H atoms shifted along the bond vector. Recently, single particle cryo-electron microscopy (cryo-EM) achieved atomic resolution protein structure determination [1, 2] . Nakane et al. determined apoferritin and the GABA A receptor structures at 1.22 and 1.7 Å resolutions, respectively. H density peaks can be seen even at 1.7 Å, unlikely in MX experiments. Interestingly, cryo-EM/electron diffraction experiments inform on both nuclear and electron localization of H atoms.

Our research is focused on the modelling and refinement of H atoms by using different experimental data (cryo-EM, neutron and electron diffraction) integrated in a common framework, in order to provide new insights in biological processes such as enzyme mechanisms. New features in the crystallographic refinement package REFMAC5 [3], one of the flagships of the scientific CCP4 computational suite, have been developed and will be presented. CCP4 Monomer Library [4] has been implemented for more accurate H atom positions derived from neutron data analysis [5] and Quantum Mechanics (QM) calculations. Recent developments in REFMAC5 and relative tools for the refinement of structural models obtained by neutron diffraction data will also be presented.

[1] Nakane, T., Kotecha, A., Sente, A., McMullan, G., Masiulis, S., Brown, P. M. G. E., Grigoras, I. T., Malinauskaite, L., Malinauskas, T., Miehling, J., Uchański, T., Yu, L., Karia, D., Pechnikova, E. V., De Jong, E., Keizer, J., Bischoff, M., McCormack, J., Tiemeijer, P., Hardwick, S. W., Chirgadze, D. Y., Murshudov, G., Aricescu, A. R. & Scheres, S. H. W. (2020). Nature 587, 152.

[2] Yip, K. M., Fischer, N., Paknia, E., Chari, A. & Stark, H. (2020). Nature 587, 157.

[3] Kovalevskiy, O., Nicholls, R. A., Long, F., Carlon, A. & Murshudov, G. N. (2018). Acta Cryst. D74, 215.

[4] Vagin, A. A., Steiner, R. A., Lebedev, A. A., Potterton, L., McNicholas, S., Long, F. & Murshudov, G. N. (2004). Acta Cryst. D60, 2184.

[5] Allen, F. H. & Bruno, I. J. (2010). Acta Cryst. B66, 380.

Finding the Goldilocks zone for chemical crystallography via Laue single-crystal neutron diffraction – what have we learned from KOALA to improve KOALA 2.0?

A.J. Edwards, R.O. Piltz

Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organization,

New Illawarra Rd, Lucas Heights, N.S.W., Australia

Alison.Edwards@ansto.gov.au

KOALA is a single-crystal Laue neutron diffractometer standing at the end of guide position of the supermirror guide TG3 at the OPAL reactor, ANSTO. The instrument was initially modelled closely on VIVALDI[1], an instrument available in the user program at the ILL from 2001-2010. The elegantly simple concept of the instrument employs a cylindrical neutron sensitised image plate detector which is used to record a series of diffraction images from a suitable number of crystal positions to provide a sufficient data set from which valid model parameters can be derived to answer questions regarding material properties which cannot be adequately derived from more readily available methods, most particularly X-ray diffraction and more recently the hybrid methodology of quantum crystallography.

Our initial practice with the instrument adhered largely to that shared with us by the scientists at the ILL. This early experience[2] was the commencement of a steep learning curve which has, with a very limited number of other instruments brought single-crystal neutron diffraction into greater use in chemistry and chemical crystallography in the second decade of the 21st century. Key developments have been (i) the installation of an Oxford Cryosystems COBRA™ nitrogen cryostream which facilitates handling of oxygen and moisture sensitive compounds (which encompass a significant fraction of the proposals received for the instrument) and (ii) the development of a user accessible data reduction for the diffraction images. From the first proposal round for the instrument in 2009 exciting chemistry was proposed for experiments which exceeded the nominal maximum primitive unit cell volume for the recording of useful diffraction images. A simple work around for this has been to reduce the resolution of the images by manipulation of the temperature at which they are recorded – in order to obtain data against which a model may be refined.

More commonly though, it is observed that crystals for which the unit cell volume is relatively large tend, where they can be grown to a size sufficient for Laue neutron diffraction, to have a mosaic spread which limits the resolution of the pattern observed without manipulating the temperature to further reduce the resolution.

With careful attention to experimental detail and the availability of discretionary beam-time access it has been possible to undertake studies of important new materials in timeframes which have resulted in the publication of the single-crystal neutron diffraction study with the chemistry it underpins, rather than as a stand alone paper reporting only the neutron study result. It is of particular importance to note that in the case of hydride containing compounds, it can be critical to prove the location of the hydride via neutron diffraction and even a low resolution study can provide the necessary proof. In consequence of their publication with the chemistry, papers from KOALA are now submitted to and published in journals of the highest standing [4-7].

Having achieved a more routine applicability of neutron diffraction in chemical crystallography, we reached a point where elctronic components of KOALA had exceeded their serviceable lifespans and contemplation of replacing this aspect of the instrument led us to realise that reworking the existing mechanical elements with new electronics posed significant challenges and would cost a large fraction of the potential cost of building a new instrument. We are fortunate that the decision was reached to design a new instrument which is allowing us to optimise key design elements to yield maximum flexibility of the instrument across all of its possible applications in chemistry, physics, materials science and crystallography. The instrument is currently under construction and should be available for users in the second half of 2022.

[1] C Wilkinson, JA Cowan, DAA Myles, F Cipriani, GJ Mclntyre, (2002), Neutron News, 13, 37-41.

[2] AJ Edwards, (2011) Australian Journal of Chemistry 64, 869-872

[3] RO Piltz,(2018) Journal of Applied Crystallography 51, 635-645 and 963-965

[4] M Garçon, C Bakewell, GA Sackman, AJP White, RI Cooper, AJ Edwards, MR Crimmin (2019) Nature 574 , 390-393

[5] SJ Bonyhady, D Collis, N Holzmann, AJ Edwards, RO Piltz, G Frenking, A Stasch C Jones, (2018) Nature Comms 9 , 3079

[6] JAB Abdalla, A Caise, CP Sindlinger, R Tirfoin, AL Thompson, AJ Edwards, S Aldridge, (2017) Nature chemistry 9, 1256-1262

[7] R Chen, G Qin, S Li, AJ Edwards, RO Piltz, I Del Rosal, L Maron, D Cui, J Cheng Angewandte Chemie 132, 11346-11351

Keywords: neutron diffraction; Laue diffraction; chemical crystallography; instrumentation; structure

Single-crystal neutron scattering experiments have the advantage compared to X-ray experiments that it is possible to get positions for hydrogen atoms – typically replaced by deuterons in neutron protein crystallography. The hydrogens are important because they constitute approximately half of the atoms in a protein and determine the directionality of hydrogen bonds, which are key to the structure and function [1]. Therefore, neutron crystallographic experiments give important additional information to the model. However, adding all hydrogens by hand to the model is a tedious and error-prone work and most software add hydrogens at positions suggested by a statistical analysis of neutron structures and not based on the measured data. Moreover, it is important to decide for each hydrogen atom whether its position is supported by the experimental data or not.

To solve these problems, we developed an automatised procedure that places all hydrogen atoms of a protein based on local integration of the neutron 2mF_o – DF_c map. For each putative hydrogen atom, we search for the highest integrated value of the nuclear scattering length density within a sphere of the covalent radius of hydrogen. For some hydrogens, the position is dictated by the positions of the surrounding heavy atoms. However, many hydrogens can be anywhere on a circle (e.g. OH, SH and NH₃ groups) and we search all possible positions systematically for the highest integrated density. Likewise, we consider possible flips of Asn and Gln residues, we consider six possible states of His residues, and we consider alternative protonation states of Asp, Glu, Lys, Tyr and Cys residues. The method is calibrated to available neutron structures and the number of favourable hydrogen bonds are evaluated.

[1] Engler, N., Ostermann, A., Niimura, N., & Parak, F. G. (2003). Hydrogen atoms in proteins: positions and dynamics, Proc. Natl. Acad. Sci. U.S.A., 100(18), 10243-10248.

Harnessing the spin dependence of the neutron scattering cross section for hydrogen, Dynamic Nuclear Polarization (DNP) is a potentially powerful technique for neutron diffraction measurements, especially for biological systems. Polarizing the neutron beam and aligning the proton spins in a polarized sample modulates and tunes the coherent and incoherent neutron scattering cross-sections of hydrogen [1], in ideal cases maximizing the scattering from - and visibility of - hydrogen atoms in the sample while simultaneously minimizing the incoherent background to zero (see Figure 1).

ORNL has developed a prototype system for the purpose of performing proof-of-concept Neutron Macromolecular Crystallography measurements which highlight the potential of DNP [2]. We will describe DNP concepts, experimental design, labelling strategies and the most recent results, as well as considering future prospects for data collection and analysis that these techniques enable.

The fine details of the electron density distribution, typically far beyond the possibilities of standard X-ray diffraction analysis, can be approached when (ultra)high-resolution diffraction data are available, to allow abandoning the standard model of independent, spherically symmetrical atoms. This more complicated, and much more demanding (both experimentally and computationally) method allows, for instance, to analyze the redistribution of electron density into bonds, intermolecular interactions, etc. Moreover, the Atoms-In-Molecules approach, which is based on the analysis of topological features of high-quality electron density distribution, may offer an insight into the hierarchy of interactions, energetic features, etc. Even though such an approach is well-developed for small molecules, its application in macromolecular crystallography is still under development. Ultrahigh resolution in this case means resolution of at least 0.7 – 0.65 Å. Such data are extremely rare for macromolecular crystals. In addition, modelling problems, disorder, high solvent content, etc., severely limit the number of successful studies of experimental electron density distribution in macromolecules, which so far have been reported for proteins only (e.g. crambin [1], aldose reductase [2] and the high-potential iron–sulfur protein [3]).

For the present study, ultrahigh-resolution diffraction data (0.55 A) were collected for a Z-DNA hexamer with the sequence d(CGCGCG)₂. The results of the high-quality standard refinement [4] suggested that bonding and other features are visible in the difference electron density map (Fig). The quality of these data indeed allows the application of the more sophisticated multipolar model.

Fig. 1. The Watson–Crick base pair C3×G10 with the corresponding Fo map (blue, 3s) and difference Fo-Fc map (green, 2s) calculated without the contribution of H atoms.

The multipolar model has been successfully constructed and the drop in the R factor (and R free) seems to show that real experimental features have been included in this model. The topology of the electron density distribution has been analyzed and the intra- and intermolecular interactions characterized. A number of problems related to the multipolar approach, together with some expected and some unexpected results (e.g. unusual disorder of one of the C bases) will be presented. We will also consider the practical question concerning this kind of research: is the additional burden and investment of effort justified by the results?

[1] C. Jelsch, M. M. Teeter, V. Lamzin, V. Pichon-Pesme, R. H. Blessing, C. Lecomte. PNAS 97, 3171-3176 (2000).

[2] B. Guillot, C. Jelsch, A. Podjarny, C. Lecomte. Acta Cryst. D64, 567-588 (2008).

[3] Y. Hirano Y, K. Takeda, K. Miki. Nature 534, 281–284 (2016).

[4]K. Brzezinski, A. Brzuszkiewicz, M. Dauter, M. Kubicki, M. Jaskolski, Z. Dauter. Nucleic Acids Res. 39, 6238-6248 (2011).

One of the kinds of information gained from high resolution (sub-atomic) structures is the observation that electron density parameters are transferable between atoms having similar chemical topology. This stimulated creation of databases of multipolar pseudoatoms (Invariom [1], ELMAM2 [2], MATTS – successor of UBDB [3], etc.) and their applications in (a) structure refinements on standard (atomic) resolution data for small-molecule crystals, and (b) electrostatic properties and non-covalent bonding characterisations for macromolecules.

Transferable Aspherical Atom Model (TAAM) of scattering built from a pseudoatom database proved to be advantageous in refining the structure on X-ray diffraction (XRD) data compared to the Independent Atom model (IAM) [4], leading to better fit of the model to the data and improved localization of hydrogen atoms. We have recently showed [5] that also for small-molecule 3D electron diffraction (3D ED) data, a better model-to-data fit and more accurate structures should be expected from TAAM.

To improve its usability, we further extended the MATTS bank to cover 98% of atoms found in all the structures deposited in the Cambridge Structural Database [6] composed of chemical elements like C, H, N, O, P, S, F, Cl and/or Br. It is planned that the remaining 1% will be covered by the more general atom types resulting from multidimensional cluster analysis.

Some benefits of TAAM over IAM refinements were also reported for macromolecular XRD data of 0.9 Å resolution and better [7]. As most macromolecular crystals diffract to lower resolutions, we recently moved our investigation towards near-atomic resolutions. We quantified the differences between the macromolecular electron density Fourier maps obtained with TAAM and IAM, calculated with a resolution of 1.8 Å. We did the same for electrostatic potential maps, a key property in the context of 3D ED.

TAAM refinements affect not only the positions of the atoms, but also the atomic displacement parameters (ADPs) [8]. ADPs appears to be less resolution dependent with TAAM than with IAM. With IAM, ADPs increased for XRD and decreased for 3D ED by about 30%, when the resolution was reduced from 0.6 Å to 0.8 Å [5]. From modified Wilson plots we recently predicted, and then verified by TAAM refinements on macromolecular XRD or 3D ED data, what will happen with ADPs (B-factors) with a further resolution worsening, up to 1.8 Å.

All the above helps to understand if there will be any benefits of TAAM refinements on lower than atomic resolutions.

[1] Dittrich, B., Hübschle, C. B., Pröpper, K., Dietrich, F., Stolper, T. & Holstein, J. (2013). Acta Crystallogr. B 69, 91. [2] Domagała, S., Fournier, B., Liebschner, D., Guillot, B. & Jelsch, C. (2012). Acta Crystallogr. A 68, 337. [3] Kumar, P., Gruza, B., Bojarowski, S. A. & Dominiak, P. M. (2019). Acta Crystallogr. A 75, 398. [4] Jha, K. K., Gruza, B., Kumar, P., Chodkiewicz, M. L. & Dominiak, P. M. (2020). Acta Crystallogr. B 76, 296. [5] Gruza, B., Chodkiewicz, M., Krzeszczakowska, J. & Dominiak, P. M. (2020). Acta Crystallogr. A 76, 92. [6] Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Crystallogr. B 72, 171. [7]. Malinska, M. & Dauter, Z. (2016). Acta Crystallogr. D 72, 770. [8]. Sanjuan-Szklarz, F. W., Woińska, M., Domagała, S., Dominiak, P. M., Grabowsky, S., Jayatilaka, D., Gutmann, M., Woźniak, K. (2020). IUCrJ, 7, 920.

Keywords: quantum crystallography; structure refinement; X-ray diffraction, electron diffraction; 3D ED, microED, aspherical scattering factors; multipolar model; TAAM; MATTS; UBDB; ELMAM2

Support of this work by the National Centre of Science (Poland) through grant OPUS No.UMO-2017/27/B/ST4/02721 and PL-Grid through grant plgubdb2020 is acknowledged.

Lipases (E.C. 3.1.1.3) are ubiquitous hydrolases for the carboxyl ester bond of water-insoluble substrates such as triacylglycerols, phospholipids, and other insoluble substrates, acting in aqueous as well as in low-water media, thus being of considerable physiological significance with high interest also for their industrial applications. The hydrolysis reaction follows a two-step mechanism, or ‘interfacial activation’, with adsorption of the enzyme to a heterogeneous interface and subsequent enhancement of the lipolytic activity. Among lipases, Candida antarctica Lipase B (CALB) has never shown any significant interfacial activation, and a closed conformation of CALB has never been reported leading to the conclusion that its behaviour was due to the absence of a lid regulating the access to the active site. The lid open and closed conformations and their protonation states are observed in the crystal structure of CALB at 0.91 Å resolution [1]. Having the open and closed states at atomic resolution allows relating protonation to the conformation, indicating the role of Asp145 and Lys290 in the conformation alteration. Once positioned within the catalytic triad, substrates are then hydrolysed, and products released. However, the intermediate steps of substrate transfer from the lipidic-aqueous phase to the enzyme surface and then down to the catalytic site are still unclear. By inhibiting CALB with ethyl phosphonate and incubating with glyceryl tributyrate (2,3-di(butanoyloxy)propyl butanoate), the crystal structure of the lipid-enzyme complex, at 1.55 Å resolution, shows the tributyrin in the limbus region of active site [2]. The substrate is found above the catalytic Ser, with the glycerol backbone readily pre-aligned for further processing by key interactions via an extended water network with α-helix10 and α-helix5. These findings explain the lack of ‘interfacial activation’ of CALB and offer new elements to elucidate the mechanism of substrate recognition, transfer and catalysis of Candida antarctica Lipase B (CALB) and lipases in general.

[1] Stauch, B., Fisher, S. J., Cianci, M. (2015). Journal of Lipid Research, 56, 2348-2358.

[2] Silvestrini, L. & Cianci, M. (2020). International Journal of Biological Macromolecules, 158, 358-363.

Tryparedoxins are critical regulators of the redox metabolism in parasitic protozoa such as trypanosomones and leishmania, which cause the neglected tropical diseases sleeping sickness and leishmaniosis, respectively. Although tryparedoxins belong to the thioredoxin superfamily, they differ in their substrate specificity for the low molecular weight redox carrier, utilizing trypanothione, a spermidine-linked di-glutathione instead of glutathione. The unique nature of the redox carrier opens avenues for the targeted interference in the protozoan redox metabolism which hold potential for future therapeutic intervention.

We were able to obtain crystals of a tryparedoxin which have the potential to diffract to ultra-high resolution. Crystals of the oxidized protein diffract to well below 1 Å with our current highest resolution data set extending to 0.75 Å/0.85 Å resolution in the best/worst direction. Preliminary refinement indicated a mixture of oxidized and reduced states in the Cys-Pro-Pro-Cys active site with photoreduction of the disulfide bond being the reason for the appearance of the reduced state. Subsequent efforts resulted in crystal structures of the oxidized and reduced states, which at present extend to a more limited resolution in the 1 to 1.1 Å range. An analysis of the two redox states defines the redox linked conformational changes in the tryparedoxin family.

The maps of electrostatic potential from cryo-electron microscopy and micro-electron diffraction are now being obtained at atomic resolution. This extends the possibility of investigating the electrostatic potential beyond determining the non-hydrogen atom positions, taking into account also the negative regions of the maps. However, accurate tools to calculate this potential for macromolecules, without reaching to the expensive quantum calculations, are lacking. Simple point charges or spherical models do not provide enough accuracy. Here, we apply the multipolar electron scattering factors and investigate the theoretically-obtained potential maps.

The multipolar electron scattering factors are derived from the aspherical atom types from Multipolar Atom Types from Theory and Statistical clustering (MATTS) databank (successor of UBDB2018 [1]). MATTS has been created since electron densities of atom types are transferable between different molecules in similar chemical environment. These atom types can be used to recreate the electron density distribution of macromolecules via structure factors [2] and to calculate the accurate electrostatic potential maps for small molecules [3]. MATTS reproduces the molecular electrostatic potential of molecules within their entire volume better than the simple point charge models used in molecular mechanics or neutral spherical models used in electron crystallography. In this study, we calculate electrostatic potential maps for several chosen macromolecules using aspherical atom databank and compare them with experimental maps from cryo-electron microscopy and micro-electron diffraction at high resolution. Calculations at different resolutions reveal at which spatial frequencies different elements become discernible. We also consider the influence of atomic displacement parameters on the theoretical maps as their physical meaning in cryo-electron microscopy is not as well established as in X-ray crystallography.

This study could potentially pave the way for distinguishing between different ions/water molecules in the active sites of macromolecules in high resolution structures, which is of interest for drug design purposes. It could also facilitate the interpretation of the less-resolved regions of the maps and also advise in simple yet questionable issue of resolution definition in cryo-electron microscopy.

The authors acknowledge NCN UMO-2017/27/B/ST4/02721 grant.

References:

[1] Kumar et al. (2019). Acta Cryst. A75, 398-408

[2] Chodkiewicz et al. (2018). J. Appl. Cryst. 51, 193-199

[3] Gruza et al. (2019), Acta Cryst. A76, 92-109

Nanocarbon materials show attractive functions in device applications, however the structural deviations and ambiguity disturb understanding between the functions and the structures. We have worked on the synthesis of molecular nanocarbon materials based on a simple strategy of macrocyclization of aromatic units. The molecular structures and supramolecular integrated structures can be fully accessed at the precision of molecular level, and unparalleled functions derived from the unique structures were found.

For example, a macrocyclic hydrocarbon molecule, [6]cyclo-2,7-naphthylene ([6]CNAP), synthesized by single bond linkage of six naphthylene units (Figure 1a) has a cyclic structure equivalent to an atom-defective structure of graphene [1]. In this study, [6]CNAP was applied to a negative electrode active material for a rechargeable lithium battery, where graphite is conventionally and commercially used as the material. All-solid-state lithium battery with LiBH₄ as electrolyte was constructed with three layers simply by uni-directional pressing: the composite electrode with [6]CNAP, acetylene black (AB) and LiBH₄ | LiBH₄ | Li (Figure 1b and c). Depending on purification methods, the recyclability of the rechargeable batteries largely differed. Surprisingly, highly purified specimen by sublimation method showed poor recyclability, and the recrystallized specimen from organic solvents showed stable recyclability up to 65 discharge-charge cycles and around twice battery capacity than a graphite electrode. We found that the differences in battery performance were originated from the molecular packing structures in solid states by powder X-ray structural analyses with Rietveld refinement. The key for the high battery performance is the one-dimensional nanopores constructed from the assembly of the central pore of [6]CNAP and π-stacks of naphthylene units. The quantitative battery performance results and the precisely determined packing structures showed that lithium ion is stored by the intercalation between naphthylene units and also in the one-dimensional nanopores to afford the high battery capacity. We successfully revealed the relationship between unique packing structures and battery performance [2].

[1] Nakanishi, W., Yoshioka, T., Taka, H., Xue, J. Y., Kita, H. & Isobe, H. (2011). Angew. Chem. Int. Ed. 50, 5323.

[2] Sato, S., Unemoto, A., Ikeda, T., Orimo, S. & Isobe, H. (2016). Small 12, 3381.

Recently, the traditional way of perceiving crystalline matter as static and brittle has started to change, and nowadays we are witnessing a growing number of examples where crystals display a plethora of flexible response to a variety of stimuli. They were found to move, jump, split, flex, twist, curl, explode, or to display a salient behaviour under UV radiation or heating, but lately, they were also found to respond to the applied external mechanical force [1]. Organic molecular crystals present a majority of examples of crystal adaptability to external stimuli, whilst metal-organic adaptable crystals are still quite rare. In the first report on the mechanical flexibility of coordination polymers, we have shown that crystals of a family of Cd(II) coordination polymers are capable of displaying not only exceptional mechanical elasticity but also variable flexible responses to applied external pressure [2]. They can actually differently tolerate exerted force and the different tolerability is a result of slight differences in the importance of intermolecular interactions in crystal packing.

We aim to understand the feature more deeply and to shed light on the underlying principles of the phenomenon, we have recently discovered unprecedented difference in plasticity of crystals of closely related class of Cd(II) coordination polymers [3]. In addition to variable plasticity, crystals also display remarkable pliability and ductility, not hitherto observed for metal-containing molecular crystals, which we present herein. To understand the phenomenon and rationalize observations, in addition to micro-focus SCXRD and AFM, we have also performed a series of custom-designed experiments and complemented those with an in-depth theoretical analysis. The results pointed at intermolecular interactions as the crucial structural feature in determining the type and extent of these highly unusual mechanical responses of crystalline metal-based polymeric materials.

[1] Commins, P., Israel Tilahun Desta,†Durga Prasad Karothu,† Panda, M. K. & Naumov, P. (2016) Chem. Commun. 52,13941.

[2] Đaković, M., Borovina, M., Pisačić, M., Aakeröy, C. B., Soldin, Ž., Kukovec., B.-M., Kodrin, I. (2018) Angew. Chem. Int. Ed. 130, 15017.

[3] Pisačić, M., Biljan, I., Kodrin, I., Popov, N., Soldin, Ž., Đaković, M. Chem. Mat. accepted.

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

At present, the functional materials structurally switchable by stimuli such as heat, the addition of cations, changes of pH, pressure, or light are the motive of innumerable studies to be ideal models to investigate the relation structure-function and new properties derived from that change. In this work, we studied a family of spirorhodamines (SRAs) in solid-state photochemical reactions. These are photochromic molecules with a switching mechanism based on the differences in the fundamental electronic state between isomers.[1] It involves changes in the molecule structure and is thermally reversible.[2,3] In this work, assuming as the hypothesis that in solid-phase the permanence time in the optically active isomer is associated with its structural characteristics, a family of compounds modifying the substituent was synthesized.

These equilibria were characterized in solid-state by reflection, absorption and emission fluorescence spectroscopy, single-crystal X-ray diffraction,[4] atomic force microscopy coupled to infrared spectroscopy[4] and computational calculations, evaluating the changes produced after irradiating the corresponding close isomer with ultraviolet light for each compound.

[1] Dürr, H., Bouas-Laurent, H. (2003) Photochromism: Molecules and Systems, Eds.

[2] Di Paolo, M., Bossi, M. L., Baggio, R. and Suarez, S. A. (2016) Acta Crystallogr. Sect. B Struct. Sci. Cryst. Eng. Mater., 72, 684.

[3] Di Paolo, M., Boubeta, F., Alday, J., Michel Torino, M., Aramendía, P., Suarez, S.* and Bossi, M.* (2019) J. Photochem. Photobiol. A,. 384, 112011.

[4] Brazilian Synchrotron Light Laboratory (LNLS) beamlines MX2 and IR1.

In this work, the effects of pressure and temperature on the nonlocalized two-electron multicentric covalent bonds (‘pancake bonding’) in closely bound radical dimers were probed by single-crystal X-ray diffraction on a 4-cyano-N-methylpyridinium salt of 5,6-dichloro-2,3-dicyanosemiquinone (DDQ∙4CN) and I-methylpyridinium salt of tetrabromosemiquinone radical anion (Br₄Q∙NMePyr) as the sample compounds.

The DDQ∙4CN crystal structure can be described as closely bound stacked dimers of radical anions with interplanar separation <3.2 Å, which is known as non-localized two electron covalent bonding. At ambient conditions, the stacks of pancake bonded radical anions are formed by two types of distances: short intra-dimer and long inter-dimer contacts. On cooling, the anisotropic structural compression was accompanied by continuous changes in molecular stacking; the discontinuities in the changes in volume and b and c cell parameters suggest that a phase transformation occurs between 210 and 240 K. At a pressure of 2.55 GPa, both distances between radical dimers shortened to 2.9 Å, and become roughly equal, which corresponds to distances observed in extended-bonded polymers. Increasing pressure further to 6 GPa reduced the interplanar separation of the radicals to 2.75 Å, which may indicate that the covalent component of the interaction significantly increased [1]. The linear strain analysis shows that most deformations of pressure and temperature occur in the direction of pancake bonding.

The Br₄Q∙NMePyr crystal structure is built of infinite stacks of equidistant radical anions with no Peierls distortion [2]. On cooling the structure is compressed monotonically, the distance between radicals changes non-linearly, compress to <3.3 Å, but the space group remains the same. Upon pressure, the structure is compressed monotonically with no phase transformations in all the pressure range (0 – 6.0 GPa), the lowest interplanar distance is <2.9 GPa, which may indicate the increase of the covalent component in pancake bond and a significant decrease of the electron jumping barrier which may influence semiconductivity.

Azulene is a dark-blue, polar, bicyclic aromatic hydrocarbon (Figure 1) that is a non-benzenoid isomer of naphthalene. In addition to its long-standing medicinal and pharmaceutical relevance, the polar nonbenzenoid aromatic framework of azulene constitutes an attractive building block in the design of redox-addressable, optoelectronic, and conductive materials. This presentation will highlight our recent developments in the chemistry of hybrid metal/azulene platforms featuring isocyanide and thiolate junctions X along their molecular axis (Figure 2).

Figure 1. Electronic structure of azulene: resonance forms Figure 2. Two ways of functionalization of azulene at 2- and and origin of a molecular dipole. 6- positions that are important for its fixation on a solid support.

Single crystal X-ray structural analysis of a series of novel 2,6-functionalized azulenes will be presented [1,2]. In particular, heterobimetallic ensembles that incorporate the first examples of a conjugated p-bridge equipped with both isocyanide and thiol junction groups in the same molecular linker will be discussed (e.g., Figure 3B).

Figure 3. Two different functional groups – isonitrile and thiol – used for chemical modification of azulenes.

[1] Applegate, J.C.; Okeowo, M.K.; Erickson, N.R.; Neal, B.M.; Berrie, C.L.; Gerasimchuk, N.N.; Barybin, M.V. (2016) Chem. Sci., 7, 1422–1429. [2] Hart, M.D.; Meyers, J.J.; Wood, Z.A.; Nakakita, T.; Applegate, J.C.; Erickson, N.R.; Gerasimchuk, N.N.; Barybin, M.V. (2021). Molecules, 26, 981. https://doi.org/10.3390/molecules26040981

To investigate the salt formation of acridine with 4-amino salicylic acid (I), 5-chloro salicylic acid (II) and hippuric acid (III), the single crystal X-ray structure analysis have been performed. The present study allows to understandthe effect of molecular conformation adopted by acridine with hydroxyl group during the stabilization of crystal packing of these salt molecules, and to quantify the propensity of the intermolecular interactions to form the supramolecular assembly. The analysis of atom to atom or residue to residue contacts remains a favoured mode of analyzing the molecular packing in crystals. More importantly, they complement each other and are giving the complete picture of how these molecules assemble in molecular crystals. Hirshfeld surfaces, fingerprint plots and enrichment ratios were generated and further analyzedthe intermolecular interactions, and evaluatedtheir quantitative contributions to the crystal packing of the above saidthree salt molecules (I,II & III). The non-covalent interactionisosurfaceshave employed here, which allowsvisualizing where the hydrogen bonding and dispersion interactions contribute within the crystal.

Oxide ion conductors, used in separation membranes, electrolysers and fuel cells, are typically three dimensional isotropic materials, providing fast ion diffusion pathways. These are typically oxides that have been aliovalently substituted to enhance the concentration of mobile defects, most notably oxygen vacancies. One alternative strategy is to consider materials with anisotropic conduction pathways, and with excess oxygen, accomodated as interstitials. Based on this strategy we have recently investigated a series of oxides, including CeTaO4.17, CeNbO4+d (d = 0, 0.08, 0.25) and developed from this our interest in the structurally related La(Nb,W)O4+d compositions.

Each of these oxidised Ce based phases are known to adopt either a commensurate of incommensurate modulated structure, depending on the level of excess oxygen accommodated [1,2], but from a device perspective performed poorly as the Ce³⁺/Ce⁴⁺ ratio introduced undesriable electronic conductivity. In an effort to maintain the modulated structure(s), suppress electronic charge transport and enhance oxygen transport, we have targeted the LaNb_1-xW_xO_4+d sereis of materials. Our studies have developed the solid solution series phase chemistry and from application of X-ray, neutron and electron diffraction techniques, identified a sequence of modulated monoclinic and tetragonal phases. We have probed the ion transport of a select number of these phases, proving their capability as oxide ion conductors. We highlight the local structrure and variation in the coordination environments that facilitate the fast ion transport, offering routes to optimise and develop new functional oxides.

The collective motion of electrons has always been a fascinating topic in condensed matter physics. In charge density wave (CDW) systems, transport measurements were the first to provide a clear signature of the collective motion of condensed electrons. A non-linear conductivity is observed above a threshold current IT and is attributed to depinning of the CDW on impurities. An excess current then arises as well as a broad band noise and current oscillations. Although the electron density modulation involved in CDWs is very small, x-ray diffraction provides information about the structure of the CDW as it is associated with a periodic lattice distortion. We will show here how state-of-the art x-ray diffraction techniques - coherent and nanoprobe XRD - can reveal the different steps of CDW deformations, from pinning to sliding, in systems of increasing dimensions.

The structures of the rare earth metal polychalcogenides REX_2–δ (RE = La-Nd, Sm; Gd-Lu; X = S, Se, Te; 0 ≤ δ ≤ 0.2) attracted some attention due to their distorted square planar chalcogenide layer and the motives observed within these layers. All structures share a common structural motif of an alternating stacking of puckered [REX] and planar [X] layers (Figure 1a) and are closely related to the ZrSSi structure (space group P4/nmm), which is regarded as their common aristotype [1]. For electronic reasons, the planar [X] layer shows distortions from a perfect square net, forming dianions X₂^2– for the non-deficient REX₂. By reducing the chalcogenide content vacancies are observed within the planar layer, resulting in different superstructures for the REX_2–δ compounds depending on the vacancy concentration. For the sulfides and selenides this results in additional X^2– anions along vacancies to maintain a charge balanced layer. The tellurides, however, show different ordering patterns in the planar [Te] layer for the non-deficient RETe₂ compounds, but also a tendency to form larger anionic fragments for the deficient RETe_2–δ compounds, as seen for the commensurate structure of GdTe_1.8, e.g. [2].

LaTe_1.94 and LaTe_1.82 are two examples of different incommensurate crystal structures for RETe_2–δ compounds, separated by the number of vacancies in the planar [Te] layer [3, 4]. Both compounds share an average tetragonal unit cell with a ≈ 4.50 Å and c ≈ 9.17 Å, based on the structure of their aristotype (Figure 1a). The major difference of these compounds are their respective q vectors, which are compatible with tetragonal symmetry for LaTe_1.94, but indicate a loss of the fourfold rotational axis for LaTe_1.82, ending up in an orthorhombic superspace group. The [Te] layer of LaTe_1.94 is mainly composed of single vacancies (point defects), isolated Te^2– anions and Te₂^2– anions. LaTe_1.82 is more Te deficient and features adjacent vacancies in addition to Te₃^4– anions, to compensate for the missing charges (Figure 1b). To evaluate the formation of possible larger anionic fragments, like a bent Te₃^2– anion and the influence of additional vacancies to the structure, DFT based ELI-D real space analysis of approximant structures were performed (Figure 1c).

Figure 1. a) Average structure of LaTe_1.82; b) section of the modulated [Te] layer of LaTe_1.82; c) orthoslices of ELI-D of the Te layer of LaTe_1.82 with isocontour lines based on a commensurate approximant.

[1] Doert, T. & Müller, C. J. (2016). Reference Module in Chemistry, Molecular Sciences and Chemical Engineering, Elsevier.

[2] Poddig, H., Donath, T., Gebauer, P., Finzel, K., Kohout, M., Wu, Y., Schmidt, P. & Doert, T. (2018). Z. Anorg. Allg. Chem. 644, 1886–1896.

[3] Poddig, H., Finzel, K., Doert, T. (2020) Acta Crystallogr. Sect. C 76, 530–540.

[4] Poddig, H., Doert, T. (2020), Acta Crystallogr. Sect. B, 76, 1092–1099.

Ni-Mn-Ga-based Heusler alloys are broadly studied for their magnetic shape memory (MSM) functionality originating from coupling between ferroelastic and ferromagnetic orders. The ferroelastic order is established after martensitic transformation. Formed ferroelastic domains with different orientation are separated by twin boundaries. In modulated phases, these boundaries are extremely mobile and can be manipulated by magnetic field. Thanks to these, the single crystals of five-layered modulated 10M martensite of Ni-Mn-Ga exhibits magnetically induced reorientation (MIR) of ferroelastic (twin) domains in a moderate field of the order of 0.1 T [1, 2]. This results in 6 % magnetic field induced strain (MFIS) down to liquid helium temperature [3]. Such unique behaviour makes the 10M martensite a perfect candidate for applications in actuators, sensors and energy harvesters.

The ferroelastic microstructure represents a challenge for proper determination of martensite phase structure. Due to the modulated nature together with complex hierarchical twinning (compound and type I and II a/c twins; and non-conventional twins) [4, 5], the structure of the 10M martensite has not yet been completely solved. There is even an ongoing discussion about the nature of the modulation where two main concepts are considered: i) general crystallographic wave modulation approach, and ii) nanotwinning. As the structural modulation seems to be the critical factor for the extremely high twin boundary mobility [5], the problem is pressing.

Using the X-ray and neutron diffraction, we investigated on the character and temperature evolution of 10M martensite phase. We found transition from commensurate to incommensurate 10M modulated structure in Ni₅₀Mn₂₇Ga₂₂Fe₁ single crystal [6]. The modulation vector gradually increases upon cooling from commensurate q = (2/5) g₁₁₀, where g₁₁₀ is the reciprocal lattice vector, to incommensurate with q up to pseudo-commensurate q = (3/7) g₁₁₀. Further cooling results in transition to 14M with q = 2/7 g₁₁₀. Upon heating, reverse changes of the commensurate-incommensurate transition are observed with a thermal hysteresis of ≈ 60 K. We detected the same hysteretic behaviour in the electrical resistivity and the effective elastic modulus. Scanning electron microscopy showed that the changes are accompanied by the refinement of the a/b laminate.

Furthermore, we observed continuous modulation changes within the 10M martensite of wide range of Ni-Mn-Ga(-Fe) compositions that undergo the Austenite → 10M → 14M martensite transition sequence. Based on these observations, we suggest that the commensurate state is a metastable form of 10M martensite. Upon cooling, this phase evolves through nanotwinning into a more irregular and more stable incommensurate structure, further supported by recent high-resolution TEM observation [7].

[1] Ullakko, K., Huang, J. K., Kantner, C. & Handley, R. C. O. (1996) Appl. Phys. Lett. 69, 1966–8.

[2] Kellis, D., Smith, A., Ullakko, K. & Müllner, P. (2012) J. Cryst. Growth 359, 64-68.

[3] Heczko, O., Kopecký, V., Sozinov, A. & Straka, L. (2014) Appl. Phys. Lett. 103, 198-211.

[4] Straka, L., et al. (2011) Acta Mater. 59, 7450–63.

[5] Seiner, H., Straka, L. & Heczko, O. (2013) J. Mech. Phys. Solids 64, 072405.

[6] Veřtát, P., et al. (2021) J. Phys.: Condens. Matter, accepted, https://doi.org/10.1088/1361-648X/abfb8f

[7] Ge, Y. et al., "Transitions between austenite and martensite structures in Ni₅₀Mn₂₅Ga₂₀Fe₅ thin foil", available at: http://dx.doi.org/10.2139/ssrn.3813433

This work was supported by Operational Programme Research, Development and Education financed by the European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports, project number SOLID21 CZ.02.1.01/0.0/0.0/16_019/0000760. P.V. thanks for the support by the Grant Agency of the Czech Technical University in Prague, grant number SGS19/190/OHK4/3T/14. We acknowledge the Institut Laue-Langevin and the project LTT20014 financed by the Ministry of Education, Youth and Sports, Czech Republic, for the provision of neutron radiation facilities.

The tungsten bronzes are low-dimensional transition metal oxides of great interest for their electronic instabilities. They show exotic physical properties such as superconductivity and charge density wave (CDW) phases. An important subfamily is (PO₂)₄(WO₃)_2m, which is interesting for its optical/magnetic behaviours, where the band filling and CDW phases coupled in different way with the lattice. These properties can be tuned by m, the thickness of the perovskite-like WO₆ –octahedra block¹.

