Dynamic orientational disorder in crystals of fluoroelpasolites, structural refinement of (NH₄)₃AlF₆, (NH₄)₃TiOF₅ and Rb₂KTiOF₅

Electron-density profiles indicate the cations to be tetrahedrally shifted from the 8c position into the 32f site of the Fm3m unit cell as a new feature of the fluoroelpasolite structure refinement.

Structure of LaTi₂Al₉O₁₉ and reanalysis of the crystal structure of La₃Ti₅Al₁₅O₃₇

The crystal structure of LaTi₂Al₉O₁₉ determined by X-ray powder diffraction is presented together with its dielectric properties. The structure of La₃Ti₅Al₁₅O₃₇ is critically reviewed.

The not so simple cubic structure of PbZr_1 − xTi_xO₃ (PZT): complex local structural effects in perov­skites

High-resolution neutron diffraction of the important piezoelectric lead zirconate titanate (PZT) has found that oxygen disorder exists well into the cubic phase.

Water channel structure of bassanite at high air humidity: crystal structure of CaSO₄·0.625H₂O

In the presence of high relative air humidity the crystal structure of CaSO₄·0.5H₂O transforms due to the incorporation of additional water of hydration. The crystal structure of CaSO₄·0.625H₂O was solved by single-crystal X-ray diffraction at 298 K with 75% relative air humidity.

Stacking faults and superstructures in a layered brownmillerite

Stacking faults in Ca₄Fe₂Mn_0.5Ti_0.5O₉ have been examined using X-ray diffraction and high-resolution transmission electron microscopy. Electron diffraction revealed two superstructures with ordered stacking sequences.

[Ni(H₂O)₆](NO₃)₂·(15-crown-5)·2H₂O: three phase transitions and an intermediate modulated phase stable over a range of ca 40 K

The structure of single-crystal [Ni(H₂O)₆](NO₃)₂·(15-crown-5)·2H₂O has been studied in the range 90–308 K in intervals of ≤ 10 K as the crystal passed through three phase transitions. An unusual intermediate, modulated phase described in a commensurate approximation (Z′ = 7) has been characterized.

Structural study of piracetam polymorphs and cocrystals: crystallography redetermination and quantum mechanics calculations

A joint theoretical and experimental investigation of the structure of piracetam, in which the conformational space of piracetam is explored by a scan of the two dihedral angles and predicted conformations with intramolecular hydrogen bonds are compared with CSD geometries. Single crystals and the structure of piracetam are obtained and statistical comparison with CSD forms shows only three dihedral angle families.

Determining the structure of a benzene7.2-silicalite-1 zeolite using a single-crystal X-ray method

An orthorhombic benzene-silicalite-1 single crystal was obtained from a monoclinic twin crystal, and the structure was determined by a single-crystal method for the first time.

Diffuse scattering resulting from macromolecular frustration

Distinctive diffuse scattering in the form of diffuse rings around Bragg positions has been observed in the diffraction patterns of a crystal of the N-terminal fragment of the Gag protein from Feline Foamy Virus. It is shown that these are caused by geometric frustration as molecules try to pack on the triangular b–c mesh of the space group P6₁22.

Crystal packing and melting temperatures of small oxalate esters: the role of C—H⋯O hydrogen bonding

Dialkyl oxalates are cryocrystallized and the crystal structures have been analysed. The distinctive nature of two oxalates that are solid at room temperature is rationalized on the basis of C—H⋯O interactions.

Towards crystal structure prediction of complex organic compounds – a report on the fifth blind test

The results of the fifth blind test of crystal structure prediction, which show important success with more challenging large and flexible molecules, are presented and discussed.

The whole range of hydrogen bonds in one crystal structure: neutron diffraction and charge-density studies of N,N-di­methylbiguanidinium bis­(hydrogensquarate)

Neutron and high-resolution X-ray diffraction experiments at 100 K have been used to derive the precise geometry and the electron density of a wide range of X—H⋯O interactions in the title compound. The shortest O—H⋯O bond does not follow the trend of the remaining hydrogen bonds: it is significantly more symmetric, and energy density criteria support the concept of an interaction with intermediate character between covalent and closed-shell.

Molecular origins of commercial laser dye functionality in azacoumarins and 2-quinolones: LD 425, LD 489 and LD 473

The structural data of two azacoumarins, LD 425 and LD 489, and one 2-quinolone, LD 473, are reported. Bond-length patterns and characteristic spectral blue shifts in these compounds are examined using resonance theory and structural comparisons with their coumarin analogues.

Experimental and theoretical electron-density study of three iso­indole derivatives: topological and Hirshfeld surface analysis of weak intermolecular interactions

Weak intermolecular contacts of C—H⋯C(π), C,N(π)⋯C,N(π) and H⋯H types occurring in crystals of isoindole derivatives were analysed in terms of topological electron-density parameters and Hirshfeld surfaces derived from high-resolution X-ray diffraction experiments.