Determination of the crystal structure of magnesium perchlorate hydrates by X-ray powder diffraction and the charge-flipping method

The crystal structures of the magnesium perchlorate tetrahydrate and dihydrate were determined using the charge-flipping method and powder diffraction data. The structural evolution of the Mg(ClO₄)₂·nH₂O system during dehydration was examined.

The modulated structure of the calcium aluminate Ca₆(AlO₂)₁₂·Bi₂O₃

The structure of incommensurate bismuth calcium aluminate, Bi₂Ca₆Al₁₂O₂₇, has been solved using single-crystal X-ray diffraction data. The origin of the modulation is related to the ordering of Bi₂O₉Lp₂ clusters within tunnels within the Ca₆Al₁₂O₂₄ framework.

Structure and electrical properties of the new pyrochlore-type protonic solid electrolyte K_0.88Nb₂O_7.58H_4.28

Single-crystal, synchrotron powder X-ray diffraction and neutron powder diffraction studies of the novel pyrochlore-type compound with the structural formula K_0.88(OH)_0.54H_1.66(H₂O)_1.04Nb₂O₆ are reported. Owing to the extended stability range and resistance to water solubility, the compound can be considered as a candidate for intermediate temperature solid-oxide fuel-cell applications.

Crystal chemistry of transition metal diarsenates M₂As₂O₇ (M = Mn, Co, Ni, Zn): variants of the thortveitite structure

Mn₂As₂O₇ and the high-temperature β-M₂As₂O₇ (M = Mn, Co, Ni) polymorphs crystallize in the thortveitite aristotype structure, whereas the low-temperature α-M₂As₂O₇ polymorphs and β-Zn₂As₂O₇ are hettotypes.

Structure of N-(5-ethyl-[1,3,4]-thia­diazole-2-yl)­toluenesulfonamide by combined X-ray powder diffraction, ¹³C solid-state NMR and molecular modelling

A multi-technique approach that combines X-ray powder diffraction (XRPD) with ¹³C solid-state NMR (SSNMR), and molecular modelling using the GIPAW gauge (gauge including projector augmented-wave) method is employed for structural determination on microcrystalline powders. This approach is shown to be very robust in simplifying the crystal structure search protocol, as well as in clearly identifying the non-covalent interactions (C—H⋯π) responsible for stabilizing the three-dimensional crystal structure of the title compound.

Thermal motion of tert-butyl groups III. tert-Butyl substituents in aromatic hydrocarbons, the view from the bottom of the well

Low-temperature crystal studies of five strained aromatic hydrocarbons yield anisotropic displacement parameters that vary widely in magnitude and precision. The rigidity of tert-butyl substituents is tested; thermal motion analysis indicates that crowded ortho tert-butyls do not `move' with respect to the aromatic core, while rigid-body models for meta and para tert-butyls suggest low rotation barriers (4–10 kJ mol⁻¹), in some cases with additional motion of a tert-butyl methyl group.

Direct observation of arylnitrene formation in the photoreaction of arylazide crystals

Seven kinds of arylazide crystals were investigated but only one, 2-azidobiphenyl, formed an observable nitrene on exposure to UV light at 80 K. The structure of a single crystal containing both starting material and unstable 2-biphenylnitrene was analyzed using X-rays.

Direct observation of various reaction pathways of arylnitrenes in different crystal environments caused by acid–base complex formation

Various reaction pathways of arylnitrenes produced by photo-irradiation in complex crystals composed of 2-, 3- or 4-azidobenzoic acid and a diaryl- or dicyclohexylamine were directly observed by X-ray crystal structure analysis.

Structures of cyclic dipeptides: an X-ray and computational study of cis- and trans-cyclo(Pip-Phe), cyclo(Pro-Phe) and their N-methyl derivatives

The crystal structures of a set of eight closely related cyclodipeptides are determined. By comparing with density functional theory gas-phase and periodic calculations, the intra- and intermolecular interactions governing these crystals are investigated.

Solid solution of two diastereomers of [3a(R,S),7a(R,S)]-3-[(1′R)-1-phenylethyl]perhydro-1,3-benzo­thiazol-2-iminium chloride

The solid solution of two diastereomers of [3a(R,S),7a(R,S)]-3-[(1′R)-1-phenylethyl]perhydro-1,3-benzothiazol-2-iminium chloride has been studied by single-crystal X-ray diffraction, while density functional theory (DFT) calculations helped to establish the charge distribution within the thiazolidin-2-imine part of the molecular cation. The similarity of the molecular shapes and the formation of strong hydrogen bonds, unaffected by changes of chirality, explain the impossibility of resolving the diastereomers by crystallization.

Electron density studies on hydrogen bonding in two chromone derivatives

The experimental electron densities of two chromone derivatives have been determined from X-ray synchrotron diffraction data at low temperature (100 K). The presence of intramolecular resonance-assisted hydrogen bonds and π-electron delocalization within the hydrogen-bonded ring were confirmed by geometrical and topological parameters.

Diffuse scattering study of aspirin forms (I) and (II)

Full three-dimensional diffuse scattering data have been recorded for both polymorphic forms [(I) and (II)] of aspirin and these data have been analysed using Monte Carlo computer modelling. The observed scattering in form (I) is well reproduced by a simple harmonic model of thermally induced displacements. The data for form (II) show, in addition to thermal diffuse scattering (TDS) similar to that in form (I), diffuse streaks originating from stacking fault-like defects as well as other effects that can be attributed to strain induced by these defects.