The X-ray restrained/constrained wavefunction (XRW/XCW) fitting approach [1, 2] is one of the well-established methods of modern quantum crystallography [3-5], an approach that allows the determination of wavefunctions from experimental X-ray diffraction measurements by minimizing a functional (i.e., the so-called Jayatilaka functional) given by the sum of the electronic energy of the system under exam and of the statistical agreement between experimental and computed structure factor amplitudes.

Initially proposed in the framework of the restricted Hartree-Fock formalism [1, 2], over the years the method has been gradually extended to other techniques of quantum chemistry (e.g., unrestricted Hartree-Fock formalism, density functional theory, relativistic methods and extremely localized molecular orbital (ELMO) strategy), but practically remaining always limited to a single Slater determinant ansatz for the wavefunction to be determined.

In this presentation, two recent XRW fitting techniques that went beyond the previous limitation will be discussed: the X-ray restrained extremely localized molecular orbital – valence bond (XR-ELMO-VB) method [6, 7] and the X-ray restrained spin-coupled (XRSC) strategy [8, 9]. Both of them are multi-determinant XRW approaches and, above all, they are strongly rooted in Valence Bond theory, thus allowing the extraction of traditional chemical descriptors (e.g., weights of resonance structures) compatible with measured X-ray diffraction data

The XR-ELMO-VB technique, which can be considered as the first prototype multi-determinant XRW approach, exploits the use of pre-computed and frozen ELMOs to define the basis of pre-determined Slater determinants on which expanding the desired wavefunction [6]. The method is particularly useful to investigate systems characterized by a multi-reference character. The performed calculations have also clearly shown that the technique is able to reveal how the relative importance of resonance structures changes when structure factors measured at different conditions (e.g., at ambient or high pressure) are used as external restraints [7].

The XCSC method can be considered a step forward compared to the XR-ELMO-VB strategy. In fact, through the coupling of the XRW philosophy with the spin-coupled technique of Valence Bond theory, the approach enables not only the determination of resonance structure weights, but also the optimization of the so-called spin-coupled orbitals, which are quite localized and allow us to shed light on the spatial rearrangements of the electronic clouds and the hybridization of atoms [8, 9]. Preliminary tests have shown that XCSC computations can provide resonance structure weights, spin-coupled orbitals and global electron density distributions that are different from those obtained through corresponding gas-phase calculations [9]. These differences are probably due to the capability of the X-ray restrained spin-coupled approach in getting information contained in the experimental data employed in the computations (e.g., correlation and crystal filed effects).

References:

[1] Jayatilaka, D. (1998). Phys. Rev. Lett. 80, 798.

[2] Jayatilaka, D. & Grimwood, D. J. (2001). Acta Cryst. A57, 76.

[3] Genoni, A., Bučinský, L., Claiser, N., Contreras-García, J., Dittrich, B.; Dominiak, P. M., Espinosa, E., Gatti, C., Giannozzi, P., Gillet, J.-M., Jayatilaka, D., Macchi, P., Madsen, A. Ø., Massa, L. J., Matta, C. F., Merz, K. M. Jr., Nakashima, P. N. H., Ott, H., Ryde, U., Schwarz, K., Sierka, M. & Grabowsky, S. (2018). Chem. Eur. J. 24, 10881.

[4] Grabowsky, S., Genoni, A. & Bürgi, H.-B. (2017). Chem. Sci. 8, 4159.

[5] Genoni, A. & Macchi, P. (2020) Crystals 10, 473.

[6] Genoni, A. (2017). Acta Cryst. A73, 312.

[7] Casati, N., Genoni, A., Meyer, B., Krawczuk, A. & Macchi, P. (2017). Acta Cryst. B73, 584.

[8] Genoni, A., Franchini, D., Pieraccini, S. & Sironi, M. (2018). Chem. Eur. J. 24, 15507.

[9] Genoni, A., Macetti, G., Franchini, D., Pieraccini, S. & Sironi, M. (2019). Acta Cryst. A75, 778.

Acknowledgments:

The French Research Agency (ANR) is gratefully acknowledged for financial support of this work through the Young Investigator Project “QuMacroRef” (Grant No. ANR-17-CE29-0005-01).

We are developing in the CRM2 laboratory a new software: Mollynx. As MoPro or XD, Mollynx is derived from Molly (Hansen and Coppens, 1978) but allows to differentiate the electron spins. This new algorithm has been successively applied to paramagnetic coordination compounds (Deutsch et al., 2012, Deutsch et al., 2014) to organic radicals (Voufack et al., 2017) and to small unit cells inorganic crystals (Voufack et al., 2019).

A more general model based on atomic orbitals (Tanaka, 1988; Tanaka, 1993; Bytheway et al., 2001; Schweitzer, 2006), has also been coded in the Mollynx software. This model should allow calculation of properties derived from the atomic wave functions such as covalency, populations of atomic orbitals, energy, optical properties and can in principle describe bonded pair of atoms with orbitals centered on different atoms (two centres orbital products). This model, extended to spin resolved orbitals, has been applied to the YTiO₃ perovskite (figure 1, Kibalin et al., 2021) The radial extension, orientation and population of outer atomic orbitals for each atom have been modelled leading to a clear description of the bonding in this crystal .

Thus Mollynx can refine a spin resolved electron density model based on multipolar or on orbital approach. This presentation will describe some of these results and will focus on the experimental spin resolved atomic orbitals model obtained on the YTiO₃ including a comparison with a refinement based on theoretical structure factors calculated using density functional theory and the WIEN2k code (Blaha et al., 2020).

Blaha, P.; Schwarz, K; Tran, F.; Laskowski, R; Madsen G. K. H. and Marks, L. D., WIEN2k: An APW+lo program for calculating the properties of solids editors-pick, J. Chem. Phys. 152, 074101 (2020); https://doi.org/10.1063/1.5143061

Bytheway, I., Figgis, B. N. & Sobolev, A. N., 2001. Charge density in Cu(glygly)(OH2)2·H2O at 10 K and the reproducibility of atomic orbital populations. J. Chem. Soc., Dalton Trans., Volume 22, pp. 3285-3294.

Deutsch, M., Claiser, N., Pillet, S., Ciumacov, Y., Becker, P. J., Gillon, B., Gillet, J.-M., Lecomte, C. & Souhassou, M. (2012). Acta Cryst. A 68, 675-686.

Deutsch, M., Gillon, B., Claiser, N., Gillet, J.-M., Lecomte, C. & Souhassou, M. (2014). IUCR J, 194-199.

Hansen, N. K. & Coppens, P. (1978). Acta Cryst. A34, 909–921.

Kibalin I., Voufack A.B., Souhassou M., Gillon B., Gillet J.M., Claiser N., Gukasov A., Porcher F. and Lecomte C. (2021) Acta Cryst A77, 96-104

Schweizer, J. (2006). Chapter 4: Polarized Neutrons and Polarization analysis, in Neutron Scattering from magnetic materials. Ed. T. Chatterji, Elsevier

Voufack, A. B. et al., 2017. When combined X-ray and polarized neutron diffraction data challenge high-level calculations: spin-resolved electron density of an organic radical. Acta Cryst., Volume B73, pp. 544-549.

Voufack, A. B. et al., 2019. Spin resolved electron density study of YTiO3 in its ferromagnetic phase: signature of orbital ordering. IUCrJ, 6(5), pp. 884-894.

Tanaka K., (1993). Acta Cryst., B49, 1001-1010.

Tanaka, K., (1988) Acta Cryst., A44, 1002-1008.

This work retraces different methods that have been explored to account for the atomic thermal motion in the reconstruction of one-electron reduced density matrices from experimental X-ray structure factors (XSF) and directional Compton profiles (DCP).
Attention has been paid to propose the simplest possible model, which obeys the necessary N-representability conditions, while accurately reproducing all available experimental data.
The deconvolution of thermal effects makes it possible to obtain an experimental static density matrix, which can directly be compared with theoretical 1-RDM. It is found that above a 1% statistical noise, the role played by Compton scattering data becomes negligible and no accurate 1-RDM becomes reachable.
Since no thermal 1-RDM is available as a reference, the quality of an experimentally derived temperature-dependent matrix is difficult to assess. However, the accuracy of the obtained static 1-RDM is strong evidence that the Semi-Definite Programming method is robust and well-adapted to the reconstruction of an experimental dynamical 1-RDM.

Several physico-chemical properties of materials and biological molecules crucially depend on the hydrogen atom positions. Therefore, obtaining reliable three-dimensional structures of molecules and materials is a crucial step to have accurate results.

Unfortunately, the weak X-rays scattering power of hydrogen atoms makes them usually very hard to detect accurately. Besides, the choice of the refinement method has also a strong influence. The most widely used approach, the independent atom model (IAM), describes the total electron density as the sum of spherical atomic densities centred on the nuclei. This approximation evidently fails when applied to hydrogen atoms because their only electron is delocalized in forming a bond. As a result, bonds lengths involving hydrogen atoms are generally too short.

Over the years, different methods have been proposed to overcome this drawback. Within the field of quantum crystallography, the Hirshfeld atom refinement (HAR) approach is one of the most promising strategies [1]. HAR is a technique exploiting fully quantum mechanical calculations to obtain tailor-made ab initio electron densities, which are partitioned into aspherical atomic contributions to fit experimental structure factors without further approximations. HAR is able to provide X-H bond distances that are in very good agreement with those obtained from neutron diffraction experiments [1-3]. Moreover, the introduction of crystal environment effects is crucial to carry out better refinements, especially when strong intermolecular interactions are present. This is usually done by adding point charges at symmetry-related atomic positions around the selected reference crystal unit [1-3].

In this contribution, we introduce an improvement to the description of crystal field effects in HAR exploiting the recently developed quantum mechanics/extremely localized molecular orbitals (QM/ELMO) technique [4,5]. In our new modified version of HAR, the reference crystal unit is treated variationally at quantum mechanical level as in the traditional HAR, while the symmetry-related crystal units are described using pre-computed frozen extremely localized molecular orbitals [6]. The ELMOs contribution describing the crystal environment is included in the Hamiltonian of the reference crystal unit through an electrostatic embedding.

Other than discussing the theoretical framework at the basis of the new strategy, we will show test refinements performed on the xylitol crystal, a system characterized by an extended network of strong hydrogen bonds. The results show that the new ELMO-embedded HAR approach gives bond lengths involving hydrogen atoms in optimal agreement with neutron results, outperforming not only the traditional HAR but also the charge-embedded HAR technique in practically all the cases [6].

Given the promising results, we envisage the application of the new ELMO-embedded HAR technique to refine structures of crystals with strong intermolecular interactions. However, further test-bed refinements will be necessary to draw final conclusions, also considering other aspects such as basis-sets and theoretical methods dependence.

[1] Jayatilaka, D. & Dittrich, B. (2008). Acta Cryst. A64, 383.

[2] Woińska, M., Grabowsky, S., Dominiak, P. M., Woźniak, K. & Jayatilaka, D. (2016). Sci. Adv. 2, e1600192.

[3] Capelli, S., Bürgi, H.-B., Dittrich, B., Grabowsky, S. & Jayatilaka, D. (2014). IUCrJ 1, 361.

[4] Macetti, G. & Genoni, A. (2019). J. Phys. Chem. A 123, 9420.

[5] Macetti, G, Wieduwilt, E. K., Assfeld, X. & Genoni, A. (2020). J. Chem. Theory Comput. 16, 3578.

[6] Wieduwilt, E. K., Macetti, G. & Genoni, A. (2021). J. Phys. Chem. Lett. 12, 463.

Relativistic effects in chemistry manifest themselves in many ways and influence various physical and chemical properties of materials. The well-known of them is the yellow color of gold or the high voltage of the lead-acid car battery^1,2. Therefore, a description of these effects is of great importance for a better understanding of the chemistry of heavy atoms.

A perspective method is quantum crystallography that relies on the high-resolution and high-quality XRD data to describe crystal structure in unprecedented detail^3-4. Intensities of the diffracted beam are affected not only by relativistic effects but also by absorption⁵, anharmonic motion⁶, anomalous dispersion⁷, and many other effects which highly influence electron density distribution in the crystal and, in consequence, derived properties.

We collected the data sets for the chloro(triphenylphosphine)gold(I) and di(triphenylphosphine)mercury(II) nitrate using Mo X-ray source at 100K, where the data sets for (3-(4-chlorophenyl)-3-oxoprop-1-yn-1-yl)(triphenylphosphine)gold(I) and chloro(dimethylsulfide) gold(I) were collected using synchrotron radiation at 80K.

Here, we present the results of relativistic Hirshfeld atom refinements⁸ carried out as implemented in NoSpherA2⁹ for high-resolution X-ray diffraction data sets. The outcome of DFT-based refinements with the nonrelativistic and quasi-relativistic approaches will be compared, including analysis of the influence of disorder on relativistic effects, description of aurophilic interactions, and the nature of the Me–X bonds in Au and Hg crystals.

Acknowledgment:

Support of this work by the National Science Centre, Poland through grant PRELUDIUM no. UMO-2018/31/N/ST4/02141 is gratefully acknowledged.

The experiment was carried out at the Spring-8 with the approval of the Japan Synchrotron Radiation Research Institute (Proposal Number 2019A1069).

