Single particle cryo electron microscopy (cryo-EM) has developed into a powerful technique to determine 3D structures of large macromolecular complexes. Due to improvements in instrumentation and computational image analysis, the number of high-resolution structures is steadily increasing. The method cannot only be used to determine high-resolution structures but also to study the dynamic behavior of macromolecular complexes and thus represents a very complementary method to X-ray crystallography. Furthermore, the maximum attainable resolution by cryo-EM has constantly improved in recent years. Most of the high-resolution structures are still in the 3 Angstrom resolution regime but some have even crossed the 2 Angstrom barrier. We have recently installed a new prototype electron microscope which is equipped with a monochromator and a next-generation spherical aberration corrector. This microscope is optically superior to the currently commercially available instruments and can therefore be used to test the resolution limits in cryo-EM. We have used the test specimen apoferritin to determine its structure at 1.25 Angstrom resolution which is sufficient to visualize for the first time individual atoms clearly separated in the density map without the need for computational beam tilt corrections.

Recently, we managed to use this microscope not only to improve the resolution of the very stable and rigid protein apoferritin. We also obtained significant improvement in resolution for other more dynamic macromolecular complexes for which one could have expected that the microscope itself may not be a major resolution limiting factor.

In current high-resolution cryo-EM structures less water molecules become visible compared to X-ray crystallographic structures at nominally the same level of resolution. The number of water molecules that can be reliably build into the EM density is also not independent from the image processing software used for the three-dimensional reconstruction. We made a first attempt to use the number of water molecules that can be build into a 3D structure as a quality criterium for cryo-EM data since until now such high-resolution quality estimators are entirely missing in the cryo-EM field.

We are currently upgrading our microscope with an energy filter and a faster direct pixel detector. This will not only improve throughput but also the maximum attainable resolution even further. Therefore I will address the question of how much the resolution in cryo-EM can still be realistically improved and how this compares to X-ray crystallography.

The synthesis of inorganic compounds in form of nanoparticles of few nanometers has opened a new world for chemistry, with the discovery of unexpected properties and also of entirely new crystal structures. At the beginning, simple stoichiometries related with crystal structures of low complexity have been mainly explored. As far as nanochemistry grew searching for exotic properties, the exploration has extended towards more complex phase diagrams, where the complexity of the crystal structure is a real challenge. In these cases, the crystallographer is hampered by the limited crystal size that enlarges the powder x-ray diffraction peaks and quite often cannot rely on the knowledge of the bulk structure, which can be different from the nanocrystalline form or even not stable in the same conditions. Conversely, 3D electron diffraction (3D ED) has demonstrated its potential for solving crystallographic problems where the size of the crystal grains was the limiting factor [1]. A 3D ED single crystal diffraction experiment is performed with a beam that can be as small as few hundreds of nanometers, and the collected 3D intensity data sets are suitable for structure solution [2]. We report here the application of 3D ED to extreme cases, where the size of the crystalline grains was smaller or in the range of 100 nm and the powder x-ray diffraction was not able to give a definite answer. The challenge is to establish which is the minimum crystal size that we can investigate in this way. All the nanoparticles we analysed have unknown and not trivial crystal structures.

As first example we report the crystal structure of Cu_2-xTe, a not stoichiometric plasmonic nanocrystal that exhibits a complex 1x3x4 super-structure of a pseudo-cubic basic cell, due to the ordering of copper vacancies. The pseudosymmetry of the underlying basic structure induces a strong twinning and therefore data on single individuals could be taken only from grains smaller than 150nm. 3D ED allowed the determination of the super-structure with the identification of 27 Te and 32 Cu in the asymmetric unit and the location of copper vacancies [3].

A second example is the perovskite-related structure of Cs₃Cu₄In₂Cl₁₃ nanocrystals. This crystal structure was synthesized with the aim to obtain a double perovskite of composition Cs₂CuInCl₆, isostructural to Cs₂AgInCl₆. 3D ED on nanoparticles of 100 nm revealed that the obtained structure is instead a vacancy ordered perovskite, A₂BX₆, in which 25% of the A sites are occupied by [Cu₄Cl]³⁺ clusters and the remaining 75% by Cs⁺, while the B sites are occupied by In³⁺ ions. Interestingly, while a Rietveld refinement on powder x-ray data results in a crystal structure where Cs⁺ and [Cu₄Cl]³⁺ are disordered on 8 equivalent sites, 3D ED shows that they exists nanoparticles where [Cu₄Cl]³⁺ clusters and Cs⁺ are ordered on different sites, lowering the symmetry from cubic Fm-3m to cubic Pn-3m [4].

The last example is the crystal structure determination of Pb₄S₃Br₂, a compound never reported in bulk that we synthesised in form of nanoparticles. 3D ED revealed that this compound is isostructural with the high pressure phase of Pb₄S₃I₂ and attested that the colloidal synthesis is able to freeze a high pressure metastable phase in form of nanoparticles. 3D also revealed that once the size of the nanoparticles has increased above a certain size (> 50nm) and their shape has changed from spherical to elongated platelets, the structure relaxes with the longest cell parameter that increase from 14.6 to 15.5 Å [5]. In this last case we have reached our minimum crystal size, being able to reconstruct the 3D reciprocal space of a 50 nm nanoparticle. The examples reported demonstrate that 3D ED is a powerful tool for exploring the crystal structure of not trivial nanoparticles and we expect that, with the use of smaller parallel beam and a dedicated set up, this limit can be pushed further to investigate the crystal structure of nanoparticles in the 10 nm range.

[1] Gemmi, M., Mugnaioli, E., Gorelik, T.E., Kolb, U., Palatinus, L., Boullay, P., Hovmöller, S., Abrahams, J.P. (2019). ACS Cent. Sci. 5, 1315.

[2] Gemmi, M., Lanza, A. (2019). Acta Crystallogr. B75, 495.

[3] Muganioli, E., Gemmi, M., Tu, R., David, J., Bertoni, G., Gaspari, R., De Trizio, L., Manna, L. (2018). Inorg. Chem. 57,10241. [4] Kaiukov, R.,Almeida, G., Marras, S., Dang, D., Baranov, D., Petralanda, U., Infante, I., Mugnaioli, E., Griesi, A., De Trizio, L., Gemmi, M., Manna, L. (2020). Inorg. Chem. 59, 548.

[5] Toso, S., Akkerman, Q. A., Martín-García, B., Prato, M., Zito, J., Infante, I., Dang, Z., Moliterni, A., Giannini, C., Bladt, E., Lobato, I., Ramade, J., Bals, S., Buha, J., Spirito, D., Mugnaioli, E., Gemmi, M., Manna L. (2020). J. Am. Chem. Soc. 142, 10198.

2D nanosheets are intensely researched as new quantum materials and components of next-generation electronic and spintronic devices with unprecedented magnetic, transport and optical properties. In particular, the thickness-dependency of structural and physical properties is subject of close scrutiny. α-RuCl₃ is a spin ½ honeycomb material that exhibits exotic magnetic ground states both in bulk¹ and exfoliated² forms. Its flakes and intercalates feature high environmental stability and retain the in‐plane honeycomb structure during wet-chemistry functionalization². RuCl₃ nanosheets are a robust test-bed for fabrication of new nanocomposites in both acidic or basic aqueous solutions, and their performance as electrodes for electrochemical reduction/ion transfer reactions can be further optimized. Reliable structural and compositional characterization during downscaling and intercalation is one of the goals that will enable well-controlled nanosheet functionalization. We synthesized K-intercalated RuCl₃ by electrochemistry in an aqueous KCl solution. Conventional X-ray diffraction methods fail to characterize such intercalates due to the presence of multiple nm-sized domains, stacking faults and other defects associated with the layered morphology. Instead, we for the first time determine the local structure and capture the essential properties on the nm-length scale by collecting the multimodal 3DED–STEM–EELS–EDX data. The 3DED method is one of the very few that provides both in-plane and out-of-plane structural information, which is indispensable for layered materials. The K_0.5RuCl₃ layered intercalate (sp. gr. P-31m) is stacked differently than the α-RuCl₃ parent compound (sp.gr. C2/m): the K atoms in the interlayer space are coordinated by six equivalent Cl atoms to form the [KCl₆] octahedra that share corners with the six equivalent [RuCl₆] octahedra. As a hallmark of STEM, EELS, and EDX spectroscopy, spatial mapping techniques were used to trace local changes in the chemical composition. A multimodal data fusion³ helped to overcome the severe spectral overlap and high sparseness of EDX data. The retrieved abundance profiles revealed spatially resolved phases with differing in the K:Ru:Cl ratio, the Ru oxidation state and in the oxygen content. This microinhomogeneity is a rather local disorder, which might cause only minor local symmetry changes, and could be associated with concomitant water molecules co-intercalating into the α-RuCl₃ matrix together with the K⁺ cations.

Figure 1. a,b Reconstructed 3D reciprocal lattice of the K-doped α-RuCl₃, scale bar is 4 nm^-1, c In-plane and out-of-plane structure of K_0.5RuCl₃ found by 3DED, d TEM overview image, e,f Abundance maps from fused EDX and EELS data. Scale bar is 200 nm.

[1] Roslova, M., Hunger, J., Bastien, G., Pohl, D., Haghighi, H. M., Wolter, A. U. B., Isaeva, A., et al. (2019). Inorg. Chem. 10, 6659-6668; Bastien, G., Roslova, M., Haghighi, M. H., Mehlawat, K., Hunger, J., Isaeva, A., et al. (2019). Phys. Rev. B. 99, 214410.

[2] Weber, D., Schoop, L. M., Duppel, V., Lippmann, J. M., Nuss, J., Lotsch, B. V. (2016). Nano Lett. 16(6), 3578–3584.

[3] Thersleff, T., Budnyk, S., Drangai, L., Slabon, A. (2020). Ultramicroscopy. 219, 113116; Thersleff, T., Jenei, I. Z., Budnyk, S., Dörr, N., Slabon, A. (2021). ACS Appl. Nano Mater. 4 (1), 220–228.

Many functional materials seem to have surprisingly simple average structures with some disordered components. To understand the relationship between the structure of a material and its complex physical properties, a full description including local order is necessary. Hence, the diffuse scattering has to be analysed. The recently established three-dimensional delta pair distribution function (3D-ΔPDF) maps local deviations from the average structure and allows a straightforward interpretation of local ordering mechanisms [1].

Many functional materials can only be grown as powders. While powder X-ray and neutron diffraction experiments can give limited insight into disordered structural arrangements, electron diffraction techniques allow to capture large portions of reciprocal space even for nanocrystals. Here, we demonstrate how the 3D-ΔPDF can be used with electron diffraction to understand the complete local structure of the ion conductor calcium stabilized zirconia (Zr_0.82Y_0.18O_1.91).

Zr_0.82Y_0.18O_1.91 crystallizes in the fluorite structure and shows composition disorder on both the metal and oxygen site. Due to the vastly different bond lengths of Y-O and Zr-O, strongly structured diffuse scattering is observed alongside the Bragg reflections (see Figure (a)). By employing the 3D-ΔPDF to electron diffraction data, we can directly interpret the local correlations (see Figure (b)).

Large single crystals of Zr_0.82Y_0.18O_1.91 that are also suitable for X-ray and neutron measurements were investigated. By comparing the results from our electron ΔPDF to X-ray and neutron ΔPDFs we demonstrate the reliability of the 3D-ΔePDF.

To our knowledge, this is the first 3D-ΔePDF ever reported and this proof of principle is an important step towards the full description of a disorder model. This has important implications for the large variety of disordered materials of which single crystals for X-ray or neutron techniques are not available. In those cases, the 3D-ΔePDF will pave the way to understanding and tailoring physical properties.

Figure 1. (a) hk0 reciprocal space section with diffuse scattering and Bragg reflections. (b) 3D-ΔePDF in the ab0.25 layer showing the relaxation of metal oxygen bond distances around (0.25,0.25,0.25).

[1] Weber, T., & Simonov, A. (2012). Z. Kristallogr., 227(5), 238-247.

Metal-organic frameworks (MOFs) are a class of nanoporous materials that have developed into one of the most widely studied research fields in chemistry of the past two decades. Single crystal X-ray diffraction still remains as the preferred method for structure determination, but the technique requires sufficiently large crystals. Traditionally and still predominantly to this day, MOFs are prepared using synthesis conditions that are optimized for producing larger single crystals, which includes dissolving starting materials with polar organic solvents, such as DMF or methanol, followed by heating under solvothermal conditions.

With the emergence of fast electron diffraction (ED) techniques such as 3D ED or MicroED, solving crystal structures from small nano-sized crystals has never been easier for crystals with organic constituents that traditionally were considered too beam sensitive for transmission electron microscopy. This provides the opportunity to easily study MOFs that can only be synthesized as small nanocrystals. Many of the more stable MOFs have a tendency to form as smaller crystallites, which can now be conveniently studied by ED. In addition this also makes it easier to study MOFs made using less typical synthesis conditions which may be less hazardous, more environmentally friendly and require less energy input.

Access to fast ED has allowed us to easily focus on the development of new stable MOFs prepared under green and ambient synthesis conditions. SU-101 was prepared using nonhazardous and edible starting materials which were stirred in water at room temperature without any other energy input.[1] The reaction starts and ends as a suspension in water, nonetheless the starting materials are fully converted into the MOF. Scaling up the synthesis of SU-101 is easily achieved as the MOF forms at room temperature and ambient pressure in water. For the first time in a MOF, ellagic acid was used as the organic linker. Ellagic acid is common in many plants and is one of the building units of naturally occurring polyphenols known as tannins. It is well known as an antioxidant and is common in fruits, berries, nuts, and wine. Unlike most MOF linker molecules, ellagic acid does not contain carboxylic acids groups but instead has multiple phenol groups which can chelate to metal cations forming strong bonds and hence robust framework structures. SU-101 demonstrates excellent stability in organic solvents and water even at elevated temperatures, simulated physiological media, and also in a wide pH range (2-14). In addition to demonstrating good stability, SU-101 exhibits promising behavior in the capture of hazardous sulfur containing gases, and demonstrated one of the highest uptake capacities for hydrogen sulfide among MOFs. Due to the stable structure, the lack of heating during synthesis and the use of a poor solvent (water), SU-101 was synthesized as small nanocrystals. The crystal structure of SU-101 was solved by ED with relative ease.

The advent of fast ED techniques and the relative ease now in solving structures of nanocrystals containing organic components, has changed our habits in the chemistry laboratory regarding the synthesis of novel crystalline materials. Rather than by default using organic solvents, elevated temperatures and pressures, we now focus on using greener reagents and ambient synthesis conditions directly from the early stages in the development of novel biocompatible and stable MOFs.

Structure of high temperature “Al₃Mn” (T) phase was investigated numerously. Studies of binary and ternary extensions of T-phase resulted in many published atomic models [1-8]. Until today, exact space group and atomic positions of transition metals in this structure is a matter of dispute. In current research, atomic model of the Al₇₈Mn_17.5Pt_4.5 phase (quenched from 800 °C) was successfully derived using a combination of electron crystallography methods. This structure was regarded as ternary extension of the “Al₃Mn” T–phase. The lattice parameters of the Al₇₈Mn_17.5Pt_4.5 T-phase were found to be a = 14.720(4) Å, b = 12.628(2) Å, c = 12.545(3) Å (as refined against X-ray diffraction data). Using convergent beam electron diffraction (CBED), the space group of this ternary composition was proved to be non-centrosymmetric Pna2₁, instead of Pnam - which describes the symmetry of the binary T-phase. Atomic model was determined applying direct methods, utilized in SIR2011 [9], on electron diffraction tomography data and refined using ShelXL [10]. At the Al₇₈Mn_17.5Pt_4.5 composition, the Pt atoms were not distributed randomly in the Mn/Al sublattices, but adopted two specific Wyckoff sites, therefore, thiscomposition should be regarded as an ordered variant of the T-structure. On the other hand, CBED study of the T-phase samples with a bit different stoichiometry (Al_71.3Mn_25.1Pt_3.6) allowed attribution of their structure to the original T-phase structure type, i.e. centrosymmetric. Using Barnighausen tree [11], these two structures (centrosymmetric and non-centrosymmetric) were found to be related.

References:

1. M. A. Taylor, The space group of MnAl₃, Acta Cryst. 14(1) (1961) 84. https://doi.org/10.1107/S0365110X61000346
2. M. Audier, M. Durand-Charre, M. de Boissieu, AlPdMn phase diagram in the region of quasicrystalline phases, Phil. Mag. B 68(5) (1993) 607-618.‏ https://doi.org/10.1080/13642819308220146
3. K. Hiraga, M. Kaneko, Y. Matsuo, S. Hashimoto, The structure of Al₃Mn: Close relationship to decagonal quasicrystals, Phil. Mag. B 67(2) (1993) 193-205.‏ https://doi.org/10.1080/13642819308207867
4. N. C. Shi, X. Z. Li, Z. S. Ma, K. H. Kuo, Crystalline phases related to a decagonal quasicrystal. I. A single-crystal X-ray diffraction study of the orthorhombic Al₃Mn phase, Acta Cryst. B 50(1) (1994) 22-30.‏ https://doi.org/10.1107/S0108768193008729
5. V. V. Pavlyuk, T. I. Yanson, O. I. Bodak, R. Černý, R. E. Gladyshevskii, K. Yvon, J. Stepien-Damm, Structure refinement of orthorhombic MnAl₃. Acta Cryst. C 51(5) (1995) 792-794.‏ https://doi.org/10.1107/S0108270194012965
6. Y. Matsuo, K. Yamamoto, Y. Iko, Structure of a new orthorhombic crystalline phase in the Al-Cr-Pd alloy system, Phil. Mag. Let. 75(3) (1997) 137-142.‏ https://doi.org/10.1080/095008397179688
7. Y. Matsuo, M. Kaneko, T. Yamanoi, N. Kaji, K. Sugiyama, K. Hiraga, The structure of an Al₃Mn-type Al₃(Mn, Pd) crystal studied by single-crystal X-ray diffraction analysis, Phil. Mag. Let. 76(5) (1997) 357-362.‏ https://doi.org/10.1080/095008397178968
8. H. Klein, M. Boudard, M. Audier, M. de Boissieu, H. Vincent, L. Beraha, M. Duneau, The T-Al₃(Mn, Pd) quasicrystalline approximant: chemical order and phason defects, Phil. Mag. Let. 75(4) (1997) 197-208.‏ https://doi.org/10.1080/095008397179624
9. M. C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L. De Caro, R. Spagna, IL MILIONE: a suite of computer programs for crystal structure solution of proteins, J. Appl. Cryst. 40(3) (2007) 609-613.‏ https://doi.org/10.1107/S0021889807010941
10. G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Refinement, University of Goettingen, Germany, 1997, release 97-2.
11. H. Bärnighausen, Group-subgroup relations between space groups; a useful tool in crystal chemistry. MATCH-Commun. Math. Chem. 1980, 9, 139.