To understand the electronic instabilities, correlated to the nesting properties of the Fermi surface and the consequent CDW phases, we used the combination of two techniques: diffuse scattering (DS) and inelastic x-ray scattering (IXS). This allows rapid identification of the nature of diffuse features in the patterns and the study of the lattice dynamics. Three different members are chosen in order to show the evolution of the behaviour in the family. In this context, we will focus on the lattice dynamics and framework instability. The first member, m=2, presents a quasi-1D instability given by the WO₃-octahedra zig-zag chains, which are isolated by the phosphates. A CDW phase is found, T_C=270K, and it is linked to a rigid-body motion. Different behaviour can be found in the members m=6 and 8, where the instability is found in the WO₃ slabs, realised as correlated displacements of tungsten atoms along the octahedral 4-fold axis direction. The three members show different diffuse patterns, figure 1. The results are linked to the lattice dynamics behaviour, which present a Kohn anomaly above the transition temperature, however as predicted from the diffuse results, has a different Q- and temperature-dependence in each member.

[1] P. Roussel et al., Acta Cryst. B 57 (2001) 603-632

The novel aperiodic titanate Ba₁₀Y₆Ti₄O₂₇ has a thermal conductivity that equals the lowest reported for an oxide at room temperature. All of the atomic sites are described by crenel function occupancy modulations. The resulting localisation of lattice vibrations suppresses phonon transport of heat. Thus Ba₁₀Y₆Ti₄O₂₇ represensts a new lead material for low thermal conductivity oxides, the possibility of using the structural description to slect other new leads will be explored.

ABO₃ oxides have proven to accommodate a wide variety of chemical compositions, to crystallise with several structures in competition and to develop diverse physical properties. Hence, they are intensively studied in the search for new functional materials. Among them, the use of high-pressure and high-temperature synthesis techniques allows the stabilisation of the small Mn²⁺ cation in the larger A site. Some of the most exciting A-site manganites are spintronic (e.g. perovskite MnVO₃-II) or multiferroic (e.g. LiNbO₃-type MnTiO₃-II) [1,2]. Mixing different cations into the A and/or B sites induces cation order and further magnetic complexity. Recent studies on high pressure Mn₂BB’O₆ compounds have evidenced the accessibility to new structural derivatives, such as the double double perovskite structures (DDPv) or triple perovskites (TPv) with 1:2 order of the B-site cations [3,4]. The possibility to tune both structure and properties as a function of the chemical composition has also been observed, for instance in the Mn_3-xCo_xTeO₆ double perovskite – Ni₃TeO₆-type solid solutions [5].

Here we present a revision on the strongly frustrated magnetic structures of A-site manganites with ordered corundum or perovskite derivative structures (Fig.1). Among the corundum derivatives, magnetic frustration arises as a consequence of the stacking of honeycomb and/or triangular magnetic sublattices. In the case of the perovskite superstructures, it is usually the competition between several magnetic interactions and the combination of dⁿ with d⁰ /d¹⁰ cations what induces large frustration indexes. As a result of such frustration both types of polymorphs develop complex magnetic structures, including incommensurate helices, temperature dependent propagation vectors, elliptical and sinusoidal modulation of the magnetic moments, lock-in spin transitions and split of the main magnetic phase into coexisting ground states.

Figure 1. Representative examples of cation order and magnetic frustration in corundum (a) and perovskite (b) derivatives in high pressure A-site manganites. a) Stacked honeycomb/ triangular sublattices (top left), temperature dependence of the propagation vector in Co₃TeO₆ (right) with split into circular and elliptical helices (bottom left). b) DDPv and 1:2 TPv structures of MnRMnSbO₆ and Mn₃MnNb₂O₉ respectively with several magnetic interactions in competition. Complex thermodiffraction of Mn₃MnNb₂O₉ developing a SDW modulated structure and lock-in transition at low temperatures.

[1] Markkula, M., Arevalo-Lopez, A. M, Kusmartseva, A., Rodgers, J. A. Ritter, C., Wu, H. & Attfield J.P. (2011) Phys. Rev. B. 84, 094450.

[2] Arevalo-Lopez, A. M. & Attfield, J. P. (2013) Phys. Rev. B. 88, 104416.

[3] Solana-Madruga, E., Arévalo-López, A. M., Dos Santos‐García, A. J., Urones‐Garrote, E., Ávila‐Brande, D., Sáez‐Puche, R. & Attfield, J. P. (2016) Angew. Chem. Int. Ed. 55, 9340.

[4] Solana-Madruga, E., Aguilar-Maldonado, C., Ritter, C., Mentré, O., Attfield, J. P. & Arevalo-Lopez, A. M. (2021) Angew. Chem. Int. Ed. Under revision.

[5] Solana-Madruga, E., Aguilar-Maldonado, C., Ritter, C., Huvé, M., Mentré, O., Attfield, J. P. & Arevalo-Lopez, A. M. (2021) Chem. Commun. 57, 2511-2514.

External stimuli such as temperature, electric and magnetic field, light or guest molecules can be used to control the magnetic properties of molecule-based solids. This in turn can lead to interesting magnetic switching behavior.[1, 2] Molecular magnets are also very susceptible to mechanical stress and yet external pressure is rarely used in this field to study magneto-structural correlations. This is most probably caused by a common belief that molecular crystals are mechanically fragile. In fact, they show very good stability under high quasi-hydrostatic conditions even up to 3 GPa, which is sometimes accompanied by astonishing changes/transformations.

Herein a combined structural, magnetic and spectroscopic study of a family of octacyanoniobate(IV)-based molecular magnets {[M^II(pyrazole)₄]₂[Nb^IV(CN)₈]×4H₂O}_n [3] MNb (M = Mn, Fe, Co or Ni) will be presented and discussed. The four compounds are isostructural and exhibit a three-dimensional (3-D) cyanide-bridged framework with a diamond-like topology (Fig. 1). The 3d transition metal ions M define their optical and magnetic properties under ambient pressure: MnNb (yellow) and FeNb (dark violet) are ferrimagnetic with the critical temperatures of 25 and 9 K, while CoNb (dark yellow) and NiNb (greenish) are both ferromagnetic with Curie temperatures of 6 and 13 K, respectively. The MNb family shows also stunning differences in their pressure responses depending on the metal ion M. The MnNb exhibits one of the highest shifts of the magnetic ordering temperature from 24 K to 37 K in response to pressure,[4] FeNb is a pressure-induced spin-crossover photomagnet based on the LIESST effect (LIESST = light induced excited spin state trapping),[4] while the long range magnetic ordering in CoNb switches from ferromagnetic to ferrimagnetic character under pressure. Finally, NiNb shows significant lowering of the Curie temperature under pressure – completely opposite to MnNb.[5] The thorough high pressure magnetic studies of MNb are correlated with the high pressure single-crystal X-ray diffraction structural analysis, enabling a full understanding of the observed pressure-induced changes [4, 5].

Perovskites ABO3 are of great interest due to their large variety of electronic and magnetic properties. Their compositions can be modified to induce different cation orderings giving double perovskites AA’B2O6 or A2BB’O6, and even more complex double double perovskites (AA’BB’O6) [1]. Recently, by using high-pressure and high-temperature (HPHT) techniques, we reported a new type of double double perovskite derivatives (DDPv) where columnar ordering at A-site and rock-salt ordering at B site are combined [2]. These crystallise with space group P42/n and two families have been established; those with R (= rare earth) cations at A sites in RMnMnSbO6 [2]; and those with Ca e.g. CaMnMReO6 (M = Mn, Fe) [3].

We have successfully synthesised a new R-based series of HPHT perovskites, RMnMnTaO6. Large R cations (R = La-Sm) result in a DDPv structure with space group P4₂/n; whereas a disordered A-site DPv structure has been observed for the smaller R =Eu-Y, with space group P2₁/n. By increasing the temperature, a structural transition from DDPv to DPv was observed for the very first time (Fig.1), confirming the structural phase boundary for the RMnMnTaO₆.

Magnetic measurements show a ferrimagnetic ordering for the DDPv and a ferromagnetic ordering for the DPv. Two magnetic transitions with spin reorientation has been found for the DDPv Nd-compound. All information above indicates a very rich structural and magnetic behaviour for the RMnMnTaO₆ family.

[1] King, G., Woodward, P. M. (2010). J. Mater. Chem. 20, 5785.

[2] Solana‐Madruga, E., Arévalo‐López, Á. M., Dos Santos‐García, A. J., Urones‐Garrote, E., Ávila‐Brande, D., Sáez‐Puche, R. & Attfield, J. P. (2016). Angew. Chem. Int. Ed. 55, 9340.

[3] McNally, G. M., Arévalo-López, Á. M., Kearins, P., Orlandi, F., Manuel, P., & Attfield, J. P. (2017). Chem. Mater. 29, 8870.

The compositional flexibility of double perovskites A₂BB’O₆ gives this family of materials a huge range of properties,[1] and interest in accommodating 5d cations such as Os⁶⁺ on a B sites stems from the stronger spin-obit coupling for these heavier cations (compared with 3d transition metal cations). This gives interesting electronic and magnetic properties of these phases and the A₂NiOsO₆ (A = Ca, Sr, Ba) series spans insulating to metallic phases, with ferromagnetic to antiferromagnetic order,[2-4] and with half-metallicity proposed for Sr₂NiOsO₆.[5] These properties are very sensitive to Ni – O – Os bond lengths and angles and therefore to A²⁺ cation size.[2]

The lower symmetry environments favoured by 6s² “inert pair” cations such as Pb²⁺ give structures and properties that can be quite different from those observed for the group 2 A cation analogues.[6, 7] However, high pressure synthetic routes are often required to access these lead analogues.[1]

This presentation describes work on the structural characterisation and properties of Pb₂NiOsO₆ synthesised at high pressure (6 GPa, 1575 K).[8] The rocksalt ordering of NiO₆ and OsO₆ octahedra combined with octahedral tilts gives a crystal structure of P2₁/n symmetry (similar to Ca₂NiOsO₆). Strong coupling between Ni²⁺ and Os⁶⁺ moments gives long-range magnetic order below 58 K, with the collinear magnetic structure described by magnetic propagation vector k = (½ 0 ½) (similar to Pb₂CoOsO₆[6]). This magnetic order, imposed on the (B-site ordered) crystal structure, breaks inversion symmetry.[8]

[1] Vasala, S.; Karppinen, M., (2015), Progress in Solid State Chemistry 43, 1-36.

[2] Morrow, R.; Samanta, K.; Saha Dasgupta, T.; Xiong, J.; Freeland, J. W.; Haskel, D.; Woodward, P. M., (2016), Chemistry of Materials 28, 3666-3675.

[3] Macquart, R.; Kim, S.-J.; Gemmill, W. R.; Stalick, J. K.; Lee, Y.; Vogt, T.; zur Loye, H.-C., (2005), Inorganic Chemistry 44, 9676-9683.

[4] Feng, H. L.; Calder, S.; Ghimire, M. P.; Yuan, Y.-H.; Shirako, Y.; Tsujimoto, Y.; Matsushita, Y.; Hu, Z.; Kuo, C.-Y.; Tjeng, L. H.; Pi, T.-W.; Soo, Y.-L.; He, J.; Tanaka, M.; Katsuya, Y.; Richter, M.; Yamaura, K., (2016), Physical Review B 94, 235158.

[5] Ghimire, M. P.; Hu, X., (2016), Materials Research Express 3, 106107.

[6] Princep, A. J.; Feng, H. L.; Guo, Y. F.; Lang, F.; Weng, H. M.; Manuel, P.; Khalyavin, D.; Senyshyn, A.; Rahn, M. C.; Yuan, Y. H.; Matsushita, Y.; Blundell, S. J.; Yamaura, K.; Boothroyd, A. T., (2020), Physical Review B 102, 104410.

[7] Jacobsen, H.; Feng, H. L.; Princep, A. J.; Rahn, M. C.; Guo, Y.; Chen, J.; Matsushita, Y.; Tsujimoto, Y.; Nagao, M.; Khalyavin, D.; Manuel, P.; Murray, C. A.; Donnerer, C.; Vale, J. G.; Sala, M. M.; Yamaura, K.; Boothroyd, A. T., (2020), Physical Review B 102, 214409.

[8] Feng, H. L.; Kang, C.-J.; Manuel, P.; Orlandi, F.; Su, Y.; Chen, J.; Tsujimoto, Y.; Hadermann, J.; Kotliar, G.; Yamaura, K.; McCabe, E. E.; Greenblatt, M., (2021), Chemistry of Materials 33, 4188-4195.

Due to their specific peculiarities neutrons are a very useful probe for structural studies on various hot topics related to physics, chemistry and mineralogy. The neutron single crystal diffractometer HEiDi at the Heinz Maier-Leibnitz Zentrum (MLZ) offers high flux, high resolution and large q range, low absorption and high sensitivity for light elements. These properties apply in a similar way to its polarized sister diffractometer POLI, which is optimized for detailed studies on magnetic structures.

In 2016 a project was launched in order to allow studies on tiny samples < 1 mm³ and to develop new pressure cells for HEiDi which can be combined with its existing low temperature equipment in order to study structural properties down to temperatures below 10 K, e.g. MnFe₄Si₃ and related magnetocaloric compounds [1]. This work was supported by the Bundesministerium für Bildung und Forschung (BMBF) (grand no. 05K16PA3). As part of this project various neutron-optical components (Cu220-monochromator, solid state collimators, neutron guides) were developed and optimized in order to generate a sufficiently high flux density at the sample location at the wavelength λ = 0.87 Å. Very tiny single crystal samples (down to < 0.1 mm³) were successfully studied using various new diamond anvil cells (DAC) - developed by A. Grzechnik - up to several GPa, either with a panoramic pressure cell in combination with low temperatures [2] or in a transmission pressure cell, which allows simultaneous studies of the same sample using neutron, synchrotron as well as laboratory x-ray sources [3].

Recently, a follow up project has been launched (BMBF No. 05K19PA2) to focus on further improvements of the high pressure capabilities on HEiDi and POLI and the development of optimized pressure cells for further instruments at the MLZ (POLI, DNS and MIRA), namely advanced clamp cells (see corresponding contribution by A. Eich).

[1] A. Grzechnik et al.; Single-Crystal Neutron Diffraction in Diamond Anvil Cells with Hot Neutrons; J. Appl. Cryst. 51, 351-356 (2018).

[2] A. Eich et al.; Magnetocaloric Mn₅Si₃ and MnFe₄Si₃ at variable pressure and temperature; Mater. Res. Express 6, 096118 (2019).

[3] A. Grzechnik et al.; Combined X-ray and neutron single-crystal diffraction in diamond anvil cells; J. Appl. Cryst. 53(1), 1 - 6 (2020).

Frustrated magnets with spiral magnetic phases are currently being intensively studied owing to their ability for inducing ferroelectricity. This could potentially be exploited in spintronics and low power memories devices.[1-2] However, the low magnetic order temperatures (typically < 100 K) in most of frustrated magnets greatly restrict their fields of application. One of the most notable exceptions are Cu/Fe-based layered perovskites, featuring magnetic spiral phases whose ordering temperatures can be continuously tuned far beyond RT. [3-5]. However, the influence of magnetic field on the magnetic structures especially spiral phases, imperative for further cross-control of the magnetic and ferroelectric orders, is barely known.

Here, we report a comprehensive description of the evolution of magnetic order in the layered perovskite YBaCuFeO₅ under the application of magnetic fields up to 9.0 T and at temperatures between 1.5 K and 300 K. Using bulk magnetization measurements and neutron powder diffraction we reveal the existence of a new incommensurate magnetic phase with a weak ferromagnetic component stable at low magnetic fields. Moreover, we observe a field-induced spin reorientation in the collinear phase. The resulting H-T phase diagram of YBaCuFeO₅ will be discussed, with emphasis in the magnetic phases with the largest potential to display strong magnetoelectric effects. [6]

[1] Eerenstein, W., Mathur, N.D. & Scott, J.F. (2006). Nature. 442, 759. [2] Kimura, T., Goto, T., Shintani, H., Ishizaka, K., Arima, T.H. & Tokura, Y. (2003). Nature 426, 55. [3] Morin, M., Scaramucci, A., Bartkowiak, M., Pomjakushina, E., Deng, G., Sheptyakov, D., Keller, L., Rodriguez-Carvajal, J., Spaldin, N.A., Kenzelmann, M., Conder, K. & Medarde, M. (2015). Phys. Rev. B 91, 064408. [4] Morin, M., Canévet, E., Raynaud, A., Bartkowiak, M., Sheptyakov, D., Ban, V., Kenzelmann, M., Pomjakushina, E., Conder, K. & Medarde, M. (2016). Nat. Commun. 7, 1. [5] Shang, T., Canévet, E., Morin, M., Sheptyakov, D., Fernández-Díaz, M. T., Pomjakushina, E. & Medarde, M. (2006). Sci. Adv. 4, eaau6386. [6] Lyu, J. et al. in preparation.

In the course of biomineralization, organisms produce a large variety of functional biogenic crystals that exhibit fascinating mechanical, optical, magnetic and other characteristics. More specifically, when living organisms grow crystals they can effectively control polymorph selection as well as the crystal morphology, shape, and even atomic structure. Materials existing in nature have extraordinary and specific functions, yet the materials employed in nature are quite different from those engineers would select.

One special feature of such crystals is the entrapment of organic molecules within the inorganic crystalline host. Here I will show how we have taken this principle and trslated it to bio-inspired crystal growth to control the electronic properties of various semiconductors.

Some examples include: ZnO and Cu₂O and Hybrid Perovskite. I will discuss the incoporation mechansims, the effect on crystal stricyure and the relation to manipulation of electronic properties.

In this talk, the role that intramineral proteins have played on the shape control as well as in the biomineralization of calcium carbonate in the eggshell´s formation of different avian, crocodiles and dinosaurs will be reviewed. Particularly, the collected eggshells samples of five fossilized eggshells from dinosaurs that roamed the Earth more than 65 million years ago. We characterized the eggshells of the Theropod (bipedal carnivores) and Hadrosauridae (duck-billed dinosaurs) families and an unidentified ootaxon. We have found the existence of some proteins by using micro X-ray absorption and micro-fluorescence techniques at the synchrotron facilities. From these analyses on the dinosaur eggshells, X-ray absorption methods showed a very characteristic organic sulfur bonding similar to that semi-essential proteogenic amino acid L-cysteine, which implies that there is a possibility of having a very old intramineral protein similar to those found in emu and crocodiles. On the other hand, the spectroscopical characterization on these samples showed that calcium carbonate was the primary mineral, with smaller amounts of albite and quartz crystals. Anhydrite, hydroxyapatite, and iron oxide impurities were also present in the shells, which suggests replacement of some of the original minerals during fossilization. Then, with Fourier transform infrared spectroscopy (FT-IR), we found nine amino acids among the five samples, being lysine the only amino acid present in all of them. In addition, we have found evidence of secondary protein structures, including turns, α-helices, β-sheets and disordered structures, which have been preserved for millions of years by being engrained in the minerals. The FT-IR bands corresponding to amino acids and secondary structures could be indicative of ancestral proteins that have not been characterized before. This type of chemical, spectroscopical and structural characterization together with the optical one is a relevant contribution to the field of biomineralization of calcium carbonate research, mainly because these types of samples are unique in their type due to the biological relevance in Mexico and will, therefore, allow us to understand the species that became extinct millions of years ago as well as the importance of calcium carbonate associated to ancient proteins throughout the biomineralization processes on Earth.

Crystal texture of mineral self-organized structures from soda lake water and their implication to early Earth and prebiotic chemistry

M. Getenet, J.M. García-Ruiz

Laboratorio de Estudios Cristalográficos, Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas–Universidad de Granada, Granada, Spain

juanmanuel.garcia@csic.es

The ability of minerals to precipitate into complex shapes and textures creates fascinating patterns that has not been enough explored in natural scenarios. Among them, silica induced mineral self-organized structures have been suggested to be relevant for the earliest stages of the planet, when alkaline silica-rich oceans evolve from methane-rich to CO and CO₂-rich atmosphere and hydrosphere [1]. Under these geochemical conditions of the Hadean Earth, it is thought that silica-carbonate biomorphs and silica-metal hydr(oxide) gardens were actually forming in the alkaline oceans, rich in silica and in carbonate. In this work, we focus on chemical gardens, which are hollow membranes formed via abiotic precipitation when metal salts immerse into aqueous solutions containing anions such as silicate, carbonate, or phosphates [2]. It has been shown that these space-compartmentalized membranes are small batteries [3] that selectively catalyse the synthesis of prebiotically relevant compounds such as carboxylic acids, amino acids, and nucleobases by condensation of formamide [4]. Here, we experimentally demonstrate the formation of carbonate gardens using carbonate-rich alkaline soda lake water (Lake Magadi, Southern Kenyan rift valley). We have studied in detail the mineral composition and crystallinity of these “natural” carbonate gardens by SEM-EDX, Raman microscopy, infrared spectroscopy and X-ray diffraction, and compared to other silica and carbonate gardens made from laboratory solutions. Our result suggests that mineral self-organization could have been a geochemically plausible phenomenon in carbonate-rich closed basin environments of the early Earth, and Earth-like planets. We also discuss the implications of the textural properties of the mineral membranes to develop electrochemical potential that could catalyze prebiotic reactions.

[1] García-Ruiz, J.M., van Zuilen, M. & Bach, W. (2020). Phys Life Rev. 34-35, 62-82.

[2] Kellermeier, M., Glaab, F., Melero-García, E., & García-Ruiz, J. M. (2013). Research Methods in Biomineralization Science, edited by J.J. De Yoreo, pp. 225-256. San Diego: Academic Press.

[3] Glaab, F., Kellermeier, M., Kunz, W., Morallon, E. & Garcia-Ruiz, J. M. (2012). Angew. Chem. 124, 4393

[4] Saladino, R., Di Mauro, E. & García-Ruiz, J. M. (2019). Chem. Eur. J. 25, 3181.

Keywords: chemical gardens; self-organization; biomorphs; early Earth; Soda lakes

Acknowledgments: We acknowledge funding from the European Research Council under grant agreement no. 340863, from the Ministerio de Economía y Competitividad of Spain through the project CGL2016-78971-P and Junta de Andalucía for financing the project P18-FR-5008. M.G. acknowledges Grant No. BES-2017-081105 of the Ministerio de Ciencia, Innovacion y Universidades of the Spanish government.

Through controlled biomineralization, organisms yield complicated structures with specific functions. Here, Jania sp., an articulated coralline red alga that secretes high-Mg calcite as part of its skeleton, is in focus. It is shown that Jania sp. exhibits a remarkable structure, which is highly porous (with porosity as high as 64 vol%) and reveals several hierarchical orders from the nano to the macroscale. It is shown that the structure is helical, and proven that its helical configuration provides the alga with superior compliance that allows it to adapt to stresses in its natural environment. Thus, the combination of high porosity and a helical configuration result in a sophisticated, light-weight, compliant structure [1]. Very recently, we also showed that the high-Mg calcite cell wall nanocrystals of Jania sp. are arranged in layers with alternating Mg contents. Such non-homogenous elemental distribution assists the alga in preventing fracture caused by crack propagation. We further discover that each one of the cell wall nanocrystals in Jania sp. is not a single crystal as was previously thought, but rather comprises Mg-rich calcite nanoparticles demonstrating various crystallographic orientations, arranged periodically within the layered structure [2]. We also show that these Mg-rich nanoparticles are present in yet another species of the coralline red algae, Corallina sp., pointing to the generality of this phenomenon. To the best of our knowledge this is a first report on the existence of Mg-rich nanoparticles in the coralline red algae mineralized tissue. We envisage that our findings on the bio-strategy found in the alga to enhance the fracture toughness will have an impact on the design of structures with superior mechanical properties.

1.Bianco‐Stein N, Polishchuk I, Seiden G, Villanova J, Rack A, Zaslansky P and Pokroy B. Helical Microstructures of the Mineralized Coralline Red Algae Determine Their Mechanical Properties. Adv Sci 2020; 7:2000108.

2. Bianco-Stein N, Polishchuk I, Lang A, Atiya G, Villanova J, Zaslansky P, Katsman A and Pokroy B. Structural and Chemical Variations in the Calcitic Segments of Coralline Red Algae Lead to Improved Crack Resistance. Acta Biomater 2021; DOI:10.1016/j.actbio.2021.05.040.

Bone is a strong yet light-weight material, where several mechanical properties originate from the orientation of their molecular components – collagen fibrils mineralized with calcium phosphate in a hydroxyapatite (HA)-like structure. Knowledge of the three-dimensional (3D) microscopic orientation arrangements of the mineralized collagen in macroscopic samples, allows for a deeper understanding of the mechanical properties of bone, leading to an improved understanding of bone and cartilage-related diseases such as osteochondrosis and osteoarthritis. The distinct patterns in the HA mineral orientation can also be used to locate embedded fibres of muscle attachments in vertebrates in both modern and fossil bones. This is crucial for reconstructing evolutionary scenarios and biomechanical models of extinct species, for which soft tissues are lost during fossilization.

X-ray diffraction computed tomography (XRD-CT) is an emerging imaging technique, allowing non-destructive 3D mapping of samples with material-specific contrast [1] and has recently also been demonstrated with orientational contrast [2–4]. In this presentation we demonstrate the application of XRD-CT to study the microstructure of different types of bones without destructive sample sectioning. The HA orientation in a tibial cross-section from a fossil stem amniote Discosauriscus austriacus is used to reveal the location of muscle attachments, shown in Figs. 1a and 1b. XRD-CT can also be used to study the HA orientation close to the bone-cartilage interface in the developing bone, as illustrated in Figs. 1c and 1d. XRD-CT is becoming a powerful tool that allows studying the orientation of mineralized structures in bone, and is likely to be increasingly used due to the advent of new synchrotron sources and improved numerical methods for tomographic reconstruction.

[1] Harding, G., Kosanetzky, J. & Neitzel, U. (1987). Med. Phys. 14, 515.

[2] Liebi, M., Georgiadis, M., Menzel, A., Schneider, P., Kohlbrecher, J., Bunk, O. & Guizar-Sicairos, M. (2015). Nature. 527, 349.

[3] Mürer, F. K., Sanchez, S., Álvarez-Murga, M., Di Michiel, M., Pfeiffer, F., Bech, M. & Breiby, D. W. (2018). Sci. Rep. 8, 1.

[4] Mürer, F. K., Chattopadhyay, B., Madathiparambil, A. S., Tekseth, K. R., Di Michiel, M., Liebi, M., Lilledahl, M. B., Olstad, K. & Breiby, D. W. (2021). Sci. Rep. 11, 1.

See separate file

X-ray absorption spectroscopy (XAS) has imposed as a powerful method to track structural and chemical dynamics of metal ions hosted in nanoporous frameworks, such as zeolites and metal-organic frameworks (MOFs), for selective redox catalysis applications [1]. Analysis of the XANES and EXAFS regions offers a highly complementary view with respect to diffraction-based methods guaranteeing a unique sensitivity to the local electronic and structural properties of metal centers. These are often disorderly distributed in the crystalline matrix, and occur as dynamic mixtures of different species, responding to the physico-chemical environment while undergoing a rich redox chemistry mediated by host-guest interactions. Continuous instrumental developments at synchrotron sources today enable in situ/operando XAS studies at high time and energy resolution, allowing to monitor such dynamic systems with unprecedented accuracy [1]. In this contribution, the potential of these methods, empowered by advanced data analysis strategies and synergic integration with multi-technique laboratory characterization and computational modelling, will be exemplified by selected research results.

A first example will focus on the Cu-exchanged chabazite (Cu-CHA) zeolite, currently representing the catalyst of choice for deNO_x applications in the automotive sector via NH₃-assisted Selective Catalytic Reduction [2]. Here, the potential of Multivariate Curve Resolution (MCR) of time-resolved XANES datasets, quasi-simultaneous XANES/PXRD, and EXAFS Wavelet Transform analysis will be highlighted, to accurately quantify condition/composition-dependent Cu-speciation in CHA zeolites and therein establish robust structure-activity relationships, essential to design improved catalysts. A second case study will consider local structural and chemical transformations of Pt ions in Pt-functionalized UiO-67 MOFs [3], tracked by parametric refinement of time-resolved operando EXAFS under conditions yielding either isolated Pt^II sites anchored to the MOF framework (potentially interesting for C−H bond activation) or very small Pt⁰ nanoparticles inside the MOF cavities (potentially interesting for hydrogenation reactions).

[1] S. Bordiga et al., Chem. Rev. 2013, 113, 1736. C. Garino et al., Coord. Chem. Rev. 2014, 277-278, 130. E. Borfecchia et al., Chem. Soc. Rev. 2018, 47, 8097.

[2] A. Martini et al, Chem. Sci. 2017, 8, 6836. C. W. Andersen, et al., Angew. Chem. Int. Edit. 2017, 56, 10367. K. A. Lomachenko et al., J. Am. Chem. Soc. 2016, 138, 12025. C. Negri et al., J. Am. Chem. Soc. 2020, 142, 15884.

[3] S. Øien, et al., Chem. Mater. 2015, 27, 1042. L. Braglia, et al., Phys. Chem. Chem. Phys. 2017, 19, 27489. L. Braglia, et al., Faraday Discuss. 2017, 201, 265.

This investigation is devoted to metal-organic frameworks (MOFs) with UiO-67 topology, the materials with a three-dimensional porous structure and high surface area. Due to the diversity of species, MOFs are used in such areas as luminescent sensors, catalysts, filters, storage and transportation of light gases, and many others [1]. Using noble metals to functionalize metal-organic frameworks is a promising way for constructing new materials for catalytic applications [2, 3]. Although numerous successful synthesis of MOFs functionalized by metal ions and metal nanoparticles were reported, the exact mechanisms of structural evolution of the metal sites in many cases are still unknown. Determination of these mechanisms as well as investigation of the intermediate active sites formed during the synthesis is important for tailoring the specific catalytic properties of materials. In this work, we investigate structural changes in UiO-67 functionalized by Pd and Pt depending on the activation conditions by a combination of theoretical and experimental techniques.

Functionalization of UiO-67 by Pd and Pt was achieved via substitution of 10% standard biphenyl dicarboxylate linkers by MCl₂-2,2-bipyridine-5,5-dicarboxylic acid (MCl₂bpydc, M = Pd, Pt) [4, 5]. The obtained materials were further activated by heating to 300 °С in inert (He) and reducing (H₂/He) atmospheres. Evolution of the atomic and electronic structure was monitored by in situ extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES) spectroscopies and X-ray powder diffraction (XRPD). All spectroscopic data for Pd K- and Pt L₃-edges were analysed simultaneously by MCR-ALS approach [6] to determine the number of pure species formed during the activation and their spectra.

To interpret the experimental data, we have performed DFT-calculations and XANES simulation by FDMNES code for different potential intermediates. The atomic models included the initial MCl₂bpydc linker and a number of possible reaction pathways in presence of H₂ substitution of both chlorine atoms by hydrogen atoms with formation of Cl₂ molecule, substitution of one chlorine by hydrogen atom with formation of HCl molecule; detachment of one or two chlorines with formation of HCl molecules, detachment of MCl₂ fragment from the linker with its substitution by two hydrogens bonded to nitrogen atoms of the linker; and simulating inert conditions: simple detachment of MCl₂ fragment, detachment of chlorines with formation of Cl₂ molecule. All reaction pathways were ranged according to the calculated reaction enthalpies and XANES spectra were calculated for the most probable ones.

The reaction pathways with the lowest reaction enthalpies were verified by good agreement between calculated and experimentally observed XANES spectra. For UiO-67-Pd, detachment of PdCl₂ is the most probable pathway in both inert and H₂ atmospheres which correlate with experimental results. For UiO-67-Pt, four different structures have been identified. In the presence of hydrogen, detachment of one chlorine atom should occur first. The second possible transition in the same environment is the detachment of PtCl₂ from the linker with the addition of two hydrogen atoms to nitrogen atoms with the further formation of Pt nanoparticles at temperatures above 200 °C. While formation of bare Pt-sites occurs from 200 to 300 °C in the inert flow [7, 8]. Thus, the XANES spectroscopy supported by theoretical calculations allowed verifying and describing intermediate states from the experimental spectra.

[1] Evans J. D., et al., Coord Chem Rev. (2019) 380 378-418. [2] Tanabe K. K., Cohen S. M., Chem Soc Rev. (2011) 40 (2) 498-519. [3] Wang Z., Cohen S. M., Chem Soc Rev. (2009) 38 (5) 1315-29. [4] Braglia L., et al., Phys Chem Chem Phys. (2017) 19 (40) 27489-27507. [5] Bugaev A. L., et al., Faraday Discuss. (2018) 208 287-306. [6] Jaumot J., et al., Chemom Intell Lab Syst. 140 (2015) 1-12. [7] Bugaev A. L., Skorynina A.A., et al., Catal. Today. (2019), 336, 33-39. [8] Bugaev A. L., Skorynina A.A., et al., Data Brief. (2019) 25, 104208.

Keywords: XANES; XRD; MOFs; MCR; DFT

This research was supported by the Russian Science Foundation, project № 20-43-01015.

Many catalysts for energy related applications, in particular metallic nanoalloys, readily undergo atomic-level changes during the electrochemical reactions driving the applications. The origin, dynamics and impact of the changes on the performance of the catalysts under actual operating conditions are, however, not well understood. This is largely because they are studied on model nanocatalysts under controlled laboratory conditions. We will present results from recent studies [1, 2, 3] on the dynamic behavior of metallic nanoalloy catalysts inside an operating proton exchange membrane fuel cell. Results show that their atomic structure changes profoundly, from the initial state to the active form and further along the cell operation. The electrocatalytic activity of the nanoalloys also changes. The rate and magnitude of the changes may be rationalized when the limits of traditional relationships used to connect the composition and structure of nanoalloys with their electrocatalytic activity and stability, such as Vegard’s law, are recognized. In particular, deviations from the law can well explain the behaviour for Pt-3d metal nanoalloy catalysts under operating conditions. Moreover, it appears that factors behind their remarkable electrocatalytic activity, such as the large surface to volume ratio and “misfit” between the size of constituent atoms, are indeed detrimental to their stability inside fuel cells. The new insight into the atomic-level evolution of nanoalloy electrocatalysts during their usage is likely to inspire new efforts to stabilize transient structure states beneficial to their activity and stability under operating conditions, if not synthesize them directly.

1. V. Petkov et al. Nanoscale 11, 5512 (2019).
2. Zh. Kong et al. J. Am. Chem. Soc. 142, 1287 (2020).
3. Z.-P. Wu et al. Nature Commun. 12, 8597 (2021)

The topic of renewable energies is vastly received as an x-factor towards our energy problems in this modern world times. This notion holds tight following the current global outcry of dilapidating fossil fuels. The science fraternity continually aims at tabling innovative strategies towards engineering renewable energy sources. This transcends to efforts of making chemical fuels which are easily storable using solar energy.

Water reduction catalysts (WRCs), as widely known, are currently used for the splitting of water to H₂ and O₂. The hydrogen (H₂) generated, is eyed as a prominent potential fuel source. These catalysts are often tailored with different transition metal elements somewhat coupled with effective macro-cyclic organic scaffolds [1]; as suitable approach to store energy at times of reduced power supply by harnessing solar energy [2,3].This renowned WRC science was preceded by the prominent scientific stun of the ruthenium(III) complex {[Ru^III(byp)₃]³⁺}, as a photo-synthesizer [4]. Interestingly, different other light harvesting moieties are lately being considered, exhibiting greater photo-stability, longevity and rigidity as elemental prerequisites [5], many of whom are based on polypyridyl entities.

In this presentation we discuss aspects of the ligand design strategy and cobalt coordination chemistry as exhibited in the value chain in the scheme just above. X-ray crystallographically characterised structures will be used to discuss different relative geometric preferences and characteristics of the respective analogues.

Alternative fuel sources are needed to replace fossil fuels to reduce the emission of greenhouse gases contributing to global warming. Hydrogen gas is one popular choice to replace fossil fuels [1] as an energy storage medium, due to its high energy density per unit weight. Hydrogen can be generated renewably by sunlight driven, photocatalytic water-splitting. Metal oxides, including those with a Ruddlesden-Popper layered perovskite structures are being studied as potential photocatalysts [2]. The structure contains multiple cationic sites, which allows for different combinations of metal cations for tuning the bandgap. The layered structuring also allows for the intercalation of different cations within the structure that allows for modifications post synthesis, therefore further optimising the photocatalyst [3].

KLaTiO₄ is a n=1 Ruddlesden-Popper that can be used as a Hydrogen Evolution Catalyst (HEC), producing 9.540 μmol of H₂ gas per hour from 20 mg of catalyst, when using methanol as sacrificial electron donor and platinum co-catalyst, and illuminated by a Hg lamp with a 305 nm cut-off filter. The main disadvantage of KLaTiO₄ is its high bandgap (4.09 eV) that is above the visible light region, which makes it a poor choice for a HEC that uses solar energy. Reduction of the bandgap of KLaTiO₄ for sunlight driven hydrogen evolution was attempted by cationic and anionic doping. The crystal structures, and sample purity, was determined using synchrotron X-ray powder diffraction (PXRD) and Rietveld refinement.

Cationic doping of KLaTiO4 was achieved by partially replacing lanthanum with praseodymium or ytterbium, yielding two solid solution series: KLa_xPr_1-xTiO₄ and KLa_xYb_1-xTiO₄ (x = 0.005, 0.01 and 0.03). While none of the samples from KLa_xPr_1-xTiO4 series produced hydrogen, all the KLa_xYb_1-xTiO₄ were able to produce H₂. In comparison to KLaTiO4, ytterbium-doped samples have reduced catalytic activity compared to KLaTiO₄, as seen in figure 1.

Anionic doping of KLaTiO₄ was attempted with nitrogen. Attempts to synthesise KLaTiO₃N were done by using TiN as a reagent in place of TiO2 with annealing the sample under N₂ flow at 800 °C. PXRD patterns of initial samples show good crystallinity, and no observable structural difference to KLaTiO₄. When tested as HEC in identical testing condition stated above all nitrogenated samples had similar rates of hydrogen evolution.

Strontium iron oxide is a candidate for many different energy applications, including solid oxide fuel cells, chemical looping, and thermochemical energy storage. Upon the redox reactions, SrFeO_x cycles between two end forms: an oxygen deficient form SrFeO_2.5 with a brownmillerite structure and an oxidized form SrFeO_3-δ with a perovskite structure. Two intermediate structures are reported from ex situ and in situ X-ray and neutron powder diffraction [1–3]. However, in real applications, submicron sized crystals are used and X-ray and neutron diffraction techniques are not able to access structural information on an individual submicron crystal. In situ 3D electron diffraction (3D ED) performed on a transmission electron microscope (TEM) is the only way to obtain single crystal data on all structural changes occurring during the actual redox reactions. Due to the single-tilt design of the environmental holders combined with the complexity of these structures, in-zone electron diffraction and high resolution imaging on random crystallites are unrealistic, but 3D ED does not require in zone orientation and could thus be successfully applied to gather structural data on the different phases.