References:

1. Pyykko, P. (1988). Chemical Reviews, 88, 563–594.

2. Yatsimirskii, K. B. (1995) Theoretical and Experimental Chemistry, 31, 153–168.

3. L. J. Farrugia, C. Evans, D. Lentz and M. Roemer, Journal of the American Chemical Society, 2009, 131, 1251–1268.

4. T. S. Koritsanszky and P. Coppens, Chem. Rev., 2001, 101, 1583–1628.

5. J. Als‐Nielsen and D. McMorrow, in Elements of Modern X-ray Physics, John Wiley & Sons, Ltd, 2011, pp. 1–28.

6. R. Herbst-Irmer, J. Henn, J. J. Holstein, C. B. Hübschle, B. Dittrich, D. Stern, D. Kratzert and D. Stalke, The Journal of Physical Chemistry A, 2013, 117, 633–641.

7. S. Caticha-Ellis, Anomalous dispersion of x-rays in crystallography, University College Cardiff Press, Cardiff, Wales, 1981.

8. Bučinský, L., Jayatilaka, D., Grabowsky, S. (2016) The Journal of Physical Chemistry A, 120, 6650–6669.

9. Kleemiss, F.; Dolomanov, O. V.; Bodensteiner, M.; Peyerimhoff, N.; Midgley, L.; Bourhis, L. J.; Genoni, A.; Malaspina, L. A.; Jayatilaka, D.; Spencer, J. L.; White, F.; Grundkötter-Stock, B.; Steinhauer, S.; Lentz, D.; Puschmann, H.; Grabowsky, S. (2021) Chem. Sci., 12, 1675-1692.

That composition and structure profoundly impact the properties of crystalline solids has provided impetus for exponential growth in the field of crystal engineeringover the past 25 years. Crystal engineering has evolved from structure design (form) to control over bulk properties (function). Today, when coupled with molecular modeling, crystal engineering can offer a paradigm shift from the more random, high-throughput methods that have traditionally been utilized in materials discovery and development. Custom-design of the right crystalline material for the right application could therefore be at hand.

Porous crystalline materials exemplify this situation. Whereas purely inorganic materials (e.g. zeolites) and those based upon coordination chemistry (e.g. Metal-Organic Frameworks, MOFs, and Porous Coordination Polymers, PCPs) are well studied and offer great promise for separations and catalysis, they are often handicapped by cost or performance (e.g. poor chemical stability, interference from water vapour, low selectivity) limitations. Ultramicroporous Materials, UMs, are built from metal or metal cluster “nodes” and combinations of organic and inorganic “linkers” and their pore chemistry and size (< 0.7 nm) can overcome some of the weaknesses of existing classes of porous material (Figure 1). Three families (platforms) of UMs will be detailed and their performance with respect to important gas separation (e.g. CO₂ capture [1], C₂H₂ capture [2]) and water purification applications will be discussed. Most recently, we have shown that UMs can function synergistically to address complex gas mixtures [3] or perform effectively for CO₂ capture even in the presence of humidity [4].

[1] Nugent, P. Nugent, P.; Belmabkhout, Y.; Burd, S.D.; Cairns, A.J.; Luebke, R.; Forrest, K.; Pham, T.; Ma, S.; Space, B.; Wojtas, L.; Eddaoudi, M.; Zaworotko, M.J. (2013) Nature 495, 80-84.

[2] Cui, X.; Chen, K.J.; Xing, H.; Yang, Q.; Krishna, R.; Bao, Z.; Wu, H.; Zhou, W.; Dong, X.; Li, B.; Ren, Q.; Zaworotko, M.J.; Chen, B. (2016). Science 353, 141-144.

[3] Chen, K.J.; Madden, D.G.; Mukherjee, S.; Pham, T.; Forrest, K.A.; Kumar, A.; Space, B.; Kong, J.; Zhang, Q.Y. Zaworotko, M.J. (2019). Science, 366, 241-246.

[4] Mukherjee, S.; Sikdar, N.; O’Nolan, D.; Franz, D.M.; Gascon, V.; Kumar, A.; Kumar, N.; Scott, H.S.; Madden, D.G.; Kruger, P.E.; Space, B.; Zaworotko, M.J. (2019). Science Adv. 5, eaax9171.

Noncovalent interactions play a fundamentally important role in the properties of solid materials. For instance, guests are taken up into the host framework of porous materials as a result of the interactions between these species, while the manner in which they interact has an influence on the sorption ability of the porous material. In this work calculations on a range of porous frameworks allow us to explain the role that noncovalent interactions play in the sorption properties of these compounds. For instance, the origin of anomalous sorption isotherms are shown to be the result of interactions between acetylene^[1] or carbon dioxide^[1,2] and the host frameworks, as well as interactions between guests. Similarly, noncovalent interactions are responsible for the change in colour along an hourglass pattern of a crystalline porous compound during sorption of particular solvents. Calculations show that the origin of this effect is that the channels in the porous framework are anisotropic, allowing sorption only from particular faces.^[3]

References

[1] Jacobs, T.; Lloyd, G. O.; Gertenbach, J. A.; Esterhuysen, C.; Müller-Nedebock, K. K.; Barbour, L. J., Angew. Chem. Int. Ed., 2012, 51, 4913-4916.

[2] Bezuidenhout, C. X.; Smith, V. J.; Bhatt, P. M.; Esterhuysen, C.; Barbour, L. J., Angew. Chem. Int. Ed. 2015, 54, 2079–2083.

[3] Bezuidenhout, C. X.; Esterhuysen, C.; Barbour, L. J., Chem. Commun., 2017, 53, 5618–5621.

Mesoporous materials are excellent materials to be used in energy and environmental related applications. Methods to characterize the pore structures and the filling and emptying processes are physisorption and small-angle scattering. Gas physisorption in mesoporous materials and the associated capillary hysteresis intrigue the scientific community since decades. These phenomena are largely exploited for the characterization of porous solids, which justify the strong need for their complete understanding. To date, the major hurdle lies in a reliable description of the state of the confined fluid, which is usually given by measuring macroscopic observable, i.e. the amount of adsorbed gas.

Despite computational methods, in situ techniques combining gas physisorption with X-ray scattering methods showed in the last years to be valuable tools to get deeper insights into gas adsorption phenomena [1, 2]. Combining the different contrasts of SAXS and SANS and applying contrast matching [1], a more detailed, locally resolved description of the process could be given by the analysis of the scattering signals of the material pore structure. However, clear and comprehensive assessment of the adsorption process is still missing since the adsorbate evolution in the mesoporous host could be only indirectly investigated.

This presentation deals with the development of a novel in situ method based on the combination of anomalous small-angle X-ray scattering (ASAXS) and X-ray absorption near edge structure (XANES) spectroscopy to directly probe the evolution of the xenon adsorbate phase in mesoporous silicon during gas adsorption at its boiling point of 165 K [3]. The interface area and size evolution of the confined xenon phase alone were determined from ASAXS demonstrating that filling and emptying the pores follows two distinct mechanisms. The mass density of the confined xenon was found to decrease prior pore emptying. XANES analyses showed that Xe exists in two different species when confined in mesopores. This combination of methods provides a smart new tool for the study of nanoconfined matter for catalysis, battery electrodes, and for gas and energy storage applications.

The instrumental setup used allowed us to reach the Xenon L₃ X-ray absorption edge at 4.781 keV. The combination of that three experiments, ASAXS, XANES and physisorption were done in situ on different points of the adsorption and desorption branch of the isotherm. Thus, from the resonant scattering curves of xenon the mesoscopic evolution of the adsorbate (multilayer formation, capillary condensation and desorption) could be directly investigated.

[1] Mascotto, S., Wallacher, D., Brandt, A., Hauss, T., Thommes, M., Zickler, G. A., Funari, S. S., Timmann, A. & Smarsly, B. M. (2009). Langmuir 25, 12670−12681.

[2] Jähnert, S., Müter, D., Prass, J., Zickler, G. A., Paris, O. & Findenegg, G. H. (2009). J. Phys. Chem. C 113, 15201−15210.

[3] Gericke, E., Wallacher, D., Wendt, R., Greco, G., Krumrey, M., Raoux, S., Hoell, A. & Mascotto, S. (2021). J. Phys. Chem. Lett. 12, 4018−4023.

Mankind is now in the “age of gas”[1] and there are urgent needs in gas purification that will likely only be solved by a new generation of physisorbent porous materials that offer reduced cost and superior performance. Engaging the principles of crystal engineering, hybrid ultramicroporous materials, HUMs (pore size < 0.7 nm) [2], by means of combining small pores (< 0.7 nm) with strong electrostatics offer an ideal sorbent platform suited for tight-fit of the target sorbate, resulting in performance benchmarks over the recent years [3, 4]. However, due to narrow pore networks imposing steric restrictions, crystal engineering of modular HUMs on account of organic ligand functionalisation has remained largely elusive.

Moving one step ahead of the synergistic sorbent separation technology[5], herein we address single-step purification of ethylene (C₂H₄), the highest volume product of the chemical industry, by crystal engineering of two HUMs of formula [Ni(pyz-NH₂)₂(MF₆)]_n (pyz-NH₂ = aminopyrazine, 17; M = Si, Ti), MFSIX-17-Ni [6]. Isostructural pyrazine analogues (SIFSIX-3-Zn [7], SIFSIX-3-Ni [8]) are the benchmark physisorbents for trace carbon capture but are unsuited for acetylene capture. No single physisorbent has the requisite selectivity to purify C₂H₄ from ternary C₂-CO₂ mixtures (C₂H₄/C₂H₂/CO₂) under ambient conditions until now. Indeed, both MFSIX-17-Ni sorbents produce polymer grade ethylene (> 99.95% purity) from a 1:1:1 ternary mixture (Figure 1). Regarding insights for the future, we attribute the observed properties to the unusual binding sites in MFSIX-17-Ni that offer comparable affinity to both CO₂ and C₂H₂, thereby enabling coadsorption of C₂H₂ and CO₂. In situ synchrotron x-ray diffraction, in situ IR spectroscopy and molecular modelling provide insight into these binding sites and why they differ from those of the pyrazine-linked materials.

Metal-Organic frameworks (MOFs) and porous molecular materials represent a new platform for achieving and exploring high-performance sorptive properties and gas transport. The key lies in the modular nature of these materials, which allows for tuning and functionalization towards improved gas capture.

Self-assembly of polyfunctional molecules containing multiple charges, namely, tetrahedral tetra-sulfonate anions and bi-functional linear cations, resulted in a permanently porous crystalline material in which the channels are decorated by double helices of electrostatic charges that governed the association and transport of CO₂ molecules (Fig. 1). These channels electrostatically compliment the CO₂ molecules and forms strong interactions of 35 kJ mol⁻¹, ideal for CO₂ capture/release cycles.[1]

The CO₂ adsorption properties were modulated for an isoreticular series of Fe-MOFs by varying the decoration of fluorine atoms within their channel (Fig. 2). A host of complementary experimental and computational techniques gives a holistic view of the host-CO₂ properties towards the potential selective removal of CO₂ from other gases. GCMC and DFT were employed for a detailed description of the CO₂ diffusion and interactions in the porous materials. CO₂–matrix adsorption enthalpies of 33 kJ mol−1 was accurately measured in-situ by simultaneous acquisition of micro-calorimetric and volumetric-isotherm data. Direct measurements of adsorption heats are not common and such data helps to validate mathematical models and protocols for sorption-derived adsorption enthalpies. [2]

[1] Xing, G.; Bassanetti, I.; Bracco, S.; Negroni, M.; Bezuidenhout, C.; Ben, T.; Sozzani, P.; Comotti, A., Chemical Science 2019, 10 (3), 730-736.

[2] Perego, J.; Bezuidenhout, C. X.; Pedrini, A.; Bracco, S.; Negroni, M.; Comotti, A.; Sozzani, P., Journal of Materials Chemistry A 2020, 8 (22), 11406-11413.

Metal-Organic Frameworks (MOFs) are a class of synthetic porous crystalline materials based on metal ions connected through spacing ligands. They possess interesting properties such as high porosity [1], high concentration of metal centres and flexibility [2]. Additionally, MOFs can maintain their crystal structure upon removal, inclusion, exchange or reaction of a wide selection of guests, making them useful for multiple applications, e.g. in selective gas adsorption/separation. The synthesis of chemically and thermally stable MOFs, the comprehension of their properties and knowledge of their crystallographic features, are indispensable for the design and development of well performing materials. As MOFs’ properties are intrinsically related to their crystal structure, a deep understanding of the host-guest interactions during adsorption processes is a fundamental aspect [3].

Here, a high-resolution powder X-ray diffraction (HR-PXRD) crystallographic study of the host-guest interactions in Fe₂(BDP)₃ [H₂BDP = 1,4-bis(pyrazol-4-yl)benzene] upon CO₂ adsorption is presented. This MOF is characterised by a 3D network with 1D triangular channels. The peculiar shape of its channels and its good Brunauer-Emmett-Teller specific surface area (1230 m²/g) [4] prompted its investigation as CO₂ storage material, revealing an uptake capacity of 298.0 cm³/g at P_CO2 = 0.99 bar and T = 195 K.