Oxygen deficient perovskites are investigated as oxygen carriers for many different energy applications, based on the possibility to change their oxygen content while maintaining the cation framework. The most well-known oxygen deficient perovskite type structure is brownmillerite, with alternating layers of octahedra and tetrahedra. However, even for this common structure there are complexities such as ordered rotations of tetrahedra that are often missed during structure determination using, for example, powder diffraction, resulting in the persistent use in literature of inaccurate structure models for DFT calculations and properties explanations. When the extra reflections corresponding to the anion related order are picked up in single crystal neutron or X-ray diffraction, the refinement is often still hindered by high amounts of twinning or correlated disorder. In such cases, TEM can shed a light on the structure, in the past through mostly qualitative techniques like high resolution imaging of the structure and visualization of the reflections using electron diffraction, nowadays also through refinement of the structure from single crystal 3DED data. Electron diffraction is more sensitive to low Z atoms such as oxygen next to heavier atoms than X-rays and can be used on submicron sized crystals; the problems there once were with dynamical scattering are overcome using 3DED [1] combined with dynamical refinement [2]. Using TEM, compounds that were commonly accepted to be brownmillerites were proven to have a completely different anion deficient perovskite type structure, for example Pb₂Fe₂O₅ [3] and related compounds, "disordered" brownmillerites like Sr₂Fe₂O₅ [4] and Sr₂Co₂O₅ [5] were shown be ordered, and clear oxygen-vacancy order that escaped characterization with other techniques was found in many oxygen deficient perovskites, such as in LaSrCuO_3.5 [6] and SrMnO_3.5 [7]. So far, such crystal structures were derived in TEM experiments after reduction outside the microscope, however, the results of the first in situ 3DED redox experiments will also be shown, which allow to follow the structure evolution between oxygen deficient and oxidized perovskite by acquiring in situ 3DED data on submicron sized single crystals in different oxidizing and reducing gasses. In short, I will show that there might be more complexity underlying still many published structures, which we are now better equipped to uncover using electron crystallography, no longer only by observing the superstructures but now also by quantifying them, reliably refining the structures and taking control of the oxygen content during the TEM experiments themselves.

[1] Kolb, U., Gorelik, T., Kübel, C., Otten, M.T., Hubert, D. (2007) Ultramicroscopy 107, 507. [2] Palatinus, L., Petříček, V., Antunes Corrêa, C. (2015) Acta Crystallogr., Sect. A: Found. Adv. 71, 235-244 [3] Abakumov, A.M., Hadermann, J., Bals, S., Nikolaev, I.V., Antipov, E.V., Van Tendeloo, G.(2006) Angew. Chemie Int. Ed. English. 45, 6697–6700

[4] D’Hondt, H., Abakumov, A.M., Hadermann, J., Kalyuzhnaya, A.S., Rozova, M.G., Antipov, E.V., Van Tendeloo, G., (2008) Chem. Mater. 20, 7188–7194

[5] Sullivan, E., Hadermann, J., Greaves, C. (2011) J. Solid State Chem. 184, 649–654

[6] Hadermann, J., Pérez, O., Créon, N., Michel, C., Hervieu, M. (2007) J. Mater. Chem. 17, 2344

[7] Gillie, L.J., Wright, A.J., Hadermann, J., Van Tendeloo, G., Greaves, C. (2002) J. Solid State Chem. 167, 145–151

Ferroelectric perovskite oxides have recently been used in solar applications because their polarity allows for the separation of photocarriers when under illumination to generate a photocurrent. Oxides, however, often have band gaps that are beyond the solar-optimal regime (>3.3 eV); for this reason, perovskite-structured chalcogenides have been proposed as suitable candidate materials owing to their lower band gaps (≈ 2 eV). An understanding of the thermal expansion behavior of photovoltaic materials is important so as to prevent large stresses and strains during fabrication and operation of the photovoltaic device. Here, we evaluate the structural, lattice dynamical, and thermodynamic properties of Ruddlesden-Popper chalcogenide Ba_n+1Zr_nS_3n+1 (n=1,2,3, ∞) using the self-consistent quasi-harmonic approximation within density functional theory. These responses are compared to the thermal expansion of Ruddlesden-Popper oxides and recent experimental data, which allows us to suggest guidelines for engineering thermal expansion in the Ruddlesden-Popper structure type with diverse chemistries.

This work was supported by the National Science Foundation’s MRSEC program (DMR-1720139.) at the Materials Research Center of Northwestern University.

Octahedral tilting is integral to the structure and functionality of perovskites: tilt distortions influence the electronic and magnetic properties [1] and reduce the macroscopic symmetry, as rationalised by group theory [2]. Since tilts are driven by the relative sizes of the metal ions, compositional modification can allow for the control of tilt patterns to achieve desired functionality, such as multiferroicity [3]. A class of materials closely related to perovskites are the Prussian blue analogues (PBAs), where cyanide anions replace the oxides to give the formula A_xM[Mʹ(CN)₆]_1−y□_y⋅nH₂O (A is an alkali metal, M and Mʹ are transition metals and □ denotes a vacancy). Like double perovskites, the parent structure (aristotype) adopts the space group Fmm, although ordered A-site cations (x > 1) or vacancies (y > 1) may reduce the symmetry to F3m or Pmm.

Due to the similarity to perovskites, octahedral tilting also features in PBAs and can have a strong impact on the functional response. To illustrate, the tilts in Na₂MnMn(CN)₆ nearly triples the magnetic ordering temperature compared to the cubic Cs₂MnMn(CN)₆ [4]. However, the tilting in PBAs is poorly understood, which is evidenced by considerable confusion in the literature. A systematic understanding of the factors underlying octahedral tilting in PBAs would be highly beneficial and facilitate tilt engineering approaches.

Here, density functional theory (DFT) calculations and literature surveys are used to identify and rationalise the trends in octahedral tilting for PBAs. A high concentration of A-site cations is a prerequisite for tilting and PBAs with x < 1 are almost invariably cubic, even upon cooling. Moreover, the A-site cation radius dictates the particular tilt pattern [Fig. 1], in line with the behaviour of perovskites. Mʹ(CN)₆ vacancies—which have no analogue in oxide perovskites—do not appear to play a major role, but the presence of interstitial water dictates which tilt pattern that appears in response to external or chemical pressure. Functional implications of the tilts include the tilt-driven improper ferroelectricity in the high-pressure Pn phase of RbMnCo(CN)₆ [5], or the undesirable tilt transition upon Na intercalation in cathode materials based on PBAs [6]. More generally, our results help develop a unified picture of the structural behaviour of PBAs and also improve the understanding of tilting distortions in general.

[1] Bull, C. L., & McMillan, P. F. (2004). J. Solid State Chem., 177, 2323.[2] Howard, C. J., Kennedy, B. J., & Woodward, P. M. (1999). Acta Cryst. B, 59, 463. [3] Pitcher, M. J., Mandal, P., Dyer, M. S., Alaria, J., Borisov, P., Niu, H., Claridge, J. B. & Rosseinsky, M. J. (2015). Science, 347, 420.

[4] Kareis, C. M., Lapidus, S. H., Her, J.-H., Stephens, P. W., & Miller, J. S. (2012). J. Am. Chem. Soc., 134, 2246.

[5] Boström, H. L. B., Collings, I. E., Daisenberger, D., Ridley, C. J., Funnell, N. P., & Cairns, A. B. (2021). J. Am. Chem. Soc., 143, 3544.

[6] Asakura, D., Okubo, M., Mizuno, Y., Kudo, T., Zhou, H., Ikedo, K., Mizokawa, T., Okazawa, A., & Kojima, N. (2012). J. Phys. Chem. C, 116, 8364.

Study of pressure induced structural phase transitions in perovskites has received considerable attention as it can tune many physical properties like band gap, resistivity, piezoelectric coefficients and ferroelectric polarization, etc. PbTiO₃ (PT) is one such model compound whose high pressure behaviour has been a topic of extensive research in recent years because of its technological importance as the end member of the commercial piezoelectric solid solution compositions in the electronics industry [1]. However, the structural phase transition sequence of PT at high pressures has remained very controversial with two entirely different propositions. As per the first principles calculations of Wu & Cohen [2] and subsequent experimental studies [3], pressure can induce polarization rotation due to a tetragonal to monoclinic phase transition much in the same way as the composition does in the morphotropic phase boundary (MPB) based commercial piezoelectric solid solution systems. First principles calculations and experimental studies by Kornev and his co-workers [4], on the other hand, present a completely different picture whereby PT undergoes a pressure induced antiferrodistortive (AFD) structural phase transition, albeit with decreasing tetragonality, until a ‘pseudo-cubic’ like non-ferroelectric phase appears which is followed by the emergence of a reentrant ferroelectric phase at still higher pressures. However, the evidence for AFD superlattice reflections were not observed at moderate pressures predicted theoretically [4]. Recently, we have addressed these controversies by carrying out a careful study of high pressure structural phase transitions in a tetragonal composition of PbTiO₃ solid solution containing 50% BiFeO₃ (PT-0.5BF) using synchrotron x-ray diffraction measurements at P02.2 Extreme Conditions Beamline of PETRA III at DESY. A tetragonal composition in the solid solution of PbTiO₃ with BiFeO₃ was chosen to enhance the AFD instability and hence the intensity of the superlattice peaks [5]. Our results [5] show that even at moderate pressures (~2.15 GPa), the tetragonal P4mm phase of PT-0.5BF system transforms to a monoclinic phase in the Cc space group, which permits MPB type rotation of ferroelectric polarization vector as well as oxygen octahedral tilting induced by a concomitant AFD transition (see Fig. 1). The transition pressure is very close to the theoretically predicted moderate pressure values for pure PT [4]. Our results also show that with increasing pressure, the ferroelectric distortion decreases and the structure acquires a pseudo-cubic character at intermediate pressures, as expected on the basis of Samara’s criterion [6] (see Fig. 2). But interestingly, our studies reveal that the ferroelectric distortion starts increasing above a critical pressure (~7 GPa) due to the emergence of a reentrant ferroelectric phase through an isostructural phase transition in which the oxygen octahedral tilting provides an efficient mechanism for volume reduction. Our results show that the DFT based theoretical predictions of both the groups [2,4] are correct in parts but none of the two provides the complete picture. Our results not only resolve the existing controversies but also provide an insight towards designing of new environmentally friendly Pb-free piezoelectric compositions.

Metal halide perovskites (MHPs) has shown impressive results in solar cells, light emitting devices, and scintillator applications, but its complex crystal structure is only partially understood and many open questions are still to be answered [1]. In particular, a method to image the dynamics of the nanoscale ferroelastic domains in MHPs requires a challenging combination of high spatial resolution and long penetration depth. With the recent development in X-ray optics it is now possible to focus X-rays down to the nanoscale. Combining the traditional high sensitivity to lattice spacing and tilt, as well as its characteristic to probe deep into the sample, nanofocused scanning X-ray diffraction is a unique powerful technique on the study of MHPs domain dynamics [2].

In this work, we demonstrate in situ temperature-dependent imaging of ferroelastic domains in a single nanowire of metal halide perovskite, CsPbBr₃, using scanning X-ray diffraction with a 60 nm beam [3] to retrieve local structural properties for temperatures up to 140 °C [4]. We observed a single Bragg peak at room temperature, but at 80 °C, four new Bragg peaks appeared, originating in different real-space domains, as depicted in Fig. 1 (left panels). The originally random domains were arranged in periodic stripes in the center and with a hatched pattern close to the edges, as one can see in Fig. 1 (right panels). Reciprocal space mapping at 80 °C was used to quantify the local strain and lattice tilts, revealing the ferroelastic nature of the domains. The domains display a partial stability to further temperature changes. Our results show the dynamics of nanoscale ferroelastic domain formation within a single-crystal perovskite nanostructure, which is important both for the fundamental understanding of these materials and for the development of perovskite-based devices.

[1] Zhang, W.; Eperon, G. E.; Snaith, H. J. (2016). Nature Energy 1 (6), 16048. DOI: 10.1038/NENERGY.2016.48 [2] Chayanun, L.; Hammarberg, S.; Dierks, H.; Otnes, G.; Bjorling, A.; Borgstrom, M. T.; Wallentin, J. (2019). Crystals 9 (8), 432. DOI: 10.3390/cryst9080432 [3] Bjorling, A.; Kalbfleisch, S.; Kahnt, M.; Sala, S.; Parfeniukas, K.; Vogt, U.; Carbone, G.; Johansson, U. (2020). Opt. Express 28 (4), 5069. DOI: 10.1364/OE.386068 [4] Marçal, L. A. B.; Oksenberg, E.; Dzhigaev, D.; Hammarberg, S.; Rothman, A.; Björling, A.; Unger, E.; Mikkelsen, A; Joselevich, E; Wallentin, J. (2020). ACS Nano 14, 15973. DOI: 10.1021/acsnano.0c07426

Antiferroelectric perovskites form an important family of functional electric materials, which have high potential in energy storage and conversion applications. However, a full understanding of their crystal structural formation is still lacking. PbZrO₃-based materials can serve as a model system for investigation, not only because PbZrO₃ was the first discovered antiferroelectric, but also because it undergoes a typical phase transition sequence from a high-temperature paraelectric to the low-temperature antiferroelectric phase, passing through a possible intermediate (IM) phase that is poorly understood. The IM phases usually exist only in a narrow temperature interval in pure PbZrO₃, and therefore it is hard to capture them. On the other hand, with a small amount of Ti substitution, the Zr-rich PbZr_1-xTi_xO₃ (PZT, x ≤ 0.06) also displays a room-temperature antiferroelectric structure and goes through the same phase transition process as PbZrO₃. In this case, the temperature range of the IM phase becomes wider, which makes a detailed study of the IM structures possible.

Here we employ a combination of optical and scattering experiments and theoretical calculations to reveal the nature of the intermediate state. Experimental results show that the IM phase is not a pure phase but a state containing a mixture of several short- and long-range correlated structural components that compete energetically in a complicated way. To emphasize this, we shall henceforth refer to it as the IM state rather than the IM phase. There are several types of superstructure reflections that appear in the IM state temperature range in the single-crystal diffuse scattering pattern (Fig. 1). With the aid of synchrotron powder total scattering and high-resolution neutron diffraction data analysis, we constructed the complex structural models in this temperature range [1]. Evidence is found that this peculiar state consists of multiple short-range and long-range structural components, as well as complex mesoscopic domain structure [2]. External stimuli such as temperature change or chemical substitution can easily alter each component’s energy landscape and thereby change the materials' electrical properties. These findings provide new insights in understanding antiferroelectric-ferroelectric competition and hence in designing new antiferroelectric materials.

[1] An, Z., Yokota, H., Zhang, N., Pasciak, M., Fábry, J., Kopecký, M., Kub, J., Zhang, G., Glazer, A. M., Welberry, T. R., Ren, W., & Ye, Z.-G. (2021) Phys. Rev. B 103, 054113.

[2] An, Z., Xie, S., Zhang, N., Zhuang, J., Glazer, A. M., Ren, W., & Ye, Z.-G. (2021) APL Mater. 9, 030702.

We review the efforts of many scientists around the world to discover and structurally characterize olanzapine crystal forms, clearing up inconsistencies in the scientific and patent literature and highlighting the challenges in identifying new forms amidst 60+ known polymorphs and solvates.[1] Owing to its remarkable solid-state chemistry, olanzapine has emerged over the last three decades as a popular tool compound for developing new experimental and computational methods for enhanced molecular level understanding of solid-state structure, form diversity and crystallization outcomes. This presentation highlights the role of olanzapine in advancing the fundamental level understanding of crystal forms, interactions within crystal structures, and growth units in molecular crystallization, and in influencing the way in which drugs are developed to this day.

[1] Reutzel-Edens, S.M., Bhardwaj, R. M. IUCrJ (2020). 7, 955-964 https://doi.org/10.1107/S2052252520012683

Rechargeable batteries enable switching to “green” energy production and consumption making a decisive impact in electromobility and integration of renewable energy sources into electric grids. Steadily rising demands in increasing specific energy, durability and lowering cost of electrochemical energy storage devices inspired extensive search for improved positive electrode (cathode) materials for advanced metal-ion batteries. Rational design of the cathode materials requires understanding of the intricate relationships between their crystal and electronic structures, as well as their evolution in course of reversible (de)intercalation of the alkali cations and through extended number of charge and discharge cycles. As the intercalation-type electrodes rely on long-range cationic diffusion reckoning on availability of the cation migration pathways with low energy barriers, the presence, spatial distribution, concentration and atomic structure of point and/or extended defects, which can block the ionic transport, have huge impact on capacity and rate capability of the metal-ion batteries. Polyanion cathode materials demonstrate extremely complex chemistry and crystallography of defects leading to exchange of the alkali and transition metal cations as a result of the synthesis or formed upon electrochemical cycling. Antisite cationic defects, heterovalent anionic defects and order-disorder in the alkali metal sublattice will be considered in relation with the electrochemical capacity, cycling stability and a competition between the solid-solution and two-phase (de)intercalation mechanisms in A₂MPO₄F (A – alkali cation, M – transition metal) and LiFePO₄ polyanion cathodes. Cationic disorder in the layered A_1+xM_1-xO₂ oxide cathodes is believed to play pivotal role in voltage fade and voltage hysteresis. The degree of this disorder will be characterized at different spatial scales using a combination of diffraction techniques and aberration-corrected transmission electron microscopy, both in the pristine materials and in the materials at different states of charge. Finally, the relationships between planar defects, such as twin boundaries and stacking faults, and electrochemical properties of the hierarchically-structured layered oxide cathodes will be demonstrated. The work is supported by RSF (20-13-00233).