We performed in situ oxidation of a brownmillerite SrFeO_2.5 crushed single crystal upon heating in an oxygen atmosphere in TEM using the sealed commercial holder. By acquiring 3D ED data at different steps of the reaction, we confirmed the formation of the perovskite SrFeO_3-δ structure, which we were able to reduce back to brownmillerite in a hydrogen atmosphere. The obtained data allowed us to derive the structures formed at different reaction steps, including the intermediate phases, resulting in new information about their crystal structures and microstructures. In my talk, I will compare the results of in situ 3D ED with the published data from X-ray and neutron diffraction, discuss the limitations of the method, and the next steps in improving in situ 3D ED in gas environments.

[1] A. Maity, R. Dutta, B. Penkala, M. Ceretti, A. Letrouit-Lebranchu, D. Chernyshov, A. Perichon, A. Piovano, A. Bossak, M. Meven, W. Paulus (2015). J. Phys. D. Appl. Phys. 48, 504004. [2] D.D. Taylor, N.J. Schreiber, B.D. Levitas, W. Xu, P.S. Whitfield, E.E. Rodriguez (2016). Chem. Mater. 28, 3951–3960. [3] J.P.P. Hodges, S. Short, J.D.D. Jorgensen, X. Xiong, B. Dabrowski, S.M.M. Mini, C.W.W. Kimball (2000). J. Solid State Chem. 151, 190-209.

Keywords: brownmillerite; TEM; 3D ED; in situ

This work was supported by BOF 38689 - New method to acquire in situ information on crystal structures changed by chemical reactions

Timescales of dynamic processes in extended solids span many orders of magnitude owing to the large number of degrees of freedom. Additionally, scaling laws dictate that discrete temporal domains comprising the entire continuum consist of associated spatial domains within which specific dynamics are dominant. Ideally, one would be able to probe the entire spatiotemporal range on a single specimen spot with a single instrument. Modern TEMs are exceptionally versatile in this regard, providing access to spatial and energy ranges that span sub-Å to micrometres and sub-10 meV to 1,000s of eV, respectively. However, timescales of the associated physical phenomena span 100s of attoseconds (10^-18 s) to minutes and longer, a range that cannot be fully covered by even the fastest direct detectors. Indeed, dynamics faster than ~0.1 ms are largely inaccessible to detector-based TEM approaches.

Here, an overview will be provided of ongoing efforts aimed at pushing TEM temporal resolutions well beyond the limits imposed by detectors and by peak dose rates. Emphasis will be placed on laser-driven nanosecond single-shot and fs stroboscopic modalities, currently the two most widely used approaches (Figure 1) [1-3]. Common hardware configurations based on modified commercial TEM platforms will be described, and current state-of-the-art performance specifications will be discussed. This will be followed by a brief survey of discoveries and advances that have been made with imaging, diffraction, and spectroscopy. Particular focus will be placed on experiments that have led to deeper understanding of materials and to new physics [4]. The talk will conclude with a brief look toward new emerging approaches and expanded applications, such as pulsed-beam damage mitigation [5, 6].

[1] Park, S. T., Flannigan, D. J. & Zewail, A. H. (2011). J. Am. Chem. Soc. 133, 1730.

[2] Cremons, D. R., Plemmons, D. A. & Flannigan, D. J. (2016). Nat. Commun. 7, 11230.

[3] Plemmons, D. A., Suri, P. K. & Flannigan, D. J. (2015). Chem. Mater. 27, 3178.

[4] Barwick, B., Flannigan, D. J. & Zewail, A. H. (2009). Nature 462, 902.

[5] VandenBussche, E. J. & Flannigan, D. J. (2019). Nano Lett. 19, 6687.

[6] VandenBussche, E. J., Clark, C. P., Holmes, R. J. & Flannigan, D. J. (2020). ACS Omega 5, 31867.

At present report time resolved methods and measurements of rocking curves (RC) and reciprocal space maps (RSM) under external dynamic ultrasonic loads are described. These measurements were made by using adaptive X-Ray optic (ABXO) elements.

Conducting experiments with time resolution using x-ray and synchrotron radiation is one of the advanced modern scientific problems. Today, there are three main directions in the development of such experiments - the creation of new sources (synchrotrons and XFELs), the development of detecting equipment, and the rapid tuning of experimental parameters. The first two directions have gained significant development in recent years, and the last direction rests on the impossibility of quickly adjusting experimental parameters using existing goniometric systems. As a result, the existing hardware and methodological base practically does not cover the range of time resolutions from seconds to microseconds, in which many interesting physical processes occur.

One of possibilities to overcome these limitations of traditional approach is using of non-mechanical adaptive X-ray optic elements, such as X-ray acoustic resonators of longitudinal oscillations or bimorph piezo-actuators [1]. It allows fast and precise variation of X-ray diffraction parameters, varying the angular position of the X-ray beam and controlling its wavelength. An important feature of the method is the possibility of conducting experiments not only in laboratory conditions, but also at synchrotron stations.

The method has been successfully applied to the study of processes occurring in crystals under dynamic ultrasonic loads. Using this method, studies of a silicon crystal subjected to quasistatic mechanical load were carried out [2]. The studies of the evolution of the defective structure of lithium fluoride (LiF) and TeO₂ single crystals under the conditions of dynamic ultrasonic loading in a wide range of amplitudes have also been studied [3]. It is shown that the diffraction pattern (shape and FWHM of rocking curves) under the action of ultrasound can differ significantly from the original, and the proposed method allows monitoring its changes with a temporal resolution of up to 10 μs, inaccessible when using mechanical goniometric systems. Studies of the evolution of the defective structure using the new method showed its significant (at least 3 orders of magnitude on a laboratory source) superiority in speed over existing methods.

The technique was also successfully applied for conducting experiments in a three-crystal X-ray diffraction scheme. It was shown that with its help it is possible to carry out fast (several minutes even with laboratory X-ray source) measurements of the reciprocal space maps from the studied samples under dynamic ultrasonic loads, as well as studying the distribution of ultrasonic vibrations in resonator crystals.

The reported study was funded by RFBR and DFG 19-52-12029 and by RFBR according to the research project №18-32-20108.

1. Blagov A.E., Bikov A.S and etc // IET. 2016. № 5. С. 109
2. Eliovich I.A., Akkuratov V.I. and etc. // Crystallography reports, 2018, Vol. 63, № 5, p. 708
3. Blagov A.E., Pisarevskii Yu.V. and etc. // PSS. 2017. Vol. 59. № 5. p. 947.

Many phase transformations associated with solid-state precipitation look structurally simple, yet take place with great difficulty. Classic cases of surprisingly difficult phase transformations can be found in alloy systems forming the basis for a broad range of high-strength lightweight aluminium alloys. In these systems, the difficult nucleation of strengthening phases, which are usually semi-coherent, is often preceded by the easy nucleation of another phase with strong structural similarities, typically a coherent precipitate. It is therefore of interest to investigate the reasons behind the difficult transformation from coherent to semi-coherent precipitate phases.

Using scanning / transmission electron microscopy (S/TEM) techniques both ex situ and in situ, combined with atomic scale simulations (density functional theory and semi-empirical potentials) we examined phase transformations in several alloy systems, including the textbook Al-Cu and Al-Ag systems. We show that certain microalloying additions, or different processing conditions applied to samples in bulk or nanoscale form, result in previously unreported precipitate phases [1-2] – see Figs. 1-2, or promote the nucleation of existing phases [3-4]. The nucleation mechanisms of these phases involve structural templates provided by coherent precipitates [1-3] and depend critically on the availability of vacancies [1-2,4]. Based on our observations atomic-scale mechanisms are proposed for phase transformation pathways. We also characterised the surface structure and growth mechanisms of voids, uncovering a crystallographic relationship necessary for the growth of high-aspect ratio voids [5]. These findings suggest several approaches to not only stimulate known precipitate transformations, but also discover new phases and transformation pathways.

The sensitiveness to the electron beam of nanocrystalline metal-organic frameworks (MOFs) has always posed an objective criticality for the accurate determination of their structure by single crystal electron diffraction. The reversible atomic displacement caused by the high flexibility of the organic linkers further complicates the characterization of the framework and the understanding of their complex functional properties at the atomic level ^[1]. Although standard diffraction experiments can elucidate dynamic phenomena ^[2,3], an analysis of the anisotropic displacement parameters (ADPs) obtained after refining MOFs against electron diffraction data has never been performed. In this study, we solved and refined the structures of UiO-67 /MIL-140C, coexisting in mixture, by using continuous rotation electron diffraction (cRED). For both structures, restricted small-angle librations of the linker were revealed by analysing the ADPs at room temperature and in cryogenic conditions (98 K). Our work shows that continuous rotation electron diffraction (cRED) not only provides reliable and accurate crystallographic models as that obtained by single crystal X- ray diffraction (SCXRD), but it represents a powerful tool to investigate the dynamic in the molecular fragments of the framework.

[1] Bennett, T.; Cheetham, A.; Fuchs, A.; Coudert, F.-X. (2017) Nature Chem., 9, 11–16

[2] Smeets, S.; Parois, P.; Burgi, H- B; Lutz, M. (2011) Acta Cryst, B67, 53-62

[3] Lock, N.; Wu, Y.; Christensen, M.; Cameron, L. J.; Peterson, V. K.; Bridgeman, A. J.; Kepert, C. J.; Iversen, B. B. (2010) J. Phys. Chem. C, 114, 16181− 16186

Zeolites represent a unique class of inorganic compounds, which have a simple idealized composition TO₂ and uniform tetrahedral and bridge coordination of the T and O atoms. However, such simplicity gives rise to extremal diversity in the topologies of the zeolite frameworks, which is comparable with the variety of organic compounds: theoretically, the number of the framework topologies is infinite and the databases of hypothetical frameworks generated by computer procedures contain hundreds of thousands of entries. All the more surprising that the number of zeolites existing in nature or obtained in the laboratory is quite modest: currently, in the database produced by the International Zeolite Association there are only 248 topologically distinct zeolite frameworks, which compose less than 0.1% of the known low-energy hypothetical frameworks. Many efforts were undertaken to explain this phenomenon, as well as to predict new zeolite topologies. Paradoxically, most of the proposed explanations of this topological scarcity were based on geometrical or energetic properties of the frameworks, but not on their topological properties. However, low energy of the zeolite framework is not the sufficient proof of its feasibility; no less important are the kinetic factors that drive the framework assembly. While the framework energy is reflected to some extent by the geometrical parameters, which characterize the framework distortion, the assembly of the framework is encoded in its topological parameters. Thus geometry and topology meet to feature the thermodynamics and kinetics of the framework formation.

We explain the feasibility of the zeolite frameworks within the topological model of natural tiling, which represents covering of the crystal space by non-crossing minimal cages (natural tiles) built from the nodes and edges of the framework. We show that the assembling of the framework from natural tiles reflects kinetic factors, which complement the thermodynamic criteria, and explains the inconsistency in the number of hypothetical and realized framework motifs [1]. Moreover, the model of natural tiling enables one to predict more thoroughly new robust zeolite frameworks. We have extended this model and included parts (halves) of tiles into consideration. This extension allowed us to find many hidden relations in the zeolite topological motifs and particularly to interpret and predict the intergrowth phenomena in the zeolite minerals and synthetic phases [2]. Natural tiles can also be considered as building units in modelling crystal growth by Monte Carlo methods [3]. We have implemented the natural tiling model in the ToposPro program package (https://topospro.com) and developed a database of all natural tiles that occur in known zeolite frameworks (TTT collection). This enabled us to explore the natural tilings in hypothetical zeolites and find those of them that could be easily assembled and hence obtained in the experiment. We also apply the tiling model for the purposeful sampling of organic structure directing agents and propose a list of them for a target synthesis of the hypothetical zeolite frameworks.

[1] Kuznetsova, E.D., Blatova, O.A. & Blatov, V.A. (2018). Chem. Mater. 30, 2829.

[2] Golov, A.A., Blatova, O.A. & Blatov, V.A. (2020). J. Phys. Chem. C, 124, 1523.

[3] Anderson, M., Gebbie, J., Hill, A., Farida, N., Attfield, M., Cubillas, P., Blatov, V.A., Proserpio, D.M., Akporiaye, D., Arstad, B., Gale, J. (2017). Nature, 544, 456.

This work was supported by the Russian Science Foundation (Grant No. 16-13-10158).

According to Löwenstein’s rule [1], Al-O-Al bridges are forbidden in the aluminosilicate framework of zeolites. A graph-theoretical interpretation of the rule, based on the concept of independent sets, was proposed by Klee [2] and reviewed by Eon [3]. It was shown that one can apply the vector method to the associated periodic net and define a maximal Al/(Al+Si) ratio for any aluminosilicate framework following the rule; this ratio was called the independence quotient of the net. This presentation deals with practical issues regarding the calculation of the independence quotient of mainly 2-periodic nets and the possible existence of disordered structures with this ratio.

We first show that applying Proposition Calculus to the determination of independent sets in finite graphs leads to introducing a multivariate polynomial, called the independence polynomial. This polynomial can be calculated in an automatic way and provides the list of all maximally independent sets of the graph, hence also the value of its independence quotient. Some properties of this polynomial are discussed; the independence polynomials of some simple graphs, such as short paths or cycles, are determined as examples of calculation techniques.

The determination of the independence quotient of a periodic net requires finding a subgroup of the translation group of the net for which the quotient graph and a fundamental transversal have the same independence quotient. See Fig. 1 for an illustration based on the hbt net, with independence quotient of 4/7; the only maximally independent set in the quotient graph and in the transversal associated to a primitive unit cell is shown in red. In most nets, however, a non-trivial translation subgroup has to be found. We show that this subgroup should be chosen to eliminate every cycle in the quotient graph that is shorter than structural cycles, or rings, of the net. Several examples are then analysed, which show that the choice of the fundamental transversal is critical; no rule, however, can yet be formulated concerning this choice.

The existence of disordered materials with substitution ratio equal to the independence quotient of the respective periodic net is related to the multiplicity of solutions for maximally independent sets of its quotient graph. Some examples are analysed, summarizing different possible situations in 2-periodic nets. The disorder can be complete in two directions or partial and limited to one direction.

[1] Löwenstein, W. (1954). Am. Mineral. 39, 92. [2] Klee, W. E. (1974). Z. Kristallogr. 140, 154. [3] Eon, J.-G. (2016). Struct. Chem. 27, 1613.

[2] Klee, W. E. (1974). Z. Kristallogr. 140, 154. [3] Eon, J.-G. (2016). Struct. Chem. 27, 1613.

[3] Eon, J.-G. (2016). Struct. Chem. 27, 1613.

A 3-fold fabric denoted by , consists of three congruent non-parallel layers of strands in a plane together with a preferential ranking or ordering of the three layers at every point of that does not lie on the boundary of a strand, such that hangs together. The ranking must satisfy the fact that if belongs to a strand of layer and of layer (, ), then if layer is ranked before at , then layer must be ranked before layer at every point of . The fabric hanging together means it is impossible to partition the set of all strands, belonging to all the layers, into two nonempty subsets so that each strand in the first subset passes over (is ranked before, or takes precedence over) every strand in the second subset. The fabric is 3-way, if the strands lie in three different directions in [1].

This paper will discuss symmetry groups of 3-way 3-fold fabrics. The symmetry group of the fabric is a layer group and consists of isometries of the Euclidean space which map each strand of onto a strand of that either preserves the rankings at each point of (preserves the sides of ) or reverses all the rankings (interchange the sides of ). The approach to describe the symmetry group of will be to construct a corresponding design of , which characterizes the fabric in terms of the rankings of the layers.

To represent , we consider on the plane of , sets of equidistant parallel lines to represent the edges (boundaries) of the strands; with lines lying in three different directions. These lines divide into a set of polygonal regions or tiles, each of which is assigned a color indicating the ranking of the layers at every point of the region or tile. The result is a coloring of a tiling which is called the design of , An example of a sketch of a 3-way 3-fold fabric called the mad weave is shown in Figure 1. Its design is shown in Figure 2, given by a 3-coloring of the tiling by triangles. The colors yellow, blue and red represent the rankings (123), (231) and (312) respectively, where the three directions of the strands are represented with vectors at with each other, with labels 1, 2 and 3. is shown in Figure 2. The ranking (123) for example would mean a strand with direction 1 goes over a strand with direction 2, which goes over a strand with direction 3.

The layer group representing the symmetry group of is given by , where each element in will correspond to a symmetry of that either preserves or interchanges the sides of . The elements in that correspond to a symmetry of that preserve the sides of constitute the group , which is of index 1 or 2 in .

For the mad weave we have where , is the counterclockwise rotation centered at the point labeled P, is the horizontal reflection passing through P and are translations with vectors indicated. The group is the color group of and consists of all the elements of the symmetry group of the uncolored triangle tiling that effects a permutation of the colors. On the fabric , there corresponds is a counterclockwise rotation with center at and translations with vectors indicated, that preserve the sides of , and a reflection whose axis is the horizontal line through that reverses its sides.

This paper will discuss all possible layer groups of a 3-way 3-fold isonemal fabric, and give corresponding designs of the fabrics arrived at using color symmetry theory.

Figure 1. The sketch of the mad weave. Figure 2. The design of the mad weave. [1] B. Grünbaum, B., Shephard,G. C. (1998). Isonemal Fabrics. The American Mathematical Monthly 95, pp. 5-30.

Keywords: 3-way 3-fold fabric; layer group; symmetry group; color group; color symmetry

A conventional representation of a periodic crystal by its primitive unit cell and motif is well-known to be ambiguous. Indeed, any crystal can be generated from infinitely many primitive unit cells and motifs containing differently located atoms. Niggli’s reduced cell is unique but discontinuous under perturbations. Continuity of crystal representations is important for filtering out near duplicates in big datasets [1, Fig. 2d] of simulated crystals in Crystal Structure Prediction (CSP). Symmetry groups and many other descriptors discontinuously change under perturbations. So CSP landscapes are plotted only by two coordinates: the structural energy and density.

We describe a new geometric approach to generating a unique code (called a crystal isoset) of any periodic crystal, which continuously changes under perturbations of atoms [2-3]. This isoset is a material genome or a DNA-type code that allows an inverse design of new periodic crystals. Using these complete isosets, one can define numerical invariants via interatomic distances [4] and density functions [5]. For any crystal dataset irrespective of symmetries or chemical compositions, invariant vectors of crystals can be joined in a minimum spanning tree due to continuous distances quantifying crystal similarities. The Python code of distance-based invariants [4] has produced the map of over 12,000 structures from the Cambridge Structural Database overnight on a modest desktop, see Figure 1 in the attached pdf.

[1] Pulido, A., Chen, L., Kaczorowski, T., Holden, D., Little, M.A., Chong, S.Y., Slater, B.J., McMahon, D.P., Bonillo, B., Stackhouse, C.J. and Stephenson, A., 2017. Functional materials discovery using energy–structure–function maps. Nature, 543(7647), pp.657-664.

[2] Anosova, O., Kurlin, V. (2021). An isometry classification of periodic point sets. Peer-reviewed proceedings of Discrete Geometry and Mathematical Morphology, available at http://kurlin.org/research-papers.php#DGMM2021.

[3] Anosova, O., Kurlin, V. (2021). Introduction to Periodic Geometry and Topology. Available at https://arxiv.org/abs/2103.02749.

[4] Widdowson, D., Mosca, M., Pulido, A., Kurlin, V., Cooper, A.I. (2021). Average Minimum Distances of a periodic point set. Available at https://arxiv.org/abs/2009.02488.

[5] Edelsbrunner, H., Heiss, T., Kurlin, V., Smith, P, Wintraecken, M. (2021). The density fingerprint of a periodic point set. Peer-reviewed proceedings of Symposium on Computational Geometry. Available at http://kurlin.org/research-papers.php#SoCG2021.

Keywords: crystal similarities; maps of crystal datasets; crystal structure prediction; continuous classification of crystals

We thank all our co-authors of the joint papers above and all reviewers in advance for their valuable time and helpful suggestions.

Intriguing magnetic behaviour has been studied in perovskite structure type materials with the generic formula ABO₃ for decades. Here, A is usually an alkaline earth metal, or a rare earth element, while B is typically a transition metal. In the related double perovskite structure, two different B cations alternate in a rock salt ordering pattern, leading to the general formula A₂BB´O₆ [1]. One of the common features in perovskites is the tilting of the octahedra. As an effect, it tunes the band width of multiple orbitals and the strength and sign of the more typical exchange interactions.

The B-site ordered double-perovskite oxides, where A is Sr or Ba, B is Cu and B‘ is a diamagnetic hexavalent ion, crystallize in a tetragonal structure with short Cu-O bonds in the ab plane and long Cu-O bonds along the c axis, due to the cooperative Jahn-Teller effect of the octahedrally coordinated d⁹ Cu²⁺ ion. While structurally three dimensional, many of these compounds show low-dimensional magnetic properties [2].

The purpose of our study is to find and investigate high degeneracy frustrated magnetically correlated materials. Sr₂CuTe_0.5W_0.5O₆ has recently been reported as a spin-liquid, where the random distribution of Te occupying d-shell on the W (empty d-shell) position blocks a key superexchange path [3]. So, the main goal of this work was to investigate the nearby phase diagrams with the aim of searching new materials with interesting properties and promising characteristics.

Systematically spaced compositions were attempted in polycrystalline solid state reactions for Ba_xSr_2-xCuTe_0.5W_0.5O₆ and Sr₂Cu(Te_xMo_1-x)O₆ systems at atmospheric pressure. These efforts were characterized by X-ray diffraction and SQUID magnetometry where successful, and these results as well as future plans will be presented.
[1] Vasala S., Karppinen M. (2015). Prog. Solid State Chem. 43, pp. 1-36.
[2] Todate Y., Higemoto W., Nishiyama K., Hirota K. (2007). J. Phys. and Chem. of Solids, 68, 11, pp. 2107-2110.
[3] Mustonen O., Vasala S., Sadrollahi E., Schmidt K. P., Baines C., Walker H. C., Terasaki I., Litterst F. J., Baggio-Saitovitch E. & Karppinen M. (2018). Nat. Commun. 9, 1085, pp. 1-8.

The GPR52 receptor is a Class-A orphan G protein-coupled receptor (GPCR) whose endogenous ligand remains elusive. Highly expressed in the brain, it represents a promising therapeutic target for treating psychiatric disease and Huntington’s disease. However, tool ligand and drug discovery have been largely hampered by a lack of structural information due largely to the low homology (<20%) of GPR52 to any known GPCR structure. We reported three high resolution human GPR52 structures with and without a bound ligand. According to the structures, we observed a unique configuration of extracellular loop 2 (ECL2) that occupies the orthosteric pocket, a novel side pocket and a special winding mode for Transmembrane helix 5 (TM5). Mutagenesis and functional assay suggested the self-activation by ECL2. These findings provide unprecedented insights into the structural basis of GPR52 ligand recognition that will be valuable for GPR52 deorphanization and will guide the design of diverse ligands with distinct pharmacological properties that have not yet been possible.

Integrative modeling is an increasingly important tool in structural biology, providing structures by combining data from varied experimental methods and prior information. As a result, molecular architectures of large, heterogeneous, and dynamic systems, such as the ~52 MDa Nuclear Pore Complex, can be mapped with useful accuracy, precision, and completeness. Key challenges in improving integrative modeling include expanding model representations, increasing the variety of input data and prior information, quantifying a match between input information and a model in a Bayesian fashion, inventing more efficient structural sampling, as well as developing better model validation, analysis, and visualization. In addition, two community-level challenges in integrative modeling are being addressed under the auspices of the Worldwide Protein Data Bank (wwPDB). First, the impact of integrative structures is maximized by PDB-Dev, a prototype wwPDB repository for archiving, validating, visualizing, and disseminating integrative structures. Second, the scope of structural biology is expanded by linking the wwPDB resource for integrative structures with archives of data that have not been generally used for structure determination but are increasingly important for computing integrative structures, such as data from various types of mass spectrometry, spectroscopy, optical microscopy, proteomics, and genetics. To address the largest of modeling problems, a type of integrative modeling called metamodeling is being developed; metamodeling combines different types of input models as opposed to different types of data to compute an output model. Collectively, these developments will facilitate the structural biology mindset in cell biology and underpin spatiotemporal mapping of the entire cell.

Axonal degeneration is responsible for disease progression and accumulation of disability in many neurodegenerative conditions. Sterile alpha and Toll/interleukin-1 receptor motif-containing 1 (SARM1) is a nicotinamide adenine dinucleotide (NAD⁺)- cleaving enzyme whose activation triggers axon destruction [1-4]. Loss of the biosynthetic enzyme NMNAT2, which converts nicotinamide mononucleotide (NMN) to NAD⁺, activates SARM1 via an unknown mechanism. Using crystallography, cryo-EM, NMR and biochemical assays, we demonstrate that SARM1 is activated by an increase in the ratio of NMN to NAD⁺ and show that both metabolites compete for binding to the autoinhibitory N-terminal armadillo repeat (ARM) domain of SARM1 [5]. We show that NMN binding disrupts ARM-TIR interactions in the full-length SARM1 octamer, enabling its TIR domains to self-associate and form a catalytic site capable of cleaving NAD⁺ [5]. These structural insights identify SARM1 as a metabolic sensor of the NMN/NAD⁺ ratio, define the mechanism of SARM1 activation, and may enable a path to the development of allosteric inhibitors that block SARM1 activation.

[1] Essuman, K. et al.(2017). Neuron 93, 1334-1343.

[2] Essuman, K. et al. (2018). Curr. Biol. 28, 421-430.

[3] Horsefield, S. et al. (2019). Science 365, 793-799.

[4] Wan, L. et al. (2019). Science 365, 799-803.

[5] Figley, M. et al. (2021). Neuron 109, 1118–1136.

De novo cysteine biosynthesis is a pathway responsible for metabolizing inorganic sulfur to produce L-cysteine, which holds significance in the cellular activities of several organisms, majorly plants and microbes. Absence of this pathway in humans, accompanied by differential roles of accumulated L-cysteine in aiding adaptation of microbes in the harsh host environment, promoting toxin inactivation, biofilm formation, and development of antimicrobial resistance (AMR), make this pathway a lucrative target for novel therapeutics. The pathway is fuelled by a bienzyme complex, the Cysteine Synthase Complex (CSC), made up of CysE and CysK enzymes, where a hexameric CysE binds two CysK dimers, one on either end, to further cysteine production in a two-step fashion from L-serine. Recognition of industrial value in addition to the therapeutic potential of this pathway urges the need for further molecular investigations for its optimal exploitation. However, the large size of the molecular complex has put to question the feasibility of resolving its 3-D structure, partially reasoning the inability to obtain a 3-D structure even after nearly three decades of the complex’s discovery. Klebsiella pneumoniae, a pathogen with its multi-drug resistance (MDR) recognized in WHO’s list of six extensively MDR pathogens grouped as ES‘K’APE group of pathogens. Targeting the CSC of K. pneumoniae is a promising approach to up our armamentarium against the growing menace caused by the pathogen.

The success of rational structure-based drug discovery is driven by the availability of a crystal structure of the target protein complex. With a recent study reporting the SAXS-modelled CSC from E. coli, we aim to model the CSC complex using the K. pneumoniae CysE structure previously made available by our group, adopting a knowledge-based approach. The present poster reports the purification and characterization of recombinant CSC from K. pneumoniae, as an essential first step in progressing towards understanding its structure and biochemical function. Purified recombinant CSC was obtained and subjected to - (i) gel filtration chromatography to separate and estimate molar mass of the complex, (ii) dynamic light scattering for determining hydrodynamic radius and verifying homogenous population, and (iii) negative stain electron microscopy to visualize the purified complex. Simultaneous utilization of in silico tools integrated with techniques of structural biology is being carried to predict the 3-D structure of CSC, and identify residues involved in protein-protein interface stabilization. Following physical analysis and attempts to crystallize the CSC complex obtained from K. pneumoniae we observed heterogeneity in the CSC preparation, with a flexible/dynamic nature of the association between the two interacting proteins posing considerable challenges. Additionally, identification of interacting residues using in silico predictions would facilitate a better understanding of useful molecular recognition inferences within CSC, which presently are far from being well-understood.

Arsenic is a widely distributed toxic metalloid that poses a significant threat to human health by contaminating ground water systems [1]. Arsenic can exist in both organic and inorganic forms, with arsenite (AsO₃^3-) and arsenate (AsO₄^3-), being toxic species. Although arsenic is hazardous to human health, some prokaryotes have developed unique mechanisms that utilise arsenite (AsO₃^3-) and arsenate (AsO₄^3-) for respiration and therefore as energy sources.

The organism Rhizobium sp. NT-26, respires with arsenite and employs the arsenite oxidase enzyme (Aio) for its crucial respiratory activity, which catalyzes the oxidation of arsenite (AsO₃^3-) to arsenate (AsO₄^3-). The Aio enzyme consists of a large catalytic subunit (AioA), which contains a molybdenum centre and a 3Fe-4S cluster, and a small subunit (AioB) containing a Rieske 2Fe-2S cluster. Arsenite is oxidized to arsenate at the Mo site,concomitantly reducing Mo(VI) to Mo(IV) [2]. The electrons are then passed to the 3Fe-4S cluster, the Rieske cluster in AioB and finally to an electron acceptor, which is cytochrome c₅₅₁ (cyt c₅₅₁) [2, 3]. Structures of interprotein transfer complexes are interesting as they form via extensive electrostatic interactions, which are highly transient. Structural flexibility at the protein-protein interface promotes fast dissociation of the complex following electron transfer [4]. To date, the structure of the Aio and cyt c₅₅₁ complex has not been investigated, and the kinetics and thermodynamics of the Aio to cyt c₅₅₁ interaction are unknown. In this study, we describe the structure of the Aio/cyt c₅₅₁ complex, determined by X-ray crystallography. The structure provides insight into various types of interactions (hydrogen bonding, salt bridges and electrostatic interactions) of the complex that can be studied further to understand the mechanism and specificity between the partner proteins during electron transfer.

[1] H. V. Aposhian, and M. M. Aposhian, “Arsenic toxicology: five questions,” Chem Res Toxicol, vol. 19, no. 1, pp.1-15, Jan, 2006.

[2] T. P. Warelow, M. Oke, B. Schoepp-Cothenet, J. U. Dahl, N. Bruselat, G. N. Sivalingam, S. Leimkühler, K.

Thalassinos, U. Kappler, and J. H. Naismith, “The respiratory arsenite oxidase: structure and the role of residues surrounding the rieske cluster,” PLoS One, vol. 8, no. 8, pp. e72535, 2013.

[3] P. J. Ellis, T. Conrads, R. Hille, and P. Kuhn, “Crystal structure of the 100 kDa arsenite oxidase from Alcaligenes faecalis in two crystal forms at 1.64 Å and 2.03 Å,” Structure, vol. 9, no. 2, pp. 125-132, 2001.

[4] D. Leys, and N. S. Scrutton, “Electrical circuitry in biology: emerging principles from protein structure,” Curr Opin Struct Biol, vol. 14, no. 6, pp. 642-7, Dec, 2004.

α-L-Fucosidases (EC 3.2.1.51) catalyse hydrolysis of the α-L-fucosyl moiety from the non-reducing terminus of oligosaccharides and glycoconjugates. New representatives are sought for their unique functional properties or particular specificity, especially in connection with the transglycosylation ability to enable targeted modification of compounds for biomedical applications. They belong to several glycosyl hydrolase families, GH29, GH95, GH139, GH141, and GH151, and utilize either the retaining or inverting mechanism. While members of some families, e.g. GH29, have been studied thoroughly, the structural information and mechanistic details for other families, including GH151, are missing.

In our previous studies [1,2] and our more recent results we bring structural and functional insights into the mechanism, active site complementation and specificity of two isoenzymes from bacterium Paenibacillus thiaminolyticus. The proteins were characterised using a range of biophysical techniques, small angle X-ray scattering, X-ray crystallography, and in silico analysis (substrate docking), together with assays of α-L-fucose hydrolysis and transglycosylation ability. The crystal structure of α-L-fucosidase isoenzyme 1 (GH29) showed a new and unusual organization of the enzyme in a hexamer, with the active sites exposed to the surrounding environment and suggested active site complementation. Mutagenesis and catalytic assays confirmed the first case of active site complementation in α-L-fucosidases [2]. Our recent crystal structure of isoenzyme 2 from the same bacterium brings the first structural insight into the GH151 family, with unexpected oligomerization, enclosure of the active site inside the oligomer, and, again, proven active site complementation. Mutations modifying the complemented amino acid lead to changes in the catalytic properties of both enzymes. The comparison on the level of structure, functional, and biophysical data for the two isoenzymes brings answers to some principal questions regarding α-L-fucosidase substrate specificity and raises new questions about the functionality and stability of complemented active sites within these families of α-L-fucosidases.

This work was supported by the Czech Academy of Sciences (86652036), by the European Regional Development Fund (CZ.02.1.01/0.0/0.0/15_003/0000447, CZ.02.1.01/0.0/0.0/16_013/0001776, CZ.1.05/1.1.00/02.0109), by the Ministry of Education, Youth and Sports of the Czech Republic (LM2015043 and LM2018127, support of Biocev-CMS – Crystallization, Biophysics and Diffraction facilities of CIISB, part of Instruct-ERIC).

1. Benešová E, Lipovová P, Krejzová J, Kovaľová T, Buchtová P, Spiwok V & Králová B (2015) α-L-Fucosidase isoenzyme iso2 from Paenibacillus thiaminolyticus. BMC Biotechnol. 15, 36.

2. Kovaľová T, Kovaľ T, Benešová E, Vodičková P, Spiwok V, Lipovová P, Dohnálek J (2019) Active site complementation and hexameric arrangement in the GH family 29; a structure–function study of α-L-fucosidase isoenzyme 1 from Paenibacillus thiaminolyticus. Glycobiology, 29(1), 59–73.

Molecular flexibility has a profound impact on the number of possible ways molecules can pack in the solid state. The phenomenon of Conformational Polymorphism has been well-studied (Cruz-Cabeza, 2014) and recognised to be very common in complex pharmaceuticals (Cruz-Cabeza, 2015).

Perhaps what is less well understood is how molecular flexibility impacts crystallisation. In previous works, we studied the nucleation and growth kinetics of a number of rigid benzoic acid derivatives (Cruz-Cabeza, 2017). We have now studied the nucleation and growth kinetics of a number of flexible benzoic acid derivatives asking the fundamental question “Can Molecular Flexibility Control Crystallisation?” (Tang, 2021). Our kinetic data shows that when the energy barriers for conformational change are small, molecular flexibility is not rate controlling in crystallisation. Aromatic stacking was found, again, to be the key controlling step in the kinetics of crystallisation (Tang, 2021).

References:

Cruz-Cabeza., A.J., and Bernstein, J. (2014). Conformational Polymorphism. Chem. Rev. 114, 2170-2191.

Cruz-Cabeza., A.J., Reutzel-Edens, S.M. and Bernstein, J. (2015). Facts and Fictions about Polymorphs. Chem. Soc. Rev. 44, 8619-8635.

Cruz-Cabeza., A.J., Davey, R.J., Sachithananthan, S.S., Smith, R., Tang, S.K., Vetter, T. and Xiao, Y. (2017). Aromatic Stacking-a key step in nucleation. Chem. Commun. 53, 7905-7908.

Tang, S.K., Davey, R.J., Sacchi, P. and Cruz-Cabeza, A.J. (2021). Can Molecular Flexibility Control Crystallisation? The Case of para substituted benzoic acid. Chem. Sci. accepted.

Purpose

Molecular and crystallographic modelling can be used to de-risk the development of active pharmaceutical ingredients into drug products. Here we present an application of multi-scale modelling workflows to characterise polymorphism in ritonavir with regard to its stability, bioavailability and processing.

Methods

Molecular conformation, polarizability and stability are examined using quantum mechanics (QM). Intermolecular synthons, hydrogen bonding, crystal morphology and surface chemistry are modelled using empirical force fields.

Results

The form I conformation is more stable and polarized with more efficient intermolecular packing, lower void space and higher density, however its shielded hydroxyl is only a hydrogen bond donor. In contrast, the hydroxyl in the more open but less stable and polarized form II conformation is both a donor and acceptor resulting in stronger hydrogen bonding and a more stable crystal structure but one that is less dense. Both forms have strong 1D networks of hydrogen bonds and the differences in packing energies are partially offset in form II by its conformational deformation energy difference with respect to form I. The lattice energies converge at shorter distances for form I, consistent with its preferential crystallization at high supersaturation. Both forms exhibit a needle/lath-like crystal habit with slower growing hydrophobic side and faster growing hydrophilic capping habit faces with aspect ratios increasing from polar-protic, polar-aprotic and non-polar solvents, respectively. Surface energies are higher for form II than form I and increase with solvent polarity. The higher deformation, lattice and surface energies of form II are consistent with its lower solubility and hence bioavailability.

Conclusion

Inter-relationship between molecular, solid-state and surface structures of the polymorphic forms of ritonavir are quantified in relation to their physical-chemical properties.

The solvent influence on crystallisation outcome has been shown in a large number of cases, most often as the observation of different crystal forms crystallising from recrystallization from different solvents. More detailed work has been conducted to investigate solute-solute and solute-solvent interaction in solution with increasing saturation to mimic the crystallisation process, and to understand and use the solvent influence on crystallisation with the ultimate aim to control the crystallisation outcome.[1, 2, 3] However, to date there are contradicting opinions whether solution interaction drives the nucleation of a particular crystal form or if other factors such as the exact nucleation pathway, solvation state of clusters and solute conformations, outweigh the solvent influence.[4]

But can the nucleation step be completely ignored? Our hypothesis is that strong intermolecular interactions in dilute solution are likely to be carried through the nucleation step into the final crystal structure independent from the nucleation pathway followed, and weak interactions are unlikely to survive the nucleation step. Verification of this hypothesis would allow us to directly connect dilute solutions with the crystallisation product, and even allow for prediction of the existence of a particular crystal form before performing crystallisation experiments.

Using a combination of vibrational and nuclear magnetic spectroscopy, X-ray and neutron diffraction and molecular dynamics simulations, I will show the link between solution and solid-state interactions for multi-component crystal forms and how the microscopic structure of the solution can influence the crystallisation outcome.[5]

[1] Davey, R. J., Dent, G., Mughal, R. K., Parveen, S. (2006). Cryst. Growth Des. 6, 1788. [2] Hunter, C. A., McCabe, J. F., Spitaleri, A. (2012). CrystEngComm 14, 7115. [3] Derdour, L., Skliar, D. (2014). Chem. Eng. Sci. 106, 275. [4] Du, W., Cruz-Cabeza, A. J., Woutersen, S., Davey, R. J., Yin, Q. (2015). Chem. Sci. 6, 3515. [5] Jones, C. D., Walker, M., Xiao, Y., Edkins, K. (2019). Chem. Commun. 55, 4865.

Pharmaceutical cocrystals are the subject of interest in academic and industrial research as they offer better control over physicochemical, mechanical and pharmacokinetic properties of active pharmaceutical ingredients (API) while their therapeutic activity remains intact. This class of materials, as well as single component pharmaceutical solids, is prone to exhibit the different packing arrangements and molecular conformations within the crystal lattice with the same chemical composition i.e. polymorphism. Hot melt extrusion (HME) is a solvent-free, continuous and scalable technique which makes it an important candidate for the industrial application in a continuous synthesis of pharmaceutical cocrystals. However, processing APIs and coformers with significant difference in their melting temperatures is limited by the possibility of a lower-melting substrate decomposition. As a consequence, reduction of the conversion to a cocrystal during extrusion may be observed.