At the ESRF ID22 beamline, HR-PXRD data were collected in situ and operando at T = 273 and 298 K while varying the CO₂ loading in the pressure range 0-8 bar. The obtained results will be presented after an in-depth data analysis, ranging from assessment of unit cell parameters variation to location of the primary adsorption sites and quantification of the adsorbed guest (Fig. 1). These results provide key information to better understand the CO₂-host interactions during the whole adsorption process, thus disclosing the chemical and structural features a MOF should possess to favour CO₂ uptake at mild conditions.

[1] I. M. Hönicke, I. Senkovska, V. Bon, I. A. Baburin, B. S. Raschke, J. D. Evans, S. Kaskel, Angew. Chem. 2018, 57, 42, 13780-13783 [2] A. Schneemann, V. Bon, I. Schwedler, I. Senkovska, S. Kaskel, R. A. Fischer, Chem. Soc. Rev. 2014, 43, 6062-6096; J. H. Lee, S. Jeoung, Y. G. Chung, H. R. Moon, Coord. Chem. Rev. 2019, 389, 15, 161-188 [3] C. Giacobbe, E. Lavigna, A. Maspero, S. Galli, J. Mater. Chem. A 2017, 5, 16964 [4] Z. R. Herm, B. M. Wiers, J. A. Mason, J. M. van Baten, M. R. Hudson, P. Zajdel, C. M. Brown, N. Masciocchi, R. Krishna, J. R. Long, Science 2013, 340, 960-964

Rational and creative design of organic and metal building blocks has successfully enabled the genesis of a variety of coordination polymers or metal-organic frameworks (MOFs) that are of fundamental scientific importance as well as provide a myriad of practical applications including gas storage and separation, catalysis, and sensing. One of the most attractive features in MOFs is flexibility because they show distinctive properties that cannot be achieved with rigid MOFs and other porous inorganic materials. In this talk, we will present strategies that exploit flexible MOFs for effectively separating hydrogen isotopes through the dynamic pore change of flexible MOFs. Especially, a unique isotope-responsive breathing transition of the flexible MOF was studied, which selectively recognize and respond to only D₂ molecules through a secondary breathing transition, monitored by in situ neutron diffraction experiments.

Biomacromolecules, such as enzymes, are ubiquitous in nature and essential for maintaining basic life activities. Apart from the fundamental biological functions, biomacromolecules are also of great values in industrial applications, especially in food and pharmaceutical production. However, their industrial applications are often handicapped by low operational stability, poor robustness, difficult recovery and reuse. Incorporation of biomolecules within protective exteriors has been proved to be an effective method to promote their stabilities and applications. As new classes of crystalline solid-state materials, porous frameworks materials (such as covalent-organic frameworks, COFs and metal-organic frameworks, MOFs) feature high surface area, tunable pore size, high stability, and easily tailored functionality, which entitle them as ideal supports for encapsulation of biomolecules to form novel composite materials for various applications. Moreover, the formed composites can combine the properties of both constitutes, where crystalline frameworks materials and biomolecules are indeed mutually beneficial. Our researches mainly focus on their biocatalysis, separation and medicinal applications. This novel crystalline platform composed of biomolecules-incorporation and framework materials exhibited various functionality and superior poteintials in biocatalysis, bioseparation, and biopharmaceutical formulations.

Supramolecular chemistry places focus on the weak non-covalent interactions between molecules in the solution or solid phases. These “soft” interactions are reversible and allow one to build materials which are responsive to their chemical or physical environment, changing form and properties under the influence of heat, light, pressure or chemical probes.

Dynamic materials, capable of responding to their environment, require flexibility which may be achieved using interactions such as hydrogen- or halogen-bonding or through the use of suitable metals and ligands in coordination compounds. Frameworks may be made up of relatively strongly bound entities such as those that make up metal-organic frameworks (MOFs) or may be more loosely bound such as host-guest systems where the host molecules crystallise as independent entities but leave spaces which can accommodate guest molecules. The process of guest exchange within porous solids can be used in a range of applications, such as selective absorption or separation of gases and heterogeneous catalysis. Among the more interesting examples of dynamic processes in frameworks are those which result in thermochromic and/or mechanochromic effects. Materials of this type are particularly of interest if they are able to revert to their original state on application of another external perturbation signal. Rational design of such systems remains a challenge however, and is thus an exciting area for application of crystal engineering principles.

In this presentation, examples from recent work in our laboratory will be presented, including MOFs and 3D hydrogen bonded frameworks constructed from the same flexible ditopic ligands. The influence of halogen versus hydrogen bonding on a molecular host-guest system will also be described. Frameworks exhibit thermochromic and mechanochromic properties, depending on the application of external stimuli such as heat, grinding or exposure to solvent vapours. Further examples will include the selective inclusion of halogenated volatile organic compounds in a porous metal-organic framework (Fig. 1).

The use of mechanical bonds for the synthesis of catenanes is a challenging process because of the many factors controlling the interpenetration process.[1,2] We report the kinetic control in the presence of various aromatic solvents of a poly-[n]-catenane (1). The polymeric structure is composed of interlocked M₁₂L₈ icosahedral nanometric cages with internal voids of ca. 2500 ų.[3] Using the symmetric exotridentate tris-pyridyl benzene (TPB) ligand and ZnCl₂ with appropriate templating solvent molecules due to the good ligand aromatic interactions are used, the metal-organic nanocages can be synthesized very fast, homogeneously, and in large amounts as microcrystals (Figure 1). Synchrotron single-crystal X-ray data (100 K) allowed the resolution of nitrobenzene guest molecules at the internal walls of the M₁₂L₈ cages, while in the centre of the nanocages the solvent is disordered and not observable by X-ray diffraction data. The guest release occurs in two steps with the disordered nitrobenzene released in the first step (lower temperatures) because of the lack of strong cage-guest interactions. Solid-state quantum mechanics provided a rationalization of the results, in particular, solid-state approaches, showed theoretical evidence of the kinetic nature in the formation of the polycatenation of the M₁₂L₈ nanocages by the analysis of the packing energy considering monomeric and dimeric cages.

Figure 1. Synthesis of the M₁₂L₈ interlocked nanocages forming the poly-[n]-catenane 1 under aromatic control.

[1] J. F. Stoddart (2009). Chem. Soc. Rev. 38, 1802-1820.

[2] Frank, M., Johnstone, M. D. & Clever, G. (2016). Chem.- Eur. J. 22, 14104-14125.

[3] Torresi, S., Famulari, A. & Martí-Rujas, J. (2020). J. Am. Chem. Soc. 142, 9537-9543.

The synthesis and conception of coordination polymers and supramolecular networks based on gold(I) complexes used as metallo-ligands (especially dicyanoaurate) is an established procedure to obtain materials with exciting properties: phosphorescence, non-linear optical behaviour, vapochromism and non-classical response to temperature and pressure [1-2]. However, the appearance of these solid-state properties is often connected to the manifestation of aurophilic interaction. The Au(I)‧‧‧Au(I) interaction, an attraction between closed shell d¹⁰ metal centres, is a relativistic effect that has a strength comparable to that of classical hydrogen bond [3]. Therefore, the study of new functional materials based on gold(I) properties must encourage the formation of these contacts in the crystal environment. We prepared, by a judicious choice of chelating ligands and balance in coordination equilibria [4], a series of 12 new coordination polymers or supramolecular networks based on dicyanoaurate anion and copper complexes presenting aurophilic interactions. The choice of copper as metal centre to connect to [Au(CN)₂]^- makes the synthesis particularly predictable due to the Jahn-Teller effect in the case of Cu(II), and the appearance of Cu(I) compounds due to redox effect of specific ligands will be commented. These compounds have been tested for vapochromism, and their behaviour in presence of ammonia has been interpreted with Raman, Ir and Uv-Vis absorption spectroscopy. On the same time, the response to temperature (T= 100-420 K) and pressure (P= 0.1-1.5 GPa) of {Cu(bipy)₂[Au(CN)₂]}[Au(CN)₂] (bipy =2,2’-bipyridine), a prototypical bimetallic aurophilic supramolecular network, has been investigated. Both the dependence of structural and reticular parameters to thermal and compression stimuli has been studied, and a phase transition at 1.2 GPa has been revealed. Moreover, we investigated the possibility to modulate the structural behaviour with the cocrystallization with other d¹⁰ metal tectons, and we demonstrate the possibility to obtain inclusion compounds with the presence of Hg(CN)₂ with a 3D weakly interacting framework still presenting Au‧‧‧Au contacts.

The supramolecular compound catena-{[Co(amp)₃][Cr(C₂O₄)₃]·6H₂O}(I) was synthetized as reported earlier [1,2]. To get insight into the structural modifications of its architecture within the water sorption processes (see Fig.1 (a)), in situ powder X-Ray Diffraction (PXRD) measurements were performed on a Bruker D8 Advance Diffractometer in a Bragg−Brentano geometry, using Cu(Kα₁) radiation. The humidity was controlled by exposing the sample to a nitrogen flow heated at 40°C and having humidity rates ranging from 0 to 90% relative humidity (r.H.) and then from 90 to 0% r.H. The PXRD carpet plot diagram ((see Fig.1 (b)) and the refinements of the PXRD patterns coupled with the single crystal diffraction results were used. During the adsorption and desorption processes, only two phases are involved, that of the dehydrated phase ([Co(amp)₃][Cr(C₂O₄)₃] (I’), P 2₁/n, a= 12.0542, b=16.0920, c = 13.8841, β = 99.8013) and the hydrated phase (I, P 2₁/n; a= 13.2330, b=18.2611, c = 14.1396, β = 100.5016). For the adsorption process, during the first step (from 0 to 30% r.H) corresponding to an adsorption of ∼ 1 mol H₂O / mol of I’, only phase I’ is involved and the volume of its unit cell does not change significantly. During the second step (from 30 to 35% r.H.) corresponding to an abrupt adsorption of ∼5.6 mol H₂O / mol of I’, both phases are involved with different percentages (deduced from Rietveld refinements) progressing to the complete conversion of I’ to I. During the third phase where the quantity of water adsorbed shows a plateau (from 35 to 90 % r.H.), only phase I is present and the volume of its unit cell does not change significantly with the humidity. For the desorption process, the same observations apply. During the first step (from 90 to 20 % r.H.) only I is present and its volume decreases just slightly. During the deep desorption process (from 20 to 14 % r.H.), both phases are involved with different percentages and during the last step (from 14 to 0% r.H) at the contrary to the adsorption process, both phases are still present while the sorption isotherm in this region looks like a type-I isotherm in the IUPAC classification [4]. These results suggest a quick capillary condensation followed by a pore filling process that produces a type-V isotherm profile [4], in relation with the first order structural transition followed by insignificant changes of the unit cell volume. The adsorption and desorption branches in the S- shaped isotherms of H₂O-vapor for this compound occur at the values of relative humidity at which these phase transitions start. The conversion of I to I’ and vis-versa is followed by the cleavage and formation of the hydrogen bonds in the architectures of these materials.

Propertios of halogen (X), chalcogen (E) and pnictogen (Pn) bonds can be modulated by changing (i) the nature of the X, E and Pn, (ii) the chemical environment of the X, E and Pn, and (iii) properties of the electron donor. Apart from small molecular complexes, this has been demonstrated in protein-ligand complexes, e.g. on a series of aldose reductase inhibitors. The counterintuitive ability of heteroboranes to form strong σ-hole interactions was found and attributed to the multicenter bonding. It breaks the classical electronegativity concept and results highly positive σ-holes on heterovetices that are incorporated into the skeleton via multicenter type of bonding. X, E and Pn elements in neutral heteroboranes can thus have highly positive σ-holes that are responsible for strong σ-hole interactions. The E···π, X···π, Pn···π and Pn···H-B types of σ-hole interactions of heteroboranes have been observed in the corresponding crystal packings. σ-Hole interactions can be used for designing protein-ligand interactions as well as for crystal engineering.

Materials which switch their optical spectroscopic properties (i.e., color, fluorescence) upon physical external stimulation (i.e., pressure, temperature) arouse much interest owing to their potential applications in fields as varied as sensing, construction, recording, display technologies or rewritable paper [1]. In the quest for new organic stimuli responsive materials, the 2,1,3-benzothiadiazole moiety (BTD) have emerged as a promising building block, since the absorption and emission properties of this moiety is strongly influenced by its external environment. In the last few years several BTD-based chromogenic and fluorogenic materials have been reported, but although there are some recent exceptions, in most examples crystalline-to-amorphous transitions are in the origin of this behaviour. This fact prevents an in-depth study of the mechanism behind this process and limits the rational development of new chromophores with predesigned properties.

Herein we present a variety of BTD-derivatives, which crystallizes in different polymorphs with layer-like organization, exhibit distinct light emitting properties under UV illumination and can be readily interconverted by means of external stimuli [2, 3]. Through a joined crystallographic, spectroscopical and theoretical approach we have been able to unravel the origin of the polymorphic transformation and fluorogenic behavior.

In this communication we will discuss interesting design principles, to obtain novel BTD stimuli-responsive organic materials that we have been able to establish as a result of this study. A special emphasis will be placed on the role of “2S–2N” square synthon [4] in the supramolecular arrangement and switchable light emission properties of BTD derivatives.