Using the tools of group theory we have mapped out the symmetry consequences of structural distortions in hybrid layered perovskites. These distortions include octahedral tilting and cation ordering within the inorganic layers as well as orientational ordering of organic cations in the organic layers. This analysis is coupled with synthesis and crystal structure determination of a wide variety Ruddlesden-Popper phases. The combined analysis shows that certain modes of octahedral tilting are strongly favored in large part because they lead to favorable hydrogen bonding interactions between the halide ions of the inorganic layers and the ammonium-type protons of the organic cations that sit between the layers. This information is used to guide our search for new lead-free ferroelectrics and multiferroics among this large class of compounds.

The A-site ordered quadruple perovskites AA’₃B₄O₁₂ can accommodate transition metal cations at the square-planar A’ site. When the B site is occupied by non-magnetic cations, the complex magnetic interactions between the spins at the orthogonally-oriented A’-sites can result in a wide variety of non-trivial magnetic orders. For example, A’-site Cu²⁺ (S = 1/2) spins can align either ferromagnetically (FM) in CaCu₃Sn₄O₁₂ or CaCu₃Ge₄O₁₂ (T_C = 10 and 13 K respectively), or antiferromagnetically (AFM) in CaCu₃Ti₄O₁₂ (T_N = 25 K) as a result of competition between direct exchange and superexchange interactions. A’-site Mn³⁺ (S = 2) in YMn₃Al₄O₁₂ yields a G-type AFM structure (T_N = 37 K) and Mn²⁺ (S = 5/2) spins in LaMn₃V₄O₁₂ break the symmetry to form a helix-type AFM structure (T_N = 44 K).

We recently revisited the material CaFe₃Ti₄O₁₂ with S = 2 (Fe²⁺) centers at the A’-sites for which initial studies did not find any long range magnetic order down to 4.2 K. This absence of magnetic ordering was notably unconventional. We discovered that the Fe²⁺ (S = 2) spins in CaFe₃Ti₄O₁₂ order in a complex triple-k AFM ground state at T_N = 2.8 K. In contrast to most magnetic insulating oxides, the Heisenberg superexchange between first- and second-neighbour spins are minimised by strong easy-axis anisotropy. Further-neighbour interactions yield the resulting spin ground state. On application of magnetic field, a canted FM spin structure is induced. This magnetic ordering is contrastingly different from those previously reported for A’-site magnetic quadruple perovskite materials. Furthermore, our results show that exotic long-range magnetically ordered ground states can emerge in large-spin systems when the symmetric exchange is quenched.

Charge ordering is prone to occur in crystalline materials with mixed-valence ions. It is often accompanied by a structural phase transition between a low-symmetry phase and a more symmetric high-temperature parent crystal structure. Such a structural transition may be absent if the mixed-valence ions are already located in inequivalent crystallographic sites in the parent structure. In this work, we investigate the representative case of the homometallic Co ludwigite (Co²⁺)₂(Co³⁺)O₂BO₃ (Pbam space group) with four distinct Co crystallographic sites surrounded by oxygen octahedra [Co(1)-Co(4)]. X-ray Absorption Near-Edge Spectroscopy provide experimental support for a Co²⁺/Co³⁺ mixed-valence scenario at all temperatures. X-ray and neutron diffraction confirm that the oxygen octahedron surrounding the Co(4) site is much smaller than those associated with the Co(1)-Co(3) sites at low temperatures, consistent with a localization of the Co³⁺ ions at the Co(4) site. The size differentiation of the Co(4)O₆ and Co(2)O₆ octahedra is continuously reduced upon warming above ~ 370 K, revealing a gradual charge redistribution along the Co(4)-Co(2)-Co(4) (424) ladder. In addition, small anomalies in specific Co-O bond lengths in the Co(3)-Co(1)-Co(3) (313) ladder are observed at 470 K and 495 K, respectively, matching the temperatures where sharp transitions were previously revealed by calorimetry and resistivity measurements. These bond length anomalies occur without an accompanying space group change within our sensitivity. An increasing structural disorder, clearly beyond a conventional thermal effect, is noted above ~ 370 K, manifested by an anomalous increment of some XRD Debye-Waller factors and broadened vibrational modes observed by Raman scattering. The local Co-O distance distribution, revealed by Co K-edge Extended X-Ray Absorption Fine Structure (EXAFS) data and analyzed with an evolutionary algorithm method, is similar to that inferred from the XRD crystal structure below ~ 370 K. At higher temperatures, the local Co-O distance distribution remains similar to that found at low temperatures, indicating that the size differentiation between smaller Co³⁺ ions and larger Co²⁺ions is maintained despite the growing oxidation-state disorder within the 424 ladder upon warming. This study provides insight into the physics of ludwigites and other related complex oxides at high temperatures.

Acknowledgments: This work was supported by CNPq Grants 134752/2016-3 and 308607/2018-0,
FAPESP Grant 2018/20142-8, and CAPES, Brazil.

Transition metal oxides are a platform for a plethora of exotic electronic phases where multiple degrees of freedom of correlated d-electrons, together with an underlying lattice topology, are at play. The ground states of these systems are governed by a subtle balance of relevant electronic parameters such as Coulomb repulsion, bandwidth, and crystal fields. 4d ruthenium compounds have been playing a significant role in providing novel electronic states such as unconventional superconductivity, metal-insulator transition and quantum magnetism.

Besides metallic or Mott insulating ground states, some ruthenium compounds exhibit a nonmagnetic ground state, which is accompanied by the formation of molecular orbitals generated by direct hopping between spatially extended 4d orbitals. A prominent example is the honeycomb ruthenate Li₂RuO₃, which undergoes dimerization of Ru atoms below ~ 550 K and forms a "molecular orbital crystal", where the 4d electrons are accommodated into the bonding and antibonding molecular orbitals localized on the dimers.

In heavy-transition-metal compounds such as ruthenates, another key ingredient for their exotic electronic states is spin-orbit coupling (SOC) which produces spin-orbit entangled J_eff pseudospins. Probably the most striking impact on magnetism is realised in Ru⁴⁺ ruthenates with a d⁴ configuration. While SOC produces a nominally non-magnetic J_­eff = 0 singlet, “excitonic” magnetism can arise via the interaction between excited states, and spin-orbit excitons may condense into an exotic long-range magnetic order. Up to date, excitonic magnetism has been only established in a layered perovskite Ca₂RuO₄ and remains unexplored in other ruthenates.

The competition between electronic phases including molecular orbital crystal and spin-orbit magnetism is expected to be more pronounced in ruthenates with a frustrated lattice, such as pyrochlore ruthenates A₂Ru₂O₇ (A: trivalent cation). The pyrochlore ruthenates have been regarded as S = 1 Mott insulators due to the presence of a trigonal distortion which may lift the degeneracy of the t_2g orbitals and thus competes with SOC. While most of them order magnetically at low temperatures, Tl₂Ru₂O₇ exhibits a metal to non-magnetic insulator transition at ~ 120 K. The origin of the nonmagnetic ground state has been attributed to the formation of a Haldane gap in the one-dimensional zigzag chains of Ru atoms on top of the pyrochlore lattice. The distinct behaviour of Tl₂Ru₂O₇ may be related to the covalency of Tl-O bonds, which has been discussed as playing a key role in the metal-insulator transition. The covalent character of A-O bonds thus may be an important parameter for the ground state of pyrochlore oxides. On the other hand, the role of spin-orbit coupling has not been fully investigated in pyrochlore ruthenates.

In an attempt to explore the novel phase competition in pyrochlore ruthenates, we discovered a new compound In₂Ru₂O₇ using high pressure synthesis. At high temperatures above ~ 450 K, In₂Ru₂O₇ crystallizes in a cubic pyrochlore structure, but adopts a weakly distorted tetragonal structure at room temperature as elucidated with single crystal x-ray and powder neutron diffraction. From the spectroscopic measurements, In₂Ru₂O₇ was found to host a spin-orbit-entangled J_eff = 0 -like state at room temperature, despite presenting the largest trigonal distortion among the family of pyrochlore ruthenates. The spin-orbit entangled singlet state is expected to display excitonic magnetism. Strikingly, through successive structural transitions likely associated with the covalent In-O bonds, the singlet state collapses and In₂Ru₂O₇ forms a non-magnetic state below ~ 220 K as evidenced by muon spin rotation. The non-magnetic ground state was found to originate from a molecular orbital formation in the semi-isolated Ru₂O trimer molecules decorating the pyrochlore lattice. Such molecular orbital formation, which involves not only the Ru⁴⁺ ions but the O^2- anions as well, has not been reported in other pyrochlore oxides.

In this talk we discuss the subtle competition between spin-orbit coupling and molecular orbital crystal formation in pyrochlore ruthenate In₂Ru₂O₇. We present the structural details of the Ru₂O trimer formation and its impact on the magnetism and electronic structure of In₂Ru₂O₇. We argue that the unique molecular orbital formation involving an oxygen atom, distinct from dimers with direct overlap of d-orbitals commonly found in other transition metal oxides, is assisted by the distortion of the In-O network. Our result demonstrates that bond covalency of constituent ions can be an additional key parameter in understanding phase competitions in complex transition-metal oxides.

The scheelites are a family of compounds with chemical formula ABO₄, and a characteristic crystal structure consisting of AO₈ dodecahedra and BO₄ tetrahedra. This structure is flexible and can accommodate a large variety of cations with a range of atomic radii and valence combinations. Scheelite-type oxides, such as CaWO₄, BiVO₄ and NaLa(MoO₄)₂ have been extensively studied due to their diverse range of physical and electronic properties [1]. In particular, Bi³⁺ containing molybdates have been found to be efficient photocatalysts due to the strong repulsive force of the 6s² lone pair of Bi³⁺, resulting in distortion of the BO₄ tetrahedra and alteration of the band gap [2, 3].

In 1974 Bi₃FeMo₂O₁₂ (BFMO) was reported as the first scheelite-type compound containing trivalent cations on the tetrahedral sites [4]. Interestingly, two different polymorphs of BFMO can be isolated by varying the synthesis conditions [5]. The tetragonal scheelite-type polymorph, described by space group I4₁/a with a = 5.32106(13) Å and c = 11.656(4) Å, can be prepared by a sol-gel route from aqueous solution of the constituent ionic species and has a disordered arrangement of the Fe and Mo cations. When heated above 500 °C, a 2:1 ordering of the Mo and Fe cations occurs, which lowers the symmetry to monoclinic (C2/c). The corresponding superstructure has a tripling of the a axis (a = 16.9110 (3) Å, b = 11.6489(2) Å, c= 5.25630(9) Å, β = 107.1395(11)°). The two structures are illustrated in Fig. 1.

In the present study, both polymorphs of BFMO were synthesized and their structure and magnetic properties characterized using a combination of powder diffraction, microscopy and magnetometry techniques. In situ neutron powder diffraction (NPD) measurements of the structural evolution of disordered tetragonal BFMO with increasing temperature showed that no amorphization takes place prior to the formation of the ordered monoclinic phase. The lack of a structural break-down, despite the substantial cation movement required in such a transformation, suggests that a certain degree of local cation order exists in the “disordered” tetragonal phase, facilitating the direct conversion to the fully ordered monoclinic structure. Instead of the expected amorphization and recrystallization, the conversion takes place via a 1^st order phase transition, with the tetragonal polymorph exhibiting negative thermal expansion prior to its conversion into the monoclinic structure. Zero-field-cooled/field-cooled and field-dependent magnetization curves of the monoclinic structure revealed the existence of a magnetic transition below 15 K. The long-range nature of the low-temperature magnetic structure in the monoclinic polymorph was verified by high-resolution NPD data, which revealed the emergence of an incommensurate magnetic structure. There is no evidence for long-range magnetic order in the tetragonal polymorph. This is, to the best of our knowledge, the first study of the phase transition mechanism and magnetic properties of this complex system and represents a milestone in the structural understanding and targeted design of Bi³⁺ containing molybdates as efficient photocatalysts.

[1] Brazdil, J. F. (2015). Catalysis Science & Technology 5, 3452-3458.

[2] Feng, Y., Yan, X., Liu, C., Hong, Y., Zhu, L., Zhou, M. & Shi, W. (2015). Appl Surf Sci 353, 87-94.

[3] Tokunaga, S., Kato, H. & Kudo, A. (2001). Chem Mater 13, 4624-4628.

[4] Sleight, A. W. & Jeitschko, W. (1974). Materials Research Bulletin 9, 951-954.

[5] Jeitschko, W., Sleight, A. W., Mcclellan, W. R. & Weiher, J. F. (1976). Acta Crystallogr B 32, 1163-1170.

A detailed account of the local atomic structure and disorder at 5 K across the phase diagram of the high-temperature superconductor K_xFe_2-ySe_2-zS_z (0≤z≤2) is obtained from neutron total scattering and associated atomic pair distribution function (PDF) approaches [1]. Various model-independent and model-dependent aspects of the analysis reveal a high level of structural complexity on the nanometer length scale. Evidence is found for considerable disorder in the c-axis stacking of the FeSe S slabs without observable signs of turbostratic character of the disorder. In contrast to the related FeCh (Ch = S, Se)-type superconductors, substantial Fe-vacancies are present in K_xFe_2-ySe_2-zS_z, deemed detrimental for superconductivity when ordered. Our study suggests that the distribution of vacancies significantly modifies the iron-chalcogen bond-length distribution, in agreement with observed evolution of the PDF signal. A crossover-like transition is observed at a composition of z≈1, from a correlated disorder state at the selenium end to a more vacancy-ordered (VO) state closer to the sulfur end of the phase diagram. The S-content-dependent measures of the local structure are found to exhibit distinct behavior on either side of this crossover, correlating well with the evolution of the superconducting state to that of a magnetic semiconductor toward the z≈2 end. The behavior reinforces the idea of the intimate relationship of correlated Fe-vacancy order in the local structure and the emergent electronic properties.

[1] P. Mangelis et al., (2019) Physical Review B 100, 094108.

Work at Brookhaven National Laboratory was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (DOE-BES) under Contract No. DE-SC0012704. Alexandros Lappas acknowledges support by the U.S. Office of Naval Research Global, NICOP Grant Award No. N62909-17-1-2126. This research used resources at the Spallation Neutron Source, a U.S. Department of Energy Office of Science User Facility operated by the Oak Ridge National Laboratory.

A proposal for a high brilliance upgrade to the SOLEIL synchrotron radiation source is expected to increase the beam brightness by > 50 times on beamlines used for life sciences. The combined expertise of the life sciences beamline teams at SOLEIL form the HelioBiology section, which has been, for the last 4 years, developing a post-upgrade approach to structural biology. This approach will be presented, paying particular attention to facilities that are novel to SOLEIL including in-vivo crystallisation [1] , microfluidic devices and their synchrotron applications [2], and concrete efforts towards an integrated approach to structural problems. Initial proposals for structural biology facilities (including an on- and off- beamline portfolio of instruments) will be presented, drawing on recent examples to illustrate the approach.

This work is presented on behalf of the members of the HelioBio scientific section at SOLEIL (https://www.synchrotron-soleil.fr/en/research/house-research/biology-health-heliobio).

References

[1]. Banerjee, S., Montaville, P., Chavas, L.M.G., Ramaswamy, S. "The New Era of Microcrystallography" Journal of the Indian Institute of Science., 98(3): 273–281. (2018).

[2]. Chaussavoine, I., Beauvois, A., Mateo, T., Vasireddi, R., Douri, N., Priam, J., Liatimi, Y., Lefrançois, S., Tabuteau, H., Davranche, M., Vantelon, D., Bizien, T., Chavas, L.M.G., Lassalle-Kaiser, B. "The microfluidic laboratory at Synchrotron SOLEIL" Journal of Synchrotron Radiation., 27(1): 230-237. (2020).

The global need to collect diffraction data from micro-crystals has been reflected by the development of dedicated microfocus beamlines for macromolecular crystallography worldwide. The increased intensity and brightness of these beamlines imposes a fundamental limitation however which precludes successful structure determination from a single microcrystal: radiation induced damage. X-ray induced radiation damage means that data must often be merged from many crystals to yield a complete dataset for structure solution [1, 2]. This is frequently the case for challenging projects when only crystals of limited size are available. Increasing the X-ray energy beyond the typical 10-15 keV range promises to provide a solution to this problem via an increase in the amount of information that can be obtained per unit absorbed dose or ‘diffraction efficiency’ [3-5].

To date however hardware limitations have negated any possible high energy gains. Typically the sensor material of detectors used in macromolecular crystallography is silicon. With its low atomic number, silicon becomes transparent as the X-ray energy is increased and the detector quantum efficiency falls rapidly as a function of energy. Recently, detectors using cadmium telluride as a sensor material have been developed; resulting in a quantum efficiency of 90% below the cadmium absorption edge (26.7 keV) and nearly 80% up to energies of 80 keV [6].

Through use of a new cryogenic permanent magnet undulator and a Cadmium Telluride Eiger2 detector high photon fluxes at high energies (>20 keV) can be generated and resulting microcrystal diffraction efficiently detected. Our results show that at higher energies fewer crystals will be required to obtain complete data, as the diffracted intensity per unit dose increases significantly between 12.4 and 25 keV. In an additional gain for the crystallographer, we observe that data collected at higher energies typically extend to higher resolution. Taken together our results illustrate that the use of high energies allows the best possible data to be collected from small protein crystals pointing to a high energy future for synchrotron-based macromolecular crystallography.

During the last decades, structural biology had a major impact in understanding the structure-functional aspects of some of the most important biological machineries. The new ESRF Extremely Brilliant Source opened a new age in microcrystallography and permitted to extend further the capabilities of the macromolecular crystallography beamlines and will open new pathways in the study of time-dependent structural changes. This is the scope of the upgrade of the ID29 beamline.

The new beamline combined cutting edge instrumentations to fully exploit serial crystallography experiments at room temperature. This presentaition will present the the beamline design with particular relevance to the new instrumentations and present the new scientifc opportunities that it will offer to the structural biology user community.