In this work we used mechanochemical approach to obtain two pharmaceutical cocrystals known to exist in at least two polymorphic forms: theophylline (TP) with benzamide (BZ) [1] and nicotinamide (NCT) with malonic acid (MA) [2] via matrix assisted cocrystallization (MAC) using hot melt extrusion [3] and polymer assisted grinding (POLAG) [4]. The polymers used in the experiments were polyethylene glycol derivatives of different molecular weight (in range from 200 to 20000), Tween^® 20 and 80, Span^® 80, Brij^® 93 and Poloxamers of different HLB values. The milling procedures were performed using a ball-mill (Fritsch Mini-Mill Pulverisette 23) while hot melt extrusion processing was conducted using a co-rotating twin-screw Process 11 extruder (Thermo Fisher Scientific, Karlsruhe, Germany). Structures of the synthesised products were investigated using X-ray powder diffraction (D2 PHASER, Bruker AXS, Karlsruhe, Germany) and Fourier Transform Infrared Spectroscopy (Nicolet 380, Thermo Scientific, USA) whereas phase transitions were assessed using differential scanning calorimetry (DSC 214 Polyma, Netzsch, Germany).

The physical mixture of TP and BZ is difficult to process in the hot melt extrusion process because of the melting temperature difference (m_pTP = 273 °C, m_pBZ = 128 °C). In case of processing neat mixture of API and coformer, the barrel temperature of 120 °C was necessary to perform a successful cocrystal extrusion whereas the addition of a polymer matrix allowed to decrease the process temperature to 40 °C. In the formulations of higher polymer concentration, i.e. 30% and more, the extrusion led to TP:BZ (1:1) cocrystal form I occurrence while polymer content below 20% resulted in form II cocrystallization. In contrast both polymorphic forms of TP:BZ (1:1) cocrystal were obtained in grinding experiments by neat and liquid assisted grinding as reported previously [1] while all POLAG led exclusively to form I formation. The addition of solid state polymers in a milling procedure accelerated the cocrystallization rate, however, presence of the liquid polymers inhibited cocrystal formation due to both difficulties in mixing or dissolution of one of the components in liquid polymer. Changes in the polymer content and polarity of the matrix (controlled via chain length of polyethylene glycol), did not result in obtaining of TP:BZ (1:1) form II. Furthermore, time required for complete cocrystallization was significantly shorter (3-5 minutes) in the hot melt extrusion as compared to the grinding experiments (40 min). In contrast to TP:BZ cocrystal, the melting temperature of API and coformer of NCT:MA (2:1) cocrystal are significantly closer (m_pNCT = 129 °C, m_pMA = 135 °C) which simplifies extrusion process. In the examined range of polymer concentrations form I of NCT:MA (2:1) was obtained, similarly grinding of NCT and MA (neat, liquid assisted and polymer assisted grinding) resulted also in form I appearance of NCT:MA (2:1) cocrystal.

Polymers used in matrix assisted techniques can act as cocrystallization rate accelerating agents enabling to obtain higher cocrystal yield. In addition, polymers can act as the functional components of the formulation enabling to tailor important pharmaceutical parameters e.g. tabletability, dissolution rate or release profile. The addition of polymers in continuous cocrystallization via hot melt extrusion allows to reduce the time and temperature of the process enabling processing of thermolabile substances. Furthermore, control over polymorphic outcome enabled selective synthesis of a stable polymorph which prevents unwanted structural changes during formulation and storage of the final product. On these terms matrix assisted cocrystallization, as a modification of hot melt extrusion method, holds a promise in the development of polymorph selective cocrystallization processes.

[1] Fischer, F., Heidrich, A., Greiser, S., Benemann, S., Rademann, K. & Emmerling, F. (2016) Cryst Growth Des. 16, 1701.

[2] Lemmerer, A., Adsmond, D.A., Esterhuysen, C. & Bernstein, J. (2013) Cryst Growth Des. 13, 3935.

[3] Boksa, K., Otte, A. & Pinal, R. (2014) J Pharm Sci. 103, 2904.

[4] Hasa, D., Carlino, E. & Jones, W. (2016) Cryst Growth Des. 16, 1772.

The CSD currently contains more than 1.1 million structures.[1] This impressive number is the result of at least the same number of experiments, which were for the most part all manually set up. There are very few reports about robots that were used to set up crystallization trials for the growth of single crystals of small molecules.[2]

Recently, we have developed an anion screen to crystallize organic [3, 4] and inorganic [5] cations of small molecules from aqueous solutions. For some of these studies [3, 5], we employed robotic systems such as the Crystal Gryphon LCP and the Rock Imager 1000, both of which are well established in protein crystallography [6, 7].

In this presentation, we would like to present our work, which resulted in a cation screen. This screen consists of 96 different aqueous solutions with almost 90 different cations, inorganic and organic ones. There exists a commercial cation screen dedicated exclusively for protein crystallography, but this screen only contains seven different inorganic cations. We will present anions that could be crystallized with the help of this screen and thereby elucidating on the possibilities and limitations of our novel cation screen.

[1] Taylor, R. & Wood, P. A. (2019). Chem. Rev. 119, 9427. [2] Tyler, A. R., Ragbirsingh, R., McMonagle, C. J., Waddell, P. G., Heaps, S. E., Steed, J. W., Thaw, P., Hall, M. J. & Probert, M. R. (2020). Chem 6, 1755. [3] Nievergelt, P. P., Babor, M., Čejka, J. & Spingler, B. (2018). Chem. Sci. 9, 3716. [4] Babor, M., Nievergelt, P. P., Čejka, J., Zvoníček, V. & Spingler, B. (2019). IUCrJ 6, 145. [5] Alvarez, R., Nievergelt, P. P., Slyshkina, E., Müller, P., Alberto, R. & Spingler, B. (2020). Dalton Trans. 49, 9632. [6] Cherezov, V. (2011). Curr. Opin. Struct. Biol. 21, 559. [7] Broecker, J., Morizumi, T., Ou, W.-L., Klingel, V., Kuo, A., Kissick, D. J., Ishchenko, A., Lee, M.-Y., Xu, S., Makarov, O., Cherezov, V., Ogata, C. M. & Ernst, O. P. (2018). Nat. Protoc. 13, 260.

This research was funded by the University of Zurich and the R’Equip programme of the Swiss National Science Foundation (project No. 206021_164018).

Febuxostat (FB) is a poorly water-soluble BCS class II drug that is used for the treatment of the inflammatory disease arthritis urica (gout). FB has a rich solid form landscape, including many polymorphs, solvates, salts and a few co-crystals [1, 2]. With the aim of improving the aqueous solubility of FB we expanded the search for novel salts and co-crystals by applying modeling techniques followed by directed crystallization experiments. Novel salt and co-crystal forms of FB were obtained in a controlled manner using the Crystal16 platform [3]. Making use of the integrated transmission technology together with 16 parallel reactors at a volume of 1 mL, the Crystal16 easily allows the scientist to assess salt or co-crystal formation.

The salt/co-crystal formation was evidenced by powder X-ray diffraction and differential scanning calorimetry. Aqueous powder dissolution was carried out to determine if solubility improvement is achieved. Within the scope of this workflow, the nanocrystalline powders were not ideal for crystal structure elucidation from powder/single crystal X-ray diffraction but suited for electron diffraction experiments [4 -5 ]. By using a dedicated electron diffractometer [6], the crystalline structures of these materials were easily accessible.

Here we report on the successful crystallization and characterization of pharmaceutical relevant co-crystals using a new workflow: AI (artificial intelligence) predictions [7], the Crystal16 platform and an electron diffractometer.

[1] Maddileti D., Jayabun S. K., Nangia A. (2013) Crystal Growth & Design 13 (7), 3188.
[2] Li L. Y., Du R. K.,. Du Y. L, Zhang C. J., Guan S., Dong C. Z., Zhang L. (2018) Crystals 8 (2), 85.

[3] Li W., de Groen M., Kramer H. J. M., de Gelder R., Tinnemans P., Meekes H., and ter Horst J. H. (2021) Cryst. Growth Des. 21 (1), 112.

[4] Andrusenko I., Potticary J., Hall S. R., Gemmi M. (2020) Acta Cryst. B76, 1036.

[5] Hamilton V., Andrusenko I., Potticiary J., Hall C., Stenner R., Mugnaioli E., Lanza A. E., Gemmi M., Hall S. R.(2020) Cryst. Growth Des. 20, 4731.

[6] ELDICO Scientific AG has developed a dedicated device for electron diffraction experiments. This device, its capabilities, and advantages over (modified)-TEMs will be showcased in this congress too. A scientific publication on a dedicated device for ED experiments is in preparation too.

[7] Devogelaer J.J, Meekes H., Tinnemans P., Vlieg E., de Gelder R. (2020) Angew.Chem. Int.Ed. 59, 21711.

The word “chiral”, introduced by Lord Kelvin in 1904, refers to an object whose image in a plane mirror does not coincide with itself [1]. One intuitive example is the left and right hands, which are mirror images of each other but are not superimposable. The two forms of a chiral object are called enantiomorphs or enantiomers for molecules. The chirality is a key property which is found in all branches of science, from biology to physics and at different scales, from microscopic to macroscopic objects. For instance, in biology, the notion of chirality is crucial for living organisms and plays a critical role in molecular recognition [2]. In parallel, in fundamental physics, the chirality is also an important property, as shown by the example of the weak interaction, not invariant under mirror symmetry [3], which only interacts with left-chiral fermions or right-chiral anti-fermions. The chirality can also be found in solid state physics, in crystallography where it refers to the concept of spatial inversion symmetry rather than mirror symmetry, or again in magnetism, where it refers to the sense of rotation of the spins on oriented loops [4].

In this talk, I will focus on the concept of chirality in magnetic ordered systems. I will present the archetype chiral magnetic compound, Ba₃NbFe₃Si₂O₁₄, which hosts three different types of chirality. This system belongs to the family of langasite materials providing interesting geometrically frustrated spin lattices. It crystallizes in the non-centrosymmetric P321 space group and displays a structural chirality. The magnetic Fe³⁺ ions form an original triangular network in the (a,b) planes, stacked along the c-axis (see Figure 1). Below T_N ~ 27 K, the system orders magnetically with a 120° spins structure within each triangle, in the (a,b) planes, and presents a helical modulation along the perpendicular direction, i.e. the c-axis, with a period of ~ 7 lattice parameters (see Figure 1) [5]. Surprisingly, this magnetic ground state displays a unique sense of rotation of the spins within the triangles (triangular chirality) as well as a unique sense of rotation of the spins along the helices (helical chirality). This multi-chiral magnetic ground state is correlated to the structural chirality through a twist of the inter-plane exchange interactions (see Figure 1) [5-7]. I will present the scientific arguments that led to the discovery of such complex multi-chiral magnetic structure and the consequences on its physical properties. I will conclude by presenting our last results focusing on the critical regime and the nature of the phase transition toward this peculiar multi-chiral magnetic order.

[1] Lord Kelvin, (1904). Baltimore Lectures. London: C. J. Clay and Sons 619.

[2] Inaki, M., Liu, J., & Matsuno, K., (2016). Phil. Trans. R. Soc. B 371, 20150403.

[3] Lee, T. D. & Yang, C. N., (1956). Phys. Rev. 104, 254. Lee, T. D., Oehme, R. & Yang, C. N., (1957). Phys. Rev. 106, 340.

[4] Simonet, V., Loire, M. & Ballou, R., (2012). Eur. Phys. J. Spec. Top. 213, 5.

[5] Marty, K., Simonet, V., Ressouche, E., Ballou, R., Lejay, P. & Bordet, P., (2008). Phys. Rev. Lett. 101, 247201.

[6] Loire, M., Simonet, V., Petit, S., K. Marty, Bordet, P., Lejay, P., Ollivier, J., Enderle, M., Steffens, P., Ressouche, E., Zorko, A. & Ballou, R., (2011). Phys. Rev. Lett. 106, 207201.

[7] Chaix, L., Ballou, R., Cano, A., Petit, S., de Brion, S., Ollivier, J., Regnault, L.-P., Ressouche, E., Constable, E., Colin, C. V., Zorko, A., Scagnoli, V., Balay, J., Lejay, P., & Simonet, V., (2016). Phys. Rev. B 93, 214419.

In metallic heavy fermion materials the magnetic ground state is often a spin density wave (SDW) phase in which the magnetization vary periodically with a period that is usually incommensurate with the parent structure lattice. These phases are associated to the itinerant character of the f-electron present in the system and are intimately related to the electronic structure near the fermi energy.

This is the case in the tetragonal heavy-fermion compound CeAuSb₂ which shows the development of a SDW phase below T_N~6.5 K with a propagation vector k₁ = (0.136, 0.136, 0.5) [1-2]. This phase is very sensitive to external stimuli and, indeed, the systems shows two metamagnetic phase transitions with magnetic field applied along the [001] direction [1-2]. An additional parameter which can tune the magnetic ground state is the application of a uniaxial stress, for example along the [010] direction. Extensive transport and thermodynamic measurements [2, 3, 4] indicate a sudden and anisotropic jump of the resistivity at an induced strain along the axis of compression of 0.5% indicating a first order transition.

In this talk we present single crystal time of flight neutron diffraction data collected under the application of a [010] uniaxial stress to characterize the magnetic phases of CeAuSb₂. The neutron data indicate a change of the propagation vector from k₁ at low stress to k₂ = (0, 0.25, 0.5) at high stress. Even with the geometrical constrains imposed from the experiment sample environment, which allows to collect only a limited number of magnetic reflections, we will show that it is possible to determine and refine the magnetic structure with the support of group theory calculations and magnetic symmetry analysis. The commensurate nature of the propagation vector is attributed to the presence of a lock in invariant in the free energy and we will show that the magnetic ground state under compressive stress is characterized by the presence of two primary order parameters related to different irreducible representations of the parent structure.

[1] Marcus, G. G., Kim, D.-J., Tutmaher, J. A., Rodriguez-Rivera, J. A., Birk, J. O., Niedermeyer, C., Lee, H., Fisk, Z., Brohol, C. L. (2018). Phys. Rev. Lett. 120, 097201

[2] Zhao, L., Yelland, E. A., Bruin, J. A. N., Sheikin, I., Canfield, P. C., Fritsch, V., Sakai, H., Mackenzie, A. P., Hicks, C. W. (2016). Phys. Rev. B 93, 195124.

[3] Park, J., Sakai, H., Erten, O., Mackenzie A. P., Hicks, C. W. (2018). Phys. Rev. B 97, 024411 [4] Park, J., Sakai, H., Mackenzie A. P., Hicks, C. W. (2018). Phys. Rev. B 98, 024426.

[4] Park, J., Sakai, H., Mackenzie A. P., Hicks, C. W. (2018). Phys. Rev. B 98, 024426.

Magnetic interactions are the fundamental components for the fascinating variety of complex magnetic structures and properties found in many functional materials. Identifying, understanding, and finally predicting these interactions is an essential step towards their utilization in novel devices. One of these basic interactions is the Dzyaloshinskii-Moriya interaction (DMI) – an antisymmetric exchange coupling favouring a perpendicular arrangement of magnetic moments, and thus a canting in otherwise collinear structures [1,2]. The DMI, originally introduced in the late 1950s to explain ‘weak ferromagnets’ (not perfectly collinear antiferromagnets), regained the interest in current condensed matter research as it was found to be the driving force to stabilize various novel topological noncollinear magnetic structures, such as spin spirals [3], magnetic skyrmions [4], magnetic soliton lattices [5] and others. In particular for spintronic applications, the DMI shows promising characteristics towards the development of next-generation devices [6]. Although the magnitude of the DMI-induced canting is usually small, the direction can have a fundamental impact on the spin chirality and the resulting magnetic and multiferroic properties [7]. Here, we present polarized neutron diffraction (PND) as an efficient technique for the determination of the absolute direction of the DMI in weak ferromagnetic materials, as recently established by us [8].

We provide the basic formalism for a symmetry analysis of the DMI in crystal structures and show how to relate the measured PND data with the absolute DMI direction. We exemplify this approach in weak ferromagnetic MnCO₃ and identify the magnetic moment configurations for a positive or negative sign of the DMI with an applied magnetic field as shown in Fig. 1. Using PND [9], we can distinguish even from the measurement of a single suitable Bragg reflection between the two configurations and unambiguously reveal a negative DMI sign in MnCO₃. This is in agreement with previous results obtained by resonant magnetic X-ray scattering and thus, validates the method [10]. We demonstrate the generality of our method by providing further examples of topical magnetic materials with different symmetries and support our findings with ab-initio calculations, which reproduce the experimental results.

Figure 1. The local environment of the z=0 manganese atom in the hexagonal unit cell of MnCO₃. The six nearest-neighbour manganese atoms of the other magnetic sublattice are shown as light and dark blue spheres located above and below the central atom, respectively. The oxygen atoms between these manganese layers are shown as small yellow spheres. Panels (a) and (b) show the two possible magnetic moment configurations stabilized dependent on the sign of the D_z DMI component by applying an external magnetic field along the [110] direction aligning the weak ferromagnetic moment.

[1] V. E. Dzyaloshinskii, Sov. Phys. - JETP 5(6), 1259 (1957)

[2] T. Moriya, Phys. Rev. 120(1), 91 (1960)

[3] M. Bode et al., Nature 447, 190 (2007)

[4] S. Heinze et al., Nat. Phys. 7, 713 (2011)

[5] Y. Togawa et al., Phys. Rev. Lett. 108, 107202 (2012)

[6] S. S. P. Parkin et al., Science 320, 190 (2008)

[7] J. Cho et al., J. Phys. D: Appl. Phys. 50, 425004 (2017)

[8] H. Thoma et al., Phys. Rev. X 11, 011060 (2021)

[9] H. Thoma et al., J. Appl. Crystallogr. 51, 17 (2018)

[10] V. E. Dmitrienko et al., Nat. Phys. 10, 202 (2014)

Ca₂RuO₄ (CRO), the close neighbour of the famous superconductor Sr₂RuO₄ displays surprisingly different behaviour to its neighbour, exhibiting insulating behaviour below an irreversible metal-insulator transition at T_MI = 357K. In the insulating state CRO displays orbital ordering at T_OO = 260K and antiferromagnetic ordering below T_N = 110K. This material has been extensively investigated but still questions remain regarding the nature of the insulating state and whether Mott gaps are opened only on certain orbitals, or whether the insulating state is a result of purely structural change. While recent publications have tended towards the latter of these possibilities, previous results observing varying orbital concentrations with temperature have not been explained. Here we will show new resonant elastic x-ray scattering (REXS) results from the Ruthenium absorption edge made on the synchrotron beamline I16 at Diamond. The resonant spectra provide a unique way of looking at the ordered magnetic and orbital structure of this material and we will present a systematic approach to understanding the different contributions to these signals.

Binary rare-earth intermetallic compounds of R₇Rh₃ type attract possess complex magnetic phase diagrams and rich variety of magnetic structure transitions. In particular, three temperature induced magnetic phase transitions were observed at T_N = 32 K, T_t1 = 21 K, and T_t2 = 9 K [1, 2]. In this work, a comprehensive study of the low-temperature magnetic state of Ho₇Rh₃ was carried out using neutron diffraction and nonlinear AC magnetic susceptibility.

Analysis of the neutron diffraction data and the temperature dependence of the harmonics χ_nω'(T) and χ_nω''(T) (n = 1, 2, 3) (Fig. 1) showed that the magnetic phase transition at a temperature T_N = 32 K is associated with emergence of an incommensurate magnetic structure of spin density wave type described by the magnetic superspace group Cmc2₁1'(00g)0sss. Upon further cooling below the temperature T_t1 ~ 21 K, a "squaring-up" process begins reflecting evolution of the amplitude modulated incommensurate magnetic structure towards a rectangular structure of the "antiphase domains" type. At T<T_t2 ~ 9 K, the magnetic structure can be described by the magnetic supersymmetry groups Cm'c2₁'(00g)ss0 or Cmc'2₁'(00g)000, which are subgroups of index i = 2 of the Cmc2₁1'(00g)0sss magnetic superspace group. Symmetry breaking associated with {1’|0 0 0 1/2} operation lost at the transition allows the emergence of a spontaneous magnetization confined in the basal plane of the hexagonal structure Ho₇Rh₃ while magnetic structure keeps its incommensurate character. Measurements of the linear and nonlinear AC magnetic susceptibility revealed that emergence of the weak spontaneous magnetization in the sample are accompanied by pronounced anomalies in the temperature dependencies of the 2nd and 3rd harmonics of the AC susceptibility ascribed to a symmetry breaking due to the loss of the time inversion symmetry {1’|0 0 0 1/2}.

[1] Tsutaoka, T., et al, (2003). Physica B. 327, 352-356.

[2] Tsutaoka, T., et al, (2016). J. of Alloys and Compounds. 654, 126-132.

Monovalent inorganic gallium compounds are very rare, whereas this is not the case for indium compounds. As the chemistry of Ga(I) can be assumed to be dominated by its lone pair that favors unsymmetrical environments, the influence of the lone pair of In(I) is usually not very pronounced. Thus, there are very few isostructural Ga and In compounds. Starting from the elements, we have now obtained the new telluridogallates(I) REGaTe₂ and related compounds REInTe₂ (RE = La – Nd). Although their orthorhombic unit-cell dimensions are similar, the structures combine modular entities in different ways that enable more or less space for lone pairs. In the case of In-containing compounds, data were collected using microfocused synchrotron radiation from microcrystals that were selected and pre-characterized by electron microscopy

The compounds REGaTe₂ crystallize in the non-centrosymmetric space group Pmc2₁, their lattice parameters reflect the lanthanide contraction. In contrast to telluridogallates(III) such as CuGaTe₂ [1] and AgGaTe₂ [2] that contain [GaTe₄] tetrahedral, its characteristical structural feature is a chain of GaTe₃ pyramids sharing two Te atoms with neighboring pyramids. This would be typical for a telluridogallate(I), however, chemical bonding and charge distribution are not trivial. Bond valence sums confirm the electron-precise description according to RE^IIIGa^ITe^-II₂, and the coordination of gallium(I) is pyramidal as expected for a lone-pair atom. Bader charges for LaGaTe₂ (La +1.5, Ga +0.5, Te ‑0.8 – ‑0.9) suggest only partial electron transfer. Thus, REGaTe₂ are rare examples of compounds with exclusively monovalent Ga atoms, probably the first one without organic residues. In NdGaTe₂, a short Nd-Ga distance of 3.13 Å is a possible indication of an interaction of the lone pair of Ga(I) with the Nd atoms. This is stronger than, for example, in NdGaSb₂ (Nd-Ga distance 3.35 Å),[3] which has a different structure and bonding situation. Similar Nd-Ga distances are observed in intermetallic phases such as NdGa [4] or NdGaRh [5], so that a description as an oxidized intermetallic phase may also be considered. A formal consideration in the framework of the Zintl concept would assume a mixed chain-like [Ga^(‑2)Te⁽⁰⁾Te^(-1)]^3- polyanion; note that in these formal “charges” are note expected correspond to oxidation states. It is consistent with all descriptions that the distances of 2.67 Å to the terminal Te atom are shorter than those to Te atoms bridging along the chain (2.95 Å). Interactions between the polyanionic chains appear negligible. The Nd atoms are located in single-capped trigonal prisms of Te atoms, with Ga atoms forming two additional caps.

In contrast, compounds REInTe₂ are centrosymmetric, they adopt a structure with the space group Amm2. Although this can, in principle, be related to the structure of REGaTe₂ by group-subgroup relationships, the cationic modules are not shifted against each other in the indium compounds. The indium atoms are located in capped trigonal prisms that show little lone-pair influence, their environment is more symmetrical. Although these polyhedra are interconnected in a fashion that is similar to the one in REGaTe₂, the distances between the chains are not much larger than the ones within the chains so that the compound is a rare-earth indium (I) telluride rather than a telluridoindate(I) with a discrete polyanion. Still, bond valence sums correspond to RE^IIIIn^ITe^-II₂. The anionic In- or Ga-containing substructures thus show a pronounced influence on the arrangement of the cationic substructures – they interconnect similar modules is different ways. The CrB structure type may be regarded as an aristotype of both arrangements.

[1] T. Plirdpring, K. Kurosaki, A. Kosuga, T. Day, S. Firdosy, V. Ravi, G. J. Snyder, A. Harnwunggmoung, T. Sugahara, Y. Ohishi (2012) Adv. Mater. 24, 3622.
[2] S. Chatraphorn, T. Panmatarite, S. Pramatus, A. Prichavudhi, R. Kritayakirana, J.‐O. Berananda, V. Sayakanit, J. C. Woolley (1985) J. Appl. Phys. 57, 1791.
[3] A. M. Mills, A. Mar, (2001) J. Am. Chem. Soc. 123, 1151.
[4] S. P. Yatsenko, A. A. Semyannikov, B. G. Semenov, K. A. Chuntonov (1979) J. Less-Common Met. 64, 185.
[5] F. Hulliger, (1996) J. Alloys Compd. 239, 131.

Growing interest in the design of functional materials with increasingly complex crystal structures calls for a more detailed understanding of structure-property relationships in inorganic solids. Whereby functional material properties are often linked to irregular bond distances, deciphering the causal mechanisms underlying bond-length variation, and the extent to which bond lengths vary in solids, has important implications in the design of new materials and the optimization of their functional properties.

Investigation of the relation between bond-length variation and the expression of functional material properties begins with systematization of chemical-bonding behavior via large-scale bond-length dispersion analysis. Completion of the largest bond-length dispersion analysis to date for inorganic solids (177,446 reliable bond lengths hand-picked from 9210 crystal-structure refinements for oxides [1]; 6,770 bond lengths from 720 crystal-structure refinements for nitrides [2]; 33,626 bond lengths from 1832 crystal-structure refinements for chalcogenides [3]) recently enabled straightforward identification of anomalous (i.e. irregular) bonding behavior for all ions of the periodic table observed bonding to O^2-, N^3-, and S^2-/Se^2-/Te^2-. In addition to comprehensive description of bond-length variations in inorganic solids, the large amount of data on anomalous coordination environments provided by this undertaking allows (1) conclusive resolution of the causal mechanisms underlying bond-length variation in inorganic solids, and (2) quantification of the extent to which these causal mechanisms result in bond-length variation.

In a sample of 266 highly irregular coordination polyhedra covering 85 transition-metal ion configurations bonded to O^2-, the most common cause of bond-length variation is observed to be non-local bond-topological asymmetry — a widely overlooked phenomenon whose associated bond-length variation results from asymmetric patterns of a priori bond valences — followed closely by the pseudo Jahn-Teller effect (PJTE). Two new indices, and , calculated on the basis of crystallographic site, are proposed to quantify bond-length variation arising from bond-topological and crystallographic mechanisms in extended solids; is defined as the mean weighted deviation between the bond valences of a given polyhedron and that of its regular variant with equal bond lengths, while similarly quantifies the difference between a priori and observed bond valences. Bond-topological mechanisms of bond-length variation are (1) non-local bond-topological asymmetry and (2) multiple-bond formation, while crystallographic mechanisms are (3) electronic effects (e.g. vibronic mixing, lone-pair stereoactivity), and (4) crystal-structure effects (e.g. structural incommensuration).

Comprehensive bond-length dispersion analyses for inorganic nitrides [2] and chalcogenides [3] reveal several “phenomenological gaps” compared to their oxide counterparts, thus providing synthetic opportunities via the transposing of anomalously bonded coordination units bearing functional properties into new compositional and/or structural spaces. Resolving the contribution of (static) bond-topological vs (tunable) crystallographic mechanisms of bond-length variation via the and indices, combined with their spatial resolution within the coordination polyhedron and unit cell, is proposed to quantify the effective tunable extent of a functional property for a given crystal structure, e.g. via alteration of the responsible coordination unit(s). The known extent for which bond-topological and crystallographic mechanisms materialize into bond-length variations, provided by large-scale bond-length dispersion analyses, guides optimization of these properties within the constraints of physically realistic crystal structures. Such information is essential to the design of new materials with (1) increasingly complex crystal structures, and (2) superior functional properties.

[1] Gagné, O. C. & Hawthorne, F. C. (2016). Acta Cryst. B72, 602–625; Gagné, O. C. (2018). Acta Cryst. B74, 49–62; Gagné, O. C. & Hawthorne, F. C. (2018a). Acta Cryst. B74, 63–78; Gagné, O. C. & Hawthorne, F. C. (2018b). Acta Cryst. B74, 79–96; Gagné, O. C. & Hawthorne, F. C. ChemRxiv 11605698.

[2] Gagné, O. C. (2020). ChemRxiv. 11626974

[3] Gagné, O. C. et al. (2020). In preparation

This study explored the pressure dependent polymorphism of BaRhO₃ within the 7 – 22 GPa pressure range. We report the synthesis of a previously undiscovered 6H perovskite polymorph of BaRhO₃, which was stabilised between 14 – 22 GPa, below which a previously known 4H polymorph is yielded.[1] From Rietveld analysis of synchrotron X-ray powder diffraction data, the polymorph was found to crystallise in the monoclinic C2/c 6H perovskite structure, similar to the analogous BaIrO₃ 6H polymorph which is also synthesised at high pressure.[2] This data analysis also confirms a 4+ oxidation state for Rh which we believe is stabilised by the extremely high oxygen pressures accessible via high pressure synthesis. Physical property measurements and electronic structure calculations were carried out on the 4H and 6H polymorphs. Both polymorphs were found to be Pauli paramagnetic metallic oxides. Resistivity measurements confirm a metallic state for the 4H polymorph, while bulk resistivity indicates semiconductivity for the 6H polymorph. We believe this semiconducting behaviour to arise due to grain boundary effects and not to be intrinsic. High Wilson ratios of approximately 2 for either compound indicate strong electron correlations which is rationalised by strong intermetallic interactions within the Rh₂O₉ dimers. Overall this study suggests that like the neighbouring Ru, Rh oxides display physical properties driven by competing localised and itinerant electron behaviour, and that the higher oxidation states of Rh are readily accessible under high pressure, high temperature conditions.

In recent years there has been tremendous interest in perovskite-like ABX₃ hybrid frameworks, built from inorganic and organic building blocks, for their semiconducting, ferroelectric and magnetic properties. Much of the attraction in these materials lies in the well-known chemical flexibility of perovskite structures, which allows them to accommodate a wide range of cations and anions, as is well known perovskite oxides. Much of this flexibility is enhanced in inorganic-organic perovskites both with respect to their chemistry e.g. their ability to incorporate a wide range of molecular A-site cations and ligands, distortion modes and mechanical flexibility. In one key aspect, however, hybrid perovskites currently have less flexibility compared to conventional perovskites, namely the range of formal charges of cations they can incorporate. This results from the ligands in these hybrid material almost always being monovalent, which essentially restricts the A and B sites to monovalent and divalent cations, respectively.

Recent work in our group has realised a combination of monovalent and divalent ligands in perovskite-like materials via replacing HCO₂^- linker with C₂O₄^2- ligands. Most interestingly this has yielded [(CH₂)₃N]Er(HCO₂)₂(C₂O₄) and [(CH₃)₂NH₂]Er(HCO₂)₂(C₂O₄), allowing monovalent organic A-site and trivalent B-site cations to be combined for the first time in a stoichiometric ABX₃ perovskite. Our presentation will discuss the synthesis, crystal structures and magnetic properties of these materials. These exhibit A-site cation ordering up to 500 K, which will likely make related phases of interest as ferroelectrics. The greater framework flexibility in [(CH₂)₃N]Er(HCO₂)₂(C₂O₄) leads to it exhibiting significant anisotropic negative thermal expansion while the more rigid [(CH₃)₂NH₂]Er(HCO₂)₂(C₂O₄) phase does not.

The second part of our presentation will focus on the related ALn(C₂O₄)_1.5(HCO₂) (Ln = Tb-Er) phases, where we find that replacing an additional formate ligand with oxalate leads to a structure with ordered ligand vacancies. This leads to larger channels in the materials, which is likely the cause of the disorded A-site cations in these materials; ultimately the presence and nature of these A-site cations, which could not be identified crystallographically, have been confirmed by neutron and infrared spectroscopy. These two new series of materials highlight the potential to expand the flexibility of hybrid perovskite and perovskite-like materials by incorporating divalent ligands, allowing their properties to be further tailored for applications.

Rubidium tetrachloro zincate (Rb₂ZnCl₄) belongs to A₂BX₄ crystal family with the β-K₂SO₄ structure type, which are known for their ferroelectric properties and successive phase transitions. Rb₂ZnCl₄ has an orthorhombic crystal structure with Pmcn as its space group in its normal phase and goes from a normal disordered structure to incommensurately modulated structure along its c-axis at 303 K, then goes to a commensurately modulated structure around 192 K (T_c). Here we report the temperature dependent crystal structure of Rb₂ZnCl₄ in an attempt to elucidate the relation between structure and physical properties of this compound.

In the incommensurate phase the modulation wave vector is given by q = (1/3 – δ) c*, where δ is the parameter which changes with temperature, it decreases with decrease in temperature and finally becomes zero at the lock-in phase transition temperature T_c . In Rb₂ZnCl₄ the modulation wave function changes from a sinusoidal harmonic function just below the incommensurate phase transition (303K) to a strongly anharmonic function near the lock-in phase transition at T_c. The modulation function in the incommensurate phase of Rb₂ZnCl₄ is not only given by displacive modulation but also modulations of atomic displacement parameters (ADPs) and anharmonic ADPs. The structural analysis together with the lattice dynamics studies help us to understand the relation between aperiodic order and physical properties.

The development of diamond-anvil cells together with the improvement of the characterization techniques in large facilities has led to the expansion of high-pressure (HP) research. The application of HP has given rise to many important breakthroughs during the past decade because it can radically change the physical and chemical properties of materials yielding unexpected modifications. For instance, HP has allowed the discovery of new materials or new phases of known materials with unique properties, such as high T_Csuperconductors, Mott insulators, half-metals, etc.

Here, we present the study of several striking materials by two complementary techniques: x-ray absorption spectroscopy (XAS) and x-ray diffraction (XRD), both carried out in the European Synchrotron Radiation Facility (ESRF). Firstly, the iridium (Ir) metal has been investigated up to 1.4 Mbar in order to discover experimentally, for the first time, a new electronic transition predicted in the majority of 5d transition metals [1]. This new transition is known as Core Level Crossing and it involves the overlap between the 4f/5p core levels affecting the 5d valence orbitals yielding a change in the chemical bonds. The structural stability (Fig.1a) and the electronic properties of Ir metal were studied by XRD at ID15B beamline and XAS at BM23 beamline, respectively. Secondly, we have stablished a physical model to explain the pressure-induced modifications in the electronic structure of europium (Eu) monochalcogenides, EuX (X = O, S, Se, Te). All of them exhibit optical, electric and magnetic anomalies around 14 GPa [2] but the reason behind them had never been unveiled so far. We have studied one of these compounds, the EuS, by XAS up to 35 GPa at BM23 beamline (Fig. 1b). Finally, the copper(II) oxide, CuO, itself has seen renewed interest due to the discovery of multiferroicity (MF) at relatively high temperature T_N = 230 K and ambient pressure [3]. However, such a discovery is not free of controversy since different researchers have obtained contradictory results [4]. We have carried out a XAS experiment up to 18 GPa, at BM23 beamline, to analyse the static and dynamics contribution of the local environment around Cu atoms (Fig. 1c) shedding some light on this scientific problem.

Despite being the subject of numerous shock compression studies, the behavior of silicon under dynamic loading is vigorously debated [1-4]. The few studies that combine shock compression and X-ray diffraction have exclusively focused on "normal" X-ray geometry whereby X-rays are collected along the shock propagation direction, consequently sampling numerous strain states at once, and hence greatly complicating both phase identification and studies of phase transition kinetics.[5] Here, we present a novel setup to perform in situ X-ray diffraction studies perpendicular to the shock propagation direction at the Matter in Extreme Conditions end station at Linac Coherent Light Source, SLAC. Combining the extremely bright, micro-focused X-ray beam available at the LCLS with a nanosecond laser driver, we unambiguously characterize of the complex multi-wave shock response in silicon for the first time. We further combine this platform for performing simultaneous imaging with X-ray diffraction from shock compressed germanium, revealing its behaviour following shock compression. We note the transverse geometry is significantly more sensitive to the onset of both solid-solid and solid-liquid phase transformations in materials which exhibit complex multi-wave behaviour, and compare and constrast the behaviour of Si and Ge.

[1] Graham et al., JPCS, 27, 9 (1966)

[2] Turneaure & Gupta, APL, 90, 051905 (2007)

[3] Colburn et al., JAP, 43, 5007 (1972)

[4] Gust & Royce, JAP, 42, 1897 (1971)

[5] Turneaure et al., PRL,121, 135701 (2018)

We have developed and tested a new internally heated diamond anvil cell (DAC) as reported in a recent paper published in Review of Scientific Instruments [1]. The system includes a portable vacuum chamber and was designed for routine performance of x-ray and optical experiments. We have adopted a self-heating W/Re gasket design allowing for both sample confinement and heating. This solution proved to be very efficient to improve heating and cooling rates in a temperature regime up to 1500 K. The system has been widely tested and calibrated under high-temperature conditions. The temperature distribution was measured by in situ optical measurements and resulted to be uniform within the typical uncertainty of the measurements (5% at 1000 K). XAS (x-ray absorption spectroscopy) of pure Ge at 3.5 GPa were easily obtained in the 300 K–1300 K range, studying the melting transition and nucleation to the crystal phase. An original XAS-based dynamical temperature calibration procedure was developed and used to monitor the sample and diamond temperatures, indicating that heating and cooling rates in the 100 K/s range can be easily achieved using this device.

The EMA (Extreme condition Methods of Analysis) is one of the first Sirius beamlines, the 4th generation Brazilian synchrotron source. Currently under commissioning, its focus is on merging extreme thermodynamic conditions with a solid characterization platform based on spectroscopy and scattering techniques. For this, it has an undulator source and optics based on a high-dynamic double-crystal monochromator (HD-DCM) [1], 1/4 wave plates (double phase retarder), and KB-mirrors, which can provide X-ray beam sizes as small as ~ 1 x 0.5 μm² and ~ 100 nm², respectively, for two experimental stations (Microfocus and Nanofocus hutches).

Here is shown the current developments for the XRD experiments performed on both the “multipurpose setup” (@ 45 m from the source) and the 6‑circle diffractometer (@ 55 m) [2]. The former relies on a hexapod for sample positioning and angular scans and offers the most extreme temperature (0.5 – 5000 K) and pressure (~ 600 GPa) within the Microfocus hutch, allied with a 1 T magnet. The latter setup will work with tunable beam sizes ranging from ~ 13 x 3 up to ~ 300 x 300 μm² and positioning systems on top of its inner circle that delivers up to 66 mm of free working distance, expanding the possibilities for third-party sample mountings and environments, such as an available uniaxial strain cell. For this setup, the significant range in temperature (5 – 300 K), pressure (~300 GPa), and magnetic field (6T) add flexibility to the already versatile 4S+2D diffractometer. Additionally, opportunities for a broad sort of techniques supported at EMA will be discussed for powder and single-crystalline samples.