[1] Roy, B.; Reddy, M. C.; Hazra, P. (2018) Chem. Sci. 9, 3592 [2] Echeverri, M.; Ruiz, C.; Gámez-Valenzuela, S.; Martín, I.; Delgado, M. C. R.; Gutiérrez-Puebla, E.; Monge, M. Á.; Aguirre-Díaz, L. M. & Gómez-Lor, B. (2020) J. Am. Chem. Soc. 142, 17147. [3] Echeverri, M.; Ruiz, C.; Gámez-Valenzuela, S.; Alonso-Navarro, M.; Gutierrez-Puebla, E.; Serrano, J. L.; Ruiz Delgado, M. C. & Gómez-Lor, B. (2020) ACS Appl. Mater. Interfaces 12, 10929. [4] Ams, M. R.; Trapp, N.; Schwab, A.; Milić, J. V.; Diederich, F. (2019) Chem. A Eur. J 25, 323.

In the pharmaceutical area, the screening of multicomponent forms of a drug is a well-known strategy to assess new crystalline forms with improved physicochemical properties, such as solubility, dissolution, absorption, and others [1-3]. Among the possible multicomponent forms, co-crystals, salts, and solvates are obtained from the inclusion of other suitable molecules (co-formers) within the target molecule‘s crystalline structure. The process to obtain multicomponent crystalline forms of a drug could be an expensive and long-term process, since there is an infinity of possible co-former molecules, in addition to the large number of crystallization techniques that can be used [4]. Thus, it is necessary a strategy to help in the screening of new multicomponent forms of a target molecule through the rationalization of co-former selection, associated with lower consumption of materials and other costs, such as the final disposal of toxic waste. Aiming this, it is proposed a new methodology to optimize and to rationalize the co-former selection using knowledge-based supramolecular chemistry [5]. This new methodology aims to predict the formation of a multicomponent form through the evaluation of the molecular complementarity and the possible intermolecular interactions between the target molecule and the co-former through the use of three statistical tools developed by the Cambridge Crystallographic Data Centre (CCDC) [6]. The SFIMP (Statistical Analysis of Frequency of Interaction for Multicomponent Prediction) method [7] was developed based on the optimization of three CCDC tools – Molecular Complementarity (MC), Coordination Value likelihood calculation (CV), and H-Bond Propensity (HBP) [4, 8-10] – to perform a multicomponent analysis and to allow the combination of their results to obtain a single multicomponent score. Nevirapine (NVP), an antiretroviral drug that exhibits low-aqueous solubility, was used as the target molecule in this study. A bunch of 470 possible co-former molecules was evaluated and the multicomponent score obtained for each one was used to rank these molecules according to the possibility of forming a NVP multicomponent. The SFIMP method was validated through an experimental screening of new multicomponent forms of NVP. The results obtained from the prediction were used in the experimental screening and it enabled the obtention of four new co-crystals of NVP with benzoic acid, 3-hydroxybenzoic acid, 4-hydroxybenzoic acid, and 2,5-dihydroxybenzoic acid [5, 11]. The crystalline structures of these new co-crystals were characterized through single-crystal and powder X-ray diffraction, and differential scanning calorimetry. The SFIMP method shows improvements compared to what is currently available in the CSD system for the analysis and prediction of multicomponent forms. Besides, the results show this methodology as a promising strategy to evaluate the possibility of multicomponent formation in new systems.

The distribution of the electron density at the outer regions of bonded atoms is anisotropic. This feature was first proposed for explaining the noncovalent interactions formed by bonded atoms early nineteen nineties [1] and now it is successfully used for rationalizing interactions of elements of all groups of the p block of the periodic table [2]. This mindset began to be extended to d block elements four years ago, being first applied to elements of group 11, then to elements of groups 10 and 12 [3]. For instance, some theoretical studies and experimental results have shown that gold can behave as an effective acceptor of electron density in some of its derivatives, e.g., attractive interactions, named coinage bond (CiB) [3], can be formed between donors of electron density and regions of most positive electrostatic potential at the outer surface of gold nanoparticles and halides.

In this communication we describe that gold can function as acceptor of electron density not only in neutral species, as mentioned above, but also in negatively charged species. It will be proven that the Au(III)∙∙∙nucleophile supramolecular synthon is quite robust and effectively controls the packing of ionic crystals. This synthon may complement the opportunities offered by the aurophilic interactions which are now dominating the interactional landscape of gold. Specifically, we report single crystal structures wherein AuCl₄ˉ anions act as self-complementary tectons, chlorine and gold atoms functioning as donors and acceptors of electron density, respectively. Au and Cl atoms of different units form short Au∙∙∙Cl contacts and construct supramolecular anionic polymers (Figure) wherein gold forms a second CiB with a lone pair possessing atom (the oxygen of an ester group). The electrophilic role of gold and the attractive nature of Au∙∙∙Cl/O interactions will be proven by some modelling. A survey of the Cambridge Structural Database (CSD) will be reported suggesting that this behaviour is quite general. Indeed, a non-minor fraction of CSD structures containing the AuCl₄ˉ anion show the presence of the Au∙∙∙nucleophile supramolecular synthon and the same holds for structures containing the AuBr₄ˉ and Au(CN)₄ˉ anions.

Crystal engineering requires precise insight into intermolecular interactions, which results in the crystal symmetry enabling the emergence of desired physical properties [1, 2]. Such a process is based on structural and thermodynamic information, and should also consider the possibility of polymorphism or phase transitions of engineered crystals [3, 4]. Therefore, the controlled synthesis and development of new multifunctional materials and pharmaceuticals should involve the understanding of the dynamics of their interaction networks. One of the most important and abundant intermolecular interactions in crystalline systems are the hydrogen bonds. Several classifications are available for H-bond description, which are based on geometrical parameters, spectroscopic features and charge density calculations. The analysis of different molecular arrangements formed via H-bonds is crucial to understand the stability of crystal phases and the origins of their physical properties [3-5].

In this investigation, the dynamics of complicated H-bond systems in selected crystals were studied using Born-Oppenheimer molecular dynamics (BOMD) simulations. Ab initio molecular dynamics computations provide on the flight evaluation of atomic force evolution using first-principles DFT calculations at every time step. BOMD simulations enable the characterization of solid-state phase dynamics in several statistical ensembles. The insight into crystal entropy and energy is given by the appropriate ensemble averages. The canonical ensemble (NVT) gives the possibility to study the temperature influence on the molecular motion, elastic properties as well as spectroscopic features. In addition, BOMD features allow considering the influence of anharmonicity and quantum effects at the vibrational spectra of examined materials.

In our computations, different cluster sizes were used for investigated H-bonded systems. The system dynamics were studied at different temperatures mainly in the NVT ensemble. Time and space correlations between molecular motions were analysed through the detailed study of interaction network changes along the obtained trajectories. The power spectra were used to investigate the spectroscopic features and the dynamics of considered H-bond systems. Additionally, the structural analysis based on X-ray diffraction experiments was performed, including H-bond propensities and coordination scores. These methods were used to assess the likelihood of specific H-bond formation, and the efficiency of entire H-bond systems according to donor and acceptor expected saturation.

[1] Tiekink, E. R. T., Vittal, J., Zaworotko, M., Ed. (2010). Organic Crystal Engineering: Frontiers in Crystal Engineering. Chichester: John Wiley & Sons, Ltd.
[2] Nangia, A. K. & Desiraju, G. R., (2019). Angew. Chem. Int. Ed. 58, 4100.
[3] Bernstein, J., Davey, R. J. & Henck, J.-O., (1999). Angew. Chem. Int. Ed. 38, 3440.
[4] Price, S. L., (2013). Acta Crystallogr. B69, 313.
[5] Aakeröy, C. B., Forbes, S. & Desper, J., (2014). CrystEngComm. 16, 5870.

Presented computations were performed using PL-Grid Infrastructure and resources provided by ACC Cyfronet AGH. The research was supported by the Polish National Science Centre, project PRELUDIUM 15 number 2018/29/N/ST3/00703 “Study of dynamics in the interaction networks of selected co-crystals”.

There has been a growing interest in mechanically responsive molecular crystals that show reversible and unusually large positive and negative thermal expansion triggered by external stimuli, a property which could be applied to the design of actuators for soft robotics, artificial muscles, and microfluidic and electrical devices [1]. However, controlling molecular motion to execute sufficiently larger and practically useful thermal expansion in crystals remains a formidable challenge, and strong deformation of such crystals usually results in their destruction [2]. Here we report a single crystal of simple organic compound which exhibits giant thermal expansion due to collective reorientation of molecules in the crystal lattice which is reversible after more than fifty heating and cooling cycles. Such atypical molecular motion, revealed by single crystal X-ray diffraction and microscopy analyses, drives an exceptionally large expansion of the crystal. The applicability of the material as an actuator with electrical properties is demonstrated by dielectric, capacitance, conductance and current measurements. The large shape change of the crystal, combined with remarkable durability and electrical properties, suggest that this material is a strong candidate for microscopic multifunctional thermal actuating devices.

The material a-RuCl₃ has been the subject of intense study for the past few years owing to the expectation that it exhibits competing uniaxial exchange interactions characteristic of what are now termed Kitaev materials [1]. coordinated Ru³⁺ ions form a honeycomb lattice with layers weakly bonded via van der Waals interactions. The ease of formation of stacking faults and domains has made a definitive determination of the low temperature crystallographic space group difficult since many possible arrangements of the layers are energetically similar. In the absence of a magnetic field single crystals with few stacking faults show a phase transition near a Neel temperature T_N = 7 K to an antiferromagnetic structure that has zigzag order in a single plane and a 3-fold out of plane periodicity [2,3]. The introduction of stacking faults results in a structure with a 2-layer periodicity with T_N = 14 K [2,3]. The phase diagram in the presence of external in-plane magnetic field perpendicular to a Ru-Ru bond has not been fully resolved, but some features are clear, including a transition to an ordered state with a different layered periodicity near 6 Tesla and the complete suppression of zigzag order above roughly 7.5 Tesla [4,5,6]. Substitution of non-magnetic Ir4+ for Ru3+ also suppresses the zigzag order [7].This talk discusses these results in the context of measurements of the magnetic excitations, and the possible presence of a quantized thermal Hall effect and other interesting phenomena.

[1] Takagi, H., Takayama, T., Jackeli, G., Khaliullin G., & Nagler,S.E. (2019). Nature Reviews Physics 1, 264. [2] Banerjee, A. et al. (2016), Nature Materials 15, 733.

[3] Cao, H.B. A. et al. (2016), Physical Review B 93, 134423.

[4] Banerjee, A. et al. (2018), NPJ Quantum Materials 3, 8.

[5] Balz, C. et al. (2019), Physical Review B 100, 060405(R).

[6] Balz, C. et al. (2021), Physical Review B 103, 174417.

[7] Lampen-Kelly P. et al. (2017), Physical Review Letters 119, 237203.

The research discussed here used resources at the High Flux Isotope Reactor and Spallation Neutron Source, DOE Office of Science User Facilities operated by the Oak Ridge National Laboratory.

A central line of inquiry in condensed matter science has been to understand how the competition between different states of matter give rise to emergent physical properties. Perhaps some of the most studied systems in this respect are the hole-doped LaMnO3 perovskites, with interest in the past three decades being stimulated on account of their colossal magnetoresistance (CMR). However, phase segregation between ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating states, which itself is believed to be responsible for the colossal change in resistance under applied magnetic field, has until now prevented a full atomistic level understanding of the orbital ordered (OO) state at the optimally doped level. Here, through the detailed crystallographic analysis of the hole-doped phase diagram of a prototype system, we show that the superposition of two distinct lattice modes gives rise to a striped structure of OO Jahn-Teller active Mn3+ and charge disordered (CD) Mn3.5+ layers in a 1:3 ratio. This superposition leads to a cancellation of the Jahn-Teller-like oxygen atom displacements in the CD layers only at the 3/8th doping level, coincident with the maximum CMR response of the manganties. Furthermore, the periodic striping of layers containing Mn3.5+, separated by layers of fully ordered Mn3+, provides a natural mechanism though which long range OO can melt, a prerequisite for the emergence of the FM conducting state. The competition between insulating and conducting states is seen to be a key feature in understanding the properties in highly correlated electron systems, many of which, such as the CMR and high temperature superconductivity, only emerge at or near specific doping values.

Orbital molecules are clusters of transition metal cations formed by orbital- and charge-ordering in systems with direct d-d interactions [1]. Vanadium oxides exhibit a particularly rich variety of orbital molecule states, notably the V-V dimerisation that accompanies the metal-insulator transition in VO₂ [2]. In vanadium oxide spinels such as AlV₂O₄ and GaV₂O₄ the 3D connectivity of V-V nearest neighbours allows larger orbital molecules to form, and these also persist into a hidden high-temperature disordered state [3].