To study the effect of high pressure on any sample property, suitable pressure devices are a fundamental requirement. Their design has to be tailored to the experimental demands regarding the intended pressure, the employed instrumentation and the expected scientific results. Our work presents the development of high pressure cells for neutron scattering on polycrystalline and single-crystalline samples at low temperatures and with applied magnetic fields.

One of the most common devices for high-pressure neutron experiments is the clamp cell [1], where the pressure is applied ex situ and which can be used independently in various setups. Our cell design [2] has been specifically developed for neutron scattering experiments at low temperatures in the closed-cycle cryostats on the instruments DNS (diffuse scattering neutron spectrometer), MIRA (cold three axes spectrometer), and POLI (polarized hot neutron diffractometer) at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, Germany. Two variants of the compact monobloc cell (Fig. 1) were produced, one from CuBe alloy and from NiCrAl “Russian Alloy”, working up to about 1.1 GPa and 1.5 GPa, respectively. The low paramagnetic moment of both alloys allows also measurements of magnetic properties.

First tests of the cell with neutron radiation were performed to calibrate the load/pressure-curve of the CuBe cell (up to 1.15 GPa) (at POLI), to estimate its neutron absorption and background (at MIRA), and to measure magnetic reflections (at MIRA). In addition, the thermal response in the cryostat of DNS was measured, and the experimental findings were complemented by simulations.

Ultimately, these cells are intended as standard cells for high pressure measurements on different instruments at MLZ suitable for all available magnets and cryostats down to 1.5 K. Further tests under various conditions (temperature, pressure, magnetic field) as well as simulations are planned for both cells in the near future. The results will help both to establish the present cells and to optimise the design of subsequent cells to achieve higher pressures, to fit into smaller cryostats and to enable neutron-independent pressure calibration.

Figure 1. Schematic drawing of the clamp cell.

[1] Klotz, S. (2013). Techniques in High Pressure Neutron Scattering. CRC Press.

[2] Eich, A., Hölzle, M., Su, Y., Hutanu, V., Georgii, R., Beddrich, L. & Grzechnik, A. (2020). High Press. Res. 41[1], 88–96.

High-end x-ray scattering techniques such as BIO-SAXS (e.g. SEC-SAXS), non-ambient SAXS and GISAXS rely heavily on the x-ray source brightness for resolution and exposure time. Traditional solid or rotating anode x-ray tubes are typically limited in brightness by when the e-beam power density melts the anode. The liquid-metal-jet technology has overcome this limitation by using an anode that is already in the molten state.

We have previously demonstrated prototype performance of a metal-jet anode x-ray source concept with unprecedented brightness in the range of one order of magnitude above current state-of-the art sources. Over the last years, the liquid-metal-jet technology has developed from prototypes into fully operational and stable X-ray tubes running in many labs over the world. Small angle scattering has been identified as a key application for this x-ray tube technology, since this application benefits greatly from high-brightness and small spot-sizes, to achieve a high flux x-ray beam with low divergence. Multiple users and system manufacturers have since installed the metal-jet anode x-ray source into their SAXS set-ups with successful results. With the high brightness from the liquid-metal-jet x-ray source, time resolved and in-situ SAXS studies can be performed – even in the home laboratory.

This presentation will review the current status of the metal-jet technology specifically in terms of flux and brightness and the impact of SAXS measurement. Such as the influence of the size of the x-ray source and its distance to the x-ray optics on the divergence will be discussed, and how to minimize the divergence and maximize the flux in SAXS experiments targeted to specific applications. It will furthermore refer to some recent SAXS and GISAXS data from users of metal-jet x-ray tubes.

For the first time, holistically optimized laboratory x-ray absorption spectroscopy (XAS) systems enable XAS measurements of most elements in the periodic table (Z>13) in minutes with energy resolution better than 0.7 eV, approaching capabilities of XAS facilities using bending magnet beamlines at second generation synchrotron light sources. The optimizations include:

• High brightness x-ray source with high thermal conductivity target incorporating diamond substrate, multiple target materials providing smooth spectrum free from characteristic x-ray lines, x-ray source size and shape optimized for using low miller index diffraction planes of cylindrically bent Johannsson crystal analyzers at low-medium Bragg angles, which provides optimal tradeoff between x-ray energy resolution and flux.
• Making use of dispersion of cylindrically bent Johannsson crystal analyzers in both tangential and sagittal directions for efficient use of source x-rays.
• 2D photon counting detector for recording x-rays dispersed by the crystal analyzer in tangential and sagittal directions and rejecting harmonics reflected by a crystal analyzer.

With those options, we have developed laboratory XAS systems operating from 1.7 keV to 25 keV, providing monochromatic x-ray flux over 2*10^7/s, and achieved energy resolution better than 0.7eV. The design and performances of the systems will be presented.

A particular family of stable organic radicals, the 1,2,3,5-dithiadiazolyls (DTDAs), has been the focus of much research due to their potential as building blocks for molecular materials, in particular materials with interesting magnetic or conducting properties [1]. However, DTDAs frequently dimerise in the solid state via an interaction known as pancake bonding (Fig. 1 left) [2], rendering them diamagnetic. Our various efforts to understand and overcome this pancake bonding interaction will be presented.

The potential of co-crystallisation as a means to overcome dimerisation in DTDAs has been investigated [3]. Thus far, all DTDA-DTDA co-crystals characterised crystallise as pancake-bonded dimers. This has been probed computationally. In related studies, control of polymorph and crystal morphology of a monomeric DTDA by co-sublimation has been demonstrated.

A DTDA has been included in a porous metallocyclic host in an effort to produce materials with interesting magnetic behaviour through interaction between the radical and the host (Fig. 1 right) [4]. The coordination of DTDAs to metalloporphyrins has also been extensively investigated. One particularly interesting DTDA-porphyrin polymer will be discussed [5]. In these systems, dimerisation has been overcome either by restriction of space available for the radical, or by formation of a DTDA-metal bond.

In order to gain a deeper understanding of pancake bonding, experimental charge density analysis has been carried out on a number of DTDA homodimers, heterodimers and monomers [6]. These data, as well as various computational results, have been assessed to probe the nature of the pancake bonds in DTDAs, and reveal how pancake bonds differ from both covalent bonds and conventional intermolecular interactions.

It is clear that DTDAs show great potential as building blocks in the construction of molecular materials.

Figure 1. (left) A DTDA pancake-bonded dimer. (right) DTDA included in a porous metallocycle.

[1] Haynes, D. A. (2011). CrystEngComm 13, 4793. [2] (a) Beneberu, H. Z., Tian, Y.-H. & Kertesz, M. (2012). Phys. Chem. Chem. Phys. 14, 10713. (b) Cui, H., Lischka, H., Beneberu, H. Z. & Kertesz, M. (2014). J. Am. Chem. Soc. 136, 12958. (c) Preuss, K. (2014). Polyhedron 79, 1-15. [3] (a) Alan,C., Haynes, D. A., Pask, C. M. & Rawson, J. M. (2009). CrystEngComm, 11, 2048. (b) Robinson, S. W., Haynes, D. A. & Rawson, J. M. (2013). CrystEngComm, 15, 10205. [4] Nikolayenko, V. I., Barbour, L. J., Arauzo, A., Campo, J., Rawson, J. M. & Haynes, D. A. (2017) Chem. Commun., 53, 11310. [5] Haynes, D. A., van Laeren, L. J. & Munro, O. Q. (2017). J. Am. Chem. Soc., 139, 14620. [6] (a) Domagała, S., Kość, K., Robinson, S. W., Haynes, D. A. & Wozniak, K. (2014). Cryst. Growth Des. 14, 4834. (b) Domagała, S. & Haynes, D.A. (2016). CrystEngComm, 18, 7116. (c) Voufack, A. B., Claiser, N., Dippenaar, A. B., Esterhuysen, C., Haynes, D. A, Lecomte, C. & Souhassou, M. Manuscript in preparation.

Quantum information theory is developing at a rapid pace and one can easily envisage a bright future, demonstrated by the growing number of quantum computing simulations offered at large scale computation facilities and by the construction of the first prototypes of quantum computers.

In this area, the contribution of crystallography, and especially of quantum crystallography, is seamlessly vital, because the inner mechanism at hearth in the transmission of signal is tightly connected with the chemical bonding, the electron charge and spin density distribution, and, ultimately, the wavefunction.

Quantum Crystallography [1,2,3] deals, in fact, with the application of quantum theory in crystallography. Among the various quantities investigated within this field, the electron delocalization and the spin electron density play a fundamental role in spintronic materials.

Over the years, several theoretical analysis emerged that can be applied to computed as well as to experimental electron densities. Moreover, the modelling techniques enable the reconstruction of many quantities from ever more precise and sophisticated experiments.

In this lecture, novel spintronic materials, such as magnetic coordination polymers [4,5], will be discussed, within the framework of recent quantum crystallographic studies. The role of the linkers in the magnetic exchange is not fully clear yet. A combinatorial approach, including studies on materials at high pressure shed light on the subtleties of exchange mechanisms.

References

[1] A. Genoni et al. Chemistry, Eur. J., 2018, 24, 10881-10905.

[2] P. Macchi Cryst. Rev. 2020, 26, 209-268.

[3] P. Macchi Quantum Crystallography: Fundamentals and applications 2022, De Gruyter to be published.

[4] Kubus, M., Lanza, A., Scatena, R., Dos Santos, LHR., Wehinger, B., Casati, N., Fioka, C., Keller, L., Macchi, P., Rüegg, C., Krämer, KW. (2018) Inorg. Chem. 57, 4934-4943.

[5] R. Scatena, R. D. Johnson, P. Manuel, P. Macchi, J. Mater. Chem. C 2020, 8, 12840–12847.

We have investigated the magnetic and electronic structures of crystalline dimethylammonium copper formate [(CH₃)₂NH₂]Cu(HCOO)₃; a model compound that belongs to a wide class of hybrid organic-inorganic perovskites. We present the results of a combined experimental approach, where neutron diffraction and magnetisation measurements were used to solve the ground state magnetic structure in which the same ligand mediate antiferromagnetic and ferromagnetic interactions, while electron charge density distribution and orbital occupancy were determined by high-resolution x-ray diffraction [1]. The latter provided a microscopic analysis of the chemical bonding from which we established a detailed correlation between the structural, electronic, and magnetic properties of [(CH₃)₂NH₂]Cu(HCOO)₃, demonstrating the primary role of Cu-O bonding in establishing the nature of the exchange. Our results elucidate the mechanism of magnetic exchange mediated by formate anions, from which we examine the applicability of foundational theories of purely inorganic perovskites and define characteristics that the ligands should meet to support the use of the Goodenough-Kanamori-Anderson (GKA) rules [2]. The derived criteria for the applicability of GKA rules where used to predict the magnetic structure, then verified experimentally, of hybrid perovskites including different ligands, such as [(CH₃)₂NH₂]Cu(HCOO)₂(NO₃) and Cu(HCOO)₂(pyrimidine). Charge density analysis enabled us to account for qualitative and quantitative differences in the superexchange mediated by formate, nitrate and pyrimidine.

[1] R. Scatena, R. D. Johnson, P. Manuel, P. Macchi, J. Mater. Chem. C 2020, 8, 12840–12847.

[2] S. V. Streltsov, D. I. Khomskii, Uspekhi Fiz. Nauk 2017, 187, 1205–1235.

This talk will underscore the importance of developing fast Quantum Crystallographic (QCr) [1] approaches to accurately calculate the electric fields and their associated electrostatic potentials of large molecules such as proteins.

Crystallographic structures of ATP synthase from five species have been used to calculate (approximately) and compare their intrinsic electrostatic potentials and fields [2-4]. Striking consistent patterns (and differences) in the topographies of these scalar and vector fields are uncovered across the five studied ATP synthases [2]. The role of these fields in the biological function of ATP synthase will be discussed within the context of Mitchell’s chemisomotic theory.

Our calculations suggest that, due to the intrinsic field of ATP synthase itself, the standard equation of chemiosmotic must be augmented by including a term that accounts for the contribution to ΔG of the difference in ATP synthase’s electrostatic potential, ΔΨ_ATPase, between the points of entry and exit of the protons in the mitochondrion. With this inclusion, our proposed amended equation for the chemisomotic ΔG, in standard notation, becomes [2-4]:

ΔG = ΔG_chem.+ ΔG_elec.+ (ΔG_ATPase (NEW TERM)) = 2.3 nRT ΔpH + nFΔΨ + nFΔΨ_ATPase

Our results can be summed-up into assigning two separate but complementary roles to ATP synthase ^[2]:

(1) Its putative role, and that is the catalysis (i.e. lowering the ΔG^‡) of the reaction: ADP + P_i ↔ ATP + H₂O.

(2) A novel role, that is, of altering the ΔG of the reaction of translocation of protons from the inter-membrane gap in the mitochondrion to the mitochondrial matrix, i.e. the reactions: H⁺_{inter-membrane space} ↔ H⁺_{mitochondrial matrix}.

Said differently, due to the enzyme’s very structure and due to the chemiosmotic origin of the free energy it harnesses, ATP synthase functions over an above its role as an enzyme and is more than strictly a biological catalyst.

The crucial role played by the enzyme’s own electric properties calls for their accurate and fast determinations especially with the advent of QCr [1]. An example of such approaches is the Kernel Energy Method [5-6] fragmentation whereby, given a molecular geometry, one can perform quantum calculations on fragments and obtain an approximate total electrostatic potential of the full molecules.

Since this is a part of a larger project, time permitting, the talk may touch upon some of the hot current open questions such as the one we term “Mitochondrion Paradox” [7-10].

[1] Genoni, A. ; Bucinskż, L.; Claiser, N.; Contreras-Garcia, J.; Dittrich, B.; Dominiak, P. M.; Espinosa, E.; Gatti, C.; Giannozzi, P.; Gillet, J.-M.; Jayatilaka, D.; Macchi, P.; Madsen, A. Ų.; Massa, L.; Matta, C. F.; Merz Jr., K. M.; Nakashima, P.; Ott, H.; Ryde, U.; Scherer, W.; Schwarz, K.; Sierka, M.; Grabowsky, S. (2018) Chem. Eur. J. 24, 10881-10905.

[2] Vigneau, J. N.; Fahimi, P.; Ebert, M.; Cheng, Y.; Tannahill, C.; Muir, P.; Nguyen-Dang, T.-T.; Matta, C. F. (2021) Submitted, in review.

[3] Cheng, Y. (2019). A Computational Investigation of the Intrinsic Electric Field of ATP Synthase (M.Sc. Thesis); Saint Mary's University: Halifax, Canada.

[4] Matta, C. F. (2016). Dipolar field of ATP Synthase: Unpublished results presented in a number of seminars.

[5] Huang L.; Massa, L.; Karle, J. (2010). Chapter 1 in: Quantum Biochemistry: Electronic Structure and Biological Activity, Vol. I; Matta, C. F. (Ed.), Wiley-VCH: Weinheim, 2010.

[6] Polkosnik, W.; Matta, C. F.; Huang, L.; Massa, L. (2019). Int. J. Quantum Chem. 119, e26095.

[7] Fahimi, P. ; Matta, C. F. (2021). Phys. Biol. 18 , in press (DOI: 10.1088/1478-3975/abf7d9).

[8] Fahimi, P. ; Matta, C. F. (2021) Submitted, in review.

[9] Nasr, M. A.; Dovbeshko, G. I.; Bearne, S. L.; El-Badri, N.; Matta, C. F. (2019). BioEssays 41, 1900055.

[10] Matta, C. F.; Massa, L. (2017). J. Phys. Chem. A 121, 9131-9135.

Melt-quenched glasses from metal-organic frameworks (MOF) represents a new class of hybrid functional materials, which have generated a lot of attention amongst the material science community due to their novel short-range structures and potential applications such as gas-mixture separations, ion conductivity, etc [1]. To improve the thermal stability window of the liquid phase of MOFs, substantial efforts are directed to lower the melting temperature of the crystalline MOF state [2, 3]. However, in this context, the relationship between chemical bonding and melting/decomposition of MOFs is still unexplored.

In this work, we compare the electron density distribution of two isostructural Zeolitic Imidazole Framework (ZIF) molecules-meltable Zn-ZIF-zni with Co-ZIF-zni that undergoes thermolysis, using high-resolution synchrotron single-crystal X-ray diffraction data measured at 25 K. Several ZIFs such as ZIF-4, ZIF-1, ZIF-3, ZIF-zeg, ZIF-nog undergo thermal amorphization and recrystallization to ZIF-zni prior to melting/decomposition [4]. Charge density analysis along with derived topological parameters based on Bader’s QTAIM theory [5] shows that Zn‒N bonds are primarily closed shell ionic in nature and weaker in strength. On the other hand, Co‒N bonds are dominated by polar covalent interactions with significant electron density accumulation in bonding region and distinct π-backbonding features (Fig. 1).

In situ temperature dependent Raman spectroscopy (300 K-773 K) revealed a greater degree of bond weakening in the imidazolate ligands of Co-ZIF-zni during heating. In addition, variable temperature crystallography (25 K-400 K) confirmed that Zn-ZIF-zni are less prone to framework distortion in comparison to a more rigid framework in Co-ZIF-zni. To further validate the role of metal‒ligand bonds on thermal behavior of these ZIF compounds, for the first time we prepared a set of eight novel solid solutions-Co_xZn_1-x-ZIF-zni where mole fraction (x) of Co ranges from 0.4 to as low as 0.003. Using differential scanning calorimetry (DSC)/ thermogravimetric analysis (TGA), we observed that a presence of very low quantity (~4%) of doped Co in Zn-ZIF-zni lattice results in thermal decomposition of the crystal framework. We identified this phenomenon as ‘butterfly effect’ of Co‒N bonds on thermal stability of these solid solution MOFs.