Fast EXAFS measurement in piezo-driven single-crystal monochromatization scheme

At the “Langmuir” station of the Kurchatov Synchrotron-Neutron Research Complex, a single-crystal monochromator based on adaptive bending X-ray acoustic element [1] was implemented for X-ray beam energy fast tuning and for rapid recording K-edge absorption spectra (XANES-spectrum) of Bromine in NaBr powder sample.

To control beam parameters and record the absorption spectrum, Si single-crustal monochromator, driven by ultrasonic vibrations excitation in piezo-actuator, and monitoring system were used. Diffracted synchrotron beam was collimated by slits and recorded using a scintillation detector, connected with multi-channel analyzer. X-ray acoustic element was excited via the inverse piezoelectric effect by applying a AC electronic signal with first harmonic resonance frequency f_rez = 239 Hz. During the experiments, the beam intensity was recorded in relation to control signal phase, further converted into an absorption spectrum.

After data processing the results it was established that the position of absorption edge and the first coordination sphere radius coincided for X-ray acoustic and traditional mechanical scan. Achieved energy scan range was 13.25–13.65 keV (400 eV). Maximum time resolution available using the x-ray acoustic method is 2.1 ms, and actual time required to record qualitative spectrum, achieved in this experiment, was about 30 seconds and can be reduced by using detector with a higher dynamic range and counting rate, as well as optimizing X-ray optical scheme.

The developed scheme is promising for QEXAFS methods implementation, useful for chemical reactions kinetics study, for example, the Belousov-Zhabotinsky self-oscillation reaction [2], as well as the deformation processes kinetics research under external influences.

This work was partially supported by RFBR grants No. 18-32-20108 mol_a_ved, as well as the Council on Grants of the President of the Russian Federation МК-2451.2018.2.

1. A.E. Blagov, A.S. Bykov et al. PTE, 2016, No. 5, p. 109

2. M Hagelstein, T Liu et al. // J. of Physics: Conference Series 430 (2013) 012123

Skutterudite-type compounds based on □Co₄Sb₁₂ pnictide are promising for thermoelectric application due to their good Seebeck values and high carrier mobility. Filling the 8a voids (in the cubic space group Im3̅) with different elements (alkali, alkali earth, and rare earth) helps to reduce the thermal conductivity and thus increases the thermoelectric performance. A systematic characterization by synchrotron X-ray powder diffraction of different M-filled Co₄Sb₁₂ (M = K, Sr, La, Ce, and Yb) skutterudites was carried out under high pressure in the range ∼0–12 GPa. The isothermal equations of state (EOS) were obtained in this pressure range and the Bulk moduli (B₀) were calculated for all the filled skutterudites, yielding unexpected results. A lattice expansion due to the filler elements fails in the description of the Bulk moduli. Topochemical studies of the filler site environment exhibited a slight disturbance and an increased ionic character when the filler is incorporated. The mechanical properties by means of Bulk moduli resulted in being sensitive to the presence of filler atoms inside the skutterudite voids, being affected by the covalent/ionic exchange of the Co–Sb and Sb–Sb bonds.

The extreme densities of matter relevant to most exoplanets are not reachable by static compression, i.e., in diamond anvil cell (DAC), or by single shock compression techniques. Multiple shocks generated by tailored laser pulses allow reaching higher densities, but the thermodynamic state of the system is not easy to measure. Instead of using the multi-shock compression technique, we can send a laser-induced shock wave through a sample that is pre-compressed at high static pressures inside a DAC. The equation-of-state of the system is then directly measured through the Rankine-Hugoniot equations from the shock and particle velocities, and temperature can be measured independently with pyrometry. Several experiments demonstrated the combination of these two techniques [1-5] at kJ laser facilities and documented material properties at unprecedented conditions.

We introduce a new design of a shock diamond anvil cell (SDAC) for sub-kJ laser-driven dynamic compression experiments at X-ray sources. We designed a system of two thin diamond anvils, one of which is perforated. The perforation is envisioned to allow shock waves created by low/moderate energy lasers to propagate through the sample. Being developed to be usable by any user community at the High Energy Density (HED) instrument at European-XFEL, or other large-scale facilities around the world, the unique design of the SDAC will make it possible to reach higher density states of matter in dynamic compression experiments and probe previously unexplored regions of the pressure-temperature-density phase diagram, combined with x-ray techniques at XFEL sources. We will present technical details and first results of the pre-compression pressures achieved using SDAC along with hydrodynamic simulation results of dense Krypton, among other samples, laser-shocked at different initial densities.

[1] Loubeyre, P. et al (2003). High Pressure Research. 24, 1, 25-31

[2] Eggert, J. et al (2008). Phys. Rev. Lett. 100, 124503

[3] Celliers, P. M. et al (2010). Phys. Rev. Lett. 104, 184503

[4] Loubeyre, P. et al (2012). Phys. Rev. B. 86, 144115

[5] Millot, M. et al (2018). Nat. Phys. 14, 297-302

Part of this work was prepared by LLNL under Contract DE-AC52-07NA27344 and supported by LDRD 19-ERD-031.

The structure of liquid and glass is usually described by the atomic pair-distribution function (PDF), g(r), which expresses the statistical distribution of distances between atoms. The PDF can be determined by diffraction experiments using x-rays or neutrons. However, liquid is dynamic in nature, and we have to be sensible about what the PDF means for liquid. For crystalline solids the atomic structure is determined by the elastic scattering of x-rays, neutrons or electrons, because the momentum is transferred to the whole rigid body of the sample in scattering. But the elastic scattering intensity from liquid is zero because of the lack of rigidity. The scattering from liquid is purely inelastic, described by the dynamic structure factor, S(Q, ω), where Q is the momentum transfer and E = hω/2π is the energy transfer in scattering. To measure S(Q, ω) we need an elaborate inelastic scattering instruments. In particular for inelastic x-ray scattering (IXS) we need a very high energy resolution with ~ meV and ΔE/E < 10^-7. This can be achieved only with a large backscattering crystal analyzer with a long flight path. However, in regular x-ray diffraction measurement the energy resolution is poor, ~ 1 eV, far exceeding the typical energies of vibrational excitations. As a result, the measured structure function, S(Q), is the S(Q, ω) integrated over energy, thus representing the same-time correlation among atoms. Thus, the PDF, obtained by the Fourier-transformation of S(Q), is the same-time density correlation function which shows the time averaged snapshot of correlations. Therefore, the PDF does not describe the structure in a regular sense. For a long time, the PDF has been used in representing the structure, because it was the only readily available structural descriptor, and various theories have been proposed to predict dynamic properties from the PDF. On the other hand, the dynamic two-body correlation can be directly expressed by the Van Hove function, G(r, t), obtained by the double-Fourier-transformation of S(Q, ω). But, to carry out the double-Fourier-transformation accurately S(Q, ω) has to be measured over a wide Q-E space. Until recently this was unpractical, because the inelastic scattering measurement, typically done with a triple-axis-spectrometer, was extremely time-consuming. But the advent of pulsed neutron sources with large two-dimensional detector arrays and advances in the IXS instrumentation made it possible to determine the Van Hove function in a reasonable time, 4 – 12 hrs. We applied this technique to various liquids, including water, aqueous solutions of salt, metallic alloy liquids, liquid Ga, and organic electrolytes. New physical insights obtained by these measurements will be discussed. Now that this technique is available we should expand the definition of the “structure” of liquid to include the dynamic structure represented by the Van Hove function.

Pd_42.5Ni_7.5Cu₃₀P₂₀ (PNCP) has at present the most excellent glass-forming ability (GFA) among metallic glasses. The critical cooling rate (CCR) reaches of 0.067 K/s and can form a massive bulk glass with a diameter of more than 40 mm [1]. On the other hand, almost the parent alloys of Pd₄₀Ni₄₀P₂₀ (PNP) and Pd₄₀Cu₄₀P₂₀ (PCP) have worse CCRs of about 1 K/s [2] and 100 K/s [3], respectively, indicating that the mixture of Ni and Cu elements causes a better CCR in these bulk metallic glassy alloys.

In order to find a structural origin of the GFAs of these Pd-based glasses, we have carried out anomalous x-ray scattering (AXS) and neutron diffraction (ND) experiments on PNP [4], PCP [5], and PNCP (preliminary results were given in [6]), and the experimental results were analysed by using reverse Monte Carlo (RMC) modelling. The obtained atomic configurations of these alloys were discussed by using a Voronoi tessellation for the short-range atomic arrangements and a persistent homology analysis [7] for the hyper-ordered atomic structures.

Although the general features of the atomic configurations look similar to one another, i.e., most of atomic configurations around all elements are basically icosahedral-type, the main results of these analyses are as follows:

1) A large fraction of “pure” icosahedra are observed around only Ni atoms (5.8%) in PNP [4], whereas that around Cu in PCP is a half value of 2.9% [5]. Very interestingly in PNCP, large fractions of “pure” icosahedra are detected not only around the Ni atoms of 4.8%, but around the Cu atoms of 5.6%.

2) Large sizes of partial persistent homology rings are observed for the Ni/Cu atoms in all the glasses. However, the size highly depends on the GFA of the glasses, i.e., that in PNCP is slightly larger than in PNP, and much larger than in PCP.

In conclusion, the GFA of Pd-based metallic glasses is not understood as clearly characterized structures such as the existence of clusters of crystal-like fragments. It is realized through hyper-ordered structures, i.e., profound structural features in the short- and intermediate-range atomic order in the glasses.

[1] Nishiyama, N. and Inoue, A., (2002), Appl. Phys. Lett. 80, 568.[2] Drehman, A. J., Greer, A. L., and Turnbull, D., (1982). Appl. Phys. Lett. 41, 716.[3] He, Y. and Schwarz, R. B., (1997), Mater. Res. Symp. Proc. 455, 495.[4] Hosokawa, S. et al., (2019). Phys. Rev. B 100, 054204.[5] Hosokawa, S. et al., (2021), J. Non-Cryst. Solids 555, 120536.[6] Hosokawa, S. et al., (2009), Phys. Rev. B 80, 174204.[7] Hiraoka, T. et al., (2016), Proc. Natl. Acad. Sci. USA 113, 7035.

When sample conditions for conventional crystallography are not met (i.e. a large, well-ordered crystal) then x-ray diffraction techniques often do not yield an unambiguous 3D atomic structure. This can occur in powder diffraction and small-angle x-ray scattering (SAXS), where ensembles of crystals or particles in random orientations produce isotropic diffraction around the beam axis. It also occurs for disordered materials, such amorphous solids and liquids, where randomness at the molecular scale has a similar suppression of accessible structural information via x-ray scattering. The accessible structural information is the distribution of atom-pair distances (known as the pair distribution function or PDF). The PDF has no information about local angular structure, such as bond angles, and in many cases does not uniquely determine the 3D structure.

Fluctuation x-ray scattering (FXS) [1,2] aims to measure the local angular structure in disordered materials using a small x-ray beam to enhance angular scattering fluctuations. We have developed a method of inverting FXS data to recover a sum of three- and four-atom distributions in real-space[3]. We call this 3D function the Pair-Angle Distribution Function (PADF). It is a natural generalisation of the widely used PDF to higher dimensions. The PADF contains, for example, a bond angle distribution and massively increases the amount of structural information beyond that of the PDF.

There are exciting opportunities to combine PADF analysis with crystallography, powder diffraction and SAXS. It could yield new routes to crystal structures, nanoscale disorder, amorphous structure and liquid structure. Here we give an introduction to the PADF and report on our early experimental results with synchrotron, x-ray free-electron lasers and electron microscopes. These include applications to self-assembled lipids[4], disordered carbon materials[5], protein crystals[6] and liquids.

[1] Kurta, R.P., Altarelli, M. and Vartanyants, I.A. (2016). “Structural analysis by x-ray intensity angular cross-correlations” in Advances in Chemical Physics (eds S.A. Rice and A.R. Dinner).

[2] Kam, Z. (1977). Macromolecules, 10(5), 927–934.

[3] Martin, A. V. (2017). IUCrJ, 4, 24–36.

[4] Martin, A. V., et al., (2020). Small, 2000828, 1–6

[5] Martin, A. V., et al., (2020). Communications Materials, 1(40), 1–8.

[6] Adams, P.,, et al., (2020). Crystals, 10, 724.

Commonly classical nucleation theory has been used to explain nucleation, but this is now being challenged as atomic scale techniques has been developed to study solutions showing larger clusters before nucleation [1, 2]. Thus, a new theory including these clusters with predictive value is needed. To achieve this, it is essential to investigate the atomic structure of precursors across different elements as well as chemical environments.

In this study the precursors of group 13 metal oxides have been examined. Al, In and Ga form similar oxides and hydroxides such as M(OH)₃, MOOH and M₂O₃ in solvothermal synthesis. The individual systems exhibit complex polymorphism, which can be controlled with different synthesis parameters such as solvent and temperature, however, the actual mechanisms are unknown.

The precursor structures of the group 13 metal oxides have been determined by combining PDF and EXAFS analysis of the three metal nitrates in various solvents. Across element and solvents the structures were determined to be octahedrally coordinated metal-oxygen with further structure.[3] For the gallium system variation of pH, anions and concentration were further investigated using PDF analysis revealing the diverse solution chemistry of gallium [4].

Based on the results, the formation mechanisms of the group 13 metal oxides are discussed, for example reason for the production of AlOOH at most synthesis conditions instead of the desirable γ-Al₂O₃ phase [3,5].

Figure 1. Modelling of both EXAFS and PDF data for the same models.

[1] Bøjesen, E. D. & Iversen, B. B. (2016). CrystEngComm. 43, 8332-8353 [2] Gebauer, D., Kellermeier, M., Gale, J. D., Bergström, L. & Cölfen, H. (2014). Chem. Soc. Rev. 43, 2348-2371. [3] Sommer, S., Nielsen, I. G. & Iversen, B. B. (2020). Chem. – Eur. J. 26, 1022-1026. [4] Nielsen, I. G., Sommer, S., Dippel, A.-C. Skibsted, J. & Iversen, B. B. (2021). Submitted to JACS. [5] Nielsen, I. G., Sommer, S. & Iversen, B. B. (2021). Nanoscale 13, 4038-4050.

Due to its sensitivity to local structure, X-ray absorption spectroscopy is a powerful tool to study disordered systems. One of the most interesting property of XAFS is the sensitivity not only to pair distribution function, but also to three-body distribution, which contains information on bond angles between nearest neighbours. Reverse Monte Carlo (RMC) is a structural modelling method from which this information can be obtained [1], but it requires to know the density of the system being investigated, which may not be available especially in extreme thermodynamic conditions. Being a simulation method, it is also costly in terms of time. In recent years, neural networks (NN) have become a widely used tool to tackle different problems and have also been applied to the analysis of EXAFS data [2]. We wanted to investigate whether the same methodology could be applied to disordered systems and whether it would be possible to obtain information beyond the pair distribution function.

The critical point of any NN is the dataset used for the training process, that should be sufficiently large and heterogeneous. For this purpose, we ran several MD simulations of mono-atomic nickel at various temperatures for different crystal configurations, varying also the first-neighbour distance. The temperature was increased past the melting point to also include liquid configurations. From each configuration, we calculated the number distribution function, bond-angle distribution of the nearest neighbours and the EXAFS signal, using GNXAS suite of programs [3]. The created dataset was then used to optimize and train a set of deep NN to estimate number and bond-angle distribution from a given EXAFS signal.

We used the NN to analyse data of nickel at different temperatures and phases. Results from each NN are averaged and standard deviation calculated to estimate errors. Obtained results show that the NN is able to distinguish between ordered and disordered configurations and is also able to detect small changes in the local ordering of liquid structure, comparable with previously published results [4].

[1] Di Cicco A., Trapananti A., Faggioni S. & Filipponi A. (2003). Phys. Rev. Lett. 91, 135505.

[2] Timoshenko J., Anspoks A., Cintins A., Kuzmin A., Purans J. & Frenkel A. I. (2018). Phys. Rev. Lett. 120, 225502.

[3] Filipponi A. & Di Cicco A. (1995). Phys. Rev. B 52, 15135.

[4] Di Cicco A., Iesari F., De Panfilis S., Celino M., Giusepponi S. & Filipponi A. (2014). Phys. Rev. B 89, 060102.

Molecules and molecular ions, unlike individual atoms, have rotational degrees of freedom. This simple observation means that they can be particularly good building blocks for disordered crystal structures. Such behaviour is not merely a crystallographic curiosity: it is responsible for many important materials properties. For instance, if, in some material, a molecule with a permanent dipole moment is free to rotate at high temperatures but freezes into place at low temperatures, the two phases will have different entropies and dielectric constants. The result will be a dielectric switching material; it is likely to be an electro- and/or barocaloric, where the phase transition responds to an external electric field or pressure; and it may also be pyro- and even ferroelectric if the low-symmetry phase is polar.

Studying such materials requires a combination of experimental and computational techniques. Traditional crystallographic methods remain vital, but entail a time and space average that can obscure the behaviour of the disordered phase. Thus it is also important to use methods such as total scattering, which are sensitive to local deviations from that average; and to study also the dynamics, or how structures change over time. Neutron scattering methods are especially appropriate because they reveal the behaviour of hydrogen atoms, which is essential to understanding these rotating molecules, and provide both structural and dynamic information.

A particular focus of recent interest has been the family of molecular perovskites, in which molecular ions on the “A” site almost always display this sort of order-disorder transition [1]. This site is a cubic interstice of the perovskite framework, which provides both structural stability and the freedom for the ions to rotate. But of course order-disorder behaviour does not require this specific coordination framework, or indeed any framework at all: similar molecular “scaffolding” can be provided by other weak interactions, including van der Waals and hydrogen bonding.

Here we compare “free” to “caged” molecules and molecular ions that undergo entropic transitions. We consider the cyanide-bridged elpasolite (double perovskite) analogues (C₃H₅N₂)₂K[M(CN)₆], C₃H₅N₂ = imidazolium, M = Fe, Co [2]; the molecular material adamantane, C₁₀H₁₆ [3], and the molecular-ionic compound ammonium sulfate, (NH₄)₂SO₄ [4]. We have studied these materials’ structure by Bragg and total neutron scattering, and their dynamics by inelastic and quasielastic neutron scattering, complemented by density-functional theory simulations. Combining these methods provides a detailed picture of the actual rotational and vibrational freedom that molecules have in these materials, and hence of the structural origins of their useful properties. In particular, we show that the limiting cases of free rotation and harmonic oscillation can both be inaccurate and even seriously misleading, with the true situation lying somewhere between these extremes. Our results will direct future attempts at “entropic engineering”: designing molecular materials to have specific order-disorder behaviour.

[1] Kieslich, G. & Goodwin, A. L. (2017). Mater. Horiz. 4, 362–366.

[2] Duncan, H. D., Beake, E. O. R., Playford, H. Y., Dove, M. T. & Phillips, A. E. (2017). CrystEngComm 19, 7316–7321; Phillips, A. E. & Fortes, A. D. (2017). Angew. Chem. Int. Ed. 56, 15950–15953; Phillips, A. E., Cai, G. & Demmel, F. (2020). Chem. Commun. 56, 11791–11794.

[3] Beake, E. O. R., Tucker, M. G., Dove, M. T. & Phillips, A. E. (2017). ChemPhysChem 18, 459–464.

[4] Cai, G. (2020). Studying orientational disorder with neutron total scattering, Ph.D. thesis, Queen Mary University of London, U.K.

NMR spectroscopy provides an element-specific, sensitive probe of the local environment, enabling detailed information to be extracted. However, in the solid state the vast majority of this information remains unexploited, owing to the challenges associated with obtaining high-resolution spectra and the ease with which these can be interpreted. Recent advances enabling accurate and efficient calculation of NMR parameters in periodic systems have revolutionized the application of such approaches in solid-state NMR spectroscopy, particularly among experimentalists. As NMR is sensitive to the atomic-scale environment, it provides a potentially useful tool for studying disordered materials, and the combination of experiment with first-principles calculations offers a particularly attractive approach. There are, however, significant experimental and computational challenges in the application of NMR spectroscopy to disordered materials. For example, there is no longer a single arrangement of atoms in a simple model structure that matches the material under study, and many different atomic arrangements may be required to gain insight into the interpretation and assignment of NMR spectra, and ultimately, into the structure of the material under study.

The crystal chemical flexibility of pyrochlore-based (A₂B₂O₇) oxide materials has resulted in a wide range of applications, including energy materials, nuclear waste encapsulation and catalysis. There is, therefore, considerable interest in understanding the structure–property relationships in these materials, i.e., investigating how cation/anion disorder and local structure vary with composition. Here we combine a range of ⁸⁹Y, ¹¹⁹Sn and ¹⁷O NMR experiments with periodic planewave calculations to explore cation disorder in ¹⁷O-enriched (Y,La)₂(Sn,Ti,Zr,Hf)₂O₇ phases. We show how a variety of NMR crystallographic approaches from cluster-based approaches, to ensemble-based modelling and the use of grand canonical ensembles can provide insight into the atomic-scale structure and disorder in these materials.[1-6]

[1] Reader, S. W., Mitchell, M. R., Johnston, K. E., Pickard, C. J., Whittle, K. R., & Ashbrook, S. E. (2009). J. Phys. Chem C 113, 18874.

[2] Mitchell, M. R., Reader, S. W., Johnston, K. E., Pickard, C. J., Whittle, K. R., & Ashbrook, S. E. (2011). Phys. Chem Chem. Phys. 13, 488.

[3] Mitchell, M. R., Carnevale, D., Orr, R., Whittle, K. R., & Ashbrook, S. E. (2012). J. Phys. Chem . 116, 427.

[4] Fernandes, A., Moran, R. F., Sneddon, S., Dawson, D. M., McKay, D., Bignami, G. P. M., Blanc, F., Whittle K. R. & Ashbrook, S. E. (2018). RSC Advances 8, 7089.

[5] Moran, R. F., McKay, D., Tornstrom, P. C., Aziz, A., Fernandes, A., Grau-Crespo R., & Ashbrook, S. E. (2020). J. Am. Chem. Soc. 141, 17838.

[6] Fernandes, A., Moran, R. F., McKay, D., Griffiths, B., Herlihy, A., Whittle K. R., Dawson, D. M. & Ashbrook, S. E. (2020). Magn. Reson. Chem. in press, DOI: 10.1002/mrc.5140.

Structure elucidation of amorphous molecular solids presents one of the key challenges in chemistry today. Knowledge of the atomic-level structure in such materials would be of great value for example to direct the optimisation of pharmaceutical formulations. However, the lack of long-range structural order prevents atomic-level characterization of these materials using methods like single crystal X-Ray diffraction. Solid state NMR on the other hand yields atomic-level information on amorphous materials and molecular dynamics (MD) can generate candidate sets of possible disordered structures. Directly relating these two techniques has been out of reach so far, due to the prohibitive cost of computing chemical shifts on large ensembles of large MD structures using DFT. Recently, a method based on machine learning, dubbed ShiftML (1), has emerged as a quick and accurate way to predict the chemical shifts of organic solids, even for large systems.

Here, using a machine learning model of chemical shifts, we determine the complete atomic-level structure of the amorphous form of a drug molecule by combining dynamic nuclear polarization-enhanced solid-state NMR experiments with predicted chemical shifts for MD simulations of large systems (2). From these amorphous structures we then identify H-bonding motifs and relate them to local intermolecular interaction energies.

1. Paruzzo, F. M.; Hofstetter, A.; Musil, F.; De, S.; Ceriotti, M.; Emsley, L., “Chemical shifts in molecular solids by machine learning.” Nat Commun 2018, 9, 4501. doi.org/10.1038/s41467-018-06972-x

2. Cordova, Balodis, Hofstetter, Paruzzo, Nilsson Lill, Eriksson, Berruyer, Simões de Almeida, Quayle, Norberg, Svensk Ankarberg, Schantz, Emsley, "Structure determination of an amorphous drug through large-scale NMR predictions." Nat Commun 2021, doi.org/10.1038/s41467-021-23208-7

Complex structures with subtle atomic-scale details are now routinely solved using complementary tools such as X-ray and/or neutron scattering combined with electron diffraction and imaging. Identifying unambiguous atomic models for oxyfluorides, needed for materials design and structure−property control, is often still a considerable challenge despite the advantageous optical responses, magnetic properties, and energy storage capability of numerous oxyfluorides. Amongst the long-stranding challenges are the lack of tools to resolve fluorine and oxygen and to characterize fluoride-ion and MF_n polyhedral dynamics. In this work, NMR crystallography is used in combination with single-crystal X-ray diffraction, X-ray absorption spectroscopy, and property measurements to provide a comprehensive structural picture of a series of new oxyfluoride materials and highlight the presence of previously unidentified selective fluorine-mediated dynamics.

This talk will focus on insights from ¹⁹F NMR across early transition metal oxyfluoride materials including newly discovered hafnium oxyfluorides, spin singlet Mo(IV) cluster compounds, and emerging hybrid organic–inorganic low-dimensional compounds. The first system has relevance to fluoride-doped HfO₂ electronic materials [1]; the second example features a rare triangular metal oxyfluoride cluster, [Mo₃O₄F₉]⁵⁻ (Fig. 1) [2]; and the third series of compounds are structurally diverse and provide fundamental insights into competition between centrosymmetric and noncentrosymmetric crystallization [3]. Identifying the anion (dis)order is central to building design rules for noncentrosymmetric crystals with technologically relevant properties. 1D and 2D solid-state ¹⁹F NMR experiments are supported by ab initio calculations to shed light on the anion sublattice and to assign the numerous distinct fluorine environments. In compounds with ⁹³Nb and ⁵¹V, coupling between the metal and fluorine nuclei can be used to further aid the interpretation. Variable-temperature measurements reveal fluorine dynamics that are strongly correlated to polyhedral degrees of freedom. The dual scattering and spectroscopy approach is used to demonstrate the sensitivity of ¹⁹F shielding to small changes in bond length, on the order of 0.01 Å, even in the presence of hydrogen bonding, metal−metal bonding, and electrostatic interactions.

[1] Flynn, S., Zhang, C., Griffith, K. J., Shen, J., Wolverton, C., Dravid, V. P., Poeppelmeier, K. R. (2021). Inorg. Chem. 60, 4463.

[2] Ding, F., Griffith, K. J., Koçer, C. P., Saballos, R., Wang, Y., Zhang, C., Nisbet, M., Morris, A. J., Rondinelli, J. M., Poeppelmeier, K. R. (2020). J. Am. Chem. Soc. 142, 12288.

[3] Nisbet, M. L., Pendleton, I. M., Nolis, G. M., Griffith, K. J., Schrier, J., Cabana, J., Norquist, A. J., Poeppelmeier, K. R. (2020). J. Am. Chem. Soc. 142, 7555.

Three-dimensional electron diffraction crystallography (microED) can solve structures of sub-micrometer crystals, which are too small for single crystal X-ray crystallography. However, R factors for the microED-based structures are generally high (15-30% for small molecules) because of dynamic scattering. Thus, R factor may not be reliable provided that kinetic analysis is used. Consequently, there remains 1) ambiguity to locate hydrogens and 2) assignment of nuclei with close atomic numbers, like carbon, nitrogen, and oxygen. On the other hand, ¹H solid-state NMR is readily available using fast MAS probes and ¹³C, ¹⁴N, ¹⁵N, and ¹⁷O are completely different nuclei for NMR observation. Thus, information from solid-state NMR and microED is complementary.

Herein, we demonstrate combined approach using solid-state NMR and microED to solve crystalline structure. First, well established NMR crystallography approach is employed. Isotropic chemical shifts are very sensitive to local environment, thus crystalline structure, however, there are no intuitive way to predict chemical shifts from structures. GIPAW procedure paves a way to estimates chemical shifts of crystalline materials in a very high accuracy. This makes isotropic chemical shift as a reliable measure for structure validation. While wrong position of ¹H and misassignment of carbon/nitrogen/hydrogen result in poor agreement between experimental and calculated chemical shifts, right structure can be easily chosen among candidates. We show that this approach, which is well established with XRD structures, equally works well with microED. The crystalline structures are determined by microED and validated by isotropic chemical shifts [1]. To further validate the structure, next, we demonstrate another measure using dipolar-based ssNMR experiments in addition to isotropic chemical shifts. In principle, dipolar couplings provide useful information for structure elucidation, as the size of coupling is inversely proportional to the cube of internuclear distances. However, spin dynamics is often complicated due to presence of multiples of intra- and intermolecular couplings for small molecules, making structure elucidation difficult. On the other hand, it is readily calculated for given structures if the spin system is simple enough (< 8 spins). Here we utilize ¹H-¹H selective recoupling of proton (SERP) experiments [2-4] and ¹H-¹⁴N phase-modulated rotational-echo saturation-pulse double-resonance (PM-RESPDOR) as dipolar-based NMR experiments [5, 6]. While the former selects a subset of ¹H-¹H spin systems, the latter simplifies the spin system by decoupling ¹H-¹H interactions. As a result, SERP and RESPDOR probe ¹H-¹H and ¹H-¹⁴N networks, respectively. The structure is solved by microED and then validated by evaluating the agreement between experimental and calculated dipolar-based NMR results [7]. As the measurements are performed on ¹H and ¹⁴N, the method can be employed for natural abundance samples. Furthermore, the whole validation procedure was conducted at 293 K unlike widely used chemical shift calculation at 0 K using the GIPAW method.

[1] C. Guzmán-Afonso, Y.-l. Hong, H. Colaux, H. Iijima, A. Saitow, T. Fukumura, Y. Aoyama, S. Motoki, T. Oikawa, T. Yamazaki, K. Yonekura, Y. Nishiyama*, Nat. Commun. 10, 3537 (2019).

[2] N.T. Duong, S. Raran-Kurussi, Y. Nishiyama*, V. Agarwal*, J. Phys. Chem. Lett. 9, 5948-5954 (2018).

[3] N.T. Duong, S. Raran-Kurussi, Y. Nishiyama*, V. Agarwal*, J. Magn. Reson. 317, 106777 (2020).

[4] L.R. Potnuru†, N.T. Duong†, S. Ahlawat, S. Raran-Kurussi, M. Ernst, Y. Nishiyama* and V. Agarwal*, J. Chem. Phys. 153, 084202 (2020).

[5] N.T. Duong, F. Rossi, M. Makrinich, A. Goldbourt, M.R. Chierotti, R. Gobetto, Y. Nishiyama*, J. Magn. Reson. 308, 106559 (2019)

[6] N.T. Duong, Z. Gan, Y. Nishiyama*, Front. Mol. Biosci. 8, 645347 (2021).

[7] N.T. Duong, Y. Aoyama, K. Kawamoto, T. Yamazaki, Y. Nishiyama, under review.

The determination of active site protonation states is critical to gaining a full mechanistic understanding of enzymatic transformations; yet proton positions are challenging to extract using the standard tools of structural biology. Here we make use of a joint solid-state NMR, X-ray crystallography, and first-principles computational approach that unlocks the investigation of enzyme catalytic mechanism at this fine level of chemical detail. Through this process, we are developing a high-resolution probe for structural biology that is keenly sensitive to proton positions – rivaling that of neutron diffraction, yet able to be applied under conditions of active catalysis to microcrystalline and non-crystalline materials. For tryptophan synthase, this allows us to peer along the reaction coordinates into and out of the α-aminoacrylate intermediate. By uniquely identifying the protonation states of ionizable sites on the cofactor, substrates, and catalytic side chains, as well as the location and orientation of structural waters in the active site, a remarkably clear picture of structure and reactivity emerges. Most incredibly, this intermediate appears to be mere tenths of angstroms away from the preceding transition state in which the β-hydroxyl of the serine substrate is lost. The position and orientation of the structural water immediately adjacent to the substrate β-carbon suggests not only the fate of the hydroxyl group, but also the pathway back to the transition state and the identity of the active site acid-base catalytic residue. Reaction of this intermediate with benzimidazole (BZI), an isostere of the natural substrate, indole, shows BZI bound in the active site and poised for, but unable to initiate, the subsequent bond formation step. When modeled into the BZI position, indole is positioned with C-3 in contact with the α-aminoacrylate Cβ and aligned for nucleophilic attack.

Structural analysis by XRD still remains a considerable challenge for materials that can’t be isolated as single crystals. In NMR crystallography structural constraints are extracted from the modern solid-state NMR techniques, and along with DFT (density functional theory) calculations.[1-4] NMR crystallography has been used to derive de novo structures and to aid the refinement of X-ray powder diffraction data.[1-4] In this work, computational integration of advanced solid-state NMR with PXRD (powder X-ray diffraction) and modelling is used to understand the structure of metal coordination polymers that are produced by the etching of metal nanoparticles in acidic solution.[6-8] Notably, these coordination polymers have some structural disorder which gives rise to broadened diffraction peaks. Solid-state NMR was applied to determine the number of molecules in the asymmetric unit and give insight into the geometry at the metal center. Then, the PXRD pattern of the coordination polymers was partially indexed to find probable unit cells. The position of heavy atoms was then optimized within the unit cell using the Free Objects for Crystallography (FOX) software. Finally, Rietveld refinement and DFT optimization was used to obtain a final structural model. The final NMR and PXRD derived structure is validated by comparing the experimental and simulated PXRD pattern and NMR parameters. This protocol was verified on scandium acetate which has a known single crystal structure from the literature. The protocol was then successfully applied to microcrystalline gallium and aluminum coordination polymers. We anticipate that this methodology could be extended to similar kind of coordination polymers with inherent heterogeneous character.

Figure 1. Schematic representation of the NMR crystallography approach used for finding the crystal structure of the coordination polymer.

[1] Ashbrook, S. E. & McKay, D. (2016). Chem. Commun. 52, 7186–7204.

[2] Bouchevreau, B., Martineau, C., Mellot-Draznieks, C., Tuel, A., Suchomel, M. R., Trébosc, J., Lafon, O., Amoureux, J.-P. & Taulelle, F. (2013). Chem. – A Eur. J. 19, 5009–5013.

[3] Thomas, B., Rombouts, J., Oostergetel, G. T., Gupta, K. B. S. S., Buda, F., Lammertsma, K., Orru, R. & de Groot, H. J. M. (2017). Chem. – A Eur. J. 23, 3280–3284.

[4] Xu, Y., Southern, S. A., Szell, P. M. J. & Bryce, D. L. (2016). CrystEngComm. 18, 5236–5252.

[6] Rossini, A. J., Hildebrand, M. P., Hazendonk, P. A. & Schurko, R. W. (2014). J. Phys. Chem. C. 118, 22649–22662.

[7]Chang, B., Martin, A., Thomas, B., Li, A., Dorn, R., Gong, J., Rossini, A. & Thuo, M. ACS Mater. Lett. 2, 1211–1217.

[8] Chang, B. S., Thomas, B., Chen, J., Tevis, I. D., Karanja, P., Çınar, S., Venkatesh, A., Rossini, A. J. & Thuo, M. M. (2019). Nanoscale. 11, 14060–14069.

For over 60 years, nanomaterials have consistently attracted the attention of the scientific community. In the field of nanomedicine, recent effort toward optimizing the therapeutic efficacy of newly discovered active compounds has resulted in the development of original supramolecular systems that execute multiple functions. However, the true potential of these systems has not been entirely utilized. Advancing these materials calls for precise structural analysis of individual elements and a description of the mutual relations between them. This is a stringent requirement, as these systems exist at the borderline between crystalline and amorphous solids, for which high-quality diffraction data are inherently unavailable. This contribution thus addresses our attempt to formulate an efficient experimental-computational strategy for obtaining deep insight into the structure of complex polycrystalline composites with micro- and nanodomain architecture. To determine the atomic-resolution structure of these systems, we apply a procedure based on ¹H NMR crystallography extended to describe the component-selective data. This strategy is based on the combined application of domain-selective solid-state NMR spectroscopy (ss-NMR), crystal structure prediction (CSP), and density functional theory (DFT)-based calculations of NMR chemical shifts. This combination of experimental and theoretical approaches enables one to determine the structural arrangements of molecules in situations which are not tractable by conventional spectroscopic techniques. Its applications should be of particular importance for systems in which phase transformations can occur, and new polymorphic forms can be spontaneously created under the influence of the matrix environment. The potential of this combined analytical approach is highlighted using the recently developed biodegradable, injectable polyanhydride microbead formulation of decitabine (5-aza-2'-deoxycytidine, DAC), an archetypal DNA methyltransferase inhibitor used as an efficient therapeutic for epigenetic cancer therapy. In this innovative drug-delivery formulation, which was developed to circumvent the problem of hydrolytic lability of the active compound, a mixture of microcrystalline domains of decitabine and nanodomains of sebacic acid (SA) is embedded in the semicrystalline matrix of poly(sebacic acid-co-1,4-cyclohexane-dicarboxylic acid) (PSA-co-PCH) carrier. The proposed method, which employs the confluence of computational data with measured NMR parameters, thus provides for a way to distinguish between alternative candidate structures exclusively existing in the composite assembles, and to select the ones that are the most compatible with available information. As the obtained results also opened a route toward the structure refinement of synthetic polymers with a limited amount of spectroscopic data available, finding a procedure for the reliable generation of a representative set of CSPs of synthetic polymers is thus of paramount importance. This contribution thus demonstrates the synergy effects of the proposed combination of several experimental and computational procedures, which considerably extends the NMR crystallography approach into the area of intricate mixtures and nanostructured composites. Potentiality of this approach will be also highlighted in de-nuovo determination of the crystal structure of chemotactic N-formyl-L-Met-L-Leu-L-Phe-OH tripeptide.

NMR crystallography uses a combination of solid-state NMR (SSNMR), X-ray diffraction (XRD), and quantum chemical calculations for the determination and/or refinement of crystal structures.^1,2 Currently, the majority of NMR crystallographic studies reply upon the measurement and calculation of isotropic chemical shifts (CS) or CS tensors and their computation by density functional theory (DFT) methods; by contrast, electric field gradient (EFG) tensors of quadrupolar nuclei are used much less extensively.^3–6 EFG tensors at the origins of quadrupolar nuclei are sensitive to their surrounding electronic environments, including longer-range interactions that do not greatly influence chemical shifts, yielding unique sets of quadrupolar parameters for each magnetically distinct environment. Furthermore, EFG tensors are less computationally demanding to compute than CS tensors. Since EFG tensors are sensitive probes of local atomic environments, we believe that it is crucial to explore and develop quadrupolar NMR-based crystal structure prediction (CSP) methods within the context of modern plane-wave DFT computational packages. In particular, such methods would be very useful for the study and characterization of organic solids, including pharmaceutical drug products, nutraceuticals, and a wide variety of multi-component crystals.⁵

Herein, we demonstrate the use of experimentally-measured and computationally-derived ³⁵Cl EFG tensor parameters in a new NMR crystallographic protocol for the refinement of crystal structures, which are developed and optimized on a training set of four organic HCl salts with known crystal structures. The stages of this protocol include: (i) selection/assignments of molecular fragments, charges, motion groups, and potential unit cells; (ii) simulated annealing using the Polymorph software package to generate tens of thousands of candidate structures, (iii) coarse geometry optimizations using DFT-D2* methods (which include dispersion effects),^7–9 and (iv) subsequent fine geometry optimizations. Between each of these stages, filters involving the unit cell dimensions, EFG tensor parameters, and static lattice energies have been optimized to select for the best candidate structures. The robustness of this new protocol is demonstrated via comparison of EFG tensors, PXRD patterns, and overlays of the known and refined crystal structures. Finally, this new protocol is demonstrated in several blind tests for the structural determination and refinement of organic HCl salts with unknown structures.