Not all AV₂O₄ spinels have orbital molecule ground states, but as the formation of V-V bonds is associated with marked lattice distortions we have employed synchrotron X-ray powder diffraction and pair-distribution function analysis to determine the structural and electronic requirements for V-V bonding to be stabilised. Studying the Zn_xGa_1−xV₂O₄ family of materials revealed that, whilst the long-range order of orbital molecules in the ground state of GaV₂O₄ is highly sensitive to A-site substitution, local V-V bonding interactions are stable to x > 0.75 before the ground state of ZnV₂O₄, which is orbitally ordered but without V-V bonding, emerges [4]. Furthermore, we have found a monoclinic distortion coincident with the reported pressure-driven metal-insulator transition in LiV₂O₄ that suggests it to be the result of orbital-molecule formation [5]. Overall, we have determined that the formation and ordering of orbital molecules bonds in AV₂O₄ spinels is principally dependent on the V-V nearest-neighbour distance.

[1] Attfield, J. P. (2015). APL Mater. 3, 041510.

[2] Goodenough, J. B. (1971). J. Solid State Chem. 3, 490.

[3] Browne, A. J., Kimber, S. A. J. & Attfield, J. P. (2017). Phys. Rev. Mater. 1, 052003(R).

[4] Browne, A. J. & Attfield, J. P. (2020). Phys. Rev. B 101, 024112.

[5] Browne, A. J., Pace, E. J., Garbarino, G. & Attfield, J. P. (2020). Phys. Rev. Mater. 4, 015002.

Perovskites are one of the most prevalent classes of functional materials and are already known to exhibit a wide range of properties, including ferroelectricity, superconductivity and magnetism amongst others [1]. Many traditional perovskites have poor toxicity and sustainability; however, the inclusion of organic components could help alleviate these issues and provide greater structural diversity. Several examples of hybrid perovskites with interesting properties have already been reported with the inclusion of complex anions such as cyanides, formates and azides on the X site of the perovskite [2]. Whilst the oxalate ligand has already been extensively used in coordination polymers, its use in perovskite materials has only recently been reported in the compound KLi₃Fe(C₂O₄)₃ [3], the compound exhibits simultaneous 1:3 ordering on both the A and B sites of the perovskite (Figure 1). In order to gain a more detailed understanding of this structure type, a series of compounds with the general formula A^ILi₃M^II(C₂O₄)₃ where A = K⁺, Rb⁺, Cs⁺ and M = Fe²⁺, Co²⁺, Ni²⁺ have been synthesised and characterised [4].

Figure 1. Comparison of hypothetical cubic perovskite with 1:3 cation ordering at the A and B site (left) and the corresponding crystal structure of the perovzalates (right). Li octahedra blue, M octahedra brown and A cation purple.

1 J. P. Attfield, P. Lightfoot and R. E. Morris, Dalt. Trans., 2015, 44, 10541–10542.

2 G. Kieslich and A. L. Goodwin, Mater. Horizons, 2017, 4, 362–366.

3 W. Yao, Y. Guo and P. Lightfoot, Dalt. Trans., 2017, 46, 13349–13351.

4 R. Clulow, A. J. Bradford, S. L. Lee and P. Lightfoot, Dalt. Trans., 2019, 48, 14461–14466.

Keywords: Perovskite; Hybrid materials; Coordination polymers

We would like to thank the EPSRC for a doctoral studentship to R. Clulow (DTG012 EP/K503162-) and the University of St Andrews for a doctoral studentship to A. J. Bradford

The Aurivillius materials are well known for their ferroelectric properties[1] and associated structural distortions.[2] They form a class of layered perovskite-related phases with general formula Bi₂A_n-1B_nX_3n+3 (X is usually oxide, but halides are also known), with structures built up from alternating fluorite-like [Bi₂O₂]²⁺ layers and [A_n‑1B_nX_3n+1]^2- perovskite-like layers. The search for magnetoelectrics, with coupled magnetic and ferroelectric order, has motivated investigations to introduce magnetic ions into the B cation sites. However, this has been challenging and the concentrations of magnetic B cations in Aurivillius oxides is typically low.[3-5] Redirecting research away from oxides and towards mixed-anion systems, including Aurivillius oxyfluorides, opens up a wider compositional range, as well as the possibility of tuning structure and properties by anion order.[6, 7]

This presentation describes work on n = 1 Aurivillius oxyfluorides including Bi₂TiO₄F₂ and Bi₂CoO₂F₄. Our symmetry analysis[8] of possible anion-ordered structures highlights the challenges of packing polar heteroanionic units to break inversion symmetry, as well as means by which this might be achieved for Bi₂TiO₄F₂. We also explore methods to determine anion ordering in materials with anions with similar scattering lengths.[9]

Increasing the fluoride content in these oxyfluorides gives access to phases with lower oxidation states for B cations, and the report of Bi₂CoO₂F₄, with long-range magnetic order of the Co²⁺ sublattice,[10] motivated our investigation using neutron powder diffraction. We’ve explored its nuclear structure and in particular, the anion sublattice and structural distortions, and determined its magnetic structure.[11] This gives insight into its physical properties and opens the door to designing and preparing new multiferroics.

[1] de Araujo, C. A. P.; Cuchiaro, J. D.; McMillan, L. D.; Scott, M. C.; Scott, J. F., (1995), Nature 374, 627-629.

[2] Guo, Y. Y.; Gibbs, A. S.; Perez-Mato, J. M.; Lightfoot, P., (2019), Iucrj 6, 438-446.

[3] Keeney, L.; Downing, C.; Schmidt, M.; Pemble, M. E.; Nicolosi, V.; Whatmore, R. W., (2017), Scientific Reports 7.

[4] Giddings, A. T.; Stennett, M. C.; Reid, D. P.; McCabe, E. E.; Greaves, C.; Hyatt, N. C., (2011), Journal of Solid State Chemistry 184, 252-263.

[5] McCabe, E. E.; Greaves, C., (2005), Journal of Materials Chemistry 15, 177-182.

[6] Charles, N.; Saballos, R. J.; Rondinelli, J. M., (2018), Chemistry of Materials 30, 3528-3537.

[7] Kageyama, H.; Hayashi, K.; Maeda, K.; Attfield, J. P.; Hiroi, Z.; Rondinelli, J. M.; Poeppelmeier, K. R., (2018), Nature Communications 9.

[8] Campbell, B. J.; Stokes, H. T.; Tanner, D. E.; Hatch, D. M., (2006), J. Appl. Cryst. 39, 607-614.

[9] Giddings, A. T.; Scott, E. A. S.; Stennett, M. C.; Apperley, D. C.; Greaves, C.; Hyatt, N. C.; McCabe, E. E., (2021), in preparation.

[10] Vagourdi, E. M.; Mullner, S.; Lemmens, P.; Kremer, R. K.; Johnsson, M., (2018), Inorganic Chemistry 57, 9115-9121.

[11] Scott, E. A. S.; Vagourdi, E. M.; Johnsson, M.; John, F.; Cascos, V. A.; Pickup, D. M.; Chadwick, A. V.; Zhang, W.; Halasyamani, P. S.; McCabe, E. E., (2021), in preparation.

Heusler alloys close to stoichiometric Ni₂MnGa undergo a sequence of diffusionless, displacive phase transformations from parent cubic austenite to various martensitic or ferroelastic phases, modulated 10M and 14M (also marked 5M and 10M) and non-modulated (NM) tetragonal phase depending on composition. Often the cascade of intermartensitic transformations (10M-14M-NM) is observed with decreasing temperature or with increasing mechanical stress [1]. Owing to the ferromagnetic state and highly mobile twin boundaries in modulated phases, the relatively weak magnetic field can induce the reorientation of ferroelastic domains via twin boundary motion [2]. This results in giant magnetic-field-induced strain up to 12% in single crystal [3] called magnetic shape memory (MSM) effect. Although the martensitic transformation is relatively well understood, the nature of intermartensitic transformation (IMT) is still disputed. One reason is that even the character of modulated phases is not settled [4-6]. Understanding the IMT can provide some clue to the character of modulated phases and has also practical impact as the IMT limits the operational range of the MSM effect. Although many diffraction studies were performed on polycrystalline samples only little neutron research has been done on single-crystals. Regarding the complex nature of the modulated phases and continuing discussion about their character (nanotwinning v. harmonic modulation) [4-6], only single crystalline studies represent the proper way in attempt to understand the 10M-14M intermartensitic transformation. The neutron diffraction as bulk method is particularly suitable for direct comparison with magnetic [7] and transport measurements [6].

Here we present study of 10M-14M transformation by neutron diffraction using the D9 and D10 single-crystal four-circle diffractometers and CYCLOPS (neutron Laue single-crystal diffractometer) in ILL Grenoble. The Laue method allowed continuous tracing of the transition and broader survey of the reciprocal space with temperature, revealing any changes in crystal orientation and newly occurring twinning in transformed phase. Additional laboratory X-ray diffraction using rotating anode diffractometer provide further insight and better precision. The q-scans measured at different temperatures across the transition revealed the details of the modulation, pointing to its nanotwinning character. Fine features in the q-scans suggested the traces of 10M within 14M phase in the temperature well below the IMT. The structural changes indicated by the diffraction were related to the changes of magnetic properties. In presentation, we will also look on preference of the 14M phase in epitaxial thin films compared to bulk single crystals.

[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 research field of magnetic frustration is dominated by triangle based lattices but exotic phenomena can also be observed in pentagonal networks. The Fe³⁺ ions in Bi₂Fe₄O₉ materialize the first analogue of a magnetic pentagonal lattice [1]. The unit cell contains two different sites of four iron atoms each, which have different connectivities with the other irons (three or four neighbours for Fe₁ and Fe₂ respectively), and that form a lattice of pentagons. Because of its odd number of bonds per elemental brick, this lattice is prone to geometric frustration. The compound magnetically orders around 240 K: the resulting spin configuration on the two sites is the same, i.e. two orthogonal pairs of antiferromagnetic spins in a plane, with a global rotation between the two sites Fe₁ and Fe_2. This peculiar magnetic structure, which is the result of the complex connectivity and magnetic frustration, has opened new perspectives in the field of magnetic frustration.

In this original compound, we have measured the spin wave excitations in the magnetically ordered state by inelastic neutron scattering. The measurements have revealed an unconventional excited state related to local precession of pairs of spins. The confrontation of the experimental results with spinwave calculations allowed to determine the Hamiltonian of the system and shows a hierarchy of the interactions. This leads to a paramagnetic state constituted of strongly coupled antiferromagnetic pairs of spins (materializing isolated dimers) separated by much less correlated spins. This produces two types of response to an applied magnetic field associated with the two nonequivalent Fe sites, as observed in the magnetization density distributions obtained using polarized neutrons.

[1] E. Ressouche, V. Simonet, B. Canals, M. Gospodinov, V. Skumryev, Phys. Rev. Lett. 103, 267204 (2009)

Crystal electric fields play an essential role in shaping the local electronic density of ions. For ions with strong spin-orbit coupling such as rare earths, this also results in defining the single-ion magnetic moment properties. Therefore, the study of crystal electric field levels is a common approach to establish the fundamental building blocks of the magnetic Hamiltonian. Indeed, the moment anisotropy and the single-ion wavefunction provide crucial information to describe complex magnetic materials such as spin liquids and multipolar systems [1,2]. In the first part of my presentation, I will illustrate this approach on the frustrated magnet SrDy₂O₄. This material exhibits two inequivalent zigzag chains of magnetic ions. The combination of low dimensionality and frustration inhibits long range order and only short range magnetic correlations are observed down to 60 mK [3]. Domain walls in the chains decay slowly and interchain interactions ultimately lead to their freezing, leading to a weakly fluctuating short range order [4]. The understanding of this complex behaviour could only be achieved from the knowledge of the moment anisotropies, established from the analysis of crystal field electric levels.

Above, we took advantage of strong spin-orbit coupling to determine magnetic properties by studying electric ones, i.e. the effect of crystal electric fields. This strong coupling between the electric charge and magnetic moment can also be used in the other direction: using magnetism to learn more about electric effects beyond the single-ion properties. As spin waves are collective excitations of the magnetic moments, the local charge densities can also sustain collective modes. Taking again the magnetic insulator SrDy₂O₄ as an example, I will demonstrate that neutron spectroscopy can measure these electric waves and that this observation is facilitated by the material’s magnetism. Interestingly, our results indicate that electric interactions dominate the magnetic interactions in this case, although they remain hidden to most measurement techniques. This observation encourages a reassessment of the description of rare-earth based magnets with unconventional properties.

[1] P. Santini, S. Carretta, G. Amoretti, R. Caciuffo, N. Magnani, G. H. Lander, Rev. Mod. Phys. 81, 807 (2009).

[2] R. Sibille, N. Gauthier, E. Lhotel, V. Porée, V. Pomjakushin, R. A. Ewings, T. G. Perring, J. Ollivier, A. Wildes, C. Ritter, T. C. Hansen, D. A. Keen, G. J. Nilsen, L. Keller, S. Petit & T. Fennell, Nat. Phys. 16, 546 (2020).

[3] A. Fennell, V. Y. Pomjakushin, A. Uldry, B. Delley, B. Prévost, A. Désilets-Benoit, A. D. Bianchi, R. I. Bewley, B. R. Hansen, T. Klimczuk, R. J. Cava & M. Kenzelmann, Phys. Rev. B 89, 224511 (2014).