[1] Bennett, T. D. & Horike, S. (2018). Nat. Rev Mat. 3, 431-440. [2] Frentzel-Beyme, L., Kloß, M., Kolodzeiski, P., Pallach, R. & Henke, S. (2019). J. Am. Chem. Soc. 141, 12362-12371. [3] Hou, J., Ríos Gómez, M. L., Krajnc, A., McCaul, A., Li, S., Bumstead, A. M., Sapnik, A. F., Deng, Z., Lin, R., Chater, P. A., Keeble, D. S., Keen, D. A., Appadoo, D., Chan, B., Chen, V., Mali, G. & Bennett, T. D. (2020). J. Am. Chem. Soc. 142, 3880-3890. [4] Bennett, T. D., Keen, D. A., Tan, J.-C., Barney, E. R., Goodwin, A. L. & Cheetham, A. K. (2011). Angew. Chem. Int. Ed. 50, 3067-3071. [5] Bader, R. F. (1990). Atoms in molecules. Wiley Online Library.

Thermoelectric materials are able to interconvert thermal and electrical energy, and thus offer the potential to harvest waste heat through solid-state devices. A particularly interesting class of thermoelectric materials are the cubic intermetallic Half-Heusler semiconductors with XYZ stoichiometry, which show promising high temperature thermoelectric properties commonly attributed to the high degeneracy of carrier pockets in the band structure and weak electron-phonon coupling.

Half-Heuslers crystallize with YZ and XY forming tetrahedrally coordinated zinc blende networks, and XZ forming a rock salt network. Stable stoichiometric Half-Heuslers have valence electron counts of 8 or 18, which has led to interpretation of their bonding and properties within Zintl chemistry [1]. Applying Zintl chemistry to Half-Heuslers, the electroposive cation, Xⁿ⁺, donates all its valence electrons to the covalently bonded [YZ]^n- polyanion, which then fulfils the 8- or 18-electron rule. Thus, ionic and covalent bonding patterns coexist and there is a clear distinction between the bonding within the polyanion and the bonding between formal cation and polyanion. Zintl chemistry is often applied for engineering thermoelectric materials, and for Half-Heuslers, it gives rise to predictions regarding the electronic structure and defect chemistry.

Expanding on previous investigations on chemical bonding in Half-Heuslers [2,3], we present the results of computational real space chemical bonding analysis using Bader’s quantum theory of atoms in molecules and delocalization indices on a range of Half-Heusler semiconductors. This shows strong deviations from predictions from Zintl chemistry for transition metal based materials and reveal interesting relations between chemical bonding and thermoelectric and response properties [4].

We construct a map of chemical bonding in Half-Heuslers based on real space indicators [5], onto which we map important calculated thermoelectric properties. This reveals that strong covalent bonding between formal cation and polyanion results in increased carrier pocket degeneracies, and therefore improved thermoelectric properties. Thus, the materials least in line with the commonly applied Zintl concept are in fact the ones with the best thermoelectric properties.

This works extends our previous studies showing the inability of Zintl chemistry to explain the unexpected isotropic properties in thermoelectric Mg₃Sb₂ [6], and thus presents a critical view on the simplistic chemical concepts too often applied for rational materials design. Furthermore, it highlights the potential of applying tools from chemical bonding analysis and quantum crystallography for materials design.

[1] Zeier, W. G., Schmitt, J., Hautier, G., Aydemir, U., Gibbs, Z. M., Felser, C., Snyder, G. J. (2016). Nat. Rev. Mater. 1, 16032

[2] Bende, D., Grin, Y., Wagner, F. R. (2014). Chem. Eur. J. 20, 9702-9708

[3] Bende, D., Wagner, F. R., Grin., Y. (2015). Inorg. Chem. 54, 3970-3978

[4] Tolborg, K., Iversen, B.B. (2021). Submitted

[5] Raty, J. Y., Schumacher, M., Golub, P., Deringer, V. L., Gatti, C., Wuttig, M. (2019). Adv. Mater. 31, 1806280

[6] Zhang, J., Song, L., Sist, M., Tolborg, K., Iversen, B. B. (2018). Nat. Commun. 9, 4716

Quantitative convergent-beam electron diffraction (QCBED) has become established as a highly accurate and precise means of measuring bonding electrostatic potentials and electron densities [1]. To date, it has almost exclusively been performed using the Bloch-wave electron scattering formalism [2], which requires 3-dimensional periodicity throughout the scattering volume. This has restricted QCBED to bonding measurements in homogeneous, single-phased crystalline materials (just like X-ray diffraction).

The multislice formalism [3] for electron scattering dispenses with the requirement of periodicity in the direction of the electron beam. Furthermore, electron probe sizes are typically of order 1 nm in dimension for QCBED, rendering even very highly curved features in nanostructured materials locally planar relative to the electron probe. This means that nanostructures that share a crystallographically coherent interface with the surrounding matrix in which they are embedded, could in principle be analysed by multislice-based QCBED. Add to this the routine sub-nanometre precision in positioning electron probes in transmission electron microscopes, and there is the potential to map bonding charge density as a function of position in nanostructured materials for the first time.

We are attempting to measure bonding electron densities within a number of different nanostructures and also across their interfaces with the surrounding matrix material, using QCBED based on the multislice formalism. We will present some early results from several nanostructured materials such as those shown in Fig. 1 below.

Figure 1. High angle annular dark field scanning transmission electron microscopy of an Al-Cu alloy [4] (a); a (ZnO)_kIn₂O₃ (k = 5) thermoelectric oxide superlattice [5] (b); an Al-Cu-Sn alloy containing Sn-coated voids [6] (c & d). The figure also presents a CBED pattern (e) from the material in part b and a CBED pattern (f) taken through a void like the one shown in parts c and d.

[1] Nakashima, P. N. H., Smith, A. E., Etheridge, J. & Muddle, B. C. (2011). Science 331, 1583.

[2] Bethe, H. A. (1928). Ann. Phys. (Berlin) 392, 55.

[3] Cowley, J. M. & Moodie, A. F. (1957). Acta Cryst. 10, 609.

[4] Bourgeois, L., Zhang, Y., Zhang, Z., Chen, Y. & Medhekar, N. V. (2020). Nature Commun. 11, 1248.

[5] Liang, X. & Clarke, D. R. (2018). J. Appl. Phys. 124, 025101.

[6] Tan, X., Weyland, M., Chen, Y., Williams, T., Nakashima, P. N. H. & Bourgeois, L. (2021). Acta Mater. 206, 116594.

We thank the Monash Centre for Electron Microscopy where all data were collected. Many thanks to A/Prof. Matthew Weyland and Prof. Joanne Etheridge for their expertise. We thank the Australian Research Council for funding (DP210100308).

Transition metal (TM) bound hydrides can be used as hydrogen storage materials, they also play a key role in processes of catalysis, energy conversion, and search for superconductivity. However, they are very difficult to study with the method of X-ray diffraction, on the one hand, due to the fact that hydrogen atom has only one electron with density is usually strongly shifted towards its bonding partner, on the other hand, because its weak diffraction signal is strongly screened by scattering from the electron-rich heavy metal. Moreover, it is difficult to collect high quality, let alone high resolution X-ray diffraction data for such compounds. The availability of neutron diffraction data, which are the benchmark of hydrogen positions, is even more limited.

Recently, it was proven that Hirshfeld Atom Refinement (HAR), using aspherical atomic scattering factors, allows locating hydrogen atoms bonded to light elements based on standard resolution X-ray diffraction data with accuracy and precision very close to the one of neutron experiments [1]. This was a significant improvement compared to the most popular Independent Atom Model (IAM). Nevertheless, excluding this study, only 5 structures of complexes with TM-H bonds have been successfully refined with HAR [1,2] for only two of which a complementary neutron data set is available.

We present the results of HAR of around 11 X-ray structures of crystals of metaloorganic compounds containing hydrogen atoms bonded to heavy metals from period IV (Fe, Co, Cu, Ni), V (Nb, Ru, Rh, Sb), and VI (Os) for which also the corresponding neutron structure is available. Refinements were performed using Olex2 with the application of atomic aspherical structure factors computed with the DiSCaMB library [3], based on Hirshfeld partition of molecular electron density calculated for the central molecule embedded in a cluster of atomic charges and dipoles centered on the atomic nuclei of the surrounding molecules within the radius of 8 Å. Additionally, HARs without a cluster of multipoles were carried out with NoSpherA2 [2]. Wave functions were calculated using the DFT method, in each case B3LYP, PBE, and M062X functionals were used. All the calculations were performed also in the version including relativistic effects as implemented in the DKH2 Hamiltonian approach. Various basis sets were tested.

Overall, the DiSCaMB-HAR procedure elongates the TM-H bond lengths, bringing them closer to the neutron values [4]. The level of improvement is dependent on the quality of the experimental data and the refinement. The most prominent example of a successful refinement is the structure of a metalloorganic complex containing a Ru-H bond, which can be refined anisotropically to obtain the Ru-H distance in very high agreement with the one in the neutron structure (neutron: 1.598(3) Å, IAM: 1.56(2) Å, DiSCaMB-HAR(B3LYP/cc-pVTZ-DK): 1.593(11) Å, DiSCaMB-HAR(PBE/cc-pVTZ-DK): 1.599(11) Å). In four cases (Fe, Ru, and Rh complexes), refinement of ADPs of hydrogen atoms was feasible. In the case of the Fe complex, HAR performed with SHADE2-estimated H ADPs was feasible and was used to evaluate the H APDs refined with HAR. For two structures X-ray and neutron experiments were performed at the same temperature, thus direct comparison of HAR and neutron isotropic temperature factors of hydrogen atoms will be presented. The data sets were ranked according to various parameters describing data quality and refinement quality both for the neutron and the X-ray data sets, which lead to the final joint neutron and X-ray data-refinement quality ranking. The ranking reflects well how favorable the HAR-neutron TM-H bond length comparison is and correlates with the number of electrons in the TM. Examples showing the influence of factors such as the position in the ranking and the method of obtaining the molecular wave function on the quality of TM-H and other X-H bond lengths obtained with HAR will be presented.

Rechargeable lithium ion batteries, because of their high energy density, have conquered most of today’s portable electronics. The development of electric transportation also largely relies on the development of such devices. Still, there is plenty of room for improvement since the energy density is far from being enough for long-driving distances. The same applies for the sister technology, Na-ion, which could become the technology of choice for stationary storage in a near future. For all these applications, finding new electrode materials and being able to follow their structural evolution on charge and discharge is essential. In this talk, I will first present the strategy we use at the lab “Chimie du Solide et Energie” at Collège de France (Paris) to get useful information from diffraction experiments on battery materials, and how important a rigorous analysis of these data is for a reliable characterization of electrodes materials. From examples based on neutron and X-ray powder diffraction, I will highlight the importance of conducting structural studies, both to understand the as-made electrodes and their behaviour on cycling. Importance of crystallography and diffraction experiments will also be highlighted in the field of ionic conductors, as an important step towards the development of safe all-solid-state batteries. Lastly, it will be shown that other communities – e.g. solid state physicists- may benefit from research in materials for batteries with the discovery of compounds presenting interesting magnetic properties.

Hollow molecular structures capable of guest inclusion represent an area of raising interest and lie at the forefront of the modern supramolecular chemistry.[1,2] Originally studied in solution, this concept has been extended in the solid-state, after the pioneering work on the “crystalline sponge method” (CSM). [3] The CSM primary application has been the unambiguous structural determination via SC-XRD of a single analyte encapsulated inside a porous MOF. However, as the host-guest systems often show severe disorder, their reliable crystallographic determination is very demanding [1,2] thus the dynamics of the guest entering and the formation of nanoconfined molecular aggregates has not been in the spotlight yet.

We extended the concept of the CSM stepwisely monitoring the structural evolution of nanoconfined supramolecular aggregates of guest molecules with the concomitant displacement of pristine DMF inside the cavities of a novel flexible MOF, PUM168. Furthermore, we correlated this phenomenon to the structural reorganization of the host framework, elucidating the dynamic interplay between the container and the content. [4] In order to deeply understand the “physiology” of PUM168 breathing during the guest uptake, we focused our attention on the three main actors involved in the play: i) the MOF structure, ii) the leaving DMF molecules trapped during the synthesis of the MOF and iii) the incoming guest molecules uptaken during the soaking process. [5]

The fate of each actor influences and is influenced by the other two characters, in a play that shows how the structure of the framework changes in the response of the guest positioning and composition. [5]

Interactive pores in porous coordination networks play a key role in trapping unstable species, chemical transformation, and so on . We reported porous coordination networks prepared by kinetic assembly which can be used to produce interactive pores. The interactive pore can be used for I₂ chemisorption and chemical transformation of small sulfur allotropes, from S₂ to bent-S₃ via cyclo-S₃. We performed selective formation of porous coordination networks kinetically/thermodynamically from CuI cluster and rigid T_d symmetry ligand, 4-TPPM (tetra-4-(4-pyridyl)phenylmethane), by changing cooling ratio of the hot DMSO solution of the mixture. Because the interactive pore is the key component to create functionality, it is required to extend the availability of interactive pores. Such interactive pores can be modified by changing metal source (clusters) and ligand coordination geometry. Here we report the kinetic assembly of porous coordination using Cu-Halide clusters and several pyridine-type ligands (Figure 1) to generate several interactive pore sites; we report new kinetic network formation using 4-TPPM and CuX cluster and the dynamic structural change of the kinetic network to produce highly luminescence coordination networks and flexible network formation using 3-TPPM and CuI cluster to show dual interactive sites showing iodide interactive pore sites and Cu pseudo-open metal sites.

When we performed kinetic/thermodynamic assembly using [Cu₄Br₄(PPh₃)₄] and 4-TPPM, we obtained coordination network composed of Cu₂Br₂ dimer and 4-TPPM as kinetic network and that composed of CuBr helical chain and 4-TPPM as thermodynamic network. When we heat the kinetic network at 573 K, it turned to luminescent crystalline powder. Both single crystal analysis and Rietveld refinement of PXRD indicates the transformation to the network composed of Cu⁺ connectors and 4-TPPM linkers with CuBr₂^- guests. The high quantum yield was obtained for this network (13%). We clarified that the electronic transitions in this network include TSCT in addition to the typical metal–ligand charge transfer (MLCT) observed in conventional Cu complexes. The atomic coordinates of the molecules determined from X-ray structure analysis enabled a clear understanding of the nature of the TSCT transitions.

When we performed kinetic/thermodynamic assembly using [Cu₄I₄(PPh₃)₄] and 3-TPPM, we obtained coordination network composed of Cu₂I₂ dimer and 3-TPPM as kinetic network and that composed of CuI helical chain and 3-TPPM as thermodynamic network. Using 3-TPPM, rotation motion of pyridine ring was restricted. Interestingly the thermodynamic network, CuI helical network shows 2I₂ chemisorption to make chemical bond with iodide in the interactive pore and Cu in the network so that Cu act as pseudo-open metal sites.

Iron fluoride (FeF₃.nH₂O) shows high capacity as cathode material for lithium-ion batteries combined to low toxicity and low cost. The water content of iron fluoride has been shown to be of prime importance in the performances of the cathode. So far, the various synthesis route doesn’t allow for a precise water content control, especially on the low amount regime which is the most interesting range of composition [1]. In addition, CrF₃ has been shown to increase significantly the conductivity of LiF film [2]. Consequently, it is of interest to look for the in-situ formation of the various MF_3-x(OH)_x.nH₂O phases (M = Cr, Fe).

In this contribution, we report on the in-situ formation of MF_3-x(OH)_x.nH₂O (M = Fe, Cr) phases using self-generated atmosphere. Traditionally, the heating MF₃.3H₂O in open air results in the full oxidation and decomposition of the fluorides giving rise to nano based oxides. Here, we make use of self-generated atmosphere to control the precise crystal chemistry of those phases upon heating preventing full oxidation at mild temperatures while stabilizing new phases relevant for battery applications.

Some of the results are presented in Figure 1 about the FeF_3-x(OH)_x.nH₂O phases. Precise controlled of the water content of the FeF_3-x(OH)_x.nH₂O series could be reached with n ranging from 1/3 to 0 with about 10 new pure phases. We demonstrate experimentally the initial assumption on the role played by the water in the stabilisation of the FeF₃.1/3H₂O phase, phase which is relevant for battery application [1]. In addition, the controlled in-situ decomposition of CrF₃.3H₂O led to the formation of a new CrF_3-x(OH)_x pyrochlore which was characterized structurally and magnetically. This work demonstrates the added value of in-situ experiment using self-generated atmosphere for synthetising new phases.

[1] Kim et al., (2010) Adv. Mater. 22, 5260; Ma et al. (2012), Energy Environ. Sci. 5, 8538.

[2] Tetsu O. (1984), Materials Research Bulletin 19, 451.

Investigations of long-lived reaction intermediates and metastable species generated upon external stimuli, such as light or heat, in chemical and biological systems are of upmost importance in the context of our understanding of the processes’ mechanisms and related phenomena. Linkage isomers can be formed by coordination compounds that contain ambidentate ligands capable of binding to a metal centre through various donor atoms. Such metastable species may exhibit lifetimes as long as hours or days and revert back to the ground state at elevated temperature. Thanks to their properties, photoswitchable materials may find various technological applications, including renewable energy solutions, biosensors or data storage.

The aim of this project was to thoroughly and systematically investigate conditions and dynamics of light-induced nitro group isomerisation reactions which occur in crystals of either designed or literature-reported 4th-row transition-metal complexes. The examined series of compounds consists of coordination compounds of nickel(II), copper(II) and cobalt(III). Metal centres in these systems are coordinated by the nitrite ligand and either (N,N,O) chelating species, NHC group, or amino ligands.

The studied complexes were thoroughly examined crystallographically, spectroscopically and computationally. In the case of Ni(II) and Co(III) nitro complexes partial conversion to metastable endo-nitrito isomers is achieved after irradiation of respective single crystal samples with adjusted UV-Vis LED light at temperatures above 100 K. The metastable-state form is usually stable up to relatively high temperatures, e.g. 240 K, while the maximum conversion may reach 100% for powder samples as indicated by solid-state IR measurements. Instead, copper systems analogous to the above-described nickel coordination compounds exist as the nitrito form in the ground state and work best at 10 K, whereas the metastable nitro form is usually stable only up to 60 K. Such behaviour makes them more difficult to be experimentally analysed and less applicable as functional photoactive materials.

