Degenerate (identity) chemical reactions in ferro­elastic crystals

The article points to the fact that there are examples of degenerate chemical reactions which occur in crystals. Such reactions are concomitant with the order–disorder phase transitions or with domain reorientations in some ferroelastic crystals. The latter case is discussed here.

A new BaCa(CO₃)₂ polymorph

A fourth polymorph of the double carbonate BaCa(CO₃)₂ has been found and it is demonstrated that this polymorph can be synthesized via three different synthesis routes. The structure was solved by a combination of density-functional-theory-based model calculations and Rietveld refinement.

Binding of metal ions and water molecules to nucleic acid bases: the influence of water molecule coordination to a metal ion on water–nucleic acid base hydrogen bonds

The interactions of nucleic acid bases with non-coordinated and coordinated water molecules were studied by analyzing data in the Protein Data Bank (PDB) and by quantum chemical calculations. The calculated interaction energies for [Mg(H₂O)₆]²⁺–nucleic acid base systems are from −12.94 to −49.96 kcal mol⁻¹, for [Na(H₂O)₆]⁺–nucleic acid base systems they are from −6.66 kcal mol⁻¹ to −19.63 kcal mol⁻¹, while for non-coordinated water–nucleic acid base they are from −4.63 to −8.93 kcal mol⁻¹, which is similar to the strength of hydrogen bonds between nucleic acid bases calculated previously.

Design, preparation, characterization and formation mechanism of a novel kinetic CL-20-based cocrystal

Intermolecular interactions of 2,4,6,8,10,12-hexa­nitro­hexa­aza­isowurtzitane–dinitrobenzene (CL-20–DNB) and CL-20–2,4,6-tri­nitro­toluene (TNT) cocrystals are analyzed and a novel energetic–energetic cocrystal of CL-20–2,4,6-tri­nitro­phenol (TNP) is designed. The crystal structures and formation mechanism of the novel kinetic CL-20–TNP cocrystal are also analyzed.

Investigations of the temperature-dependent electron paramagnetic resonance spectra and local structures for a cobalt(II) porphyrin complex within a metal–organic framework

A temperature-dependent cobalt(II) porphyrin complex within a metal–organic framework is investigated, showing six- and five-coordinated models for low- and high-temperature systems, respectively.

Formation of the cementite crystal in austenite by transformation of triangulated polyhedra

Crystal structures of the iron face-centered cubic modification (austenite) and Fe₃C carbide can be transformed into each other by diagonal flipping in a rhombus consisting of two adjacent triangular faces. This transformation mechanism determines the orientation relationship between austenite and Fe₃C carbide which has been observed in many experiments.

Elucidation of correlated disorder in zeolite IM-18

The microstructure of zeolite IM-18 with correlated disorder was elucidated by simulating the diffuse scattering of powder and single-crystal diffraction patterns. The method could be applied to other multidimensional disordered structures.

Structure and piezochromism of pyrene-1-carbaldehyde at high pressure

A series of high-pressure structure determinations using single-crystal X-ray diffraction experiments was performed for pyrene-1-carbaldehyde, a relatively simple organic compound, highly luminescent in the solid state and crystallizing in a challenging low-symmetry system. X-ray structure determinations were conducted using a multi-crystal approach. Piezochromic properties of pyrene-1-carbaldehyde were studied with UV–vis spectroscopy and periodic DFT calculations.

Perovskite phase AgCuF₃: multiple Dirac cones, 100% spin polarization and its thermodynamic properties

This work focuses on a new phase material, AgCuF₃, which has a combination of multiple Dirac cones and 100% spin polarization properties. Compared to the non-spin polarization system LaCuO₃, the spin-polarized Dirac behavior in AgCuF₃ is intrinsic and does not need the help of additional experimental conditions.

Pressure-induced transformation of CH₃NH₃PbI₃: the role of the noble-gas pressure transmitting media

A structural study of methyl­ammonium lead triiodide [CH₃NH₃PbI₃ (MAPbI₃)], at high pressures up to 20 GPa using noble gases Ne and Ar as pressure-transmitting media is reported. It is found that both noble gases are chemically active at high pressures. In particular, Ne stabilizes the high-pressure structure of Ne_xMAPbI₃ and prevents amorphization up to 20 GPa. In contrast, Ar acts as a stabilizer only up to 2.4 GPa and accelerates irreversible amorphization upon further compression.

Cocrystals in the Cambridge Structural Database: a network approach

With the aim of finding new cocrystals, a network of coformers is constructed using the data present in the Cambridge Structural Database. The network is analyzed in terms of coformer clustering, popularity and network type, providing new data-driven insights into cocrystallization.

Two new polymorphs of cis-perinone: crystal structures, physical and electric properties

The crystal structures of two polymorphs of cis-perinone derive from stacking of flat molecules arranged due to π–π interactions. The difference in direct current electric conductivity of the materials could be explained by the dependence of the mobility and concentration of charge carriers on the structure.

Simulation of diffuse scattering in DL-norleucine

It is shown how Monte Carlo methods can be used to analyse the observed diffuse scattering and yield an unprecedented and informative structural model of an intermediate step in the transition between the two end structures, α and β, of DL-norleucine.

Pressure-induced phase transitions in Na₂B₁₂H₁₂, structural investigation on a candidate for solid-state electrolyte

Herein is described the two pressure-induced phase transitions of sodium dodeca­hydro-closo-dodecaborate (Na₂B₁₂H₁₂), a candidate for a solid-state electrolyte.

Three differently coloured polymorphs of 3,6-bis­(4-chloro­phenyl)-2,5-di­propyl-2,5-di­hydro­pyrrolo­[3,4-c]pyrrole-1,4-dione

A very rare example of a diketo­pyrrolo­pyrrole derivative showing polymorphism with completely different molecular conformations and a different arrangement of neighbouring molecules is reported. The thermodynamic stability relationships between the three polymorphic forms are also interpreted.

Accurate and efficient representation of intra­molecular energy in ab initio generation of crystal structures. II. Smoothed intramolecular potentials

This article describes a recent advance in the CrystalPredictor code for crystal structure prediction, namely a smoothed intramolecular potential, that improves the accuracy and efficiency of calculations, allowing for investigations into larger and more flexible molecules. It is illustrated with four case studies into large flexible molecules: ROY, glucose, molecule (XXVI) and flufenamic acid.

Comparison of different strategies for modelling hydrogen atoms in charge density analyses

Five different methods for approximation of hydrogen-atom parameters in charge density analysis and structural properties derived from these parameters are compared with results from neutron diffraction data.

A further investigation of the complex M3 murataite structure using Hf substitution and STEM-EELS techniques

Didactic techniques for a complex, very large unit cell are reported. Here a new finding for the site preference of the Zr ion is reported using simple techniques for the characterization of the M3-type murataite.

Supramolecular networks and Hirshfeld surfaces of oxydi­acetic acid and iminodi­acetic acid salts

Molecular salts of oxydi­acetic acid and iminodi­acetic acid have been synthesized using ethyl­enedi­amine and o-phenyl­enedi­amine. The crystal structures are determined and Hirshfeld surface analysis is reported.

Kristalle verändern unsere Welt. Struktur – Eigenschaften – Anwendungen

Multi-Component Crystals. Synthesis, Concepts, Function