[4] N. Gauthier, A. Fennell, B. Prévost, A.-C. Uldry, B. Delley, R. Sibille, A. Désilets-Benoit, H. A. Dabkowska, G. J. Nilsen, L.-P. Regnault, J. S. White, C. Niedermayer, V. Pomjakushin, A. D. Bianchi & M. Kenzelmann, Phys. Rev. B 95, 134430 (2017).

Two-dimensional (2D) materials are of intense current fundamental and applied interest as a route to create novel fundamental phenomena beyond well-established classical behaviour within their topologically constrained layers. In this context 2D monolayer graphene, formed from the isolation of weakly connected van der Waals (vdW) bonded 2D layers in graphite by exfoliation, ignited widespread interest. Exotic quantum relativistic phenomena, such as Dirac semi-metals and quantum anomalous Hall insulators, have been predicted in graphene and related materials ranging from isolated 2D monolayers to quasi-2D bulk materials with vdW bonded layers. The focus has expanded to “beyond graphene” 2D vdW layered materials with intrinsic properties such as magnetism and semiconductivity not present in graphene, however the number of materials is limited and detailed understanding only just beginning.

MnPSe₃ and CrPS₄ are such layered vdW materials that are both magnetic and semiconducting, with magnetic ions forming hexagonal and rectangular 2D motifs. To access their low dimensional behaviour we probe bulk powder and single crystal samples with neutron scattering measurements [1,2]. Through magnetic symmetry analysis and spin wave analysis we are able to isolate and explore the 2D structural and magnetic behaviour in these bulk materials. Interactions shown in Fig. 1. The data highlights subtle competing interactions in both materials that leads to the stabilization of the determined magnetic ground states. These magnetic ground states were further tuned with small applied perturbations of field and temperature and found to undergo both subtle spin alterations and more dramatic metamagnetic transitions. The determination of the intralayer and interlayer exchange interactions and anisotropy within model spin Hamiltonians allowed the underlying observed exotic bulk behaviour to be explored.

The results show that for MnPSe₃ the Se ion drives unexpectedly strong magnetic interactions between the 2D layers, which forms a contrast to the wider studies S analogue MnPS₃. While for CrPS₄ a further lowering of interaction dimensionality to 1D-chains is shown to be of significance. Collectively, these results highlight the subtle role of the crystalline structure on the emergent behaviour and show the powerful insights neutron scattering can supply to studies of low dimensional materials.

[1] S. Calder, A. Haglund, Y. Liu, D. M. Pajerowski, H. B. Cao, T. J. Williams, O. V. Garlea, D. Mandrus, “Magnetic structure and exchange interactions in the layered semiconductor CrPS₄”, Physical Review B, Phys. Rev. B 102, 024408 (2020).

[2] S. Calder, A. Haglund, A. I. Kolesnikov, D. Mandrus, “Magnetic exchange interactions in the van der Waals layered antiferromagnet MnPSe₃”, Physical Review B 103, 024414 (2021).

In the dense metal-organic framework Na[Mn(HCOO)₃], Mn²⁺ ions (S = 5/2) occupy the nodes of a ‘trillium’ net. We show that this material exhibits a variety of behaviour characteristic of geometric frustration: the Néel transition is suppressed well below the characteristic magnetic interaction strength; neutron scattering indicates that short-range magnetic order persists far above the Néel temperature; and the magnetic susceptibility exhibits a pseudo-plateau at 1/3-saturation magnetisation. We demonstrate that a simple nearest-neighbour Heisenberg antiferromagnet model accounts quantitatively for each observation, and hence Na[Mn(HCOO)₃] is the first experimental realisation of this model on the trillium net. We demonstrate how both link geometric frustration within the classical spin liquid regime to a strong magnetocaloric response at low fields.

The transverse-field Ising model on a triangular lattice is predicted to support a topological Kosterlitz-Thouless (KT) phase at nonzero temperature through a mapping of the Ising spins to a complex order parameter defined for each triangular unit. Recently, the triangular lattice antiferromagnet TmMgGaO₄ has emerged as a candidate material to realize this theoretical scenario. Through the complementary use of neutron diffraction and magnetic pair distribution function (mPDF), we have quantitatively investigated the spin correlations in TmMgGaO₄ in the temperature region of interest, tracking their evolution across the proposed transitions into and out of the KT phase. We confirm the presence of the three-sublattice order predicted for the ground state and show that the local magnetic structure undergoes distinct changes in the temperature range expected for the KT phase. Modeling the real-space mPDF reveals a preferential tendency for the system to form bound vortex-antivortex pairs, the hallmark of the KT phase, precisely in the expected temperature range. These findings constitute promising evidence for the KT phase, potentially establishing TmMgGaO₄ as a rare platform for studying KT physics in a dense spin system.

Geometrically frustrated magnets, such as triangular networks of antiferromagnetically coupled spins, can display incredibly rich physical properties that may have potential applications in quantum information science and other technologies. Determining if and how magnetic order emerges from competing magnetic tendencies is an important objective in this field. Here, we discuss the Jahn-Teller active triangular AMnO₂ (A= Na, Cu; Fig. 1) antiferromagnets [1] to highlight that the degree of frustration, mediated by residual disorder, contributes to the rather differing pathways towards a single, stable magnetic ground state, albeit with varying ordering temperatures. For these insulating sister compounds, complementary high-resolution synchrotron XRD, local-probe muon-spin relaxation (μ⁺SR) studies, corroborate that the layered NaMnO₂ adopts a remarkable magnetostructurally inhomogeneous ground state. [2] In view of this peculiarity, we employ powerful neutron total scattering and magnetic pair distribution function (PDF) analysis to uncover that although CuMnO₂ undergoes a conventional symmetry-lowering lattice distortion driven by Néel order, in the Na-derivative a short-range triclinic distortion (Fig. 2) lifts the degeneracy of the isosceles triangular network on the nanoscale, thereby enabling long-range magnetism to develop with enhanced magnetic correlations above the transition. [3] More generally, the work illuminates the cooperative intertwining of the local atomic and magnetic structures that permits ground state selection when spatial inhomogeneity meets geometrical frustration, a mechanism that may also be operative in other frustrated materials with electronically active transition metal cations.

[1] M. Giot et al., Phys. Rev. Lett. 99, 247211 (2007).

[2] A. Zorko et al., Sci. Rep. 5, 9272 (2015).

[3] B. A. Frandsen et al., Phys. Rev. B 101, 024423 (2020).

The use of UV-visible light responsive catalysts in hydrogen production is of high interest owing to reduced energy and environment resources. Here, we present a highly efficient system for photocatalytic hydrogen production, comprising ordered silicate nanochannels embedded with novel visible-light-responsive catalytic phosphotungstic acids (PTA) along the silicate channel walls and arrayed co-catalytic platinum nanoparticles within the channels. The UV-visible-light-responsive PTA catalyst is synthesized by replacing a corner WO⁴⁺ of PTA with Ni for Ni-ℓPTA, and then embedded onto the walls of hexagonally packed silicate channels during synthesis at an air-liquid interface. In situ grazing incidence small-angle X-ray scattering on the air-liquid interface [1-2] evidences multi-step formation processes of the ordered and oriented silicatropic template PMS and the subsequent formation of Pt NP arrays in the PMS template. Suggested by the X-ray results, the latter process involves anion exchange of the Pt-metal precursors and the surfactant micelles of the silicate PMS channels, upon UV-visible light irradiation. The hence formed composite Pt-NP@Ni-ℓPMS, with closely packed catalytic pairs of Pt-NP and PTA, demonstrates a high hydrogen production rate upon light illumination, due presumably to efficient generation and transport of photo-electrons. The efficiency of H₂-production surpasses greatly that of PMS or Ni-ℓPMS with or without randomly disperse Pt nanoparticles.

Controlling the mesoscopic nature of materials through local interactions can lead to the formation of highly non-topologically trivial structures. The local interactions that lead to the emergence of mesoscopic structures, known as textures, is well understood in magnetic materials. The most studied textures are skyrmions as the have interesting applications in spintronics due to their topological nature and dynamic properties [1]. These features are thought to be exclusively a magnetic characteristic; however, they are purely topological in nature and arise due to a specific set of interactions which may not be limited to magnetic materials. As we have an increased understanding of what causes topological properties, we can design/search for specific interactions in non-magnetic materials that may lead to non-magnetic analogues of topologically protected phases.

For skyrmions to exist, three interactions must be present: symmetric exchange, antisymmetric exchange, and a coupling to a magnetic field [2]. To explore the possibility of creating analogues of magnetic textures in non-magnetic materials we replace magnetic dipoles with non-magnetic quadrupoles and exchange the magnetic field for a strain field and adapt the interactions accordingly. Here we look at the capability of MOFs to harbor analogous complex magnetic phases such as skyrmions. MOFs are the perfect candidates as there are a plethora of components to play with such as underlying lattice, guest species, and interactions between the framework and the guest.

Through density functional theory calculations, molecular dynamics simulations, and Monte Carlo simulations, we explore the extent to which these interactions may exist in chiral MOF frameworks with quadrupolar guests such as a benzene or CO₂ and how varying the relative strengths of the three interaction parameters with temperature effects the behaviour of the non-magnetic textures. Using small angle scattering we have been able to define six distinct phases, giving evidence of quadrupolar skyrmions and interesting textures which are not present in the dipolar analogue. This opens up the field to new ways of creating non-topologically trivial textures that could potentially be less restrictive than chiral magnets.

[1] S. Mühlbauer, B. Binz, F. Jonietz, C. Pfleiderer, A. Rosch, A. Neubauer, R. Georgii, and P. Boni, Science 323, 915 (2009).

[2] S. D. Yi, S. Onoda, N. Nagaosa, and J. H. Han, Phys. Rev. B. 80, 054416 (2009).

Artificial molecular machines promise applications in many fields, including physics, information technologies, chemistry as well as medicine. The deposition of functional molecules in 2D or 3D assemblies in order to control their collective behavior and the structural characterization of these assemblies are challenging tasks. We exploit porous materials to form rigid matrix for mechanochemical preparation of bulk or surface host−guest inclusions with functional molecules, such as molecular rotors, molecular motors and molecular switches.

Unambiguous determination of the molecular structure and monitoring of the molecular function such as rotation of a molecular rotor or on/off switching of a molecular switch cannot be studied by X-ray analysis because the systems are typically heavily disordered fine powders. We use solid-state nuclear magnetic resonance (SS-NMR) spectroscopy to obtain atomic-level insights into the structure and dynamics of these functional materials. SS-NMR spectra provide valuable information about structure, interactions and dynamics in solids not available otherwise.

It will be demonstrated that SS-NMR experiments provide unequivocal evidence of the formation of the 2D and 3D assemblies and can also be used for the observation of such a molecular function as the photoisomerization of a molecular switch deposited on a surface. We have also developed a solid-state NMR method for investigation of two dimensional arrays of light-driven molecular motors [1-4].

Figure 1. Examples of studied molecules. The shaft ensures deposition of the molecules in the porous molecular matrix, the stopper ensures surface deposition. The molecular motor is a unidirectional light-driven motor and the switch performs its function upon UV irradiation.

[1] Kaleta, J., Chen, J., Bastien, G., Dračínský, M., Mašát, M., Rogers, C. T., Feringa, B. L., Michl, J. (2017). J. Am. Chem. Soc. 139, 10486.

[2] Kaleta, J., Bastien, G., Wen, J., Dračínský, M., Tortorici, E., Císařová, I., Beale, P. D., Rogers, C. T., Michl, J. (2019). J. Org. Chem. 84, 8449.

[3] Santos-Hurtado, C., Bastien, G., Mašát, M., Štoček, J. R., Dračínský, M., Rončević, I., Císařová, I., Rogers, C., Kaleta, J. (2020). J. Am. Chem. Soc. 142, 9337.

[4] Dračínský, M., Santos-Hurtado, C., Masson, E., Kaleta, J. (2021). Chem. Commun. 57, 2132.

CO₂ is widely recognised as the main cause of greenhouse effect, causing global warming and climate change. With the aim to reduce CO₂ emissions, during the last decades, several strategies have been developed for the capture, utilization and storage of carbon dioxide (CCUS). This work focuses on the development of bifunctional catalysts for the conversion of CO₂ into dimethyl ether (DME), a fuel with no collateral emissions other than CO₂ and H₂O, a high cetane number and chemical-physical properties similar to LPG. DME is obtained from the reaction of CO₂ with H₂ through two subsequent reactions. The first one is the CO₂ reduction with H₂ to obtain methanol; this reaction is promoted by Cu-based catalysts like Cu/ZnO/Al₂O₃ and Cu/ZnO/ZrO₂. The second one is the dehydration of methanol to DME, catalysed by solid acidic catalysts, such as zeolites and γ-Al₂O_3.

In this work three different types of mesostructured acidic catalysts were synthesized: Al-SiO₂ (Al-SBA-15, Al-MCM-41), Zr-TiO₂ and γ-Al₂O₃. These materials were tested for methanol dehydration and used as supports for the Cu-based redox phase, to obtain composite materials to be used as bifunctional catalysts. Mesostructured matrix should limit the growth of redox phase nanoparticles inside the mesopores and assure a high dispersion due to the high surface area, leading to a high contact area between the two phases and, thus, granting in principle superior catalytic performances.