In turn, a very significant 90% nitro-to-nitrito conversion was reported for single-crystals of the Ni(II) nitrite system [Ni(η⁵Cp)(IMes)(η¹-NO₂)]. The studied compound crystallizes with two symmetry-independent molecules comprising the asymmetric unit. Although the two moieties are geometrically very much alike, their behaviour upon irradiation or temperature appeared to be somewhat different depending on the exact experimental conditions. At 190 K the metastable species reverted back to their ground state.

Trinitrocobalt(III) coordination compounds constitute another interesting group of photoswitchable systems. For instance, Co(Me-dpt)(NO₂)₃ complex contains three different NO₂ groups in its molecule, which form different intermolecular interactions in the crystal structure, including hydrogen bonds (one is strongly bound, the second one moderately, whereas the third group does not participate in any hydrogen-bond-type contacts). After irradiating of the sample with the UV-Vis light only one of them switches to the nitrito linkage isomer, which shows the importance of crystal packing and intermolecular interactions effects.

X-ray acoustic interactions allowing to implement the control of X-ray parameters are widely studied. Among the numerous researches, it is possible to highlight the ability of controlling the spatial and energy spectrum of X-ray radiation [1] and the effect of redistribution of intensity between transmitted and diffracted beam [2]. This paper describes the implementation of a combination of these two possibilities.

Fast control of X-ray parameters, including scanning diffraction conditions and controlling by times much shorter than possibilities of traditional approaches, is a very relevant scientific task. It will be shown that overcoming of limitation of traditional approach, such as complex goniometric systems, possible by using of non-mechanical adaptive X-ray optic elements, such as X-ray acoustic resonators of longitudinal oscillations or bimorph piezo-actuators. It allows fast and precise variation of X-ray diffraction parameters, varying the angular position of the X-ray beam and controlling its wavelength. Description of schemes and elements for fast tuning of beam parameters will be given.

The effects of the redistribution of intensities between the diffracted and transmitted X-ray beams under the conditions of excitation of resonant acoustic thickness oscillations in quartz crystals were investigated. It has been established that the effect of increasing the intensity of a diffracted beam almost linearly depends on the amplitude of ultrasound (the FWHM of the rocking curves does not change at the same time) and is observed for all the studied reflexes.

The time characteristics of the observed effects upon excitation and relaxation of ultrasonic oscillations were investigated for the first time: the process of increasing intensity takes about 250 microseconds, then its oscillation is observed for about 1 millisecond, and the process of complete relaxation takes about 1.5 milliseconds.

Design of elements combining thickness and longitudinal oscillations are considered, several schemes of implementation are proposed. For the first time, the distributions of the FWHM and peak intensities of the rocking curves in a quartz resonator in case of the simultaneous excitation of longitudinal and thickness oscillations were measured. It is shown that these two types of oscillations do not have a significant mutual influence. Therefore, this combination can be used to create universal adaptive elements of x-ray optics, which allow controlling the angular position and intensity of the diffracted beam simultaneously. The effect of intensity redistribution in Potassium and Rubidium hydrogen phthalate crystals, which are emerging materials for creating a two-frequency element, was studied for the first time.

Some results and prospects of implementation of such methods and elements at synchrotron radiation as well as laboratory sources will be discussed.

[1] A.E. Blagov, M.V. Kovalchuk et al. JETP letters, t.128, 5 (11) (2005). P.893

[2] A.P. Mkrtchyan, M.A. Navasardyan, V.K. Mirzoyan. JTP letters, 8, 677 (1982)

The reported study was partially supported in the framework of the joint programs of the Russian Foundation for Basic Research (project № 18-52-05024 Arm_a and №18-32-20108 mol_a_ved) and Science Committee of Ministry of Education and Science of Armenia (project №18RF-142).

Photochromic compounds that change color reversibly by light irradiation are not only chemically interesting but are also expected to be applied to light control materials and optical storage media. So far, we have been investigating the reactivity and photochromism of salicylideneaniline derivatives and clarified that the factor that determines the photochromic characteristics is the crystal structure [1]. The cyanoalkyl cobaloxime complex crystal is a soft crystal that undergoes crystalline state photoisomerization by irradiation with visible light. This crystalline state reaction can be used to change the molecular packing, including the intermolecular interactions and the environment around the molecule, to control the reactivity of molecules in the crystal. According to this strategy, we synthesized cyanoalkyl cobaloxime complexes coordinated by photochromic compounds such as salicylideneaniline or spiropyran derivatives, which became a “dual photoreactive” complex crystal showing photoisomerization by visible light and photochromism with ultraviolet light irradiation (Fig.1). We achieved in situ control of the fading rate of these crystals by utilizing changes in the crystalline environment due to the isomerization reaction.

In this study, we synthesized three different g-cyanopropyl cobaloximes with N-(3,5-di-tert-butylsalicylidene)-3-aminopyridine(a), N-(3,5-dibromosalicylidene)-3-aminopyridine(b). and N-(5-methoxysalicylidene)-3-aminopyridine(c), and one b-cyanoethyl cobaloxime with (2-(3,3’-dimethyl-6-nitrospiro[chromene-2,2’-indolin]-l’yl)ethyl isonicotinate)(d). When the photoreactivity in the solid-state was investigated, it was confirmed that the photochromic reaction of the salicylideneaniline derivatives(a,b,c) proceeded by UV light irradiation while the photoisomerization of the g-cyanopropyl cobaloxime complex proceeded by visible light irradiation. Thus, we succeeded in obtaining a novel dual photoreactive complex crystal. After the photochromic reaction, the crystal showed colour fading to the original colour. The fading rate was found to become slower for a, c, or faster for b after the g-a isomerization reaction of the cyanopropyl group by visible light irradiation. To elucidate the fading rate change mechanism, we calculated the reaction cavity around the central part of the salicylideneaniline moiety, which would show the largest molecular shape change. For a and c, the cavity volume was reduced by the g-a isomerization, which made the movement of the atoms in the cavity more difficult, and as a result, the fading rate slowed down. In contrast, in b, the cavity volume and the fading rate increased by g-a isomerization [2]. Similarly, in the spiropyran complexes (d), we succeeded in the in situ control of the colour fading rate by visible light irradiation. For this case, the fading rate change mechanism was again rationalized by the cavity size around the spiropyran moiety [3].

Two methods are traditionally used to characterize gas adsorption properties in porous solids: volumetric and gravimetric. They have a number of limitations, but most importantly, they yield a macroscopic picture of interactions (properties), without access to a microscopic picture (mechanisms on an atomic level). Diffraction is commonly used as a complementary technique to explain these properties, giving insight into structure and thus revealing the underlying guest-host and guest-guest interactions. Various anomalies (deviations from a typical behaviour) detected by the macroscopic methods require an in situ diffraction experiment, aiming to identify the responsible phenomena like a guest rearrangement / repacking, framework deformation etc. Thus, a separate diffraction experiment is usually providing a microscopic picture for the properties found by other physico-chemical methods.

In this presentation we will show examples of using in situ powder diffraction to simultaneously access the structure and adsorption properties of a small pore crystalline solid. (Quasi)-equilibrium isotherms and isobars can be built directly from sequential Rietveld refinements, both on adsorption and desorption, thus addressing the hysteresis and kinetics of gas adsorption/desorption. Detailed picture of guest reorganization with an increasing uptake can be obtained. Note that the reorganization of the individual guest sites is not accessible to volumetric and gravimetric methods, as they give only total amounts of gas uptake.

Interestingly, the adsorption isobars and isotherms obtained directly from diffraction data can be fitted by known equations, such as a logistic function (isobars) or a Langmuir equation (isotherms). Thermodynamic properties, such as enthalpy and entropy of gas adsorption can be extracted from these curves. The limitations of this technique are very different from traditional methods, thus making it highly complementary.

Lastly, the adsorption kinetics can be followed by in situ powder diffraction at given P,T conditions versus time. The guest uptake extracted by a sequential Rietveld refinement can be fitted and analysed in terms of Arrhenius theory giving access to the activation energies for gas diffusion. Thanks to the microscopic picture these barriers can be tentatively attributed to various diffusion paths inside the solid.

This talk will be illustrated by examples of noble gas adsorption in a porous hydride, γ-Mg(BH₄)₂ [1], featuring 1D channels suitable to distinguish and likely separate some of these gases. Besides published results [2,3], a lot of unpublished data will be shown.

[1] Filinchuk, Y., Richter, B., Jensen, T. R., Dmitriev, V., Chernyshov, D. & Hagemann, H. (2011). Angew. Chem. Int. Ed. 50, 11162. [2] Dovgaliuk, I., Dyadkin, V., Vander Donckt, M., Filinchuk, Y. & Chernyshov, D. (2020). ACS Appl. Mater. Interfaces 12, 7710. [3] Dovgaliuk, I., Senkovska, I., Li, X., Dyadkin, V., Filinchuk, Y. & Chernyshov, D. (2021). Angew. Chem. Int. Ed. 60, 5250.

Complex early transition metal oxides have emerged as leading candidates for fast charging lithium-ion battery anode materials [1,2]. Framework crystal structures with frustrated topologies are good electrode candidates because they may intercalate large quantities of guest ions with minimal structural response. Starting from the empty perovskite (ReO₃) framework, shear planes and filled pentagonal columns are examples of motifs that decrease the structural degrees of freedom. As a consequence, many early transition metal oxide shear and bronze structures do not readily undergo the tilts and distortions that lead to phase transitions and/or the clamping of lithium diffusion pathways that occur in a purely corner-shared polyhedral network[1].

In this work, we explore the relationship between composition, crystal structure, and reduction pathway in a variety of recently synthesized mixed alkali, transition metal, and main group oxides (Fig. 1), moving beyond the archetypal Ti-Nb-O and W-Nb-O phase spaces. Solid-state NMR spectroscopy, X-ray absorption spectroscopy (XANES and EXAFS), synchrotron and neutron diffraction, and DFT are combined with electrochemical experiments to present a comprehensive picture of the charge storage mechanisms. Prospects for tunability and implications for charge rate and structural stability will be discussed.

[1] Griffith, K. J., Wiaderek, K., Cibin, G., Marbella, L. M. Grey, C. P. (2018). Nature 559, 556.

[2] Griffith, K. J., Harada, Y., Egusa, S., Ribas, R. M., Monteiro, R. S., Von Dreele, R. B., Cheetham, A. K., Cava, R. J., Grey, C. P., Goodenough, J. B. (2021). Chem. Mater. 33, 4.

This Interest in metal hydrides was initially driven by the potential to develop efficient and safe on-board hydrogen stores working close to ambient pressure and temperature. In search for hydrides with higher gravimetric storage capacity, the researchers concentrated on hydrides based on light atoms, among others on Li and Na salts containing hydroborate anions such as borohydride BH₄⁻ or closo-hydroborate B₁₂H₁₂²⁻ [1]. The hydrogen absorption-desorption cycling in complex hydrides still needs more chemical ideas due to relatively strong covalent bonding. Unexpectedly, the high mobility of alkali metal cations in some complex hydrides has opened the door for their application as battery materials, mainly as solid-state electrolytes (SSE).

Replacing the liquid electrolyte by SSE offers several advantages: i) a solid material is more thermally stable, thus enhancing the overall safety of the battery; ii) being less prone to the dendrite penetration, it enables the use of alkali metals as negative electrodes and iii) acting as physical layer between the two electrodes, it has a beneficial effect on the cell performance [2].

Among the different classes of SSE, the metal hydroborates have received particular interest, being soft, highly stable toward oxidation and exhibiting fast ion conductivity, enabled by an entropically-driven phase transition. Such transitions generally occur above room temperature (rt), and it is therefore necessary to frustrate the anionic lattice, for example by anion mixing to bring the superionic regime down to rt [3-6].

The hydrogen storage and mobility of the cations in light complex hydrides depends on the structural features, pathways available in the anion packing and on the anion thermal motion. While the latter requires important experimental and theoretical effort, the first two parameters can be easily quantified from crystal structures obtained by X-ray powder diffraction.

Examples of crystallography and crystal chemistry analyses of novel solid-state electrolytes as well as proof-of-concept Na-ion all-solid-state batteries will be shown.

[1] Paskevicius M. et al. Chem. Soc. Rev. 2017, 46, 1565

[2] Zeier W. & Janek J. Nat. Energy 2016, 1, 16141

[3] Tang W.-S. et al. ACS Energy Lett. 2016, 1, 659

[4] Duchêne L. et al. Energy Environ. Sci. 2017, 10, 2609

[5] Murgia F. et al. Electrochem. Comm. 2019, 106, 106534

[6] Brighi M. et al. Cell Reports Phys. Sci. 2020, 1, 100217

Diffraction experiments typically provide clear picture of a crystal structure and basis for understanding material properties. However, for materials with high static or dynamic disorder and/or weakly occupied atomic sites, e.g. ionic conductors, the diffraction data reflecting space- and time-averaged state may struggle to distinguish several alternative models yielding similar χ². In that case, atomistic modelling may help not only to identify the more energetically stable configuration but also provide insights into the mechanism of its formation. I will present several recent examples of studies of disordered oxide-ion and proton conductors, where ab initio static and geometry optimisation calculations and molecular dynamics simulations not only helped to validate neutron diffraction analysis but also revealed the mechanism driving the disorder.

Prussian blue analogues (PBAs) with formula A_xM[M’(CN)₆]_1-y.zH₂O, show considerable promise as highly sustainable electrodes in sodium ion batteries. PBAs are formed of metal that are octahedrally coordinated by cyanide groups which act as bridges between the metal centers. This corner linked framework creates a highly porous structure into which either cations such as Na⁺ or molecules such as H₂O can insert into. However, PBAs receive criticism on their thermal stability and moisture sensitivity, which can be detrimental to the electrochemical performance or compromise safety. However, existing pessimism towards the material is based on studies of traditional Prussian blue (Fe₄[Fe(CN)₆]₃), whereas the vacancy-free compounds such as iron hexacyanoferrate (Fe-HCF), Na_xFe[Fe(CN)₆]_1-y.zH₂O (x≈2, y≈0, z≈0), do not show any similarity in terms of structural transitions or performance in a battery. In this contribution, our efforts at understanding the thermal and moisture stability of vacancy-free Fe‑HCF are presented.

We have optimised a method of consistently producing Fe-HCF with <5% vacancies on the Fe(CN)₆ site. Consequently, the effect of sodium content and moisture on structure and stability has been independently quantified. In the absence of vacancies, the moisture sensitivity of the material is determined by the Na⁺ content, with a sodium-rich structure absorbing more water and binding with higher affinity. Interestingly, despite a higher moisture sensitivity, the Na⁺ rich system features higher thermal stability. The interplay between the host framework, sodium and water also appears to influence the phase transitions of the material. The sodium-free material does not undergo any phase transitions, remaining cubic (Fm-3m) from 4K to 300K, whereas the sodium rich (x>1.5) systems exhibit several phase transitions between R-3 and P2₁/n as a function of temperature and water content. These are driven by octahedral tilting (cf. perovskites) and given that such transitions are generally rare in PBAs, their presence within a single system provides a platform for investigating driving factors.

As described, the moisture sensitivity of PBAs is often understood as the tendency to absorb water into the bulk structure. However, water can negatively affect cation rich Fe-HCF via other mechanisms. We identified that contact with airborne moisture during storage can lead to a loss of capacity in Fe-HCF. The capacity fading mechanism proceeds via two steps, first by sodium from the bulk material reacting with moisture at the surface to form sodium hydroxide and partial oxidation of Fe²⁺ to Fe³⁺. The sodium hydroxide creates a basic environment at the surface of the PW particles, leading to decomposition to Na₄[Fe(CN)₆] and iron oxides. Although the first process leads to loss of capacity, which can be reversed, the second stage of degradation is irreversible. The combination of each process ultimately leads to a surface passivating layer which prevents further degradation.

Thus, the interaction of water with cation rich PBAs is complex and should not be overlooked. Gaining an understanding of the degradation mechanisms, including structural and chemical driving forces provides substantial insight into effective design strategies for increasing the performance.

The overarching goal of this work is to understand and overcome the performance limitations of industrially relevant battery materials using powder diffraction studies, both through ex situ studies of materials and operando studies of cycling battery cells. However, the normal modalities for the collection and analysis of powder diffraction data typically lack the sensitivity to resolve the structure of battery materials with sufficiently low uncertainty to effectively resolve structure-properties correlations. We have therefore been actively been developing new approaches to data collection and analysis that overcome these limitations, permitting us to obtain robust structure-properties correlations for industrially relevant cathode materials and for industrially relevant battery cell designs.

We have recently developed a novel perspective for systematically exploring occupancy defects which we have applied to the study of the important family of NMC battery cathode materials [1]. Using these f* diagrams, we have demonstrated sufficient sensitivity to site occupancies to resolve problems with the conventional atomic form factors used for X-ray diffraction – an error of about 3% in the case of oxygen. After correcting for these problems and robustly determining atomic displacement parameters, we have demonstrated the ability to unambiguously resolve the nature of key defects as well as to determine defect concentrations with an unprecedented sensitivity of ~0.1% (absolute), as judged by the agreement between independent refinements of synchrotron and neutron powder diffraction data. From the refined occupancies for a series of NMC compounds, it was possible to determine the energy associated with the formation of anti-site defects, and to conclusively demonstrate that the conventionally accepted mechanism for defect formation was incorrect [2]. Additionally, we have utilized rapid synchrotron powder diffraction methods to carry out multidimensional diffraction studies with fine resolution not just in time but in space as well. In this manner, it has been possible to resolve both vertical [3] and lateral [4] inhomogeneity in battery cells with a sensitivity to the local state of charge (SOC) of ~0.1%. The former has illuminated the performance limitations of exceptionally thick battery cathodes with very high energy densities, while the latter has allowed us to distinguish between different potential failure mechanisms.

[1] L. Yin, G. Mattei, Z. Li, J. Zheng, W. Zhao, F. Omenya, C. Fang, W. Li, J. Li, Q. Xie, J.-G. Zhang, M.S. Whittingham, Y.S. Meng, A. Manthiram and P. Khalifah (2018). Rev. Sci. Instrum. 89, 093002.