(1) Taulelle, F. Encycl. Magn. Reson. 2009, 1–14.
(2) NMR Crystallography; Harris, R., Wasylishen, R., Duer, M., Eds.; John Wiley & Sons Ltd.: Chichester, U.K., 2009.
(3) Ashbrook, S. E.; McKay, D. Chem. Commun. 2016, 52, 7186–7204.
(4) Bryce, D. L. IUCrJ 2017, 4, 350–359.
(5) Hodgkinson, P. Prog. Nucl. Magn. Reson. Spectrosc. 2020, 118–119, 10–53.
(6) Widdifield, C. M.; Farrell, J. D.; Cole, J. C.; Howard, J. A. K.; Hodgkinson, P. Chem. Sci. 2020, 11, 2987–2992.
(7) Grimme, S. J. Comput. Chem. 2006, 27, 1787–1799.
(8) Holmes, S. T.; Vojvodin, C. S.; Schurko, R. W. J. Phys. Chem. A 2020, 124, 10312–10323.
(9) Holmes, S. T.; Schurko, R. W. J. Phys. Chem. C 2018, 122, 1809–1820.

https://github.com/scipion-ed

http://www.conplot.org/

https://topospro.com/

https://topcryst.com/

https://github.com/tproffen/DiffuseCode

Photodynamic therapy (PDT) involves the treatment of a patient with a non-toxic photosensitiser. Upon irradiation by an external light source (600-850 nm)[1,2], the photosensitiser causes the production of singlet oxygen radicals at the tumour site which in turn provokes destruction of the tumour and so arousing significant interest as a potential cancer treatment.[3] Notably, a range of Rhenium(I) tricarbonyl complexes were found to induce cell death in a manner recognisably different to that of cisplatin and overcome cisplatin resistance in several resistant cell lines.[4,5]

It has become apparent that 1,10-phenanthroline moieties show favourable fluorescence for the detection of metal ions.[6] Sensors based on the 1,10-phenanthroline moiety coordinated to various metal ions have resulted in compounds exhibiting strong fluorescent properties. El-Awady et al. reported the effects of imidazopyridine derivative binding to DNA. They found that this introduction resulted in apoptosis in lung and breast cancer cells.[7] Thapa et al. synthesised a range of phenanthroline-type derivatives. Structure-activity relationship studies of these phenanthroline-type derivatives confirmed the importance of a [2,2’;6,2”]-terpyridine skeleton for cytotoxicity toward several cancer cell lines.[8]

A range of imidazo[4,5-f]-1,10-phenananthroline type ligands were synthesised and coordinated to Rhenium(I) yielding compounds of the general formula [Re(CO)₃(N,N’)(H₂O)]⁺ where N,N’ is the imidazo[4,5-f]-1,10-phenananthroline type ligand. These ligands and complexes were characterised by multinuclear NMR spectroscopy and IR Spectroscopy. X-ray crystallography data has been obtained for several ligands thus far. The photoluminescent, as well as the DNA binding capacity to calf thymus DNA were studied.

Nucleotides are the building blocks of DNA and RNA. Metal ion play a key role for their functional activities and stability. As nucleotide contains multiple functional groups, such as nucleobases, phosphate group and hydroxyl in the sugar moiety, it is therefore necessary to know the affinities of different coordination donor of nucleotide towards a particular metal ion. In this regard, X-ray investigation have made an important contribution by providing accurate information on the geometry of metal binding to the nucleotides. Molecular structure of these metal-nucleotide complex help to understand specific interaction at a certain condition which set the stage for biological and material applications.In this present work we are specifically synthesized the monomeric structure with phosphate only metal binding where we used ferric ion as metal centre. This is the first example of Iron (III)-Nucleotide ternary complex where we used tripodal tetradentate ligand as an auxiliary ligand. Single crystal X-ray diffraction showed that crystal of [Fe₂O(TPA)₂(AMP)](ClO₄)₂[TPA=Tris pyridyl methyl amine; AMP=Adenosine 5’-monophosphate] and [Fe₂O(TPA)₂(CMP)](ClO₄)₂ [CMP=Cytosine 5’-monophosphate] were crystallized in the triclinic crystal system (space group type P1). In these two structures we observed different packing arrangements of the nucleobase moiety with respect to the metal free counterpart. Here we observed adenine-adenine (Ade-Ade) and cytidine-cytidine (Cyt-Cyt) hydrogen bond formation from two different molecules in the unit cell. Because of the non-coplanar “nature” of auxiliary ligand, we didn’t find π-π stacking interaction between TPA ligand and nucleobase, but it is believed that TPA ligand is providing hydrophobic atmosphere which is important for forming H-bonding “interaction” between nucleobases. In case of [Fe₂O(TPA)₂(GMP)](ClO₄)₂ [GMP=Guanosine 5’-monophosphate] and [Fe₂O(TPA)₂(IMP)](ClO₄)₂ [IMP=Inosine 5’-monophosphate] belong to the monoclinic system , space group P2/c where we found that guanine moiety is making π-π stacking interaction with another guanine moiety and hypoxanthine is hydrogen bonded with another hypoxanthine moiety through bifurcating water molecule. As all the nucleotides are chiral in nature, we records CD spectra of free nucleotide and Iron-nucleotide complexes in liquid state to understand the chirality of nucleotide–metal complexes and supramolecular assemblies.

Phosphine ligands are considered by many as one of the most significant class of ligands in organometallic chemistry. The search of new phosphine chelators, as well as the subsequent functionalization thereof, is a continuing process in order to induce appropriate properties for highly effective catalyst and to a lesser extend in medicinal purposes. Of particular interest is the search for water-soluble and highly stable ligands that can preserve their aquatic solubility even after metal coordination.

In this study, we aim to improve the efficiency of middle/late transition metal homogeneous catalysts (i.e. Re, Rh, Pd and Pt) and fac-[M(CO)₃] (M = Re and Tc) radiopharmaceutical synthons by selectively introducing monodentate and bidentate phosphine ligands consisting of various electronic and steric properties. The use of systematically altered bidentate phosphine ligands such as diphosphinoamine ligands has already been reported to show high selectivity improvements in catalytic reactions such as ethylene tri- and tetramerization [1].

A series of diphosphinoamine ligands was synthesized using methods described in literature [2, 3]. These ligands were then coordinated to various metal (i.e. Re(I), Tc(I), Pt(II) and Pd(II)). Results obtained from the biological analysis and catalytic evaluations have opened up a new window of opportunities for such compounds. @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-536870145 1107305727 0 0 415 0;}@font-face {font-family:Cambria; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-536870145 1073743103 0 0 415 0;}p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin-top:0cm; margin-right:0cm; margin-bottom:10.0pt; margin-left:0cm; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Cambria",serif; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-ansi-language:PT; mso-fareast-language:JA;}.MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-family:"Cambria",serif; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-ansi-language:ES-TRAD; mso-fareast-language:JA;}.MsoPapDefault {mso-style-type:export-only; margin-bottom:10.0pt;}div.WordSection1 {page:WordSection1;}

Due to their vast applications in science and technology, the thermo-responsive materials have always been the forefront of the materials science. Usually, materials expand upon heating but the negative thermal expansion (NTE) materials are unusual because they contract along one or more directions with increasing temperature.⁴ Although the NTE effects are not uncommon effect are rarely observed in organic materials and especially in single-component all-organic systems.¹ Recently focus has been shifted to develop the pure organic materials due to their benign nature and flexibility. Moreover, existence of both positive thermal expansion (PTE) and NTE in organic molecular systems are extremely rare.^1b Materials with NTE property finds immense applications in modern technologies² and lightweight, environmentally benign and easily tunable organic materials have plenty to offer in this niche area.^2,3 In an effort to discover unusual PTE and NTE in organic materials, we have studied a series of imidazoline derivatives, where 2-(4-bromophenyl)-4,5-dihydro-1H-imidazole has shown a prominent NTE effect compared to its other derivative. This unique system not only undergoes solvent mediated polymorphic modifications to form centrosymmetric (1C, space group P2₁/c) and non-centrosymmetric (1N, space group Cc) structures but each of the forms experiences single-crystal to single-crystal reversible yet isosymmetric phase transition at ~210 K upon cooling. While form 1C transforms to a structure with space group P2₁/n, the form 1N converts to a new structure but without changing the space group. Interestingly, upon cooling, across the phase transition temperature at ~210 K, 1N undergoes colossal PTE to NTE transition along the a-axis but NTE to PTE along the b-axis while c-axis experiences almost zero thermal expansion. Whereas, 1C exhibits PTE to NTE only along the b­-axis and only PTE along the other two axes. These anisotropic unusual thermal expansions, which is mainly due to the scissor like motion that molecules are undergoing upon temperature stimuli. Given these unusual properties, this novel all-organic material, which is analogous to a known molecular ferroelctric,⁴ may find potential applications in future organic electronics.

Plastic crystals (PCs), formed by certain types of molecules or ions with reorientational freedom, offer both exceptional mechanical plasticity and long range order, hence they are attractive for many mechano-adaptable technologies. While most classic PCs belong to simple globular molecular systems, a vast number of examples in the literature with diverse geometrical (cylindrical, bent, disk, etc.) and chemical (neutral, ionic, etc.) natures have proven their wide scope and opportunities. All the recent reviews on PCs aim to provide insights into a particular application, for instance, organic plastic crystal electrolytes or ferroelectrics. This tutorial review presents a holistic view of PCs by unifying the recent excellent progress in fundamental concepts from diverse areas as well as comparing them with liquid crystals, amphidynamic crystals, ordered crystals, etc. We cover the molecular and structural origins of the unique characteristics of PCs, such as exceptional plasticity, facile reversible switching of order-to-disorder states and associated colossal heat changes, and diffusion of ions/molecules, and their attractive applications in solid electrolytes, opto-electronics, ferroeletrics, piezoelectrics, pyroelectrics, barocalorics, magnetics, nonlinear optics, and so on. The recent progress not only demonstrates the diversity of scientific areas in which PCs are gaining attention but also the opportunities one can exploit using a crystal engineering approach, for example, the design of novel dynamic functional soft materials for future use in flexible devices or soft-robotic machines.

The study of fission tracks in terrestrial minerals and meteorites has demonstrated its usefulness for cosmic-ray prehistory, age, and thermal history of minerals studies [1]. The techniques based in chemical etching of natural tracks has been described by Fleisher, Price & Walker [2]. In 1965 Fleisher, Price & Walker proposed etching conditions for so many minerals. For garnets, the authors proposed a KOH etching for two hours at 150°C, but without measuring these etching conditions and their relation with the fission tracks in the garnets. Haack & Gramse [3] have demonstrated that garnets, especially andradites and spessartines, can be appropriate minerals for fission tracks dating. Posteriorly, [4] etched in boiling (-150 °C) 50 mol / 1 NaOH solution for 20 - 30 min to reveal spontaneous fission tracks in the garnet.

However, for the garnets (Ca,Mg,Fe2+,Mn)3(Al,Fe3+.Mn,Cr,Ti4+)2(SiO4)3, common rock-forming mineral in basic and ultrabasic igneous rocks and metamorphic rocks, any satisfactory or new etchant has been reported after Fleisher, Price & Walker [2], Haack & Gramse [3] and Wang, Chen & Tein [4]. Over the past years the research in fission tracks focused on minerals like Apatite and Zircon and theirs methods and techniques. In certain degree it was influenced by the fact of these minerals present low closing temperatures, in agreement with the maturity temperatures of the hydrocarbons. This research describes a satisfactory revelation of spontaneous fission tracks in garnets. The experimental method used consists in submitting the garnets to a chemical attack using an etching technique. The methodology has been based in [5], however these authors have used their methodology to revel natural fission tracks in olivines. For this reason, in this research we considered some modifications in their experimental method.

The attack has been consisted in a base-acid sequential immersion, where Potassium Hydroxide (KOH) (1mol/L^-1) and Hydrofluoric Acid (HF) were used. The garnets were submitted to KOH at 100°C for 4 minutes. After this, we insert the garnets in the HF for 30 seconds at 23°C. After chemical etching, the fission tracks in our garnets were characterized with scanning electron microscopy (SEM). The fission tracks were analyzed using a scanning electron microscopy. The SEM images were measured using a Zeiss, EVO-MA10. The samples were irradiated with an electron beam of 5kV and the images was captured at 400x magnification.

The fission tracks revealed on this experimental method have between 18.96μm and 50.06μm of length. Based on these results, it indicates that the experimental method is efficient to revel spontaneous tracks in garnets. Whtas suggests that this experimental method can be applied in others minerals and meteorites. On the other hand, new studies with variations of concentration, temperature and time of exposure in the experimental method are necessary to determine the behavior of the fission tracks in the new conditions for the garnets.

Melamine is a precursor for polymeric Carbon Nitride (p-CN) materials showing great promise in a variety of different applications including electro- and photo catalysis [1]. The structure consists of layers of extended graphite-like CN with stoichiometry close to C₃N₄ including only a small amount of hydrogen. Insight into the electronic properties of precursor materials could be valuable for understanding the catalytic properties of p-CNs. The 2,4,5-triamino-s-triazine molecule (melamine) crystalizes in the P2₁/n space group and is an archetypical example of an organic molecular crystal. This study presents the ongoing work of benchmarking synchrotron radiation (with a wavelength of ~0.25 Å) against state of the art in house diffractometers, using respectively Mo (0.71 Å) and Ag (0.56 Å) radiation. Preliminary results show no significant deviation between the three different methods, and the electron density models obtained from the data analysis are for all practical purposes the same. The experimental electron density of melamine crystals is analyzed in terms of chemical interactions. In particular Bader topology and energy frameworks are used to study the chemical importance of the inter-molecular interactions in crystal formation of melamine. Future work includes studies of other p-CN materials with structures that are even closer to the catalytically active p-CN, e.g to gain insight into the chemical effects responsible for the layer forming mechanism.

[1] F. K. Larsen, A. Mamakhel, J. Overgaard, J. E. Jørgensen, K. Kato and B. B. Iversen, Acta Cryst. (2019). B75, 621–633

The phosphorus (P)-stereogenic enantiomers are used in many fields of chemistry, for example in chiral catalysis, stereoselective transformation and optical resolution. They are in the forefront of interest in the last decade.

Several dialkyl-arylphosphine oxide compounds have been prepared by Péter Bagi and his co-workers [1]. The newly synthetized phosphorous derivatives are sensitive racemic compounds. Trying several resolving agents, resolution was performed and the enantiomers were separated with (R,R)- or (S,S) -spiro-TADDOL (-1,4-dioxaspiro[4.5]decane-2,3-diylbis(diphenylmethanol)) in gram scale. Some diastereomers of the series (i.e. methylphenylpropylphosphine oxide and ethylphenylpropylphosphine oxide) were crystallized in nitrogen atmosphere, and investigated by single crystal X-ray diffraction (Figure 1). The absolute configurations of the dialkyl-arylphosphine oxides were successfully determined [2]. We present the structures of a few diastereomers formed using TADDOL, where the SXRD results revealed the main interactions which contribute to the enantiomeric recognition. Hirshfeld surface analysis and DFT calculation were performed using the software Crystal Explorer in order to understand the secondary interaction network.

Rod-shaped single crystals of HoF(OH)₂ could be synthesized from Ho₂O₃ and HoF₃ using a high-pressure hydrothermal synthesis route in order to obtain crystalline holmium fluoride oxide (HoFO). The reaction was performed in a gold capsule filled with the starting materials and about 15 vol-% of demineralized water to provide suitable conditions. The gold capsule was sealed by cold-welding and placed into a rock-salt pressure cell. Using an end-loaded piston-cylinder high-pressure apparatus deriving from the Boyd and England design, the cell pressure was dwelled on 500 °C at 10.5 kbar for five days [1]. After quenching to room temperature, small pale-yellow crystals were isolated and investigated using single-crystal X-ray diffractometry. The hexagonal unit cell of the measured crystals showed a noticeable deviation regarding the detected axes and density, when compared to UCl₃-type Ho(OH)₃ (a ≈ 626.6 pm, c ≈ 355.3 pm, ρ_X = 5.94 g/cm³ [2]; our results for HoF(OH)₂: a ≈ 603.3 pm, c ≈ 356.8 pm, ρ_X = 6.44 g/cm³). Therefore, it was concluded that a mixed F^–/OH^– anion site is present, leading to the composition HoF(OH)₂. The F^–-to-OH^– ratio of 1:2 is plausible, when the molar volumes of UCl₃-type Ho(OH)₃ (V_m = 36.38 cm³/mol) [2] and HoF(OH)₂ (V_m = 33.86 cm³/mol) are compared with the one of YF₃-type HoF₃ (29.03 cm³/mol; d(Ho–F) = 229 – 232 pm plus 250 pm for C.N. = 8+1) [3].

The UCl₃-type crystal structure of HoF(OH)₂ (space group: P6₃/m) features one crystallographic position for each ion. Ho³⁺ is surrounded by nine anions in the shape of a tricapped trigonal prism [HoF₃(OH)₆]^6– (Figure 1) with interatomic distances of d(Ho–F/OH) = 237 pm for the prism anions and d(Ho–F/OH) = 234 pm for the capping ones. This finding contrasts with the crystal structure of Ho(OH)₃, where the bond lengths to the prism corners are with 242 pm almost 3 pm shorter than those to the caps [2].

To investigate the mixed occupation of the anion site with OH^– and F^– anions, wavelength-dispersive X-ray spectrometry (WDXS) was performed for the measured crystal. The spectrum clearly showed the presence of both the O-K_α and the F-K_α emission line in relevant intensity with a F:O ratio of 35:65 and thus confirmed the structure model derived from the single-crystal X-ray diffraction data.

High-spin Ni(II) complexes have been a very important class of molecules due to their potential application as a new type of magnetic materials. In general, multinuclear Ni(II) complexes, such as Ni₄O₄ cubane, may exhibit either ferromagnetic or antiferromagnetic interactions between the nickel ions, as well as the slow magnetic relaxation characteristic for single molecule magnets (SMM) [1].

In this work we describe the preparation of four new multinuclear Ni(II) complexes: [Ni₂(BrQ)₃(HBrQ)₃]ClO₄ (1), [Ni₂(dBrQ)₄(MeOH)₂] (2), NH₂(CH₃)₂[Ni₂(µ-Cl)₂(BrQ)₃(DMF)(H₂O)]·DMF (3) and [Ni₄(ClQ)₆Cl₂(H₂O)₂]·2DMF (4), containing molecules of halogen derivatives of 8-hydroxyquinoline: 5-chloro-8-hydroxyquinoline (HClQ), 7-bromo-8-hydroxyquinoline (HBrQ) and 5,7-dibromo-8-hydroxyquinoline (HdBrQ) (Fig. 1). The complexes were studied by infrared spectroscopy, CHN elemental analysis and single crystal X-ray analysis.

Figure 1. Structural formulas of different halogen derivatives of 8-hydroxyquinoline.

Using infrared spectroscopy, we identified individual characteristic vibrations in the measured spectra of complexes 1 – 4, which confirmed the presence of coordinated molecules of anionic ligands ClQ, BrQ or dBrQ, as well as perchlorate anion in sample 1 and solvent water and dimethylformamide molecules in samples 3 and 4.

Structural analysis revealed different bridges between the central nickel atoms in the structures of these multinuclear complexes. Nickel atoms are bridged by the hydrogen atom connecting the opposite oxygen atoms in the HBrQ molecules (1), by two oxygen atoms of the dBrQ ligands (2), by two chlorine atoms (3) and by six oxygen atoms of the ClQ ligands; four of them bridge two nickel atoms while remaining two bridge three nickel atoms (4). As a result, complexes 1, 2 and 3 are dinuclear, while complex 4 forms a tetranuclear structure. We observed the stabilization of these complexes through intermolecular interactions, such as hydrogen bonds (1 – 4) and π – π interactions (2 and 4).

[1] Gusev, A. N., Nemec, I., Herchel, R., Baluda, Y. I., Kryukova, M. A., Efimov, N. N. & Kiskin, M. A. (2021). Polyhedron. 196, 115017.

Slovak Grant Agencies (VEGA 1/0148/19 and VVGS-PF-2021-1769) are acknowledged for financial support.

Five new zinc(II) complexes, {Na[Zn(ClNQ)(SO₄)(H₂O)]}_n (1), [Zn(dNQ)₂(H₂O)₂]·1,4-dioxane (2), [Zn(dNQ)₂(H₂O)₂] (3), NH₂(CH₃)₂[Zn(ClNQ)₃]·DMF (4) and K[Zn(ClNQ)₃]·2DMF (5), (HClNQ = 5-chloro-7-nitroquinolin-8-ol, HdNQ = 5,7-dinitroquinolin-8-ol (Fig.1)) have been prepared. All complexes were characterized by IR spectroscopy, elemental analysis and X-ray structure analysis.

Figure 1. Chemical structures of HClNQ (left) and HdNQ (right)

Complex 1 has a polymeric structure. Zn(II) atom is penta-coordinated by one bidentate molecule of ClNQ ligand, one molecule of water and a pair of crystallographically equivalent sulfate anions, which interconnect adjacent zinc atoms to form a zig-zag chain.
In addition, the central atoms are also connected through ionic interactions between oxygen atoms with a partial negative charge and sodium cation.

Complexes 2 and 3 have similar molecular structures, Zn(II) atom sits at the center of the symmetry, therefore only a half of the molecule is independent. In their crystal structures, there are two trans-coordinated dNQ molecules in the equatorial plane while two water molecules occupy axial positions, forming a deformed octahedral geometry. Complex 2 also contains one uncoordinated molecule of 1,4-dioxane.

Complexes 4 and 5 are ionic compounds with very similar structures, in which Zn(II) atom is tris-coordinated by molecules of deprotonated 5-chloro-7-nitro-quinolin-8-ol with nitrogen and oxygen donor atoms coordinated in mer-fashion. The negative charge of the complex anions is counterbalanced by uncoordinated dimethylammonium and potassium cations, respectively, and interesting orientation of the oxygen atoms to NH₂(CH₃)₂⁺ (4) and K⁺ (5) ions is observed. In addition, the complex 5 contains one more solvated molecule of DMF molecule.

Slovak Grant Agencies (VEGA 1/0148/19, VVGS-PF-2020-1425 and VVGS-PF-2021-1772) are acknowledged for financial support.

Ever since their first description in 2013 [1] crystal sponges have attracted considerable attention, for their ability to provide structural information on hard to crystallize or non-crystalline compounds [2]. However, their analysis proved to be tricky, with infused compounds highly disordered in the structure channels in overlapping disorder with solvent. Since the solution of highly disordered systems requires reliable high resolution data, and considering large unit cell of crystal sponges, the use of Mo-Kα radiation was discouraged in favour of Cu-Kα radiation [3]. During our studies of crystal sponge infusion procedure, we have observed gradual darkening of studied crystals combined with gradual disappearance of strong diffractions in measured frames. We have decided to evaluate the possible radiation decay of studied (ZnI₂)₃(tpt)₂ crystal sponge, by measuring the series of identical experiments with the same crystal. We have chosen series of five experiments with 12 hours each, resulting in overall irradiation time of 60 hours. The crystal darkening was observed during the measurements, resulting in a black crystal, with apparent loss of strong diffraction spots in measured frames, see Fig. 1a. The data we obtained have shown significant loss of diffraction reliability with I/σ(I) decreasing from 3.62 to 1.67 in 0.84-0.81 Å shell and from 6.09 to 3.34 in 0.97-0.92 Å shell. The R_int increased in respective shells from 0.166 to 0.335 and from 0.099 to 0.158. The decrease of data quality was also apparent in the structure model, with R_all increasing from 8.36 % to 10.56 %. Average U_eq increased from 0.071 to 0.099 considering only the framework atoms.

We decided to evaluate the radiation decay using the Mo-Kα as well, since the radiation of lower wavelength should be less absorbed by the crystal sponge. As previously stated the use of Mo-Kα is discouraged for possibility of diffraction spot overlaps and presence of low and high angle diffraction spots in one frame, disallowing the longer irradiation times for high angle diffractions. However, both of these issues are counteracted by increasing the detector distance from the sample. Increasing the detector distance from 53 mm to 140 mm allows an experimental strategy similar to Cu-Kα experiments, with varying irradiation times without detector overflows. During the data collection following the same procedure, no significant crystal darkening or loss of strong diffraction in measured frames was observed, see Fig 1b. Although some loss of diffraction reliability was observed, with I/σ(I) decreasing from 4.75 to 4.36 in 0.85-0.82 Å shell and 8.30 to 7.65 in 1.00-0.94 Å shell, it was less pronounced. Only a minor increase of R_int in respective shells was observed, with 0.110 increasing to 0.113 and 0.063 to 0.069. The structure model behaves accordingly with R_all increasing from 10.48 to 10.97 and average U_eq increasing from 0.034 to 0.035.

Figure 1. Crystal image and selected frame before and after 60 hours of irradiation using a) Cu-Kα radiation, b) Mo-Kα radiation.

[1] Inokuma, Y., Yoshioka, S., Ariyoshi, J., Arai, T., Hitora, Y., Takada, K., Matsunaga, S., Rissanen, K., Fujita, M. (2013). Nature 495, 461–466. [2] Matsuda, Y., Mitsuhashi, T., Lee, S., Hoshino, M., Mori, T., Okada, M., Zhang, H., Hayashi, F., Fujita, M., Abe, I. (2016). Angew. Chem. Int. Ed. 55, 5785–5788. [3] Hoshino, M., Khutia, A., Xing, H., Inokuma, Y., Fujita, M. (2016). IUCrJ 3, 139–151.

Keywords: X-ray diffraction; Crystal sponge; Decay

This research was supported by the project 20-14770Y of the Grant Agency of the Czech Republic.

In 2002, Kanatzidis et al. synthesized and characterized the rare-earth metal(III) hexaselenidodiphosphate(IV) Ce_1.333[P₂Se₆], which crystallizes monoclinically in the space group P2₁/c [1]. Schleid et al. succeeded to find with Nd_1.333[P₂Se₆] [2,3] a further representative, which showed the same structured formula, but adopts a different structure type. It crystallizes in the triclinic space group P with a modified NaYb[P₂S₆]-type structure [3], whilst Ce_1.333[P₂Se₆] principally mimics the NaCe[P₂Se₆]-type structure [1]. Here we present the gap-filling Pr_1.333[P₂Se₆], which also crystallizes triclinically in the space group P with a = 685.32(5) pm, b = 759.41(6) pm, c = 962.56(7) pm, α = 90.087(3)°, β = 91.723(3)° and γ = 90.034(3)° for Z = 2 at 293 K (CSD number: 2089248), just like Nd_1.333[P₂Se₆]. An extended unit cell of the title compound is depicted in Figure 1 (mid) with highlighted [P₂Se₆]^4– units, which occur in staggered conformation, very characteristic for hexaselenidodiphosphates(IV). The interatomic distances within these ethane-like anions are also well in the usual range (d(P–P) = 220 – 221 pm, d(P–Se) = 218 – 220 pm). The environment of the two distinct Pr³⁺ cations resemble bicapped trigonal prisms with distances between praseodymium and selenium from 303 to 337 pm for C.N. = 8 (Figure 1, left and right). Bicapped trigonal prisms are also found in the neighboring compounds Ce_1.333[P₂Se₆] and Nd_1.333[P₂Se₆] with very similar interatomic Ln–Se distances. Whilst in the neodymium and praseodymium derivatives these [LnS₈]^13– polyhedra are edge-connected to form single chains for every individual cation (Ln1 and Ln2), which finally fuse to a framework, a three-dimensional network immediately emerges for the cerium compound from selenium polyhedra of the three crystallographically different Ce³⁺ cations with C.N. = 8. All three compounds have cationic defects in common, but the defect sites for Pr_1.333[P₂Se₆] are on different crystallographic positions as compared to Nd_1.333[P₂Se₆], making both structures not completely isotypic.

If the volumes of the unit cells for Ce_1.333[P₂Se₆] (a = 680.57(5) pm, b = 2296.85(15) pm, c = 1172.26(8) pm, β = 124.096(1)° for Z = 6 at 100 K), Pr_1.333[P₂Se₆] (vide supra) and Nd_1.333[P₂Se₆] (a = 682.41(5) pm, b = 757.98(6) pm, c = 961.03(7) pm, α = 90.176(3)°, β = 91.789(3)°, γ = 90.108(3)° for Z = 2 at 293 K) are compared and the effect of the lanthanoid contraction is taken into account, they can be nicely compared, if the number of formula units in the unit cell is reduced to Z = 2. Then the volumes are 0.506 nm³ for Ce_1.333[P₂Se₆], 0.501 nm³ for Pr_1.333[P₂Se₆] and 0.497 nm³ for Nd_1.333[P₂Se₆].

Synthesis, characterization and in vitro activities of aniline dithiocarbamate crystals

Ayodele Temidayo Odularu¹, Peter Adewale Ajibade², Johannes Zanoxolo Mbese¹, Opeoluwa Oyehan Oyedeji¹

¹University of Fort Hare, Alice, South Africa; ²University of Kwa Zulu-Natal, Pietermaritzburg, South Africa.; 201106223@ufh.ac.za

One pot synthesis was used to prepare aniline dithiocarbamate from aniline, carbon(IV) sulfide and sodium hydroxide [1]. Aniline dithiocarbamate crystals (ai-dtc; C₇H₁₂NNaO₃S₂) which grew from solution were washed with diethyl ether, and subjected to single x-ray crystallography. The crystals were collected and mounted on a four circles diffractometer Gemini of Oxford Diffraction, using a graphite monochromated CuKα radiation (λ = 1.54184 Å). Super flip program was used to solve the crystal structure; while refinement was done using full matrix least-squares technique with the support of Jana 2006. The resulting synthetic crystalline structure (Figure 1) appeared as crystalline polymolecule (Figure 2) which has crystal data with three dimensions of a= 2.86663(4) Å, b=6.9 386 (3) Å and c=11.3127 (3) Å. Other characterization techniques of physicochemical parameters, FT-IR, UV-Vis and NMR further confirmed ai-dtc structure. [2] For the in vitro antibacterial studies, ai-dtc was screened against four bacterial strains (Staphylococcus aureus MRSA252, Enterococcus faecalis ATCC 19433, Escherichia coli MC4100 and Pseudomonas aeruginosa PAO1). Result showed that ai-dtc had modest activity against Staphylococcus aureus [2].

Keywords: One pot synthesis, dithiocarbamates crystals, polymers, single x-ray crystallography, antibacterial activities

Figure 1: C₇H₁₂NNaO₃S₂ crystal structure. Figure 2: C₇H₁₂NNaO₃S₂ polymolecule.

References

1. Ahamad, M. M.; SureshKumar, E. V.; Rao, R. M.; Phebe, P. Arch. Appl. Sci. Res. 2016, 8, 61-64.

2. Odularu, A. T.; Ajibade, P. A. Bioinorg. Chem. Appl. 2019, 2019, 1-15.

The new orthophosphate PbNi₂Fe(PO₄)₃ have been synthesized by solid-state reaction route and characterized by X-ray diffraction, scanning electron microscopy, Infrared and Raman spectroscopy.

The analysis by single crystal and powder X-ray diffraction techniques showed that this compound crystallizes in the orthorhombic system with Imma space group and unit cell parameters a = 10,415 (3) Å; b = 13,165 (4) Å; c = 6,536 (2) Å; V = 896,15 (5) ų; Z = 4.

The three-dimensional framework of the crystal structure is built up by [PO₄] tetrahedra, [FeO₆] octahedra and [Ni₂O₁₀] dimers of edge-sharing octahedra, linked through common corners or edges. This structure comprises two types of layers stacked alternately along the [100] direction. The first layer is formed by edge sharing octahedra ([Ni₂O₁₀] dimer) linked to [PO₄] tetrahedra via common edges and vertices while the second layer is built up from a row of corner-sharing [FeO₆] octahedra and [PO₄] tetrahedra forming an infinite linear chain. The layers are held together through vertices of [PO₄] tetrahedra and [FeO₆] octahedra, leading to the appearance of two types of tunnels parallel to the a and b-axis directions in which the Pb²⁺ cations are located.

The structure affiliation of the studied phosphate to that of α-CrPO₄ and its spectroscopic properties will be discussed.

There are adequate number of molecules in nature which exhibit stimuli-response behaviour. Mimicking them, molecular crystals responding to mechanical and thermal stimuli, arraying actuating properties, comparable to that of soft materials, are yet in quest. With advances in the field of stimuli responsive molecular crystals, detailed investigation on the existing systems are helping in reformation of models which help in relating the macroscopic (kinematic) events to molecular (mechanistic) aspects.[1] Dynamic effects such as jumping, bending, popping, splitting as an outcome of thermal/mechanical/photo stimuli have become much more intriguing and explicate by linking observations from AFM/SEM/HSM to SCXRD/PXRD/Stress-Tensile test experimental data.[2,3]

On lowering temperature (258-278K), single crystals of a diphenyl phosphate 2-chloroanilium salt were observed exhibiting reversible thermal expansion/compression, [4] accompanying phase transition which simultaneously shows splitting and/or bending (morphology and size specific phenomenon) of crystals [5] (Fig 1, Right). The reversible thermoelastic phase transitioning behaviour could be classified under shape memory materials. [6,7] The elastic bending response to mechanical stimuli, on exerting force on the major face of the crystal at room temperature (Fig. 1, Left), highlights another exploitable application of this molecular crystal. [8]

Figure 1. Three-point bending experiment carried out at major face (001) of single crystal; Observation of reversible bending and splitting on carrying out cooling-heating cycle of single crystals on cold stage microscope.

[1.] Karothu D. G, Weston J., Desta I.T. & Naumov P. (2016). J. Am. Chem. Soc., 138, 13298−13306.

[2.] Devarapalli R., Kadambi S. B., Chen C-T, Rama Krishna G., Kammari B. R., Buehler M. J., Ramamurty U., & Reddy C. M. (2019). Chem. Mater., 31, 1391-1402.

[3.] Dey S., Das S., Bhunia S., Chowdhury R., Mondal A., Bhattacharya B., Devarapalli R., Yasuda N., Moriwaki T., Mandal K., Mukherjee G. D. & Reddy C. M. (2019). Nat. Commun., 10, 3711.

[4.] Liu H, Gutmann M. J., Stokes H. T., Campbell B. J., Evans I. R., & Evans J.S.O. (2019). Chem. Mater., 31, 4514−4523.

[5.] Ahmed E., Karothu D. P., Warren M. & Naumov P. (2019). Nat. Commun., 10, 3723.

[6.] Takamizawa S. & Takasaki Y. (2016). Chem. Sci., 7, 1527-1534.

[7.] Park S. K. & Diao Y. (2020). Chem. Soc. Rev., 49, 8287-8314.

[8.] Dey S., Das S., Bhunia S., Chowdhury R., Mondal A., Bhattacharya B., Devarapalli R., Yasuda N., Moriwaki T., Mandal K., Mukherjee G. D. & Reddy C. M. (2019) Nat. Comm. 10, 3711.

With carbon dioxide (CO₂) reaching a peak concentration of 416 ppm in 2019 and still increasing yearly, there still has been no viable option to reduce the CO₂ concentrations in the atmosphere. This is in part due to the relatively inert nature of CO₂. However, the biomimetic investigation of plants, specifically CAM (Crassulacean Acid Metabolism) plants (Such as cacti and succulents), illustrate how CO₂ may be converted and stored [1]. The biomimetic approach can therefore aid in discovering an approach which may help overcome the energy and financial barrier for carbon capture and sequestration (CSS).

The amidines and guanidines are two classes of organic nitrogen bases that can activate CO₂ and have been used in switchable ionic liquids (SWILs) to store CO­₂ and as cocatalysts or ligands in metal catalyzed reactions [2]. Furthermore, 2,2’-bipyrdine ligands have also shown promise in catalytic reactions of CO₂ [3].

The focal points to be discussed in this presentation are CO₂ and its uptake cycle in crassula ovata succulents (Fig.1(a)). Thereafter, the synthesized rhodium metal complexes, which contain 1,5-cyclooctadiene (COD) and the nitrogen bases as ligands, will be discussed along with characterization by single-crystal x-ray diffraction (SC-XRD). Special focus will be given to the influence the ligands have on the coordinated COD which “mimics” the Venus fly-trap plant, illustrated in Fig. 1(b-d), and the related kinetic studies by a neutral ligand to replicate CO₂ [4]. Interestingly, the results from the kinetics showed that the forward reaction rate (k₁) for the amidine-containing rhodium complex was k₁ = 2.16 x 10³ M^-1s^-1 with a half-life of 321 ms and ten-times faster for the rhodium complex containing the guanidine ligand. This can be seen to correlate with the change in angles (Fig. 1(c,d)) of the COD.

In addition to the above, five–coordinate platinum group metal complexes containing COD, a methyl/ phenyl group and various 2,2’-bipyridine ligands that have been isolated and characterized will be discussed in a similar fashion to the Rh-COD complexes [5]. An evaluation and comparison of the COD angles will illustrate the importance that crystallography has on understanding molecular structures and kinetics.

The synthesis of transition metal complexes with central metals Ni(II), Co(II) and Zn(II) with thiocyanate or chloride anions and pyridine derivative co-ligands according to the formula of Werner complexes MX₂L₄ presented structural diversity. The ‘tunability’ of the crystal structures arises from the transformation of the nature and size of the inclusion cavities. In general, octahedral coordination complexes occur with nickel and cobalt. However, zinc showed a preference for tetrahedral coordination, resulting in MX₂L₂ crystals, where M is the central metal, X the anion and L the pyridine derivative ligand.

The effect of the position of derivatives on the pyridine ring (meta- or para-) altered the interaction between the host molecules forming a variety of frameworks. In the case of nickel and cobalt, the nicotinamide ligand (meta position amide) a linear arrangement of the ligands occurs resulting in a predictable and robust framework which shows hydrogen bonding of amide tetramers. Steric hindrance between the derivatives results in torsioning of the ligands if the derivative is para to the pyridine nitrogen. Hosts Ni(NCS)₂ and Co(NCS)₂ with four isonicotinamide ligands presented a variety of frameworks ranging from spiral format to herringbone arrangement. The trans ligands present a propeller arrangement which disables the predictability of the framework.

A further discovery was made with mixed ligand complexes. The prominence of amide dimer formation via hydrogen bonds between nicotinamide ligands was emphasised yet isonicotinamide ligands showed only discrete hydrogen bonds. Sulphur hydrogen bonds O-H···S in nickel clathrates resulted in better thermal stability. This case was observed with Ni(NCS)₂(nicotinamide)₄ clathrates with an alcohol guest compared with those with carbonyl guest.