All mesostructured systems were synthesized via the Sol-Gel method, either through an Evaporation-Induced Self-Assembly (EISA) or a solvothermal approach, and characterized by XRD, TEM and N₂ physisorption. Acidic sites characterization was performed by calorimetry and FTIR spectroscopy using pyridine as a probe molecule. The catalysts were eventually physically mixed with a Cu/ZnO/Al₂O₃-based commercial redox catalyst and tested in a bench-scale plant with a fixed bed reactor for CO₂ conversion to DME. Mesostructured supports were used to disperse the CuO/ZnO/ZrO₂-based redox phase by a wet impregnation method combined with a self-combustion process or by a two-solvents impregnation strategy. The obtained bifunctional catalysts were characterized by PXRD, N₂ physisorption, TEM and HRTEM in order to determine the most promising synthetic conditions in terms of dispersion and nanosize of the active phase and textural properties of the corresponding composites.

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.

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 crystallisation of various materials from solution is an important area of study in the field of in situ X‑ray diffraction. Beamline I12 at Diamond synchrotron offers the improved experimental capabilities for in situ investigation of the large-scale synthesis process in unprecedented detail [1]. Time-resolved monochromatic high energy X-ray diffraction on the Beamline I12 is a fast and efficient method for investigation of crystallization allowing the detection of crystalline intermediates, formulating an idea about the crystallization mechanism, and the assessment of individual reaction parameters, i.e., reaction rate constants and activation energies. Thus, the optimization of the synthesis conditions of new compounds can be achieved. The high X-ray flux on the beamline I12 allows real-time monitoring the synthesis in the large containers, including standard laboratory metal autoclaves. Using monochromatic X-rays for the synchrotron experiments produces the high-quality diffraction data that permits the full structural refinements to be undertaken on metastable materials observed during the reaction.

The simplest experimental setup for low temperature in situ diffraction experiments is a metal heating block, which allows measurements during the synthesis from room temperature to approx. 90^oC. It can be used with magnetic hotplate stirrer, allowing to mix substance during the measurements providing the homogeneous distribution of material in the reaction tube. For synthesis at temperatures close to the room temperature, the remotely controlled syringe pump can be used allowing simultaneous or sequential adding the reactants, thus permitting the investigation of the reaction in the controlled way from the very early stages [2].

Figure 1. Custom design metal heating block for in situ chemistry measurements with magnetic hotplate stirrer (left); ODISC furnace with quartz tube inside and magnetic stirrer below (middle); ODISC furnace with metal autoclave inside and magnetic stirrer below (right).

For more demanding in situ synthesis – at temperatures above 100^oC or in metal autoclaves – the custom designed furnace ODISC was developed on the beamline I12 [3]. The furnace is very versatile with integrated heating, stirring, and precise sample centring and it can be used for a wide range of in situ experiments on the beamline. On the beamline I12, the furnace ODISC can be used in two configurations: 1) in situ measurements of reaction kinetic during solvothermal synthesis experiments, which performed at temperatures below boiling temperature of the solvent. In this case simple quartz tubes are used as a container during large-scale in situ synthesis [4]. 2) in situ measurements of reaction kinetic during hydrothermal synthesis, which should be performed in metal autoclaves. Despite measurements during the crystallization were performed in the metal autoclave, the data quality recorded on the beamline I12 allowed the refinement of the diffraction data and subsequent analysis of crystallization kinetic [5].The references should be in Heading 4 style (Times New Roman 9 pt, shortcut CTRL + NUM 4) and listed immediately at the end of the text without a heading.

[1] Drakopoulos M., Connolley T., Reinhard C., Atwood R., Magdysyuk O., Vo N., Hart M., Connor L., Humphreys B., Howell G., Davies S., Hill T., Wilkin G., Pedersen U., Foster A., De Maio N., Basham M., Yuan F., Wanelik K. J. (2015). Synchrotron Rad. 22, 828.

[2] Yeung H.H-M., Sapnik A.F., Massingberd-Mundy F., Gaultois M.W., Wu Y., Fraser D.A.X., Henke S., Pallach R., Heidenreich N., Magdysyuk O.V., Vo N.T., Goodwin A.L. (2019). Angew. Chem., Int. Ed., 58, 566.

[3] Moorhouse S.J., Vranješ N., Jupe A., Drakopoulos M., O’Hare D. (2012). Rev. Sci. Instr. 83, 084101

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

[5] Cook D.S., Wu Y., Lienau K., Moré R., Kashtiban R.J., Magdysyuk O.V., Patzke G.R., Walton R.I. (2017). Chem. Mater. 29, 5053–2057.

The activation of B-H bonds in σ-borane complexes is of interest not only due to their applications in catalysis (hydroborations, borylations), but because of the ambiguity of σ-borane coordination modes, which can be challenging to formerly define.^[1] Because σ-borane complexes are intermediates to B-H activation, they can be difficult to study due to the transience of the highly reactive species.

The σ-borane complexes [Rh(PONOP)(ɳ²-HBR)][BAr^F₄], (PONOP = 2,6-Bis(di-tert-butyl-phosphinito)pyridine; Ar^F = 3,5‑Bis(trifluoromethyl)phenyl; HBR = HBcat: 1; HBR = HBpin: 2) have been synthesised in good yields and have been established to undergo oxidative addition (OA) in solution at modest temperatures (< 75 °C). However, the OA products were unstable in solution, preventing their full characterisation using traditional solution-based methods. A single crystal high-pressure study of 1 was undertaken up to pressures of 25.8 kbar. An isomorphous phase transition was observed between the pressures of 4.8 and 8.8 kbar, which was accompanied by several geometrical rearrangements of the HBcat ligand with respect to the remainder of coordination complex. Most notably, the decrease in the N-Rh-B bond angle of ca. 6 ° across the phase transition suggests an increased overlap between the metal d orbital and the ‘empty’ boron orbital, indicating a stronger interaction between the metal centre and the σ-borane ligand. ^[2]

We aim to further the understanding of B-H bond activation by studying σ-borane complexes using high-pressure X-ray diffraction (HP-XRD) as the principal analytical tool. Precise structural determination and analysis of a systematic series of σ-borane complexes will ultimately allow for better modelling of their reactive transition states in associated catalytic cycles, ultimately enabling better targeted design of industrially relevant catalysts.

[1] Hebden, T. J.; Denney, M. C.; Pons, V.; Piccoli, P. M. B.; Koetzle, T. F.; Schultz, A. J.; Kaminsky, W.; Goldberg, K. I.; Heinekey, D. M. (2008) J. Am. Chem. Soc. 130, 10812–10820.

[2] Marder, T. B.; Lin, Z., Contemporary Metal Boron Chemistry I. Springer-Verlag: Berlin Heidelberg, 2008; Vol. 130, p 125-127.

Keywords: organometallic chemistry; B-H bond activation; pincer complexes; high-pressure crystallography

Alex Longcake acknowledges the Royal Society for a PhD studentship (RGFEA180160) and Diamond Light Source for time on Beamline I19 under proposal CY26847.

The development of carbon-neutral energy-generation is critical to combatting climate change. One such technology is the development of next-generation ion conductors for solid-oxide fuel cells (SOFCs). SOFCs offer a much more efficient method to extract energy from hydrogen or hydrocarbon fuels than current combustion engines due to their one-step chemical process. However, a bottleneck to the large-scale uptake of SOFCs is the poor performance of the conducting electrolytes that separate the anode from the cathode. Various lanthanoid fergusonite structures (LnBO₄) have recently been proposed as solid electrolyte candidates in solid-oxide fuel cells, with increased high-temperature ionic conductivity being measured in chemically doped lanthanum orthoniobates (LaNbO₄) [1]. However, a phase transition from I2/a to I4₁/a within the operational temperature of SOFCs makes these structures non-ideal.

To understand the effects of chemical doping on the structure and electrochemical properties of these fergusonite structures, several complex fergusonites have been investigated [2-3]. Of interest is the substitution of Nb^V for Ta^V on the B-site, which has shown a decrease in the unit cell volume of the structure [4]. This is particularly remarkable, given the two metal cations have the same ionic radius and Ta has an extra 5d valence shell compared to the 4d shell of Nb. Such substitution has further shown to increase the I2/a to I4₁/a first-order phase transition temperature, highlighting the potential of the properties of these structures to be specifically ‘tailored’ to be used for SOFCs.

Various solid-solution series of Ln(Nb_1-xTa_x)O₄ (Ln = La-Lu) have been synthesised using conventional solid-state methods. Synchrotron X-ray and neutron powder diffraction methods have been used to investigate their structures, focusing on changes in both their unit cell volumes and the temperature of the I2/a to I4₁/a phase transitions. Whilst the fergusonite structure is a monoclinic structure derived of the tetragonal scheelite aristotype, it’s structure is based on BO₆ polyhedra as opposed to BO₄ scheelite polyhedra. These studies have revealed several anomalies, revealing that different structures can be isolated by controlling the size of the Ln ion and synthetic conditions, and that the volume of the BO₆ polyhedra and length of the B–O bonds change depending on its surrounding Ln ion. This data surprisingly implies that the AO₈ polyhedra act as a rigid framework in which the BO₆ polyhedra respond. The experimental data has been further reinforced by ground state energy calculations performed using density functional theory. This is a landmark accomplishment that has not been previously used in similarly studied structures. These insights can be used in the development and engineering of novel and advanced electrolyte materials for SOFCs.

[1] - Cao, Y.; Duan, N.; Yan, D.; Chi, B.; Pu, J.; Jian, L.; Enhanced Electrical Conductivity of LaNbO₄ by A-Site Substitution. Int. J. Hydrogen Energy, 2016, 41 (45), 20633-20639.

[2] - Arulnesan, S. W.; Kayser, P.; Kimpton, J. A.; Kennedy, B. J.; Studies of the Fergusonite to Scheelite Phase Transition in LnNbO₄ Orthoniobates. J. Solid State Chem., 2019, 277, 229-239.

[3] - Ivanova, M.; Ricote, S.; Meulenberg, W. A.; Haugsrud, R.; Ziegner, M.; Effects of A- and B-Site (Co-)Acceptor Doping on the Structure and Proton Conductivity of LaNbO₄. Solid State Ionics, 2012, 213, 45-52.

[4] – Mullens, B. G.; Avdeev, M.; Brand, H. E. A.; Vaitheeswaran, G.; Kennedy, B. J.; Insights into the Structural Variations in SmNb_1-x­Ta_xO₄ and HoNb_1-xO₄ Combined Experimental and Computational Studies. Under Revision for Dalton Transactions.

Studies of "dark matter" is an important fundamental branch of modern cosmology and theoretical physics. Cryogenic scintillation detectors based on single crystals of tungstates (ZnWO₄, CaWO₄, Na₂W₂O₇) can be used to register "dark matter"; they register extremely rare signals of interaction of Weakly Interacting Massive Particles (WIMP) with the nuclei of the detector material [1].

The important requirements to scintillation materials for the search and registration of such rare events are luminescence, light yield, energy resolution, high level of radiation purity. Necessary radiation purity level and optical quality of scintillators require the development of special technologies for deep purification of starting materials and new approaches to crystal growth under conditions of low temperature gradients, the production of scintillation elements with a high utilization rate of the costly starting material. Scintillation bolometers based on Na₂W₂O₇ must also be of high mechanical strength for their practical significance since bolometric elements of specified form will have to be cut from the crystals. To improve the mechanical and optical characteristics, charge with chromium Cr⁺³ and cerium Ce⁺⁴ doping was prepared, doped Na₂W₂O₇ crystals were grown and their luminescent properties were investigated [2].

Na₂W₂O₇ crystals were grown from melt by low-thermal-gradient Czochralski technique (LTG Cz) developed at NIIC SB RAS (Novosibirsk, Russia). Major difference from conventional Czochralski technique is in temperature gradients reduced by two orders of magnitude, below 1 K/cm. Main advantages of LTG Cz are reduced thermoelastic stresses in growing crystals so that they don’t influence crystal quality, and suppression of melt components decomposition and volatilization. By LTG Cz many scintillating crystals of record size and optical quality were obtained, such as BGO, CdWO₄ and many other [3].

As precursors, Na₂CO₃, WO₃, CeO₂, TiO₂ and Cr₂O₃ powders were used. Initial charge for crystal growth was prepared by solid-state synthesis at 400 °C in muffle furnace according to the reaction:

Na₂CO₃ + 2WO₃ → Na₂W₂O₇ + CO₂ ↑

Completeness of synthesis was controlled by weight change due to CO₂ volatilization. Crystallization rate was set at 1.5 mm/h, rotation velocity at 10 rev/min. Diameter of grown Na₂W₂O₇ crystals was 30 mm, length up to 70 mm and 40 mm for pure and doped ones, correspondingly.

[1] Indra, Raj, Kim, H.J., Lee, H.S., Kim, Y.D., Lee, M.H., Grigorieva, V.D., Shlegel, V.N. (2018) Eur. Phys. J. C, 78, 973. [2] Ryadun, A.A., Rakhmanova, M.I., Grigorieva, V.D. (2020) Optical Materials, 99, 109537. [3] Shlegel, V.N., Borovlev, Yu.A, Grigoriev, D.N, Grigorieva, V.D. et al. (2017) JINST, 12, C08011.