[2] L. Yin, Z. Li, G. Mattei, J. Zheng, W. Zhao, F. Omenya, C. Fang, W. Li, J. Li, Q. Xie, E. Erickson, J.-G. Zhang, M.S. Whittingham, Y.S. Meng, A. Manthiram, and P. Khalifah (2019). Chem. Mater., 32, 1002-1010.

[3] Z. Li, L. Yin, G. Mattei, M. Cosby, B.-S. Lee, Z. Wu, S.-M. Bak, K. Chapman, X.-Q. Yang, P. Liu, and P. Khalifah (2020). Chem. Mater., 32, 6358.

[4] G. Mattei, Z. Li, A. Corrao, C. Niu, Y. Zhang, B.-Y. Liaw, C. Dickerson, J. Xiao, E. Dufek, and P. Khalifah (2021). Chem. Mater., 33, 2378.

There is a renewal in diffraction experiments with a Transmission Electron Microscope promoted by their coupling with the scanning mode. In these approaches, 2D diffraction patterns are systematically acquired with fast cameras while the focused beam is moved point by point across a 2D field of view.

Depending on the probe size the resulting 4D datasets enables the reconstruction of 2D maps highlighting either structural entities at atomic scale (when the probe convergence angle is large) or phases, crystallographic orientation and/or local stress fields at the nanoscale (for convergence angles of few mrad). Only the latter case - that ends with spot patterns - will be considered in the present work. The identification of these patterns is substantially simplified when precession electron diffraction (PED) is used. Precession allows more reflections to be captured and their intensities to be less sensitive to dynamical effects.

A significant advance related to scanning precession electron diffraction (SPED) with respect to the classical diffraction experiments is that the full set of patterns are memorized and available for further analysis. A pioneering post-processing work is the automate recognition of phases and crystallographic orientations through template matching, i.e.: by comparing the experimental patterns with a set of simulated ones and selecting the best fit in the pattern library to deduce the local crystal characteristics. Another popular facility offered by the availability of the data is the construction of so-called Virtual Bright- or Dark-Field images (VBF/VDF). These images are formed by plotting, pixel by pixel, the intensity of a user-selected reflection. The interesting point is that a 4D dataset provides the access to all dark-field images, to their combinations and allows the reconstruction of annular dark-field images by summing the intensity of incoherently scattered electrons at the rim of the patterns.

The most challenging problem for transmission diffraction patterns is the frequent crystals overlapping in nanoscaled materials. The related patterns contain the diffracting spots of all superimposed crystals in the thin foil. This is usually considered as a drawback as it renders their analysis less straightforward. It can also be seen as an opportunity that allows the 3D nature of the superimposed grains to be analyzed, by contrast to techniques, like EBSD or Transmission Kikuchi Diffraction, that give access to a surface information solely. For example, Correlation Coefficient Maps (CCM), obtained by measuring the degree of similarity between successive patterns, highlight inner boundaries and, in some conditions give access to their angle of inclination.

There are several existing approaches to isolate the superimposed information: they make use of dark-field images, involve multivariate analyses or include image segmentation algorithms. The proposed solution consists in generating a collection of components that are recognized through template matching and then to construct template related VDF images. Each image gathers the intensities of all the reflections related to a given crystal and are processed in such a way that the resulting weighted intensity improves grain recognition. With this approach each component is related to a given phase and/or orientation and consequently has a physical meaning. Non dominant – or hidden - crystals are accessible with the procedure. A workflow towards 3D reconstructions at nanoscale with electron diffraction and tomographic approaches will be presented.

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

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

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

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

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

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

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

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

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

References

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

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

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

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

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

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

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

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

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

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

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

A.J. Edwards, R.O. Piltz

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

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

Alison.Edwards@ansto.gov.au

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

References:

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

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

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

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

Purpose

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

Methods

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

Results

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

Conclusion

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The belief in the existence of a sharp boundary dividing the world of symmetry into the realm of biology and sensuality and the realm of minerals and cold rationality has had a crucial impact on studies on early life detection on Earth and elsewhere. I have explored the origin of this secular antinomy and found that such a fictitious boundary has permeated the landscape of arts and philosophy for centuries [1]. It is shown that crystals and crystallographic theories have played a crucial role in the intellectual construction of that presumed boundary. The antinomy is illustrated with a debate between the young poet Federico García-Lorca and the young artist Salvador Dali, an archetypal debate to which crystals and what they evocate were central. It is concluded that along with the invaluable contribution of crystallography to the advancement of science and technology of art preservation, the notion of crystal transcended scientific thinking to inspire the arts, from literature to painting, from architecture to dance, from music to filmmaking. Thus, the very idea of crystal and crystallographic theories has been highly influential in the world of arts, architecture, and culture. The importance and the consequences that the crystalline order has had in the conformation of the consciousness, in the conception of the world, and the history of arts goes beyond what has been considered a simple metaphor, and it is a subject that needs to be further.

This influence has evolved throughout history in correlation with increasing scientific knowledge about crystals. Since the origin of consciousness, hundreds of thousands of years ago, human fascination for crystals has been so deeply rooted in our brains as to shape our first symbolic behavior and perception of patterns. During prehistory, crystals had teleological and theological connotations derived from a hidden power of their singularity among the natural objects. Later on, from the classical world to the emergence of positive science in the eighteenth century, scholars and experts endorsed mineral crystals with healing powers. The sheer beauty of the external forms of crystals and everything it evokes fascinated illustrated people at that time. But the higher impact of crystals on the mind and cultures started in the 19th century, when it was demonstrated the extraordinary link between the external harmony, redundantly beautiful symmetry of crystals, and the perfect internal order, periodic and iterative. Since then, the word crystal is full of evocations such as purity, transparency, beauty, equilibrium, rationality, intelligence, energy, and power [2].

[1] García-Ruiz, J. M. (2018). Substantia 2, 19.

[2] García-Ruiz, J.M. et al. (2021). IUCrJ. Submitted.

This investigation has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement nº 340863, and from the Ministry of Economy and Competitiveness of Spain (Program Salvador de Madariaga).

High crystallinity, although desired in materials for a wide range of high-performance engineering applications, generally comes with undesirable attributes such as high brittleness and fragility [1]. This makes crystalline materials incompatible with many future technologies, such as flexible devices and soft-robotics. Recent progress in crystal engineering has brought into light many possible opportunities to address these issues, enabling the design of adaptive crystalline materials that respond to external stimuli with exceptional qualities [1-7]. For instance, crystals that bend (elastically or plastically), twist, curl, wind, jump, exfoliate, laminate, and explode, under external stresses, such as mechanical stress, pressure, light, heat, solvent, etc., have been shown. On the other hand, until very recent time, self-healing was observed only in soft and amorphous materials, mostly involving approaches that use chemical reactions, diffusion, solvent, vapour, electricity, etc., with typical healing time scales in minutes to weeks [8]. A new self-healing mechanism that we recently introduced [9] in materials science, enables ultrafast, near 100% autonomous diffusion-less repair in crystalline materials that uses electrostatic surface potentials generated on the freshly created fracture surfaces, inherent to certain types of polar single crystals. My talk will cover structure-property correlation for crystal engineering of adaptive materials.

Over the recent years there have been large advances in technologies at synchrotron facilities. Photo-counting detectors with high frame rates (several hundred fps) allow for rapid data acquisition. Robotic sample exchangers combined with automated sample centring enable high-throughput sample screening. Fully automated and unattended data collection set-ups offer the possibility to rapidly gather data. Taken together, all these technologies produce vast amounts of data which need to be analysed and stored. Even for an expert crystallographer it can now be very challenging to assess the data gathered during an experimental session. For novel or non-expert users, the data amounts may even feel overwhelming. Additionally, many research groups do not have access to high-performance computing infrastructure or large storage space to keep their data and analyse it and for research facilities like synchrotrons this infrastructure is limited too.

Here we present some initial results for a machine learning-based triaging system which is currently being trialled at Diamond. The aim is to refine the current brute-force experimental phasing pipelines by introducing data driven triage and decision making. The system as it is in place, relies on data fulfilling certain metrics thresholds before being triggered and executing a number of experimental phasing programs in parallel. Each of these programs can run hours and up to a day before producing an output without a guaranteed success. Based on our initial results presented here, we now propose a machine learning-based decision maker which will estimate the chances of successful experimental phasing for the different software packages available within Diamond's automated data analysis pipelines. The outcome of the classification process is then used to execute subsets in the pipelines in a hieararchical fashion.

The potential of deep learning has been recognized in structural bioinformatics for already some time, and became indisputable after the CASP13 (Critical Assessment of Structure Prediction) community-wide experiment in 2018. In CASP14, held in 2020, deep learning has boosted the field to unexpected levels reaching near-experimental accuracy. Its results demonstrate dramatic improvement in computing the three-dimensional structure of proteins from amino acid sequence, with many models rivalling experimental structures. This success comes from advances transferred from several machine-learning areas, including computer vision and natural language processing. At the same time, the community has developed methods specifically designed to deal with protein sequences and structures, and their representations. Novel emerging approaches include (i) geometric learning, i.e. learning on non-regular representations such as graphs, 3D Voronoi tessellations, and point clouds; (ii) pre-trained protein language models leveraging attention; (iii) equivariant architectures preserving the symmetry of 3D space; (iv) use of big data, e.g. large meta-genome databases; (v) combining protein representations; (vi) and finally truly end-to-end architectures, i.e. single differentiable models starting from a sequence and returning a 3D structure. These observations suggest that deep learning approaches will also be effective for a range of related structural biology applications that will be discussed in this lecture.

Detecting the ice diffraction artifacts in single-crystal datasets can be very difficult once the data have been integrated, scaled and merged. Automatic tools are available in CTRUNCATE [1], phenix.xtriage [2] and AUSPEX [3]. Recently, the AUSPEX icefinder score was improved by Moreau and colleagues [4]. Automatic recognition of these artifacts would be highly beneficial as macromolecular structure determination can be negatively impacted or even completely hindered by ice diffraction, but remains difficult.

In 2017, we have shown that inspection of plots of merged intensities against resolution permit an easy identification of ice ring contamination in integrated data sets - by eye. However, this approach could be matched by automatic routines. This has led us to attempt identification using convolutional neural networks, which are exceptionally suited to classification of multi-dimensional arrays because they can retain spatial information of the input.

Here, we present our results to employ convolutional neural networks to detect ice artefacts in processed macromolecular diffraction data, resulting in a new automatic detection called “Helcaraxe”. which outperforms previous indicators. We will also discuss the scope this may offer for the structural biology community to tap into the vast amount of data the field has accumulated in 50 years of deposition to the Protein Data Bank.

Adams, P. D., Afonine, P. V., Bunkóczi, G., Chen, V. B., Davis, I. W., Echols, N., Headd, J. J., Hung, L.-W., Kapral, G. J., Grosse-Kunstleve, R. W., McCoy, A. J., Moriarty, N. W., Oeffner, R., Read, R. J., Richardson, D. C., Richardson, J. S., Terwilliger, T. C., & Zwart, P. H. (2010). PHENIX: A comprehensive Python-based system for macromolecular structure solution. Acta Cryst. D66, 213–221. https://doi.org/10.1107/S0907444909052925

Moreau, D. W., Atakisi, H., & Thorne, R. E. (2021). Ice in biomolecular cryocrystallography. Acta Cryst. D77, 540–554. https://doi.org/10.1107/S2059798321001170

Thorn, A., Parkhurst, J., Emsley, P., Nicholls, R. A., Vollmar, M., Evans, G., & Murshudov, G. N. (2017). AUSPEX: A graphical tool for X-ray diffraction data analysis. Acta Cryst. D73, 729–737. https://doi.org/10.1107/S205979831700969X

Winn, M. D., Ballard, C. C., Cowtan, K. D., Dodson, E. J., Emsley, P., Evans, P. R., Keegan, R. M., Krissinel, E. B., Leslie, A. G. W., McCoy, A., McNicholas, S. J., Murshudov, G. N., Pannu, N. S., Potterton, E. A., Powell, H. R., Read, R. J., Vagin, A., & Wilson, K. S. (2011). Overview of the CCP 4 suite and current developments. Acta Cryst. D67, 235–242. https://doi.org/10.1107/S0907444910045749

The discovery of new functional materials can be guided by computational screening, particularly if the structure of a material can be reliably predicted from its chemical composition. For this application, we have been developing the use energy-structure-function maps [1] of the crystal structures available to a molecule. These maps help understand the properties of predicted crystal structures and their energetic stabilities. However, the use of these methods is still limited by the computational cost of crystal structure prediction (CSP), most of which is associated with the calculation of the relative energies of predicted crystal structures using energy models that are sufficiently accurate to provide reliable energetic rankings. To accelerate these methods, we have been developing machine learning approaches to predict high quality energies (e.g. from solid state density functional theory) from structures that have been generated with computationally efficient energy models. These approaches rely on statistical models, in our case Gaussian Process Regression, to relate lattice energies to geometric descriptors of crystal structures. The talk will discuss two approaches that we have developed: learning of total energies calculated using solid state density functional theory [2,3], and a fragment-based approach [4] where we learn high level dimer energies, which are used to build up the total lattice energies of predicted structures.

[1] Day, G. M. and Cooper, A. I. (2018) Adv. Mater., 30, 1704944.

[2] Musil, F, De, S., Yang, J., Campbell, J. E., Day, G. M. and Ceriotti, M. (2018) Chem. Sci., 9, 1289-1300.

[3] Egorova, E., Hafizi, R., Woods, D. C. and Day, G. M. (2020) J. Phys. Chem. A, 124 , 8065–8078.

[4] McDonagh, D., Skylaris, C.-K. and Day, G. M. (2019) J. Chem. Theory Comput., 15, 2743–2758

The ever-growing amount of crystallographic data offers the potential to uncover a range of scientific discoveries, from rapidly predicting physical properties to suggesting new materials with desirable functional behaviours. This is further enhanced by the current growth in machine learning (ML) algorithm development and implementation. There is, however, a significant obstacle to this goal; standard crystallographic information are not suitable inputs for ML algorithms. This arises due to the inherent flexibility of crystallography, such as non-unique unit cell definitions and symmetry. To overcome this problem, significant progress has been made in devising ‘descriptors’ for crystallographic ML, compressing and standardising crystallographic information into a smaller feature space. Much of the existing focus has been on molecular crystals, where the finite extent of individual molecules imposes a limit on the size of feature vector required. A large number of approaches have been proposed but do not easily extrapolate to extended (i.e. inorganic) materials. [1] The descriptors that are suitable for extended solids tend to be either hand-crafted for a specific problem, or have so many dimensions that extremely large datasets must be used to train reliable ML models. In addition, many do not scale well with variable numbers of atomic species.

Here, we present two new descriptors for crystallographic materials which are generally applicable and invariant to compositional complexity. The first is based on a real-space view of the structure, the second on a reciprocal (or diffraction) space view. Both descriptions are invariant to atomic permutations and unit cell choice, and can be considered as an ‘extended’ (i.e. more information-rich) version of the atomic radial distribution function (RDF) and powder diffraction pattern, respectively. The more complete features offered by these descriptors results in better physical property predictions. For example, our ‘extended’ RDF can predict bulk modulus from crystal structures obtained from the Materials Project [2] with a much lower error than the ‘simple’ RDF using linear ridge regression (Figure 1). It is notable that the error approaches current state-of-the-art results, [3] without any knowledge of the atom types involved.

[1] Rossi, K. & Cumby, J. (2020). Int. J. Quantum Chem., 120, e26151. [2] Jain, A., Ong, S. P., Hautier, G., et al. (2013). APL Mater., 1(1), 011002. [3] Chen, C., Ye, W., Zuo, Y. et al. (2019). Chem. Mater., 31, 3564.

The x-ray absorption near-edge structure (XANES) spectra of some nano-structures exhibit small peaks when the incident x-ray energy is lower than the main absorption edge energy. The energies of these peaks depend on local environment, valency of chemical elements and density of electronic states. Advanced quantitative analysis of the local atomic geometry around active catalytic sites requires novel experimental method e.g. the pre-edge structure of X-ray absorption near edge spectra (XANES) measured in the high-energy resolution fluorescence detected mode, the so-called HERFD-XANES. However, there is no widely used ab initio theoretical method which could be routinely applied to the analysis of such experimental data except parametric multiplet calculations. To overcome the procedure of adjusting of parameters is the using of local DFT Hamiltonian constructed on the basis of Wannier orbitals – the so called multiplet ligand-field theory (MLFT) [1]. Pre-edge region of X-ray absorption spectra could be calculated using the XTLS code in the framework of multiplet ligand-field theory using maximally localized Wannier functions (MLWF).

Computation of pre-edge XANES spectra according to MLFT approach is a complicated process, which requires using a lot of software, such as: Wien2k, Wannier90, XTLS code and some additional programs and scripts. We developed «w2auto» program, which automates all process of pre-edge XANES computation. «w2auto» emulates work in w2web interface of Wien2k software and provides opportunity to run all necessary programs without user access. The launch of the necessary calculation steps is controlled through the configuration script in Python programming language. Also we developed a simple GUI for users who does not have any experience in programming in Python language. It helps to generate configure file in form of Python script.

In recent years machine learning has become a powerful instrument for solving scientific problems. It helps to classify and sort data, make approximations, find latent dependencies and features. In this work we have applied machine learning methods for analysis of the Fe:SiO4 pre-edge XANES spectra. As recently shown,

machine learning methods have been successfully applied to the quantitative analysis of spectroscopic data in general and of X-ray near edge spectroscopy (XANES) in particular [2-4].

In the present work we show applicability of machine learning methods to retrieve structural information in system Fe:SiO4. In this research we have collected 60 pre-edge XANES spectra in differrent coordination (from 2-fold to 6-fold) and oxidation states (Fe²⁺ and Fe³⁺) using «w2auto» program. We used this dataset to train and validate several machine learning methods (Decision Tree, ExtraTrees, SVM, Logistic regression and neural network) to determine both coordination number and oxidation state by spectrum.

Acknowledgment

The work was supported by grant of President of Russia for young scientists (MK-2730.2019.2).

