Materials with negative thermal expansivity (NTE) attracts great attention of scientists because they can be combined with numerous materials with positive thermal expansion (PTE) in order to prepare a composite material with a tailored coefficient of thermal expansion, namely, zero expansion. This allows decreasing a performance deterioration caused by a large difference in expansion coefficients.[1] Among numerous metal-organic frameworks (MOFs), zeolitic imidazolate frameworks (ZIFs) are highly popular because of the possibility to combine electronic properties of the transition metal ions with structural features of zeolites. They possess large porosity, therefore alkali metals that form dense and hyper coordinated structures stayed out of the focus for its synthesis. On the other hand, magnesium imidazolate has a porous structure, as well as its borohydride(s). Although the preparation of manganese imidazolates is challenging, probably due to the difficulties of formation of non-distorted tetrahedral Mn²⁺-4N geometry preferable in ZIFs, the similarity of magnesium and manganese borohydrides was reason to try synthesis with both metals and compare the results.

Mechanochemical reactions of alkali metal imidazolates and magnesium or manganese borohydride gave novel bimetallic imidazolates AMIm₃ (A=Na, K; M=Mg, Mn) whose crystal structures have been solved from synchrotron radiation X-ray powder diffraction (PXRD) data using global optimization in program FOX[2].Pores of 30-35 ų (5-6 % of the unit cell volume) are incorporated in all structures. Detailed study of temperature-aided structural and microstructural changes, obtained from the synchrotron in situ HT-PXRD data, gave a deeper understanding of crystallization processes in the borohydride-imidazolate system and have elucidated mechanisms of the reactions which occurs during mechanochemical synthesis and thermal treatment of these systems.

Extensive study of thermal expansion properties of a series of isostructural compounds AMIm₃ (A=Na, K; M=Mg, Mn) revealed a common behavior characteristic for a structural type. However, very interesting drastic changes of thermal expansion were noticed when alkali metal imidazolate (NaIm) coexist with compound-of-interest (NaMgIm₃); volumetric thermal expansion coefficient changes from positive α_V = 35 × 10⁻⁶ K⁻¹ to colossal negative values α_V = −460 × 10⁻⁶ K⁻¹ and linear thermal expansion changes from α = 34 × 10⁻⁶ K⁻¹ to α = -210 × 10⁻⁶ K⁻¹ (Figure 1). This is caused by coherent intergrowth, lattice mismatch, a tensile strain, and microstructural properties [3] of mentioned phases and leaves a possibility of design of the material with zero thermal expansivity.

[1] Ren, Z.; Zhao, R.; Chen, X.; Li, M.; Li, X.; Tian, H.; Zhang, Z.; Han, G. (2018) Nat. Commun. 123, 1638.

[2] Favre-Nicolin, V.; Černý, R. (2002) J. Appl. Crystallogr. 35, 734−743.

[3] Matěj, Z.; Kužel, R.; Nichtová, L. (2010) Powder Diffr. 25, 125-131.

The research was supported by OP RDE project No. CZ.02.2.69/0.0/0.0/18_053/0016976 International mobility of research, technical and administrative staff at the Charles University .

The financial support of the SNSF project (SCOPES) “Metal-Hydride Organic Frameworks (HOF) - new solids for gas adsorption and separation” is acknowledged.

Molecules can crystallise either in the presence or absence of the solvent used to crystallise them with a range of intermolecular interactions between both the molecule and the solvent occurring to sustain and propagate the crystal structure. Molecules that crystallise as solvates or clathrates could be considered as host-guest materials, but it is often unclear whether a guest-free material can be obtained by heating the solvated material. If the solvent can be removed this can, in turn, lead to vacant void spaces or a partially closed material that can be used to store a secondary guest (either a gas or secondary solvent). Understanding how these materials behave upon removal of the solvent contained within them is crucial in assessing their potential applications. With the CSD recently reaching 1 million deposited crystal structures [1] there is a large resource of untested solvate structures, which may provide inspiration for new guest-uptake materials.[2]

This work presents an attempt to further understand a previously reported family of halogen-functionalised organic molecules which has been reported in 3 distinct phases (two inclusion phases and one solvent-excluded phase)[3]. The two inclusion phases adopt a 2D halogen-bonding network propagated through a halogen-halogen bonded trimer. The work presented here, initially focusing on the bromine-functionalised host molecule, used liquid-assisted grinding to screen a series of solvents to identify desirable inclusion phases. The grinding experiments also identified a previously unreported inclusion phase. Thermal stability studies demonstrated that these inclusion phases transformed to the solvent-excluded phase upon heating. Further work has involved altering the halogen functionality (using fluorine, chlorine or iodine) to see how this affects the propensity to form the desired inclusion phases and the thermal stability of these phases, as well as exploring whether phase transformation can be observed when samples are exposed to a vapour environment.

Figure 1. Overview of the solvent-dependent phases of a family of halogen-bonded networks.

MOFs, COFs, and HOFs as highly ordered porous architectures attract wide interest owing to their broad potential of application in heterogeneous catalysis, storage, sensing, drug delivery, separation, etc.

Research of organic frameworks assembled by supramolecular interactions without metal or covalent bonds taking part in the framework construction has come in the focus of interest the most lately. A well-orchestrated interplay of supramolecular interactions, molecular inflexibility, and spatial effects characterize the non-covalently bonded organic frameworks. All mentioned aspects affect the molecular and crystal symmetries. We reported recently the preparations and structures of ionic hydrogen-bonded organic frameworks, their polymorphic and solvatomorphic forms were described [1]. Further attempts were made to prepare hydrogen-bonded organic frameworks, either ionic or neutral. Our systematic study inspired by the Maruoka type chiral phase-transfer catalysts resulted in some new series of solvatomorphic hydrogen-bonded organic framework materials. We will present (Fig. 1), that the most important aspects in the HOF formation include (1) the intramolecular interactions which are responsible for the inflexibility of the molecule, (2) the intermolecular interactions which are responsible for framework construction, (3) the terminal spacer groups for void formation, (4) the molecular symmetries which prove to be important in the tightening of the molecule, and (5) all the aforementioned features affect the crystal symmetry which may coincide with the molecular symmetry.