Keywords: Na₂W₂O₇; Czochralski technique; scintillators; elementary particles; luminescence

This work was supported by Russian Foundation for Basic Research (grant No. 20-43-543015).

Correlation between structural studies and third order NLO properties

of three new semi-organic compounds

R. Benali-Cherif R¹, R. Takouachet ¹, E-E Bendeif², N. Benali-Cherif R³

¹Abbes Laghrour Khenchela University. Algeria, ² Laboratoire de Cristallographie, Résonance Magnétique et Modélisations (CRM2, UMR CNRS 7036). France, ³ Houari Boumédiène (USTHB) and Member of Algerian Academy of Sciences and Technology (AAST) Algiers. Algeria Algeria

The study of semi-organic compounds has been of growing interest for a few years. In addition to their fundamental interest in the nature of the bonds occurring between inorganic anions and organic cations, these compounds also have remarkable physico-chemical and optical properties. Recently, the variety of semi-organic hybrid crystals has been developed for NLO applications. The combination of organic compounds, especially amino acids with mineral acids, gives rise to new hybrid crystals with strong NLO properties.Semi-organic compounds play an important role in cell metabolism; they intervene in transfer of energy because of their richness in hydrogen bonds. Inter-ionic interactions through the hydrogen bridges present in this type of semi-organic compounds can serve as mimes explaining some bio-inorganic mechanisms.

Measurement of nonlinear third order electrical susceptibilities was performed for three new compounds (Table 1) by the Third Harmonic Generation (THG) technique. Figure 1 shows the intensity of the THG signal as a function of the angle of incidence, it exhibits the same behavior as the silica.

Table 01. Experimental values of nonlinear susceptibility of the third order.

The third order nonlinear electrical susceptibility values of studied compounds are stronger than that of silica (reference material). The largest value is observed for the first compound, = 9,63×10^-21 m²/V² (Table 1) due to the increase in charge transfer and the large number of hydrogen bonding which increases the dipole moment of the compound .

Figure 1. Intensity of the third harmonic for the three samples

These optical measurements revealed different optical behaviors of the three compounds studied. It is therefore very interesting to analyze and discuss the different structural factors correlated with these interesting physical properties. Several structural parameters affect the physical and optical properties of these materials such as: atomic arrangement, intra- and intermolecular interactions, crystal symmetry and electron density distribution.

Keywords: semi-organic compounds - NLO properties - THG technique

[1] Publication of a book on May 05, 2017 entitled “Corrélations structures propriétés ONL de 3 nouveaux composés hybrides »in the “Éditions Universitaires Européennes »

Materials family of A₃B’₂B’’O₉ (A = alkaline–earth metal ions with valence +2, B’ and B’’= transition metal ions with valences +3 and +6 respectively) were subjected to extensive studies, and have attracted significant interest owing to their physical properties and technological applications. The discovery of colossal magnetoresistance (CMR) in the ordered A₂B’B’’O₆ double perovskite oxides has given rise to many recent research [1–3].

Polycrystalline samples of the series of triple perovskites Sr_3−xPb_xFe₂TeO₉ (0 ≤ x ≤ 2.25) were synthesized using solid state reaction [4]. These materials have been studied by a combination of XRPD, Mössbauer spectrometry, Raman and UV–Vis spectroscopies. The crystal structures were resolved by the Rietveld refinement method, and revealed that this Sr_3−xPb_xFe₂TeO₉ (0 ≤ x ≤ 2.25) system shows one space group change from tetragonal I4/m (0 ≤ x ≤ 1) to another tetragonal form I4/mmm (1.25 ≤ x ≤ 1.88) and a second transition to hexagonal R-3m (2.08 ≤ x ≤ 2.25). The valence state of iron in the Fe site was determined to be Fe(III) by Mössbauer spectrometry, which also revealed two sites in a concordance with the XRPD measurements. ⁵⁷Fe Mössbauer spectra measurements show paramagnetic and magnetic ordering behaviors. The observed Raman spectra as a function of composition show obvious changes on the positions (wavenumbers), the FWHM and the intensities of the modes confirming the phase transformations observed by the XRPD results. These structural transitions led to a distinct change in the optical band gap energy, varying from 2.14 to 1.85 eV.

[1] K.I. Kobayashi, T. Kimura, H. Sawada, K. Terakura, Y. Tokura. Nature, 1998, 395, 677–680.
[2] M. García–Hernández, J.L. Martínez, M.J. Martínez–Lope, et al., Phys. Rev. Lett., 2001, 86, 2443.
[3] W.R. Branford, S.K. Clowes, Y.V. Bugoslavsky, et al., J. Appl. Phys., 2003, 94(7), 4714–4716.
[4] A. El Hachmi, F. El Bachraoui, S. Louihi, Y. Tamraoui, S. Benmokhtar, et al., J. Inorg. Organomet. Polym., 30, 1990–2006 (2020). https://doi.org/10.1007/s10904-020-01446-4

An important element in the reduction of CO₂ is the change of vehicles with internal combustion engines to electric battery powered vehicles. The as such produced renewable energy can be used for individual mobility as well as for a temporary intermediate storage of excess energy. A viable electric mobility concept requires however stable cycle batteries with high specific energy (minimising weight, maximising driving range).

Li ion batteries are widely used in applications such as mobile phones and laptops, and will likely be key to future electromobility. An alternative promising battery is the lithium sulfur battery with a potential twofold energy density increase. The requirements for such batteries present major challenges; e.g. energy capacity, deactivation/stability and safety. A detailed understanding of the charge, discharge and deactivation mechanisms are thus required, preferably quantitative and spatially resolved. X-ray absorption spectroscopy (XAS) is a characterisation technique which provides detailed electronic and structural information on the material under investigation, in a time- and spatially resolved manner.

Here, I will explain the strengths and limitations of XAS for battery research. A novel operando XAS cell design will be described [1], including the challenges to perform reliable experiments (electrochemically and spectroscopically). The cell allows time and spatial resolved XAS, providing insights in the type, location and reversibility of the intermediates formed in electrodes and electrolyte separately. Obtained insights in cycling and deactiviation mechanisms for the different battery types will be discussed [1-6] and future research directions described.

[1] Y. Gorlin, A. Siebel, M. Piana, T. Huthwelker, H. Jha, G. Monsch, F. Kraus, H.A. Gasteiger, M. Tromp, J. Electrochem. Soc. 162(7): A1146-A1155, 2015.

[2] Y. Gorlin, M. U. M. Patel, A. Freiberg, Q. He, M. Piana, M. Tromp, H. A. Gasteiger, J. Electrochem. Soc. 2016, 163(6), A930-A939.

[3] J. Wandt, A. Freiberg, R. Thomas, Y. Gorlin, A. Siebel, R. Jung, H. A. Gasteiger, M. Tromp, J. Mater. Chem. A 2016, 4, 18300-18305.

[4] A. T. S. Freiberg, A. Siebel, A. Berger, S. M. Webb, Y. Gorlin, H. A. Gasteiger, M. Tromp, J. Phys. Chem. C 2018, 122, 10, 5303-5316.

[5] A. Berger, A. T. S. Freiberg, R. J. Thomas, M. U. M. Patel, M. Tromp, H. Gasteiger, Y. Gorlin, J. Electrochem. Soc. 2018, 165(7), A1288-A1296.

[6] R. Jung, F. Linsenmann, R. J. Thomas, J. Wandt, S. Solchenbach, F. Maglia, C. Stinner, H. A. Gasteiger, M. Tromp, J. Electrochem. Soc. 2019, 166(2): A378-A389.

A set of sodium iron titanite samples with general formula Na_xFe⁺²_x/2Ti_2–x/2O₄ was prepared using solid-state synthesis in an inert atmosphere to test for application as cathode materials for Na-ion batteries. These materials have several advantages over analogues with Fe³⁺, demonstrating better sodium ion conductivity and higher Na+ ions capacity without phase transition or destruction of the structure. [1] In the course of the investigation, several compositions of a new compound were obtained with NSIT-like structure type similar to Na_0.9Fe³⁺_0.9Ti_1.1O₄. Among them, composition with x = 0.9 was selected due to its electrochemical performance and structural peculiarity. From the crystallographic point of view, formation of phases in Na_xFe⁺²_x/2Ti_2–x/2O₄ system with Na_0.9Fe³⁺_0.9Ti_1.1O₄ structure (having Fe³⁺ ions mixed with Ti⁴⁺ ions) is rather unusual due to different radii of mixing ions (Fe²⁺ = 0.92 Å, Fe³⁺ = 0.785 Å, Ti⁺⁴ = 0.745 Å (CN=6) [2]).

The Na_0.9Fe³⁺_0.9Ti_1.1O₄ was further studied by operando XANES spectroscopy. The sample was placed as a cathode inside custom electrochemical cell with glassy carbon X-Ray transparent windows. Li foil was used as anode and 1M LiPF6 in 1:1 EC:DMC commercial solution (Sigma) was used as electrolyte. The cell was cycled in 1.6 to 4.5 V range with current of C/20. Operando Fe K-edge XANES spectra were measured with the R-XAS Looper (Rigaku, Japan) laboratory X-Ray absorption spectrometer.

In total 200 spectra were collected for Na_xFe⁺²_x/2Ti_2–x/2O₄ sample with x = 0.9 during 10 consecutive cycles, which were further analyzed by PCA to extract spectra of phases participating the electrochemical process and corresponding phase content diagrams. 2 components were successfully extracted (fig. 1). Component corresponding to a Fe²⁺ phase shows good agreement with FeTiO₃ reference in terms of absorption edge position and overall profile of the spectrum. On the other hand, agreement with the spectrum of as-prepared sample is far from decent. Component corresponding to a Fe³⁺ phase shows good agreements with a reference compound (reference sample, fully oxidized in air). Comparison with theoretical spectra for various structural models have shown decent agreement of Fe²⁺ phase with the spectrum of freudenbergite. Fig. 2 shows the cell potential and phase concentrations from PCA as a function of time. One can clearly see the decrease in Fe²⁺/Fe³⁺ conversion rate during first 3 cycles, after that the rate remains stable and conversion is highly reversible. This decrease in conversion rate, as well as lack of agreement between Fe²⁺ phase from PCA and as prepared sample, might be accounted by electrochemical substitution of Na with Li that takes place during cycling in Li-based cell, which causes the change in local atomic and electronic structure of material, possibly leading to partially blocked or collapsed ion transfer channels. The degree and details of such substitution are subject for study by operando XRD and Mössbauer spectroscopy.

[1] Rajagopalan et al., (2017) Adv. Mater. 29

[2] Shannon, R.D. (1976), Acta Crystallogr. Sect. A 32, 751-767

Authors would like to acknowledge the financial support of Russian Foundation for Basic Research in the framework of grant 20-32-70227

Many computational algorithms devoted to the interpretation and modeling of small angle scattering (SAS) data have been developed over the last several decades. In addition to the commonly used ASCII text files containing fits to data, real space transforms, modeling parameters, etc., modeling algorithms often generate coordinate files containing 3D coordinates of atomic or coarse-grained models to describe the object. Due to their versatility and community acceptance, coordinate files have become popular for representing models from a variety of different algorithms including bead modeling, rigid body modeling, ensemble modeling, flexible fitting, molecular dynamics, etc. and have found wide spread adoption in the SAS community. As novel algorithms are developed, new representations of particles are often required that may not be compatible with conventional coordinate models. Here I will describe the program DENSS¹ which generates low-resolution 3D density maps from 1D solution scattering data using a novel ab initio reconstruction algorithm. The primary output of DENSS is an MRC file, commonly used in the electron microscopy community (and similar to the CCP4 format used in crystallography), which represents objects on a 3D grid of voxels where each voxel has a value corresponding to the density at that location. DENSS offers advantages over conventional algorithms that are implicit to its use of density to represent particles. Accurate and unbiased interpretation of a density map requires understanding how visualization programs graphically represent the 3D grid of values and how the low-resolution nature of the reconstruction affects this visualization. This includes tasks such as selecting appropriate contour thresholds and how to accurately and unbiasedly display such low-resolution density maps in publication figures and archives. Community engagement in this area will help to generate a set of standards for accurately publishing low-resolution density maps to avoid overinterpretation, as has previously been done for validation of conventional SAS models².

Proteins generally populate multiple structural states in solution. Transitions between these states are important for function, such as allosteric signaling and enzyme catalysis. Structures solved by X-ray crystallography provide valuable, but static, atomic resolution structural information. In contrast, cross-linking mass spectrometry (XLMS) and small angle X-ray scattering (SAXS) datasets contain information about conformational and compositional states of the system. The challenge lies in the data interpretation since the cross-links in the data often comes from multiple structural states. We have developed a novel computational method that simultaneously uncovers the set of structural states that are consistent with a given dataset (XLMS or SAXS). The input is a single atomic structure, a list of flexible residues, and an experimental dataset. The method finds multi-state models (models that specify two or more co-existing structural states) that are consistent with the data. The method was applied on multiple SAXS and XLMS datasets, including large multi-domain proteins and proteins with long disordered fragments. The applicability of the method extends to other datasets, such as 2D class averages from Electron Microscopy, and residual dipolar couplings.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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