References

[1] E. Gorelov, A.A. Guda, M.A. Soldatov, S.A. Guda, D. Pashkov, A. Tanaka, S. Lafuerza, C. Lamberti, A.V. Soldatov, MLFT approach with p-d hybridization for ab initio simulations of the pre-edge XANES, Radiation Physics and Chemistry, 2018, DOI: 10.1016/j.radphyschem.2018.12.025.

[2] A. Martini, S. A. Guda, A. A. Guda, G. Smolentsev, A. S. Algasov, O. A. Usoltsev, M. A. Soldatov, A. L. Bugaev, Y. V. Rusalev, A. V. Soldatov, PyFitit: the software for quantitative analysis of XANES spectra using machine learning algorithms, Computer Physics Communications, 2019

[3] A. A. Guda, S. A. Guda, K. A. Lomachenko, M. A. Soldatov, I. A. Pankin, A. V. Soldatov, L. Braglia, A. L.Bugaev, A. Martini, M. Signorile, E. Groppo, A. Piovano, E. Borfecchia, C. Lamberti, Quantitative structural determination of active sites from in situ and operando XANES spectra: From standard ab initio simulations to chemometric and machine learning approaches, Catalysis Today, V. 336, 2019, P. 3-21, DOI: 10.1016/j.cattod.2018.10.071.

[4] Guda, A.A., Guda, S.A., Martini, A., Bugaev A., Soldatov, M. A., Soldatov, A. V. & Lamberti, C. (2019). Machine learning approaches to XANES spectra for quantitative 3D structural determination: The case of CO2 adsorption on CPO-27-Ni MOF. Radiation Physics and Chemistry. 108430. DOI: 10.1016/j.radphyschem.2019.108430.

Phase separations and nematicity of transition metal impurities

Tomasz Dietl^1,2

¹International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, PL-02668 Warsaw, Poland

²WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japandietl@MagTop.ifpan.edu.pl

Semiconductors [1] and topological materials [2] doped with transition metal elements attract considerable attention due to the fascinating physics and nonospintronic functionalities associated with exchange coupling between band carries and localized spins. However, there is a growing amount of pieces of evidence that d-shells of magnetic impurities contribute also to bonding, which can affect their spatial distribution and modify key properties, such as magnetic ordering temperature [3]. It has recently been experimentally demonstrated that the resulting phase separation (spinodal decomposition) can be anisotropic and result in the hitherto puzzling rotational symmetry breaking (i.e., nematic characteristics) revealed in a certain class of dilute magnetic semiconductors [4]. This finding put in a new light a possible origin of nematicity in other systems, such as unconventional superconductors and modulation-doped semiconductor quantum wells, in which rotational symmetry breaking has so far been assigned to the unidirectional spontaneous ordering of spin, orbital or charge degrees of freedom.

[1] T. Dietl and H. Ohno, Rev. Mod. Phys. 86, 187–251 (2014).

[2] Y. Tokura, K. Yasuda, and A. Tsukazaki, Nature Rev. Phys. 1, 126–143 (2019).

[3] T. Dietl, K. Sato, T. Fukushima, A. Bonanni, M. Jamet, A. Barski, S. Kuroda, M. Tanaka, Phan Nam Hai, H. Katayama-Yoshida, Rev. Mod. Phys. 87, 1311–1376 (2015).

[4] Ye Yuan, R. Hübner, M. Birowska, Chi Xu, Mao Wang, S. Prucnal, R. Jakieła, K. Potzger, R. Böttger, S. Facsko, J. A. Majewski, M. Helm, M. Sawicki, Shengqiang Zhou, and T. Dietl, Phys. Rev. Materials 2, 114601 (2018).

Keywords: crystallographic phase separation, chemical phase separation, spinodal decomposition, nematicity, dilute magnetic semiconductors

This work has been supported by the Foundation for Polish Science through the IRA Programme financed by the EU within SG OP Programme.

A high-pressure study of a black phosphorus crystal leads to a rich phase diagram,
including a Lifshitz-type semiconductor-semimetal transition, a Weyl semimetal, and
superconductivity as well as structural phase transitions. Transport properties and
quantum oscillations under high pressure provide critically valuable information to
understand the physics behind these new phases. These properties have been measured
reliably under hydrostatic pressure and magnetic field with a large-volume apparatus.
Superconductivity in the A7 phase has been found to exhibit the largest
magnetoresistance effect in its normal state so far. The BCS superconductivity in the A7
phase as identified by the experiment can be accounted for by a first-principles
calculation.

Topology of defects in ordered states of matter is determined by dimensionality and symmetry properties of the order parameter. Larger number of variables needed to describe an ordered state gives rise to a greater diversity and complexity of topological defects, a prominent example being the A-phase of superfluid ³He. The order parameter describing non-collinear antiferromagnetic orders in the swedenborgite, CaBaCo₂Fe₂O₇, and Fe-langasite, Ba₃TaFe₃Si₂₄O₁₄, is an SO(3) matrix [1,2]. The iron langasite spin lattice is built of triangles formed by antiferromagnetically coupled Fe³⁺-ions (S = 5/2). The orientation of three co-planar spins added into the zero total spin is described by three Euler angles. This amazing material is both chiral and magnetically frustrated. It shows a non-collinear 120^o spin ordering at the scale of one unit cell, a spiral with a period of 7 lattice constants and complex spin superstructures at the scale of 1000 Å. Lifshitz invariants allowed by the lack of inversion symmetry give rise to interesting modulated magnetic phases and stabilize particle-like topological defects previously discussed in very different physical contexts, e.g. nuclear physics and superfluid ³He.

References:

[1] J. D. Reim, E. Rosén, O. Zaharko, M. Mostovoy, J. Robert, M. Valldor, and W. Schweika, Phys. Rev. B 97, 144402 (2018).

[2] M. Ramakrishnan et al., npj Quantum Materials 4, 60 (2019).

Topological semimetals have high carrier mobility in the form of quasiparticles resembling relativistic fermions. Experimental realisations of magnetic topological semimetals are relatively thin on the ground. Here we probe both the magnetic structure and interactions of the topological semimetal candidate YbMnSb₂ using neutron scattering.

YbMnSb₂ belongs to the P4/nmm space group and shows evidence of a magnetic ordering transition involving the Mn moments at ~350 K [1]. This is a relatively high Néel temperature among the family of materials AMnSb₂ (A = Ca, Sr, Ba, Yb, Eu), which has demonstrated characteristics of the topological semimetals. The quasi-2D plane formed by the Sb ‘square’ may host Weyl or Dirac fermions [1-3]. YbMnSb₂ has previously been studied via quantum oscillations, magnetometry, optical spectroscopy, ab initio band structure calculations, and angle-resolved photon emission spectroscopy [1, 4, 5]. Interestingly, these studies reached different conclusions as to the magnetic structure of YbMnSb₂, and hence its semimetal nature: the jury is out on whether it is a Dirac [4], nodal-line [5], or Weyl semimetal [1].

In this presentation I shall report the magnetic structure of YbMnSb₂ found by neutron diffraction, which is different to any previously proposed structures: C-type antiferromagnetism with the spins pointing along the c axis. This magnetic structure is shared by YbMnBi₂ [6]. Dirac physics is also seen in such AMnBi₂ materials; however, Bi rather than Sb layersresults in stronger spin-orbit coupling. This widens the band gap at any nodes and makes the resulting quasiparticles more massive [1]. We have also measured the spin wave spectrum of YbMnSb₂ and the results of this measurement will be described and compared with the spin dynamics in related materials. The implications for the topology of the electrons will be discussed.

Magnetic topological insulators (MTIs) are a hot topic of materials science, promising future availability of spintronics with low energy consumption, quantum computing and phenomena like the Quantized Anomalous Hall Effect (QAHE) [1-2]. MTIs are chemically and structurally akin to the original non-magnetic topological insulators. Of those, the tetradymites Bi₂Te₃ and Sb₂Te₃ have recently proven to allow the introduction of a third magnetic element resulting in magnetically active, topologically non-trivial compounds. A magnetic element can be incorporated either via substitution on the Bi/Sb position in (Bi, Sb)₂Te₃, or by adding a third element which introduces a new crystallographic site, resulting for example in MnBi₂Te₄. (Bi, Sb)₂Te₃ itself and all members of its family exhibit the rhombohedral Rm1 space group (No. 166) [2]. Therein interchanging sheets of Mn, (Bi, Sb) and Te build septuple layers with the central sheet being Mn (Wyckoff position 3a). Situated between the respective layers is a van der Waals gap (Fig. 1).

Our group was the first to successfully grow single crystals, and conduct an in depth study of the physical properties of MnBi₂Te₄ [4-5]. Single crystal diffraction experiments reported in that study showed intermixing of Mn and Bi and since then several studies have reported intermixing of the two elements (MnBi_2.14Te_3.96 [6], Mn_1.01Bi_1.99Te₄ and Mn_0.98Bi_2.05Te₄ [7]). While a lot of attention has been given to MnBi₂Te₄, MnSb₂Te₄ proved to be synthetically achievable too. Similar to MnBi₂Te₄, MnSb₂Te₄ features intermixing of Mn and Sb (Mn_0.852Sb_2.296Te₄ [8]). For MnSb₂Te₄, a recent study by Murakami et al. uncovers the impact of finding a certain amount of the magnetic Mn on the position of the non-magnetic Sb [9]. According to their discoveries, this changes the magnetic order from antiferromagnetic to ferrimagnetic.

These compounds are known to react sensitively to synthesis procedure and tempering history. Hence, our studies aim at understanding the greater connection between synthesis aspects and the resulting structural and physical properties. More precisely we studied MnBi₂Te₄ and MnSb₂Te₄ containing various amounts of Mn and other analogues of these systems. In these studies we uncovered, that the magnetism in MnSb₂Te₄ is even more sensitive to annealing procedures than previously expected.

[1] Y. Ando, Journal of the Physical Society of Japan, (2013), 82, 102001

[2] I. I. Klimovskikh, M. M. Otrokov, D. Estyunin, et al., Quantum Materials, (2020), 54.

[3] Y. Feutelais, B. Legendre, N. Rodier, V. Agafonov, Materials Research Bulletin, (1993), 28, 591-596

[4] A. Zeugner, F. Nietschke, A. U. B. Wolter, et al., Chemistry of Materials, (2019), 31, 2795-2806.

[5] M. M. Otrokov, I. I. Klimovskikh, H. Bentmann, et al., Nature, (2019), 576, 416-422.

[6] H. Li, S. Liu, C. Liu, et al., Physical Chemistry Chemical Physics, (2020), 22, 556-563.

[7] M.-H. Du, J. Yan, V. R. Cooper, M. Eisenbach, Advanced Functional Materials, (2020), 2006516.

[8] L. Zhou, Z. Tan, D. Yan, et al., Physical Review B, (2020), 102, 85114.

[9] T. Murakami, Y. Nambu, T. Koretsune, et al., Physical Review B, (2019), 100, 195103.

Eudialyte-group minerals (EGMs) are of a scientific and industrial interest as important concentrators of rare and strategic elements (mainly, Zr and REE) in agpaitic alkaline rocks. The general crystal chemical formula of EGMs is [N(1)₃N(2)₃N(3)₃N(4)₃N(5)₃]{M(1)₆M(2)₃M(3)M(4)Z₃(Si₉O_27-3x(OH)_3x)₂(Si₃O₉)₂Ø_0–6}X(1)X(2) where M(1) = ^VICa, ^VIMn²⁺, ^VIREE, ^VINa, ^VIFe²⁺; M(2) = ^IV,VFe²⁺, ^V,VIFe³⁺, ^V,VIMn²⁺, ^V,VINa, ^IV,VZr; M(3) and M(4) = ^IVSi, ^VINb, ^VITi, ^VIW⁶⁺; Z = ^VIZr, ^VITi; Ø = O, OH; N(1)–N(5) are extra-framework cations (Na, Н₃О⁺, K, Sr, REE, Ba, Mn²⁺, Ca) or H₂O; X(1) and X(2) are extra-framework water molecules, halide (Cl^–, F^–) and chalcogenide (S^2–) anions, and anionic groups (CO₃^2–, SO₄^2–); x = 0–1 (Rastsvetaeva & Chukanov, 2012).

The crystal structure of EGMs is based on a heteropolyhedral framework (Chukanov et al., 2004) which makes these minerals similar to zeolite-like materials and molecular sieves. The first topological analysis of the eudialyte-type structures (eudialyte, kentbrooksite, oneillite, and khomyakovite) was performed using the approach of coordination sequences {N_k} (k = 1–12), using the representation of crystal structure as a finite ‘reduced’ graph (Ilyushin & Blatov, 2002). As an invariant of the eudialyte-type structure and its derivatives the MT-layer [Zr₃Si₂₄O₇₂]_∞∞ (PBU: primary building unit, an elementary component of an MT-framework) was chosen.

Topological analysis of the heteropolyhedral MT-framework in the eudialyte-type structure and its derivatives was performed based on a natural tiling (Blatov et al., 2007) (partition of the crystal space by the smallest cage-like units) analysis of the 3D cation nets using the ToposPro software (Blatov et al., 2014). According to the modern topological classification, it is necessary to use the standard representation to determine the topological type of the net. For the topological analysis carried out in this work, atomic nets for each of the 12 structure types were simplified and the corresponding underlying nets, which characterize the connectivity of the primary structural units as well as their point symbols, were obtained. The 0-1-2-free representation was used for topological analysis of cages within the tiling approach because it represented the cages in more detail. To analyze the migration paths of sodium cations in these structures, the Voronoi method was used.

The parental eudialyte-type MT-framework is formed by isolated ZO₆ octahedra, six-membered [M(1)₆O₂₄] ring of edge-shared M(1)O₆ octahedra, and two types of rings of tretrahedra, [Si₃O₉] and [Si₉O₂₇]. Different occupancies of additional M(2), M(3), and M(4) sites with variable coordination numbers by Q, T*, and M* cations, respectively, result in 12 types of the MT-framework. Corresponding point symbols for the cationic 3D-nets of the MT-frameworks as well as tiles’ sequences have been calculated.

Based on the results of natural tilings calculations as well as theoretical analysis of migration paths, it was found that Na⁺ ions can migrate through six- and seven-membered rings, while all other rings are too small. In eight types of the MT-frameworks, Na⁺-ion migration and diffusion is possible at standard temperature and pressure, while in four other types cages are connected by narrow gaps and, as a result, the Na⁺ diffusion in them is complicated at ambient conditions but may be possible either at higher temperatures or under mild geological conditions during long times. This conclusion is in a good agreement with numerous examples of the transformation of initial EGMs into their hydrated Na-deficient counterparts as a result of natural processes of sodium leaching and hydrolysis under hydrothermal conditions.

The relationships between heteropolyhedral substitutions and topological features of the derivative framework structures have been also discussed for alluaudite supergroup (Aksenov et al., 2021) minerals and related synthetic compounds. However, in the case of eudialyte-type structures such relationships look more complicated because of multiple variants of their derivative structures. Moreover, in the case of so-called “megaeudialytes” (Rastsvetaeva et al., 2012), i.e. EGMs which are characterized by modular structures and doubling of the c parameter (c ~ 60 Å), different modules regularly alternating in the structure can represent different types of the framework, which increases the amount of topological variations. Similar influence of modularity on the topological features of zirconium silicates have been described for the lovozerite-type structures (Pekov et al., 2009), where different ways of stacking of the lovozerite modules define the unit cell parameters, symmetry, and topology of the derivative structures (Krivovichev, 2015).

This work was financially supported by the Russian Science Foundation, project No. 20-77-10065, Ministry of Education and Science of the Russian Federation for financial support within grant No. 0778-2020-0005 , and state task, state registration number ААAА-А19-119092390076-7.

References:

Aksenov, S. M., Yamnova, N. A., Kabanova, N. A., Volkov, A. S., Gurbanova, O. A., Deyneko, D. V., Dimitrova, O. V. & Krivovichev, S. V. (2021). Crystals. 11, 237.

Blatov, V. A., Delgado-Friedrichs, O., O’Keeffe, M. & Proserpio, D. M. (2007). Acta Crystallogr. Sect. A Found. Crystallogr. 63, 418–425.

Blatov, V. A., Shevchenko, A. P. & Proserpio, D. M. (2014). Cryst. Growth Des. 14, 3576–3586.

Chukanov, N. V, Pekov, I. V & Rastsvetaeva, R. K. (2004). Russ. Chem. Rev. 73, 205–223.

Ilyushin, G. D. & Blatov, V. A. (2002). Acta Crystallogr. Sect. B Struct. Sci. 58, 198–218.

Krivovichev, S. V. (2015). Proc. Steklov Inst. Math. 288, 105–116.

Pekov, I. V., Krivovichev, S. V., Zolotarev, A. A., Yakovenchuk, V. N., Armbruster, T. & Pakhomovsky, Y. A. (2009). Eur. J. Mineral. 21, 1061–1071.

Rastsvetaeva, R. K. & Chukanov, N. V. (2012). Geol. Ore Depos. 54, 487–497.

Rastsvetaeva, R. K., Chukanov, N. V. & Aksenov, S. M. (2012). Minerals of Eudialyte Group: Crystal Chemistry, Properties, Genesis Nizhniy Novgorod: University of Nizhni Novgorod.

Crystallography has many traditional and intuitive links with cultural heritage. The most scholar one is the description and analysis of symmetry in art and architecture [1-2]. The most natural is the fascination that crystals induce on human mind, as light- and color-capturing gems [3]. However virtually all artistic forms and all products derived from human activity are made of materials. The fundamental contribution that crystallography provides to our knowledge of matter is being rapidly transferred into our ability to better interpret archaeological evidence of past human activities (Fig. 1), and to manage and preserve artworks for future generations. The science of cultural heritage materials is profiting greatly of the state-of-the-art crystallographic methods and techniques, and in turns poses new and unexpected challenges to future crystallographers.

[1] MacGillavry, C.H. (1965) Symmetry aspects of M.C. Escher’s periodic drawings. Utrecht: Oosthoek

[2] Makovicky, E. (2016). Symmetry: through the eyes of old masters. Berlin/Boston: Walter de Gruyter GmbH & Co KG.

[3] Garcia-Ruiz, J.M. (2018). 2001: The Crystal Monolith. Substantia, 2, 19-25.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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