The presented work contributes to the understanding of hydrogen-bonded organic framework formation. It supports the still challenging design and preparation of framework structures with high porosity.

Figure 1. The most important aspects in the HOF formation.

[1] Horváth D. V., Holczbauer T., Bereczki L., Palkó R., May N. V., Soós T., Bombicz P. (2018) CrystEngComm, 20, 1779-1782.

This work was supported by the National Research, Development and Innovation Office-NKFIH through OTKA K124544 and KH129588.

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

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

While small molecule activation processes underpin transformations in catalysis, gathering structural information about the reactive metal-based species responsible can be challenging. Such species are often coordinatively unsaturated or possess labile ligands; they are therefore highly reactive and transient. Building on research trapping reactive species within the cavities of supramolecular assemblies or frameworks,[1] we have been using metal-organic frameworks (MOFs) to "matrix isolate" and structurally characterise catalytically important metal-based species.[2, 3] The building block synthetic approach of MOFs using chemically mutable links, coupled with long range order (crystallinity), and excellent chemical and thermal stability,[4] allows them to be used to stabilise and characterise reactive species.

To garner these insights we use a bespoke, flexible Mn-based MOF, [Mn₃L₂L’] (MnMOF-1, where L = bis-(4-carboxyphenyl-3,5-dimethylpyrazolyl)methane) with a site poised for allowing single crystal-to-single crystal (SCSC) post-synthetic metalation.[2, 3] This contribution will expand these ideas and examine ligand exchange chemistry occurring at trigonal planar Cu(I) sites chemically isolated in the MOF.[5] Insights into catalysis obtained by structurally characterising the initial catalysts and by targeting sequential “snapshots” of the catalytically active structure by single crystal X-ray crystallography will be reported.

1. R. J. Young, M. T. Huxley, E. Pardo, N. R. Champness, C. J. Sumby and C. J. Doonan, Chem. Sci., 2020, 11, 4031-4050
2. W. M. Bloch, A. Burgun, C. J. Coghlan, R. Lee, M. L. Coote, C. J. Doonan and C. J. Sumby, Nat. Chem., 2014, 6, 906-912; A. Burgun, C. J. Coghlan, D. M. Huang, W. Chen, S. Horike, S. Kitagawa, J. F. Alvino, G. F. Metha, C. J. Sumby and C. J. Doonan, Angew. Chem. Int. Ed., 2017, 56, 8412-8416; R. A. Peralta, M. T. Huxley, R. J. Young, O. M Linder-Patton, J. D. Evans, C. J. Doonan and C. J. Sumby, Faraday Discussions, 2020, 225, 84-99.
3. R. A. Peralta, M. T. Huxley, J. D. Evans, H. Cao, M. He, X. S. Zhao, S. Agnoli, C. J. Sumby and C. J. Doonan, J. Am. Chem. Soc., 2020, 142, 13533-13543; R. A. Peralta, M. T. Huxley, Z. Shi, Y.-B. Zhang, C. J. Sumby and C. J. Doonan, Chem. Commun., 2020, 56, 15313-15316.
4. H. Furukawa, K. E. Cordova, M. O’Keeffe and O. M. Yaghi, Science, 2013, 341, 1230444.
5. R. A. Peralta, M. T. Huxley, J. Albalad, C. J. Sumby and C. J. Doonan, unpublished results, 2021.

In recent years, convergent-beam electron diffraction (CBED) has been widely used for refining crystal structure parameters and low-order structure factors. It enables nanometer-scale structure analysis with high sensitivity to the distribution of valence electrons. The determination of low-order structure factors with higher precision is essential to precisely determine the chemical bonding state of materials which are closely related to their physical properties. Till date, it is considered that refinement of structure factors using CBED pattern taken at the Bragg-excited condition increases the sensitivity to the corresponding structure factor [1]. However, the origin of precision and correspondence between precision and sensitivities of CBED patterns in the refinement of structure factors, is still lacking.

In this analysis, a local structure analysis method developed by Tsuda and Tanaka [2] has been applied to potassium tantalate KTaO₃ (KTO). Isotropic atomic displacement parameters and five low-order structure factors were refined using energy-filtered CBED patterns taken at three zone-axis (ZA) and five Bragg-excited conditions. Compared to ZA patterns, the Bragg-excited CBED patterns showed higher precision in the refinement of structure factors. One to one correspondence between higher precision and sensitivity of Bragg-excited CBED pattern has been found only for structure factors of the outer zeroth-order Laue zone (ZOLZ) reflection having larger reciprocal lattice vectors. Smaller correlation coefficients among the refined structure factors in the refinement of Bragg-excited patterns lead to higher precision. From the point of view of higher precision, Bragg-excited patterns are advantageous over ZA patterns. To achieve higher precision and sensitivities in the refinements of structure factors it would be better to use both of the ZA and Bragg-excited CBED patterns. The use of large angle CBED (LACBED) or large angle rocking beam electron diffraction (LARBED) techniques should be effective for this purpose.

[1] Ogata, Y., Tsuda, K. & Tanaka, M. (2008). Acta Cryst. A64, 587.

[2] Tsuda, K. & Tanaka, M. (1999). Acta Cryst. A55, 939.