Discrimination between two guests was shown by nickel complexes for a number of equimolar guests, notably the selection of 1-butanol from an equimolar mixture with 2-pentanol; 4-methylcyclohexanone from a mixture of 3- and 4-methylcyclohexanone; and propanol was selected over isopropanol. The host Ni(NCS)₂(4-phenylpyridine)₂(isoquinoline)₂ targets meta-xylene over ortho- and para-xylene in an equimolar mixture of the isomers. Stronger C-H···π intermolecular interactions were found in the Hirshfeld surface analysis between the host and meta-xylene than in the other two isomers.

The versatility of the central metal in these Werner complexes was investigated by measuring the thermal properties of the release of the guest from isotypic clathrates using differential scanning and thermogravimetric analysis. The diversity of the complexes and the versatility of the ligands in these Werner complexes demonstrates their importance in the discriminatory ability of guest mixtures.

The method of symmetry breaking potential and first order cluster expansion technique for the partition functions adopted for the theory of ordering in liquid crystals has been extended to symmetric and asymmetric molecules. The order parameter is calculated as a function of temperature and packing coefficient as a function of position of double bond in alkenyl chain length for homologous series of 4–alkenyl bicyclohexylnitrile Compounds [1-4]. The theoretical calculations adopted the method of Shivaprakash et al [5], account fairly well for the gradient differences in the order parameters of symmetric and asymmetric molecules and packing coefficients. Variation of order parameter with temperature for 1d₁CC is shown in Figure 1.

It is of interest to compare the molecular packing formula given by Kitaigorodsky [6] of the homologous series of 4–alkenyl bicyclohexylnitrile compounds. Compound 1d₁CC & 3d₁CC possess double bond after the first carbon chain from cyclohexyl ring and exhibit nearly same packing coefficient. On the other hand, compounds 1d₃CC & 0d₃CC possess double bond after the third carbon chain from cyclohexyl ring and exhibit nearly same packing coefficient.

Figure 1. Variation of order parameter with temperature for 1d₁CC

Keywords:

Order parameter; packing coefficients; structure-property relation.

References:

[1] Sakuntala Gupta, kinkini Bhattacharyya, S. P. Sengupta, Sukla Paul, Alajos Kalman and Laszlo Parkanyi, A mesogenic alkenyl compound, Acta Cryst., 1999, C55: 403-405.

[2] S. Gupta, A. Nath, S.Paul, H. Schenk and K. Goubitz, Structures and Properties of an Alkenyl Liquid Crystalline Compound, Mol. Cryst. Liq. Cryst., 1994, Vol. 257: pp. 1-8.

[3] Sakuntala Gupta, S. P. Sen Gupta, R. A. Palmer, B. S. Potter and M. Schadt, Crystal Structure of 4(1՛՛-butenyl) 4՛(cyano)1,1՛ bicyclohexane, Mol. Cryst. Liq. Cryst., 2002, Vol. 378: pp. 193-202.

[4] Sakuntala Gupta, R. A. Palmer, M. Schadt, S. P. Sen Gupta, Structural analysis of a mesogenic 4-alkenyl bicyclohexylnitrile, Liq. Cryst., 2001, Vol. 28, No. 9: 1309-1313.

[5] N. C. Shivaprakash & Jn. Shashidhara Prasad, A Theoretical Investigation of the Lattice of Symmetric and Asymmetric Rigid Rods with Anisotropic Dispersion Forces and Rigid Body Repulsions, Mol. Cryst. Liq. Cryst., 1981,74: 215-226.

[6] A. I. Kitaigorodsky, Molecular Crystals and Molecules, Academic Press, New York-London,1973

Diketopyrrolopyrrole (DPP) is an industrially important dye. It is also expected to be used as a functional dye, and a lot of research has been done on its various applicability. The introduction of flexible alkyl groups into the amino groups of DPP is reported to lead polymorph occurrence. [1][2] A derivative of DPP in which both amino groups are substituted with a butyl group are found to exhibit three differently-coloured polymorphs (red, orange, and yellow). All polymorphs could be obtained individually using the liquid-liquid diffusion method with chloroform as the good solvent and n-hexane as the poor solvent. The preparation of the red and yellow forms was easy, whereas the orange polymorphs was infrequently obtained. The results of the crystal structure analysis indicate that the asymmetric unit of the red and yellow polymorphs is one molecule, and that of the orange polymorph is two molecules. The molecular conformation of the three polymorphs is shown in Fig. 1. The red and orange polymorphs have butyl groups extending to both sides of the molecular plane. The two butyl groups of the yellow polymorph were found to project out from the molecular plane in the same direction. The crystal structures of the three polymorphs are shown in Fig. 2. The molecules in the red polymorph are stacked along the a-axis. The orange crystal has two asymmetric units (illustrated as green and yellow molecules in Fig. 2), and each asymmetric unit is stacked along the b-axis. The yellow crystals formed a chain-like structure with the π-conjugated planes facing each other. The detailed comparison of their crystal structures and their optical and thermal properties will be presented.

Prussian Blue Analogues (PBAs) are transition metal cyanides, widely investigated due to their catalytic and optical activity, ability to transport and store ions and small gas molecules. The later property is allowed by the presence of the large number of structural hexacyanometallate vacancies, which connect to form a porous network. These vacancies are filled with water: coordinated water molecules, which replace missing cyanide groups, and zeolitic water in the spherical cavities.

In this work we report a novel diffuse scattering signal, appearing after fast freezing of the PBA crystals. This signal emerges in the form of diffuse “clouds” around the Bragg peaks, which grow in intensity at higher Q, and are caused by the corrugation of the atomic lattice. We hypothesize that this corrugation is the response of the PBA lattice to the stress developed by water freezing in the nanopores. Furthermore, we discuss the effect of freezing on mechanical properties of Mn[Co] PBA.

RHODIUM (I) N,O HYDROXAMIC ACID COMPLEXES AS MODEL CATALYSTS

Mokete Motente^a, Johan Venter^b, and Alice Brink^c

Derparment of Chemistry, University of the Free State, Bloemfontein 9300, South Africa

Email: mokete.motente@gmail.com

Key words: Rhodium, catalysis, hydroformylation

Rhodium metal complexes are some of the key catalysts utilised in homogenous catalysis, and one of the most crucial considerations when forming a metal complex is the choice of ligand systems due to their influence on the reactivity of the metal atom,[1] hence hydroxamic acids were used for the purposes of this study due to their high metal affinity.[2] Phosphine ligands on the other hand were utilised due to their unique electronic and steric properties and it is known that the presence of phosphine ligands in rhodium systems also gives way to more active, highly selective catalysts which are reactive under milder reaction conditions.[3]

The overarching aim of this study was therefore to synthesise carbonyl phosphine Rhodium(I) complexes using O,O and N,O- hydroxomate bidentate ligands as model catalysts and they were successfully characterised with various characterisation techniques including single crystal X-ray diffraction (SCXRD). The study also focused on two important reactions, oxidative addition and migratory insertion which are the two crucial steps that take place during the Monsanto catalytic process.

1 P.W.N.M. Van Leeuwen, Homogenous Catalysis: Understanding the Art, Dordrecher: Kluwer Academic publishers, 2004.

2 P.M. Maitlis, A. Haynes, G.J. Sunley, M.J. Howard, J. Chem. Soc., Dalton Trans., 1996, 2187.

3 C.A. Tolman, Chem. Rev., 1977, 77, 313.

Syntheses and crystal structures of new ruthenium(II) organometallic compounds with NSAID type ligands M.Schoeller¹, J. Moncoľ¹¹Department of inorganic chemistry, Institute of inorganic chemistry, technology and materials, Faculty of chemical and food technology, Slovak University of Technology in Bratislava, Radlinského 9, 812 37 Bratislava, Slovakia Email of communicating martin.schoeller@stuba.sk

Ruthenium compounds play key role in development of new cytostatic agents in cancer therapy. Main features for choosing ruthenium are: a) possibility of existence at least in two oxidation states under physiological conditions (+II, +III), b) variable kinetic inertness with respect to the oxidation state which allows activation by reduction mechanism, c) ability to mimic iron in transport pathways [1-3]. NSAIDs as ligands introduce interesting strategy of cytostatic effect tuning. Complexes of NSAIDs with ruth enium can affect pathways of angiogenesis and production of metastases [4]. Increased cytotoxicity of some compounds can be explained by increased lipophilicity and therefore also with cellular input [4,5].

In order to prepare new ruthenium(II) compounds we chose [Ru₂(p-cymene)₂Cl₄] organometallic precursor and NSAIDs as ligands. Figure 1 shows new four-nuclear ruthenium(II) organometallic complex with new single bond between ruthenium(II) and 5-fluorosalicylate carbon. Single crystal diffraction data were collected with four-cycle Stoe StadiVari diffractometer with PILATUS3R 300K hybrid pixel array detector using microfocused X-ray source Xenocs Genix3D Cu HF (CuKα, λ = 1.54186Å). The crystal structures were solved by direct method using SHELXS [6]. The crystal structures were drawn with OLEX2 [7]. Supramolecular structures were analysed using CrystalExplorer [8].

Figure 1. Molecular structure of four-nuclear ruthenium(II) compound with formula [Ru₄(p-cymene)₄(5-Fluoro-SA)₂Cl₂].

[1] Housecroft, E. C., Sharpe, G. A. (2005). Inorganic chemistry. Essex: Pearson Education Limited. [2] Dabrowiak, J. C. (2017). Metals in Medicine. John Wiley & Sons. [3] Alessio, E. (2011). Bioinorganic Medicinal Chemistry. John Wiley & Sons. [4] Srivastava, P., Mishra, R., Verma, M., Sivakumar, M. Patra, K. A. (2019). Polyhedron, 172, 132-140. [5] Chen, J., Zhang, Y., Jie, X., She, J., Dongye, G., Zhong, Y. Deng, Y. Wang, J., Guo, B., Chen, L. (2019). J. Inorg. Biochem., 193, 112-123. [6] Sheldrick, G. M. (2015). Acta Crystalogr., A71, 3-8. [7] Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K., Puschmann, H. (2009). J. Appl. Cryst., 42, 339-341[8] Turner, M. J., McKinnon, J. J., Wolff, S. K., Gromwood, D. J., Spackman, P. R., Jayalitaka, D., Spackman, M. A. (2017) CrystalExplorer 17.5, University of Western Australia, Australia

Keywords: ruthenium(II); NSAID; cytostatic agents; p-cymene

This work has been created with the support of the Ministry of Education, Science, Research and Sport of SR within the Research and Development Operational Programme for the project “University Science Park of STU Bratislava, ITMS 26240220084, co-funded by the European Regional Development Found. Grand Agency of Slovak Republic (VEGA 1/0639/18, VEGA 1/0482/20, APVV 19-0087) is gratefully acknowledged for their financial support.

In an experiment to obtain single crystals of SmF₂ [1–3], a mixture of Sm, SmF₃ and NaCl (as flux) was heated up inside a sealed niobium capsule to 850 °C for four days and slowly cooled down with 5 K/h. In addition to dark red single crystals of the target compound SmF₂, also orange single crystals of SmFCl [4] were obtained. A PXRD experiment showed an additional phase, which was characterized as SmFO [5]. The ratio of them was determined via the Fullprof Suite by PXRD (Cu-K_α radiation) as about 70:5:25. By EDX analysis, the stoichiometry of all three named compounds was confirmed. SCXRD experiments (Mo-K_α radiation) were performed with single crystals (red SmF₂: CSD-2087284, orange SmFCl: CSD-2087285). While SmF₂ and SmFO crystallize with the CaF₂-type structure (cubic; Fm-3m; PXRD-data: a = 579.62(3) pm and a = 556.31(3) pm, CSD-2087286 for SmFO), SmFCl adopts the PbFCl-type structure (tetragonal, P4/nmm; a = 413.7(1) pm and c = 699.1(3) pm). The unit-cell parameters from the SCXRD measurements of SmF₂ (a = 580.31(4) pm) and SmFCl (a = 413.59(5) pm and c = 699.34(8) pm) show a good agreement to them of the PXRD experiment. The charge of the samarium cations in the named compounds was calculated by bond-valence calculations [6] and unambiguously led to Sm²⁺ in SmF₂ and SmFCl, but to Sm³⁺ in SmFO. The measured powder pattern of the three-component mixture can be seen in Figure 1 together with single crystals of SmF₂ and SmFCl and all three unit cells of the title compounds.

Figure 1. Rietveld refinement of a SmF₂–SmFCl–SmFO mixture (70:5:25) by using Cu-Kα radiation (bottom), unit cells of SmF₂, SmFO and SmFCl (left) and single crystals of SmF₂ and SmFCl (top right).

[1] E. Catalano, R. G. Bedford, V. G. Silveira, H. H. Wickman, (1969) J. Phys. Chem. Solids 30, 1613. [2] T. Petzel, O. Greis, (1973) Z. Anorg. Allg. Chem. 396, 95. [3] O. Greis, (1978) J. Solid State Chem. 24, 227. [4] H. P. Beck, (1979) Z. Anorg. Allg. Chem. 451, 73. [5] N. C. Baenziger, J. R. Holden, G. E. Knudson, A. I. Popov, (1950) Atti Accad. Ligur. Sci. 7, 44. [6] N. E. Brese, M. O'Keeffe, (1991) Acta Crystallogr. B47, 192.

Twinning prevents straightforward crystal structure analyses. Especially, for twinning by merohedry, the existence of the twinning can never be detected during the measurement. Although this kind of twinning is not a rare case for simpler crystals, a typical example of which is the Dauphine law twin of quartz, twinning by merohedry observed in the crystals of more complex compounds has been less commonly known. We have recently analyzed crystals of polyoxometalates and related compounds that show twinning by merohedry. Examples include a series of compounds of SiW₁₂O₄₀⁴⁻ with lanthanide elements that crystallize in the space group type P4₂/m. Another example is a crystal of a silver coordination compound that crystallizes in the space group type of I4₁/a. Details of the analyses of these crystal structures will be presented.

Acknowledgement: The work is supported by JSPS core-to-core program and JSPS KAKENHI 19K05510.

N,N’-diphenyl formamidines have E and Z isomers with either synperiplanar or antiperiplanar conformational combinations around the formamidine –N=C(H)–N(H)– backbone. The molecular isomerism of N,N’-diphenyl formamidines have been extensively studied in solution state [1]. However, no reports have been found regarding their preferred isomerism in the solid state. In this work, the steric and electronic effects on the molecular isomerism of eight N,N’-diphenyl formamidine derivatives in solid-state were evaluated using X-ray crystallography [2]. The eight compounds constitute of four symmetrical and four unsymmetrical N,N'-diphenyl formamidine derivatives having a general formula of [N-(Ar),N′-(Ar′)] where (Ar = Ar′) and (Ar ≠ Ar′), respectively. Five of the compounds were characterized using single crystal X-ray diffraction. Solid-state structure analysis showed two molecular isomers, E_syn and E_anti, and they form distinct classical hydrogen bonding patterns (Fig. 1). Correlations between molecular isomerism, pairwise interaction energies, infrared spectroscopy and thermal properties were established in this work. This provides a unique crystal engineering approach to predicting the isomerism of N,N’-diphenyl formamidines without crystal structure determination.

Salt and cocrystal have been reported as two main classes of the solid phase to modulate the physicochemical properties of the active pharmaceutical ingredient (API), such as increased solubility, dissolution rate, and stability. Structurally, cocrystals are composed of neutral compounds; meanwhile, salt combines the ionic components. Each solid form offers advantages and can be tailormade to gain a specific purpose. For example, cocrystals may enhance solubility and dissolution rate, but some may also decrease those parameters. On the other hand, alkaline–drug salt generally has a higher solubility than the parent drug. But how if the alkaline salt drug is combined with a similar coformer? Can it produce a salt cocrystal with superior performance?

This poster presents the development of the two most used NSAIDs (non-steroidal anti-inflammatory drugs): diclofenac acid and mefenamic acid, with a scheme shown in Fig. 1. Previously, we have found and developed neutral cocrystals of diclofenac-L-proline [1] and mefenamic - nicotinamide [2]. However, the solubility was still lower than their alkaline salt forms. Hereafter, we attempted to combine the alkaline salt with a similar coformer to modulate its performance. As a result, we successfully produced the new salt cocrystals of diclofenac and mefenamic, characterized using DSC/TG, PXRD, and structurally determined using SCXRD entirely.

First, sodium and potassium diclofenac proline (NDP/KDP) were isomorphous and had two hydrate forms, monohydrate and tetrahydrate phases [3,4]. Meanwhile, sodium mefenamate nicotinamide (SMN) constructed the hemihydrate and monohydrate forms [5]. The water's existence was crucial to stabilizing the lattice structure, coordinated with the alkaline elements and hydrogen-bonded with the other component. After that, all salt cocrystals were proven to modulate the physicochemical properties of the parent drugs, superior to the neutral cocrystals. The solubility and dissolution rate were increased by combining Na⁺ and the soluble coformer. Furthermore, the lower hydrate forms showed a higher solubility, dissolution rate, and stability than the counterpart phases. NDP monohydrate and SMN hemihydrate increased the solubility of the starting alkaline salts by 3.5 and 1.5 folds or ten to a hundred times the acid parent drug’s solubility, respectively. Finally, the powder properties of both new multi-components also were better than the parent and salt drugs. In conclusion, salt cocrystallization is a promising technique to improve the NSAIDs performance and can be developed further for the dosage form formulation.

Figure 1: Salt cocrystal development of diclofenac acid and mefenamic acid.

References:

[1] Nugrahani, I., Utami, D., Ibrahim, S., Nugraha, Y.P., Uekusa, H. (2018). Eur. J. Pharm. Sci. 117, 168.

[2] Utami, D.W.I., Nugrahani, I., Ibrahim, S. (2017). Asian J. Pharm. Clin. Res. 10, 135.

[3] Nugrahani, I., Kumalasari, R.A., Auli, W.N., Horikawa, A., Uekusa, H. (2020). Pharmaceutics 12, 690.

[4] Nugrahani, I., Komara, S.W., Horikawa, A., Uekusa, H. (2020). J. Pharm. Sci.109, 3423.

[5] Nugrahani, I., Fisandra, F., Horikawa, A., Uekusa, H. (2021). J. Pharm. Sci. available online 6 June 2021.

Keywords: salt cocrystal, solubility, dissolution, sodium/potassium diclofenac proline, sodium mefenamate nicotinamide.

We gratefully thank the Research and Innovation Institution, Educational Ministry of Republic Indonesia for the funding and Uekusa’s Laboratory Tokyo Institute of Technology for the research collaboration.

Copper (II) complexes with NSAIDs are interesting as potential drugs with different biological activity such as potential anticancer and antioxidant activities (superoxide dismutase mimicking, radical scavenging and soybean lipoxygenase inhibition).^1-3

A series of five copper(II) fenamate complexes with N,N-diethylnicotinamide ligand (den) of formula [Cu(nif)₂(den)₂] (flu = flufenamate) (1), [Cu(clo)₂(den)₂] (clo = clonixinate) (2), [Cu(flu)₂(den)₂(H₂O)₂] (flu = flufenamate) (3), [Cu(tol)₂(den)₂(H₂O)₂] (tol = tolfenamate) (4) and [Cu(mef)₂(den)₂(H₂O)₂] (mef = mefenamate) (5) have been synthesized and structural characterized. The crystal structures of five complexes (1-5) were refined using the Hirshfeld Atom Refinement model (HAR) and Hirshfeld surface analysis have been also made.

[1] J.E. Weder, et al., Coord. Chem. Rev. 2002, 232, 95.

[2] C.N. Banti, S.K. Hadjikakou, Eur. J. Inorg. Chem. 2016, 3048.

[3] G. Psomas, Coord. Chem. Rev. 2020, 412, 213259.

Up today researchers work to obtain new catalytic systems for a next-generation ammonia synthesis process, which could reduce the energy costs and CO₂ emission. Cobalt molybdenum nitrides are potential candidates in this field, since they have higher activity in the synthesis of ammonia than the commercially used promoted iron catalyst [1]. The activity of the cobalt molybdenum catalyst can be further increased by addition of alkaline promoters such as caesium or potassium [2]. However, the addition of these promoters has a negative effect on the specific surface area of ​​the cobalt molybdenum catalyst. The development of an effective method to counteract these limitations is crucial to the potential application of cobalt molybdenum nitrides on a larger scale.

Only a few studies addressing the development of the cobalt molybdenum nitrides with a higher specific surface area were conducted. The change in the conditions of the activation process by additional temperature treatment is suggested [3]. The typical precursor consisting CoMoO₄ was changed to the Co(en)₃MoO₄, in which (en) denotes ethylenediamine molecule [4]. The addition of citric acid, which acts as a chelating agent, results in increased surface area and higher activity [5]. Double promotion with the use of potassium and chromium leads to simultaneously more active and more stable material, in which chromium acts as a structural promoter [6].

In this study, the problem of low thermal stability and tendency to sinter of cobalt molybdenum nitrides during ammonia synthesis was addressed by using catalyst support in form of active carbon. The supported catalysts were formed by the wet impregnation of the support with an aqueous solution of cobalt and molybdenum salts, followed by vacuum evaporation. The precursor was filtered, dried and subjected to a reduction under an ammonia atmosphere to obtain nitrides. Despite very high surface area, activated carbon in applications as catalyst carrier has a major disadvantage. It undergoes methanation under the conditions of ammonia synthesis, i.e. reacts with hydrogen to form methane [7].

To make insight into the activation process, in this study the ammonolysis of the precursors was examined via in-situ X-ray powder diffraction with the use of PANalytical X’pert Pro MPD diffractometer equipped with Anton Paar XRK 900 reaction chamber. Under the ammonolysis conditions, several structural transformations of the precursor were observed. Apart from broad hump peaks originated from activated carbon, several sharp peaks corresponding to intermediate phases were identified during ammonolysis process. Following phases were identified: MoC, metallic Co and Co₃Mo₃C. Cobalt molybdenum nitrides which are active in the ammonia synthesis were not present in the product.

[1] Kojima, R. & Aika, K. (2001). Appl. Catal. A 215, 149.

[2] Moszyński, D., Jędrzejewski, R., Ziebro, J. & Arabczyk, W. (2010). Appl. Surf. Sci. 256, 5581.

[3] Kojima, R. & Aika, K. (2001). Appl. Catal. A 219, 157.

[4] Duan, X., Ji, J., Yan, X., Qian, G., Chen, D. & Zhou, X.J.C. (2016). ChemCatChem 8, 938

[5] Podila, S., Zaman, S.F., Driss, H., Al-Zahrani, A.A., Daous, M.A. & Petrov, L. (2017). Int. J. Hydrog. Energy 42, 8006

[6] Moszyński, D., Adamski, P., Nadziejko, M., Komorowska, A. & Sarnecki, A. (2018). Chem. Pap. 72, 425.

[7] Chunhui, Z., Yifeng, Z. & Huazhang, L. (2010). J. Rare Earths 28, 552

Keywords: Cobalt molybdenum nitrides; ammonolysis; catalyst; XRPD in-situ

The scientific work was financed by The Polish National Centre for Research and Development, grant „Lider”, project No. LIDER/10/0039/L-10/18/NCBR/2019.

Wustyt is a non-stoichiometric form of iron(II) oxide with the general formula Fe_1-xO, which is currently used as a precursor of the iron catalyst for the synthesis of ammonia. The catalyst obtained from this precursor has higher activity compared to a traditional catalyst reduced from magnetite [1]. Promoters used in the magnetite precursor may have a different role in wustite catalysts. This is due to the different valence of iron in the structure of wustite and magnetite. As a result, some promoters are more or less likely to build in the catalyst grain [2]. In this study, the influence of magnesium oxide addition on the activity and thermal stability of the catalyst was investigated. It was suspected that as a result of similar valence, magnesium ions would be more likely to build into the grain of wustite, thus stabilize the active phase of the catalyst.

Iron catalyst precursors were obtained as a result of the melting of magnetite, aluminum oxides, calcium, magnesium, potassium nitrate, and metallic iron, which acts as a magnetite reducer. The XRPD method confirm the presence of wustite phase in each precursor. Chemical composition was determined by ICP-OES method. Evolution of the phase composition of obtained precursors during reduction with hydrogen were investigated by XRPD in-situ method, with the use of PANalytical X’pert Pro MPD diffractometer equipped with Anton Paar XRK 900 reaction chamber. Crystallite sizes of iron were calculated using Rietveld method. Activity tests in the ammonia synthesis reaction were carried under pressure 10 MPa in the temperature 450°C.

The promotion of wustite precursors with magnesium oxide contributes to the significantly increase of the crystallite sizes. The crystallite size increased by 47% comparing the catalysts with the lowest and the highest concentration of magnesium oxide. Similarly activity of obtained catalysts rate were also increased. The activity increased by over 40% comparing the catalysts with the lowest magnesium oxide concentration to the catalyst with the highest concentration of this promoter.

[1] Hua-Zhang, L., Xiao-Nian, L. & Zhang-Neng, H. (1996). Appl. Catal. A General 142, 209.

[2] Lendzion-Bieluń, Z. & Arabczyk, W. (2001). Appl. Catal. A General 207, 37.

Keywords: Ammonia synthesis; wustite; XRPD in-situ; crystallite size

The scientific work was financed by The Polish National Centre for Research and Development, grant „Lider”, project No. LIDER/10/0039/L-10/18/NCBR/2019.

Nitrides of transition metals are mostly associated with hardness and mechanical strength and tend to be thermally and electrically conductive. They exhibit the properties of both metals and ceramics [1]. On the other hand, they were proven to have high catalytic activity in various chemical reactions, e.g. ammonia synthesis, ammonia decomposition, hydrodesuplhurisation and NO reduction [2].

Particularly effective ammonia synthesis catalysts are nitrides of cobalt and molybdenum. These nitrides are usually obtained during the ammonolysis process of oxide precursors. Previous studies on cobalt molybdate reduction in ammonia confirmed the presence of multiple crystalline phases in the system, mainly: CoMoO₄∙nH₂O, NH₄H₃Co₂Mo₂O₁₀, Co₂Mo₃O₈, CoMoO₄, Co, Mo_2­N, Co₃Mo, Co₃Mo₃N and Co₂Mo₃N. Co₂Mo₃N phase is especially desirable due to its high activity in ammonia synthesis [3].

The crystalline structure of cobalt-molybdenum precursors can be modified by a change of pH value during their precipitation. Commonly the precipitation from the solution of cobalt(II) nitrate and ammonium heptamolybdate is conducted at pH between 5 and 6. Alkalisation of the reaction results in a different structure of the material obtained. Also, the course of the phase transformations observed for these materials by XRD analysis differs.

In the presented study, materials obtained in pH 5.5 and 7.5 are compared. The phase transformations during calcination and ammonolysis processes were studied in the reaction chamber attached to an X-ray diffractometer (Anton Paar XRK900, Philips X’Pert Pro MPD).

At first, two different precursor phases, CoMoO₄∙nH₂O and NH₄H₃Co₂Mo₂O₁₀, were obtained for pH 5.5 and pH 7.5, respectively. After 2 hours of calcination at 300°C under an inert atmosphere, both precursors transformed into the CoMoO₄ phase. At 500°C, besides the dominant CoMoO₄ phase, for precursor obtained in pH 7.5, Co₂Mo₃O₈ phase occurred. At 700°C, the CoMoO₄ phase gradually transforms into Co₂Mo₃O₈, Co₃Mo and metallic cobalt. After the ammonolysis, the concentration of main phases, Co₃Mo₃N and Co₂Mo₃N, for both samples was similar, but the width of the diffraction peaks and the content of trace phases were significantly different.

[1] Oyama, S. T. (1996). The Chemistry of Transition Metal Carbides and Nitrides. Blackie Academic and Professional: Glasgow.

[2] Gurram, V.R.B., Enumula, S.S., Chada, R.R., Koppadi, K.S., Burru, D. R. & Kamaraju, S.R.R. (2018). Catal. Surv. from Asia, 22, 166.

[3] Adamski, P., Moszyński, D., Komorowska, A., Nadziejko, M., Sarnecki, A. & Albrecht, A. (2018). Inorg. Chem. 57, 9844.

Acknowledgements: The scientific work was financed by The Polish National Centre for Research and Development, grant „Lider”, project No. LIDER/10/0039/L-10/18/NCBR/2019.

Ternary transition metals nitrides are a relatively new group of materials studied extensively nowadays. One of the most important properties of ternary transition metals nitrides is their tendency to form defected structures, with variable composition. Within these inorganic compounds, the Co-Mo-N system exhibits many promising properties. Among others, cobalt molybdenum nitrides could be used as catalysts, magnetic materials and electrodes. Cobalt molybdenum nitrides exhibit very high catalytic activity in ammonia synthesis, which makes them a plausible candidate to replace industrial iron catalyst [1-3].

The most widely used procedure to form cobalt molybdenum nitrides is a two-stage process consisting of a precursor preparation and a subsequent ammonolysis of mixed oxides. More insight into these stages, especially on structural and crystallographic transformations of precursors and intermediate compounds, is crucial for the enhancement of the material properties. The synthesis process is influenced by numerous parameters, i.e. composition and temperature of precipitation process, final precursor composition, ammonolysis temperature, composition and flow of a reducing agent. Consequently, the ammonolysis often results in the formation of mixtures of different crystallographic phases of transition metal nitrides with mismatched properties. Lack of reproducibility is a major disadvantage, which inhibits technology upscaling.

A synthesis method of cobalt molybdenum nitrides greatly affects its composition and properties. The stoichiometry alteration could be beneficial or detrimental to the cobalt molybdenum nitrides properties. For example, their catalytic activity in ammonia synthesis depends on Co₂Mo₃N to Co₃Mo₃N ratio [4]. Therefore, favourable is a synthesis method, which can affect stoichiometry in a controlled way. Such a procedure is the one used in this study. It bases on the mechanochemical formation of the mixture of cobalt and molybdenum salts with the controlled Co:Mo molar ratio, which is later reduced under the ammonia atmosphere.

To make insight into the activation process, the ammonolysis of the mixture of cobalt and molybdenum salts with the controlled Co:Mo molar ratio was examined via in-situ X-ray powder diffraction with the use of PANalytical X’pert Pro MPD diffractometer equipped with Anton Paar XRK 900 reaction chamber. A transformation of mixed cobalt molybdenum oxides into mixed cobalt molybdenum nitrides was observed. In the sample subjected to the temperature of 200°C the reflections corresponding to cobalt molybdate CoMoO₄ were identified. Instead of a separate step of precursor precipitation, a simple mechanochemical technique was implemented. As a result, the phase described as the precursor in the mentioned earlier synthesis methods was obtained. This result suggests that in the studied system the intermix of cobalt and molybdenum atoms, obtained via the mechanochemical method, allows the formation of a bimetallic phase at medium temperature. In the sample at 700°C under an ammonia atmosphere, the reflections corresponding to Co₂Mo₃N and Co₃Mo₃N were identified.

[1] Jacobsen, C.J.H. (2000). Chem. Commun. 1057.

[2] Kojima, R. & Aika, K. (2001). Appl. Catal. A 215, 149.

[3] Moszyński, D., Jędrzejewski, R., Ziebro, J. & Arabczyk, W. (2010). Appl. Surf. Sci. 256, 5581.

[4] Moszyński, D., Adamski, P., Nadziejko, M., Komorowska, A. & Sarnecki, A. (2018). Chemical Papers 72, 425.

Keywords: Cobalt molybdenum nitrides; ammonolysis; XRPD in-situ

Financed as a part of PROM Programme “International Scholarship Exchange of PhD Candidates and Academic Staff” co-financed by Polish National Agency For Academic Exchange and European Union through European Social Fund within the frame of Knowledge, Education, Development Operational Programme, project no. PPI/PRO/2019/1/00008/U/00001.

Tungstite (WO₃.H₂O), was successfully immobilized on the surface of mesoporous Silica SiO₂/WO₃ by in-situ reaction using poly (ethylene oxide) as polymeric template and Na2WO4 as precursor and immobilized tungsten trioxide SiO₂/WO₃-C was obtained by calcination of SiO₂/WO₃ at 350°C. The as-obtained materials were characterized by N₂ sorption, SEM, PXRD, FT-IR, UV-Visible and TGA.

Structural characterization of both materials indicates the succeed immobilization of tungstite and tungsten trioxide in amorphous silica. The diffraction picks in SiO₂/WO₃ are arising from two different phases corresponding to WO₃ and WO₃.H₂O, Rietveld refinement assume the orthorhombic crystal lattice for both compounds to with parameters value a=5.25 Å, b=10.72 Å, c=5.13 Å for WO₃ and a=5.25 Å, b=10.72 Å, c=5.13 Å for WO₃.H₂O. phases quantification assumes the presence of tungstite (WO₃.H₂O) as a majority phase by 75.3%, which allow us to investigate it crystallographic structure. The crystal structure of the immobilized tungstite is generally formed by layers of distorted octahedral building blocks of WO₆ in which one axial oxygen position is occupied by water molecule. After calcination at 330°C a phase transformation to the monoclinic structure is observed and water molecules are eliminated from the structure, lattice parameters obtained after Rietveld refinement are a=7.32 Å, b=7.54 Å, c=3.85 Å.

The as-prepared materials are highly efficient in the oxidative photo-degradation of sulfamethazine in water with an efficiency of 92.14% and 92.84% for SiO₂/WO₃and SiO₂/WO₃-C respectively, with different stability aspect. Indeed, SiO₂/WO₃-C show a poor stability when it reused for 6 times due to leaching problem. In the other hand SiO₂/WO₃ could be reused with a small loss of activity after 6 cycles of photocatalysis. The stability difference is due to crystallographic structure differences that is characterized by the presence of water molecules in SiO₂/WO₃ and its absence on SiO₂/WO₃-C. The good stability can be attributed to the strong van-der-walls interaction between the oxygen of silica network and the hydrogen of water molecule encapsulated in tungstite structure.

Palladium-based catalysts are extensively used in petrochemical industry for hydrogenation of unsaturated hydrocarbons. The catalytic process is associated with the formation of surface, subsurface and bulk palladium carbides and hydrides which affects the catalytic properties of materials. Here, combination of in situ and operando synchrotron-based X-ray absorption near edge structure (XANES) with extended X-ray absorption fine structure (EXAFS) spectroscopies with X-ray diffraction (XRD) provided the detailed information about the structure of supported palladium nanoparticles during their interaction with hydrogen and hydrocarbons.

The industrially relevant samples for investigation were provided by Chimet S.p.A. (Arezzo, Italy) and represented palladium nanoparticles with the average size of 2.6 nm and narrow size distribution supported on wood-based carbon. X-ray absorption and diffraction experiments were performed at BM31 beamline of the European Synchrotron Radiation Facility (ESRF, Grenoble, France). The beamline allows fast switching (30 s) between absorption and diffraction setups allowing quasi-simultaneous measurements within a single experiment. The samples were loaded inside 1 mm quartz glass capillaries and connected to a remotely controlled gas line. Hydrogen, acetylene and ethylene were used as reactive gases; helium was uses as a carrier gas. The output of the capillary was monitored by a mass spectrometer (MS).

In the case of pure hydrogen was used, a combination of EXAFS and XRD analysis allowed highlighting the difference between the core and shell parts of the nanoparticle [1-2]. To provide an unambiguous proof of this hypothesis, we have performed more than 200 in situ measurements in the wide range of hydrogen partial pressures and temperatures. For the nanostructured samples, EXAFS data showed more smooth behavior of metal-hydride phase transition compared to XRD data, while for the reference bulk materials both methods provided identical results. The difference was explained by the contribution of the amorphous surface part of the nanoparticle to EXAFS, while only bulk region contributes to XRD. The latter was shown to behave similar to the bulk crystals having a sharp phase transition when forming the palladium hydride. Hypothesizing the ranges of the surface-to-bulk ratio for the given particle sized, we have discriminated the evolution Pd-Pd distances in the bulk and at the surface during the hydride phase formation.

In the following experiment we have introduced acetylene though the catalyst. In this case, XANES spectra allowed unambiguous differentiation between the hydride and carbide phases that can be formed in presence of both hydrogen and hydrocarbons [2-3]. Moreover, XANES region was shown to be sensitive to the adsorption and desorption of hydrocarbon molecules at the surface of the particles, which makes no effect on EXAFS and XRD data, therefore, allowing the detection of the relevant catalytic species [4-5]. During continuous operation of the catalyst in the mixture of ethylene and hydrogen, XANES spectroscopy demonstrated gradual and irreversible formation of palladium carbides even in the excess of hydrogen in the gas phase [5-6].

Thus, we have successfully shown that a combination of XRD, EXAFS and XANES techniques can highlight the difference of the structure in the bulk, subsurface and surface region of the nanoparticles. The above examples have shown, that such difference can occur under catalytic reaction conditions even for monometallic palladium particles due to the interaction with re reactive molecules.

References:

[1] A. L. Bugaev, A. A. Guda, K. A. Lomachenko, et al. J. Phys. Chem. C 121, 18202 (2017)

[2] A. L. Bugaev, O. A. Usoltsev, A. Lazzarini, et al. Faraday Discuss. 208, 187 (2018)

[3] A. L. Bugaev, A. A. Guda, A. Lazzarini, et al. Catal. Today 283, 144 (2017)

[4] A. L. Bugaev, O. A. Usoltsev, A. A. Guda, et al. J. Phys. Chem. C 122, 12029 (2018)

[5] A. L. Bugaev, A. A. Guda, I. A. Pankin, et al. Catal. Today 336, 40 (2019)

[6] A. L. Bugaev, O. A. Usoltsev, A. A. Guda, et al. Faraday Discuss. In press. DOI: 10.1039/C9FD00139E

Ceria supported nanoparticles (NPs) of noble metals are well-known catalysts for diverse hydrogenation and oxidation reactions [1, 2]. Their catalytic activity depends on the dispersion and shape of NPs, support, functionalization, etc. However, the use of high Z-support and small NPs limits their diagnostics especially in laboratory conditions [3]. In this study, we demonstrate a possibility of in situ monitoring the size and surface morphology of Pd/CeO₂ catalysts during the growth by using FTIR spectroscopy of adsorbed CO.

Ceria NPs used as support were synthesized according to the method described in [4] and impregnated by PdCl₂ [3]. Then, the material was put into the reaction chamber and heated in a flow of Ar up to 30, 150 or 300 °C (samples Pd-30, Pd-150, Pd-300) for 30 min. A mixture of H₂, CO and Ar (2.5, 1 and 46.5 mL/min) was passed through the sample for 1 hour to reduce Pd NPs.

XRPD didn’t allow distinguishing Pd NPs for all samples (Fig.1a). This fact could be explained by the small size of synthesized Pd NPs which caused broadening of peaks. Tests of catalytic (procedure described in [3]) shown that CO conversion was 25-70% for all samples at 150 °C even without calcination (in case of Pd-150 and Pd-300) and decreased in row Pd-30>Pd-150>Pd-300.

Figure 1. (a) XRPD patterns of all samples; (b) series of FTIR spectra during the synthesis of Pd-30.

The series of spectra collected in situ demonstrated that the reduction at high temperature (Pd-300 and Pd-150) was much faster than at low temperature (Pd-30). Also, it was observed that reduction was not complete for all samples: peaks of CO adsorbed on Pd²⁺ and Pd⁺ ions were observed (ca. 2160 and 2110 cm^–1). The last fact is explained by ceria support that prevented complete reduction. The process of reduction was observed in detail for the Pd-30 (Fig.1b) where the decrease of CO adsorbed on Pd ions was accompanied by the increase of peaks related to bridged carbonyls – evidence of appearing and growth of the extended surfaces. FTIR spectra allowed to determine the size of NPs which is proportional to the ratio of areas under peaks attributed to bridged (below 2000 cm^–1) and linear (2000-2100 cm^–1) carbonyls. Size decreased in row Pd-300>Pd-150>Pd-30. The dynamics of growth was clearly observed for Pd-30 and Pd-150 sample whereas for Pd-300 CO adsorbed only at 2- and 3-folded sites. Only carbonyls on Pd(111) faces were detected for Pd-150 and Pd-300 when both Pd(100) and Pd(111) facets were found for the Pd-30 sample.

While conventional techniques are limited by size of NPs (XRPD), poor contrast (TEM), require large scale facilities (XAS, SAXS), described laboratory technique allows determining the size and surface morphology in situ, at any desired moment of NPs growth.

[1] Zang W., Li G., Wang L., Zhang X. (2015) Catal. Sci. Technol., 5, 2532-2553.

[2] Liang Q., Liu J., Wei Y., Zhao Z., MacLachlan M. J. (2013). Chem. Comm., 49, 8928-8930.

[3] Tereshchenko A., Polyakov V., Guda A., Lastovina T., Pimonova Y., Bulgakov A., et al. (2019). Catalysts, 9, 385.

[4] Benmouhoub C., Kadri A., Benbrahim N., Hadji S. (2009). Materials Science Forum, 609, 189-194.

Keywords: palladium; ceria; nanoparticles; CO probing molecules; FTIR; adsorption;

The study was carried out with the financial support of the Russian Foundation for Basic Research (RFBR) in the framework of the scientific project №20-32-70227. Tereshcheno A. also acknowledge RFBR for funding according to the research project № 20-32-90048

An important frontier in materials science is to understand, characterize and quantize disorder in inorganic materials and its relation to their properties. This requires deep knowledge of both the average structure and the defects present in the samples. Spinel-type compounds form a family of industrially relevant materials¹ that potentially exhibit both atomic and/or magnetic disorder.^{2, 3} Spinel ferrites, AFe₂O₄, in particular have seen use in high-frequency applications due to their magnetism in conjunction with electrically insulating properties. The spinel structure consists of a distorted cubic closest packing of oxygen, in which 1/8 of the tetrahedral holes and 1/2 of the octahedral holes are occupied by cations. The general formula is AB₂O_4, where A are divalent and B trivalent cations.

Single crystals larger than 1 mm³ of ZnFe₂O₄ and NiFe₂O₄ have been grown using the flux method. These where chosen as model spinel ferrites exhibiting the normal and inverse configuration, respectively, with the possibility of magnetic disorder studies in ZnFe₂O₄.⁴ X-ray fluorescence measurements confirmed a low degree of flux inclusions in the crystals, on the order of 0.1 wt%.

Extensive diffraction data has been collected for initial benchmark structure determination, with synchrotron powder X-ray diffraction and single crystal X-ray diffraction being collected at SPring-8 in Japan, and single crystal neutron diffraction being collected at the Spallation Neutron Source at Oak Ridge National Laboratory.

Initial data modelling shows some systematic discrepancies between the structural parameters obtained from the different sets of diffraction data. Rietveld modelling of the powder data gives lower lattice parameters than either single crystal method, which has been attributed to abnormal peak asymmetry caused by a non-symmetric X-ray beam profile. The atomic displacement parameters obtained from the X-ray single crystal and powder data of ZnFe₂O₄ differs both in magnitude and temperature dependence, the cause of which has not been identified yet.

The powder patterns of NiFe₂O₄ reveal left shoulders at reflections with miller indices that are all multiples of four, which could be related to the compound’s magnetism.

The single crystal data show peak splitting indicating a degree of twinning on both spinel samples. Maximum entropy method analysis of the structure factors from the single crystal X-ray data showed no evidence of residual electron density at potential interstitial sites in the structure.

1. N. Grimes, Physics in Technology, 1975, 6, 22.

2. S. Sommer, E. D. Bøjesen, N. Lock, H. Kasai, J. Skibsted, E. Nishibori and B. B. Iversen, Dalton Transactions, 2020, 49, 13449-13461.

3. K. Kamazawa, Y. Tsunoda, H. Kadowaki and K. Kohn, Physical Review B, 2003, 68, 024412.

4. Y. Yamada, K. Kamazawa and Y. Tsunoda, Physical Review B, 2002, 66, 064401.

Newly discovered, and still uncommon, modulated crystal structure in organic systems require a deeper investigation. No exact and detailed solution of such systems has not been done up-to-date. One possibility is to use an approximation of commensurate modulation which enables constructing a supercell, extending to the case, where translational symmetry (periodicity) is recovered, and simplify the analysis [1]. An assumption of commensurateness of the modulation is, however, questionable and rather unverifiable.

The goal of our studies was to use a novel, original statistical method of structural modeling which enables a refinement based on the average unit cell with (commensurate or incommensurate) modulation without unclear assumption of commensurateness and supercell approach. The main concept of the statistical method is to express structure in terms of the statistical distribution of atomic positions concerning the periodic reference lattice with lattice constant related to characteristic length-scale present in the structure. The average unit cell, defined as a probability distribution, constructed for periodic crystal is the same as the unit cell. The statistical approach was successfully used to describe not only periodic crystals or quasicrystals but also to expand on modulated structures and aperiodic structures with singular continuous components in the diffraction pattern [2].

Our model system is a pathogenesis-related protein (Hyp-1) complex with fluorescent probe 8-anilino-1-naphthalene sulfonate (ANS), which is a unique example of a macromolecular system with a modulated crystal structure. Previous studies have shown that Hyp-1/ANS complexes are tetartohedral twinned and crystallized in an asymmetric unit cell containing a repetitive motif of four protein molecules arranged with 7-fold noncrystallographic repetition along the c axis of the C2 space group. Assumption of commensurate structure modulation demanded description of structure in the highly expanded unit cell with 28 unique protein molecules inside [3]. The Hyp-1/ANS structure was solved by molecular replacement and refined using maximum-likelihood targets with reliability factors R_work/R_free of 22.3/27.8%.

Our approach involved re-integration of raw data, development of the original software in Matlab environment, and multidimensional analysis used to build the structure model and perform the refinement for significant improvement of results. The problem of incorporating disorder in the form of phonons into structural analysis was also carried out traditionally by the Debye-Waller factor.

[1] Sliwiak, J., Dauter, Z., McCoy, A., Jaskolski, M. & Read, R.J. (2014). Acta Cryst. D70, 471-480.
[2] Wolny, J., Buganski, I., Kuczera, P. & Strzalka, R. (2016). J. Appl. Crystallogr. 49, 2106-2115.
[3] Sliwiak, J., Dauter, Z., Kowiel, M., McCoy, A., Read, R.J & Jaskolski, M. (2015). Acta Cryst. D71, 829-843.

Among inorganic and metal-organic materials, there are numerous instances where modulated structure determines material's unique and useful properties: (super)conductivity of layered cuprates[1], ferroelectricity of certain perowskites[2] or, in particular, quantum yields of fluorescence in complex molybdates and tungstates with the scheelite-type (A', A'')_n[(Mo/W)O4]_m structures, where A', A'' = alkali, alkaline-earth or rare-earth elements[3]. One of the earliest and most important examples of modulations that relate to specific physical properties for organic compounds is the case of TTF-TCNQ cocrystals. Modulation of the crystal structure (i.e. a slip of the TTF molecules) at temperatures below 60K results superconductivity of the system[4,5]. However, the general number of reported cases of organic modulated structures remains relatively low[6]. This is because interpretation of modulations in molecular crystals is very challenging: modulation affects positions and atomic displacement parameters of many atoms, while satellite reflections, necessary to describe them, are inherently less intense than the main reflections and therefore more difficult to collect or even detect during standard diffraction experiment. For instance, in the case of TTF-TCNQ, the strongest satellite reflections were 10000 weaker than Bragg reflections and required specific data reduction procedure[5].

This communication presents an instance where a pyrene-based fluorophore, 1-acetylpyrene (1AP), crystallized as incommensurately modulated polymorph which displayed particularly efficient luminescence in the solid state. Its crystal structure has been formerly solved and presented in its supercell approximation with Z’ = 6. Since the compound has been shown to yield several polymorphs[7], the increased efficiency of luminescence in the modulated form can be attributed directly to the modulation in its crystal structure. Structural parameters most affected by the modulation are an interplanar distance in a 1AP dimer and relative lateral shift of its constituents. This results in the presence of an assembly of dimers in the crystal, varying slightly in the extent of orbital overlaps, which apparently broadens the range of effective UV absorption in the sample.

Materials with low electronic dimensionality are known to exhibit remarkable properties such as thermoelectricity, high electron mobility or superconductivity. In addition, this low dimensionality also favors the appearance of another phenomenon: charge density wave instability (CDW). The transition to a CDW state is described by Peierls [1] as a gap opening at the Fermi Surface of the material leading to the modulation of its electronic density accompanied by a periodic distortion of its atomic lattice. Therefore, a transition to a CDW state is characterized by the appearance of an anomaly in the electron transport properties and of additional reflections in the X-ray diffraction pattern, called satellite reflections.

A resistive signature, characteristic of a CDW transition, was observed for the compounds {R}Pt₂Si₂, with R = La, Nd and Pr, at 112 K, 77 K and 88 K respectively [2,3]. The thermal study of the X-ray diffraction pattern of these materials reveals not only the appearance of satellite reflections associated with the reported CDW transitions but also the existence of another transition, at higher temperature, leading to a modulated structure [4 ,5]. This unexpected phase transition, for which no anomaly in the electron transport properties is observed, is characterized by the appearance of an incommensurate modulation characterised by the wave vectors q₁ = 0.360a*, 0.323a * and 0.326a * for LaPt₂Si₂, NdPt₂Si₂ and PrPt₂Si₂, respectively. In the case of LaPt₂Si₂, this vector is very similar to the nesting vector of a CDW transition determined by ab initio calculations [6]. At lower temperature, a new set of satellites appears, coexisting with the first one, corresponding to the CDW transition reported in the literature and characterized by the wave vectors q₂= (0.187; 0.187; 0.5); (0.158; 0.158; 0.5) and (0.168; 0.168; 0.5) for LaPt₂Si₂, NdPt₂Si₂ and PrPt₂Si₂, respectively.

These observations raise a new question: what is the nature of the first structural transition of {R}Pt₂Si₂?

Acknowledgments : This study was funded by the ERDF project NANOCENT : Nanomaterials Centre for Advanced Applications (CZ.02.1.01/0.0/0.0/15_003/0000485).

References:

[1]: Peierls, R.E. (1955). Quantum Theory of Solids. London, Oxford Univ. Press.

[2]: Gupta, R., Dhar, S.K., Thamizhavel, A., Rajeev, K.P., & Hossain, Z. (2017). J.Phys.: Condens. Matter 29, 255601.

[3]: Nagano, Y., Araoka, N., Mitsuda, A., Yayama, Y., Wada, H., Ichihara, M., Isobe, M., & Ueda, Y. (2013) J. Phys. Soc. Jpn. 82, 064715.

[4]: Falkowski, M., Doležal, P., Andreev, A.V., Duverger-Nédellec, E., & Havela, L. (2019). Phys. Rev. B 100, 064103.

[5] : Falkowski, M., Doležal, P., Duverger-Nédellec, E., Chamoreau L.-M., Forté J., Andreev, A.V., & Havela, L. (2020), Phys. Rev. B 101, 174110

[6]: Kim, S., Kim, K., Min, B.I. (2015). Sci. Rep. 5, 15052.

While many low-dimensional systems exhibit charge density wave modulations, sliding of charge density waves (CDWs) has been proven only in a few components, including NbSe₃ and NbS₃-II. They form crystals in which quasi-one-dimensional chains are connected in layers separated by van der Waals gaps. Because NbS₃-II grows in the form of thin, needle-like crystals, its basic and CDW modulated structures were only recently determined [1] using a combination of several techniques.

Both materials are also each modulated by two wave vectors with only slightly different components along the chains. While diffraction techniques clearly show that both CDWs are present at sufficiently low temperatures, it is impossible to rule out the possibility of nanometer-sized domains with different modulations without real space information. We revisit this topic using low temperature Scanning Tunneling Microscopy (STM) on NbSe₃ samples cleaved in UHV. Performing 1D Fourier transform analysis along the crystal chains on long enough images with atomic resolution guarantees the necessary k-space resolution in combination with real space information, making it possible to unambiguously determine the presence of CDW modes on individual columns [2]. In addition, this allows for quantitative comparison of modulation amplitudes on different chains of the same type at different scanning parameters and studies of modulation variations along individual columns.

[1] E. Zupanič et al., PRB 98, 174113 (2018).

[2] M. A. van Midden et al, PRB 102, 075442 (2020).

Aperiodic crystals are long-range ordered crystals that lack periodicity. A good description of these materials is provided by the superspace approach [1;2]. Although their structure are in general well described, the atomic realisations and properties of their dynamics are more debated. Phason modes that should arise from the new degrees of freedom due to the aperiodic order have been experimentally observed in very few incommensurately modulated phase and quasicrystals [1;3] . Also, low thermal conductivity in those systems asks for an investigation of there dynamics.

The Rb₂ZnCl₄ phase displays several transitions [4]. Above T_i= 303 K the high temperature phase is described as a crystal structure where the orientations of ZnCl₄ tetrahedrons are randomly oriented with a space group Pmcn and lattice parameters a=7,3Å, b=12,7Å and c=9,2Å. From T_i=303, down to T_C=195K, the orientation of the ZnCl₄ tetrahedrons gets incommensurately modulated along the c* axis with an increasing anharmonicity [5;6]. Below T_C, the modulation gets locked-in with a 1/3 ratio of the periodicities, the c cell parameter is then tripled. As theory predicts a different behaviour of phasons depending on the harmonicity regime, it fits well as a probe of the incommensurate phases dynamics. We probed the dynamical properties of this material through inelastic neutron scattering with the IN6-SHARP, IN5, IN12, IN22 and THALES instruments of the ILL, and with the 1T spectrometer of the LLB. In order to cover the whole incommensurate phase and go beyond the two phase transitions, working temperatures ranged from 350K to 140K.

We have measured and compared the temperature dependence of transverse acoustic phonons around a few main Bragg reflections as well as some of the satellite reflections that sign the incommensurability. In the lock-in phase, the tripling of the cell is manifested by superstructure reflections. At 140K, all the measured acoustic phonons have consistent integrated intensities whether they are associated to superstructure or substructure reflections. Although they all presented a similar sound velocity around 9meV.Å, the superstructure phonons were found to widen faster. As temperature increases, the relative integrated intensity of superstructure related acoustic phonons decreases. At the same time, a large quasi-elastic signal localised around the superstructure reflections appears and increases in intensity with temperature, evidencing a relaxation process we attribute to local reorientations of ZnCl₄ tetrahedrons. During the phase transition at T_C, the superstructure reflections are splitted along the c* axis into satellite reflections and we observe a jump in intensity of the localised quasi-elastic signal. This signal continues to grow with increasing temperatures in the incommensurate phase while the relative intensity of the acoustic phonon associated to satellite reflections continues to decrease. Above T_i, the satellites reflections disappear into large diffuse elastic spots. At 350K the localised quasi-elastic signal dominates, but despite the absence of a reflection defining the centre of a Brillouin zone, a weak and large mode is found to disperse as an acoustic-like phonon around these diffuse elastic spots, indicating weak long range correlated modes are remaining despite the prevailing disorder in the ZnCl₄ tetrahedrons orientations.

[1] Janssen, T., Chapuis, G. and de Boissieu, M., Aperiodic Crystals. From modulated phases to quasicrystals (second edition), 560 pages (Oxford University Press, Oxford,2018)

[2] van Smaalen, S., Incommensurate Crystallography, pages (Oxford University Press, 2012)

[3] de Boissieu, M., Currat, R. and Francoual, S. 2008 in Handbook of Metal Physics: Quasicrystals (eds. T. Fujiwara and Y. Ishii) 107 (Elsevier Science)

[4] Hedoux, A., Grebille, D., Jaud, J. & Godefroy, G. (1989). Acta Cryst. B45, 370-378.

[5] Aramburu, I., Friese, K., Perez-Mato, J. M., Morgenroth, W., Aroyo, M., Breczewski, T. & Madariaga, G. (2006). Phy. Rev. B 73, 014112.

[6] Li, L., Wölfel, A., Schönleber, A., Mondal, S., Schreurs, A. M. M., Kroon-Batenburg, L. M. J. & van Smaalen, S. (2011). Acta. Cryst. B 67, 205-217.

We revisited X-ray diffraction data of decagonal Al-Cu-Rh system collected previously by Kuczera et al. [1] at room temperature and at 1013-1223 K. From [1] it is known, that the best quasiperiodic ordering exists most probably between 1083 and 1153 K. The stability was proven to be most likely not phason-driven entropy lowering.

In our recent studies, we tested an application of the new correction for phasons, based on the statistical approach. It was shown [2,3], that phason flips significantly change the shape of the average unit cell, and therefore influence the structure factor, and thus the diffraction diagram. These changes in the shape of the AUC can be handled analytically. During the structure refinement, the new correction for phasons gives an extra parameter to fit. The procedure was recently applied to room-temperature d-AlCuRh data [4].

We performed a series of structure refinements including a new correction term for phasons alongside the standard perp-space Debye-Waller factor for 5 sets of X-ray diffraction data at 293, 1013, 1083, 1153, and 1223 K. In the case of every dataset, we were able to achieve better R-factor values as compared to original results reported in [1]. As a result, phasonic ADPs were refined alongside the flip probability (measuring the phasonic contribution within the new approach), which shows a distinct minimum in the temperature plot (Figure 1). This can lead to a conclusion, that the amount of phasons is minimal at around 1153 K, which is also a temperature of maximal stability of the quasicrystal.

Figure 1. Phasonic ADPs (new and from [1]) and flip probability from the refinement vs. temperature.

[1] P. Kuczera, J. Wolny, W. Steurer, Acta Cryst. B 70 (2014) 306-314. [2] J. Wolny, I. Buganski, P. Kuczera, R. Strzalka, J. Appl. Cryst. 49 (2016) 2106-2115. [3] R. Strzałka, I. Bugański, J. Śmietańska, J. Wolny, Arch. Metall. Mater. 65 (2020) 291-294. [4] I. Bugański, R. Strzałka, J. Wolny, Acta Cryst. A 75 (2019) 352-361.

Keywords: decagonal quasicrystal; phasons; entropy stabilization

3D-facets of the Delone cells of the root lattice which tile the six-dimensional Euclidean space in an alternating order are projected into three-dimensional space. They are classified into six Mosseri-Sadoc tetrahedral tiles of edge lengths 1 and golden ratio with faces normal to the 5-fold and 3-fold axes. The icosahedron, dodecahedron and icosidodecahedron whose vertices are obtained from the fundamental weights of the icosahedral group are dissected in terms of six tetrahedra. A set of four tiles are composed out of six fundamental tiles, faces of which, are normal to the 5-fold axes of the icosahedral group. It is shown that the 3D-Euclidean space can be tiled face-to-face with maximal face coverage by the composite tiles with an inflation factor generated by an inflation matrix. We note that dodecahedra with edge lengths of 1 and naturally occur already in the second and third order of the inflations. The 3D patches displaying 5-fold, 3-fold and 2-fold symmetries are obtained in the inflated dodecahedral structures with edge lengths with n^th power of the golden ratio. The planar tiling of the faces of the composite tiles follow the edge-to-edge matching of the Robinson triangles.

Modulated crystal structures consist of a basic structure that possesses 3D space group symmetry, while the constituents of the basic unit cell are modulated by a periodic deformation/modulation.¹ Depending on whether the modulation wave vector, q, is rational or irrational with respect to the basic lattice, they are termed as commensurately or incommensurately modulated structures, respectively. The (3+d)D superspace approach (d = 1,2,3) is employed to recover periodicity of the diffraction patterns and crystal structures of incommensurately modulated crystals (can be applied to commensurate cases too). 3D Sections perpendicular to the internal higher dimension(s) describe crystal structures in real space that vary as function of the phase of the modulation.¹

Following a brief discussion on the advantages of the superspace approach in understanding phase relations in molecular crystals², phase transitions, modulated phases, properties and origin of modulation with respect to intra/intermolecular interactions of the following systems will be discussed:

Case 1: Trimethyltin hydroxide exhibits a discontinuous switching of commensurate modulations below [q_T<Tc = (0,0,1/2)] and above [q_T>Tc = (0,0,3/8)] its phase transition temperature (T_c ≈ 176 K) with similar basic lattices.^3,4

Case 2: Λ–cobalt sepulchrate trinitrate undergoes phase transitions from classical 3D periodic to incommensurately modulated at T_c1 = 133 K, from incommensurately modulated to incommensurately modulated at T_c2 = 107 K and further to commensurately modulated at T_c3 = 98 K [q = (1/6,0,0)].⁵

Case 3: Upon cooling, biphenyl carboxy protected L-phenylalaninate undergoes a phase transition at T_c = 124 K from classical 3D periodic to commensurately modulated [q = (1/2,0,1/2)].

Case 4: Trifluoroborane trimethylamine molecules are highly globular and crystallize in space group R3m. The crystals are plastically bendable, ductile and can be pressed and deformed into thin films with development of possible 2D modulation.⁶

[1] van Smaalen, S. (2012). “Incommensurate Crystallography”, Oxford University Press, Oxford.

[2] Schoenleber, A. (2011). Z. Kristallogr. 226, 499–517. 10.1524/zkri.2011.1372

[3] Dey, S. et. al. (2016). Z. Kristallogr. 231, 427–434. 10.1515/zkri-2016-1952

[4] Dey, S. et. al. (2018). Cryst. Growth Des. 18, 1394–1400. 10.1021/acs.cgd.7b01295

[5] Dey, S. et. al. (2016). Acta Crystallogr. B 72, 372–380. 10.1107/S2052520616005503

[6] Mondal, A. et. al. (2020). Angew. Chem. Int. Ed. 10.1002/anie.202001060

A classification of magnetic superspace groups compatible with the helical and cycloidal magnetic modulations is presented. Helical modulations are compatible with groups from crystal classes 1, 2, 222, 4, 422, 3, 32, 6 and 622, while cycloidal modulations are compatible with groups from crystal classes 1, 2, m and mm2. For each magnetic crystal class, the directions of the symmetry allowed (non-modulated) net ferromagnetic moment and electric polarization are given. The proposed classification of superspace groups is tested on experimental studies of type-II multiferroics published in the literature.

This poster based on the paper Acta Cryst. (2021). A77, 160–172.

Very recently, Liu et. al. proposed a machine learning (ML) approach to distinguishing quasicrystals (QCs) and related approximants (ACs) from ordinary crystals. They built a supervised ML model that classifies any given chemical composition into three structural classes (QCs, ACs, others), and demonstrated its potential predictive power. In this study, we built models according to the previous study and searched for new QCs and ACs base on the predictive candidate compositions from the given models.

Our models achieved a prediction accuracy of 0.999. With this, we screened 27,220 virtual ternary alloy systems, which resulted in 701 systems predicted to be QCs or ACs. We synthesized 19 Sc-Zn-Ti alloy samples around the candidate compositions of the predicted QC/AC phase and characterized the synthesized materials by using a powder and single-crystal X-ray diffraction (XRD) method. All the peaks in the powder XRD pattern of a sample with the nominal composition of Sc₁₅Ti₂Zn₈₃ could be assigned to the 1/1 approximant with a lattice parameter equal to 13.81 Å. By performing a single-crystal X-ray structure analysis, this phase was determined to have a body-centred packing structure consisting of the Tsai-type rhombic triacontahedron cluster (space group Im-3).

Composite Polycaprolactone (PCL) materials with different amounts of clays were prepared employing two mixing techniques: a two screw extruder and an intensive mixer (Brabeder type) followed by compression moulding in a hydraulic press. Simultaneous Small and Wide angle X ray Scattering (SAXS/WAXS) measurements were done in order to evaluate the structural characteristics and preferential orientation of the composites. On the one hand, the effect of the clay inclusion in the PCL lamellar structure was evaluated, and moreover, the clay interlayer distance was compared between composites.

Upon the modification of the clays with Benzolconion Chloride (CBK), an anisotropic effect becomes noticeable in the 2D SAXS patterns recorded on Pilatus (Dectris) detector (Fig. 1), when the sample is analysed with the plane of the film parallel to the direction of the incident beam.

For all cases, there were no changes in the PCL structure due to clay inclusion. For modified clays, in two of the three analysed systems, the clay interlayer characteristic peak shifts towards lower angles, corresponding to an increment in the distance from 1.3 to 1.7nm. And in all cases, a new peak appears at lower angles for the modified samples, attributed to an interlayer spacing distance of the nano sized clays of 2.7 - 2.9 nm, only for patterns of the samples placed parallel to the direction of the incident beam. Different loads yield different intensities in the most intense region, proportional to the amount of load.

It was shown that the orientation is dependent on the synthesis procedure and also on the clay characteristics. These results can be correlated with the mechanical behaviour of the developed films which is a relevant parameter for the application of material on food packaging.

X-ray absorption fine structure (XAFS) spectroscopy is one of the most widely used synchrotron radiation based methods to study local structures and electronic states of elements. Chemical reactions have been observed by in situ XAFS methods. However, XAFS is fundamentally bulk sensitive, and is difficult to apply to study surface phenomena or reactions.
We have developed a surface sensitive x-ray spectroscopy, which is named Total REflection
X-ray Spectroscopy (TREXS), to study surfaces in nanometer scale. Reflection spectra are recorded in total reflection conditions, and the surface sensitivity of about 2-3 nm is realized. In brief, TREXS enables us to obtain two kinds of information, which essentially correspond to usual XANES and EXAFS. Near edge regions of total reflection spectra are analyzed to discuss electronic structures and chemical states, and surface reactions can be monitored by tracking the changes. In addition, total reflection spectra are transformed to XAFS spectra through Kramers-Kronig relations, and regular EXAFS analysis methods can be applied.
It was reported that a reduction reaction of surface NiO layer to Ni metal with
the surface sensitivity of ~2-3 nm[1,2].
In this contribution, we will present surface chemical reactions studied by in situ TREXS, development of multi-modal surface research equipment by combining TREXS with IRRAS (Infrared Reflection Absorption Spectroscopy), and an ongoing plan to involve also scattering techniques in the TREXS experimental equipment.
This will lead to develop an experimental setup to study surfaces in nanometer scale by spectroscopy (TREXS) and scattering including diffraction at the same time under reaction conditions.
References
[1] H. Abe, et al., Jpn. J. Appl. Phys. 55, 062401 (2016).
[2] H. Abe, et al., Chem. Rec. 19, 1457 (2019).

Zirconium solutions have long been used as raw precursors in a range of applications to produce a diverse range of materials and products, including ZrO₂ nanoparticles and high temperature ceramics which are widely used as catalysts and sorbents ^[1-3]. It is commonly accepted that the structure of the species in the zirconium solution is influential in the properties, chemical and physical, of any subsequent materials. It is for this reason that it is of critical importance that we fully understand the structure of the species within these solutions, and subsequently use this information to inform and adapt synthetic methods.

There is evidence that Zr(IV), in aqueous solution, has a tendency towards hydrolysis and polymerisation. A tetranuclear species [Zr₄(OH)₈(OH₂)₁₆]⁸⁺ was proposed by Clearfield and Vaughn ^[4]. This species has a square 4 – Zr core held together by 8 hydroxyl bridges with 16 terminal waters. This structure was determined through the use of single crystal X-Ray diffraction (XRD) on solid samples of recrystallised ZrOCl₂·8H₂O solution. Since its discovery in 1956, this structure has widely been regarded as being correct and its tetramer complex considered present in the aqueous phase ^[5]. Unfortunately, any attempts to study this species whilst still in aqueous solutions have been limited due to the lack of long range order in solution species, hence disallowing traditional laboratory crystallographic methods. However, recent developments of total scattering pair distribution function (PDF) have allowed for the study of disordered systems including glasses and, more importantly, liquids. This allows for the characterisation and modelling of solution species through methods similar to those traditionally associated with XRD and Rietveld refinements. Through the use of these methods we have been able to isolate contributions to the PDF pattern from the tetranuclear species, and subsequently refine the ideal solid state model to determine its nature in solution. Recent work by Hu et al. collected PDF data on aqueous zirconyl chloride and, through a method of fitting to Gaussians, confirmed that the general structure, proposed by Clearfield and Vaughn, is indeed present, but no refined inter atomic distances were obtained ^[6]. However through the use of structural refinements we have obtained a model which, whilst similar to the original Clearfield model, has some distortion with respect to bond lengths and angles in the terminal H₂O.

In this work we propose a refined version of the original model, first proposed by Clearfield. We also discuss the use of the Topas suite’s rigid body editor and how, if a starting model is widely considered to be accurate, this offers enough flexibility to refine small differences to get a truly optimal model, with an extremely high level of precision, whilst ensuring that the statistics of the refinement are mathematically believable. The method used to obtain this refinement will be subsequently applied to further aqueous zirconium carboxylates which are yet to have their solution species identified.

[1] Geiculescu, A.C. et al., Sol-Gel Sci. and Tech., 2000. 17(1): p. 25-35. [2] De Keukeleere, K., et al., Inorg. Chem., 2015. 54(7): p. 3469-3476. [3] Feth, M.P., et al., Non-Crystalline Solids, 2005. 351(5): p. 432-443. [4] Clearfield, A. et al., Acta Cryst., 1956. 9(7): p. 555-558. [5] Hennig, C., et al., Inorg. Chem., 2017. 56(5): p. 2473-2480. [6] Hu, Y.-J., et al., American Chem. Soc., 2013. 135(38): p. 14240-14248.

Traditional Li-ion battery electrodes are highly crystalline materials in which the ions are intercalated between atomic layers or channels in the atomic lattice. Such electrodes are typically characterized by retaining their crystallinity for many charge-discharge cycles. However, a number of electrode materials undergo an irreversible loss of crystallinity upon Li-intercalation. Examples of such materials are rutile TiO₂ and orthorhombic V₂O₅, which loses long range order upon intercalation of >0.8 and >2 Li, respectively [1,2]. Very little is presently known about neither the mechanism of such order-disorder phenomena nor about how ion storage occurs in disordered structures in subsequent charge-discharge cycles. This is in spite that such materials represent cheap and effective alternatives to their crystalline counterparts, i.e. recently amorphous V₂O₅ was shown to reversibly store close to double the amount of Na-ions as compared to crystalline V₂O₅ [3].

Herein, we investigate the structural evolution during Li-intercalation and the associated disordering process in nano-rutile TiO₂ by means of combined ex situ and operando synchrotron radiation powder X-ray diffraction and total scattering with pair distribution function (PDF) analysis. We find that, the disorder mechanism entails a reconstructive phase transformation with formation of a distorted α-NaFeO₂ structure. Furthermore, small disordered domains form due to extensive dislocations between the distorted α-NaFeO₂ domains [4].

After amorphization, TiO₂ reversibly stores ~200 mAh/g with ion storage occurring via solid solution reactions with remarkable small volume changes between the end-members. Our results suggest that these materials may hold potential as cheap electrode materials despite the fact that they lose long range order. Also our methodology opens for investigating a wide range of order-disorder phenomena in electrochemically driven phase transitions.

[1] Borghols, W. J. H., Wagemaker, M., Lafont, U., Kelder, E. M. & Mulder, F. M. (2008). Chem. Mater. 20, 2949.

[2] Delmas, C., Cognac-Auradou, H., Cocciantelli, J.M., M6n6tder, M. & Doumerc, J.P. (1994). Solid State Ionics 69, 257.

[3] Uchaker, E., Zheng, Y. Z., Li, S., Candelaria, S. L., Hu, S. & Cao, G. Z. (2014). J. Mater. Chem. A 2, 18208

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

While the silicon-rich members of the series Cu₂Zn(Ge,Si)Se₄ crystallize in wurtz-kesterite type structure [1], germanium-rich samples adopt a tetrahedral structure of the kesterite type [2] (figure 1). Identification of the silicon site is straightforward from regular X-ray diffraction, as Si⁴⁺ is a light element and has less electrons than the other cations. However, Cu¹⁺, Zn²⁺, and Ge⁴⁺ are all isoelectronic and have very similar form factors. The kesterite type of the cation distribution of Cu₂ZnGeSe₄ has been established by neutron diffraction [2], which can distinguish these elements.

We now applied anomalous X-ray diffraction to this system, using Rietveld refinement and Multiple Edge Anomalous Diffraction (MEAD) [3] with data taken at the K-absorption edges of Cu, Zn, and Ge. These energies are accessible at beamline KMC-2, BESSY II, Berlin [4]. The Si-rich end member Cu₂ZnSiSe₄ has previously shown to be wurtz-kesterite by MEAD [1]. With the correct structure type, the degree of Cu/Zn disorder within the Si-rich region of the series could be determined reliably from multiple-energy Rietveld refinement. For the Ge-rich, tetragonal structures, MEAD was found to be the method of choice. In contrast to previous studies, where Sn⁴⁺ was the M(IV) species in the structure [1], in Cu₂ZnGeSe₄ all cations have very similar scattering power under normal conditions. This results in superstructure peaks (with respect to the cubic ZnS parent structure) that are very weak. For Rietveld analysis this is a drawback, as the optimization will be dominated by the main peaks of the parent structure. In MEAD, however, it increases the effect of the changing scattering power close the absorption edges. As a result, not only are Kesterite and Stannite types clearly distinguishable at the Cu-K edge (figure 2), also the Cu/Zn ordering within the Kesterite structure is clearly detectable and quantifiable at the Zn-K edge.

The degree of Cu/Zn order for the full series could thus be compared to other structural and physical parameters within the Cu₂Zn(Ge,Si)Se₄ solid solution series.

[1] Többens, D. M., Gurieva, G., Niedenzu, S., Schuck, G., Schorr, S. (2020) Acta Cryst. B 76, 1027.

[2] Gurieva, G., Többens, D. M., Valakh, M. Y., Schorr, S. (2016) J. Phys. Chem. Solids 99, 100.

[3] Collins, B. A., Chu, Y. S., He, L., Haskel, D. & Tsui, F. (2015). Phys. Rev. B 92, 224108.

[4] Helmholtz-Zentrum Berlin für Materialien und Energie (2016) J. Large-Scale Res. Facilities 2, A49

The size of nano-ceria particles can be controlled by the amount of time HMT and cerium nitrate are together in solution.[1] The interaction of HMT with cerium nitrate has been studied by in situ Small Angle Scattering (SAXS) and a core structure with a different surface structure is proposed.[2] The Diffuse Reflectance Fourier Transform Spectra (DRIFTS) of this nano-ceria shows significant adsorption of HMT on this surface that transforms to formate and finally carbonate during heating to 425 °C. The combination of PDF and DRIFTS analysis has been used to gain new insights into the structure of this nano-ceria.

A model of HMT interacting with the 111 surfaces of ceria can be made where H bonds from N in HMT can H-bond to OH groups on the ceria surface by aligning the 3-fold axes of the HMT and the 3-fold axis of the 111 surface of ceria (Figure 1). Examination of the G(r) of the Pair Distribution Function (PDF) does not show much evidence for this interaction because the scattering power of the light atoms in the HMT is too weak to show a significant signal when the heavy cerium atoms are present. However, signal enhancing techniques show some support for this model.[3]

Analysis of the PDF of the room temperature data showed that a disordered surface of ceria on a core of ceria gave an improved fit. Additional modeling shows that the disordered surface phase could also be interpreted as ceria with a CeO₈ fragment replaced with an HMT molecule (Figure 2). The refinement with the embedded HMT may not be practical, but a simplified model where one of the 8 cerium atoms has reduced occupancy fits the surface G(r).

The refinement of the temperature dependent PDF data shows the cell dimension variation found in the Rietveld refinement of the powder X-ray data. There is a spike in the cell dimension during the initial ramp which arises from the reduction of the ceria by the oxidation of the HMT or one of its decompaction products. The surface phase has a smaller cell dimension than the core phase and the size and fraction of this shell decreases on heating.

1. Zhang, F., S.W. Chan, J.E. Spanier, E. Apak, Q. Jin, R.D. Robinson, and I.P. Herman,. Appl. Physics Let., 2002. 80(1): p. 127-129.

2. Allen, A.J., V.A. Hackley, P.R. Jemian, J. Ilavsky, J.M. Raitano, and S.W. Chan, J. of Applied Cryst., 2008. 41: p. 918-929.

3. Urakawa, A., T. Burgi, and A. Baiker, Eng. Science, 2008. 63(20): p. 4902-4909.

This work was supported by NSF DMR grant 1206764 and used 28-ID-1 of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory(BNL) under Contract No. DE-SC0012704.

Alumina (Al₂O₃) has many applications, e.g., in cements, substrates of electronic materials, and high-temperature crucibles. Alumina can be classified as an intermediate between glass formers and modifiers, according to Sun [1]. It is impossible to prepare bulk alumina glass by using the melt quenching method and hence electrochemical and sol-gel methods were used to prepare the samples for studying optical properties and the behavior at high temperatures. However, the structure of alumina glass is still largely unknown due to the very limited number of structural studies.

In this study, we performed high-energy X-ray and neutron diffraction measurements on bulk alumina glass prepared by the electrochemical method. To understand diffraction data in detail, we employed a combined classical molecular dynamics-reverse Monte Carlo modelling approach, with coordination number constraints based on NMR data. The formation of OAl₃ triclusters could be confirmed. Detailed topological analyses are in progress.

[1] Sun, K. H. (1947). J. Am. Ceram. Soc. 30, 277.

Vanadium based glasses (vanadate glasses) with a sealing temperature of around 400 °C are now being applied in electronics devices, such as in crystal oscillators and Micro Electro Mechanical Systems (MEMS) as an alternative sealant to the toxic low-melting point glasses containing lead and fluorine. We have developed an Ag₂O-V₂O₅-TeO₂ glass with a sealing temperature of 200-300 °C. However, the structure of the Ag₂O-V₂O₅-TeO₂ glass is still unknown and hence it is necessary to reveal the relationship between the atomistic structure and the property of the vanadate glass.

In this study, we performed high-energy X-ray and neutron diffraction, extended X-ray absorption fine structure (EXAFS), and anomalous X-ray scattering (AXS) [1] measurements on an Ag₂O-V₂O₅-TeO₂ glass to obtain sufficient element specific structural information on constituent atoms. To uncover the glass structure in detail, we constructed a three-dimensional atomistic structure model for Ag₂O-V₂O₅-TeO₂ glass by employing the reverse Monte Carlo [2] technique based on X-ray/neutron diffraction, EXAFS and AXS data. Furthermore, topological analyses were applied to the three-dimensional glass structure model to extract topologies related to the low-melting property.

[1] Saito, M., Park, C., Omote, K., Sugiyama, K., Waseda, Y. (1997). J. Phys. Soc. Jpn. 66, 633.

[2] McGreevy, R. L., Pusztai, L. (1988). Molec. Simul. 1, 359.