Crystallographic features of ammonium fluoro­elpasolites: dynamic orientational disorder in crystals of (NH₄)₃HfF₇ and (NH₄)₃Ti(O₂)F₅

The electron-density profiles of all the constituent atoms in the structures of ammonium fluoroelpasolites enabled the refinement of their real positions. The N2 atom does not escape a special 4b position, but the H2 atoms are disordered in the 96k position instead of 24e and together with the H3 atom in the 32f position they form eight spatial orientations of the ammonium group.

Charge density analysis of metformin chloride, a biguanide anti-hyperglycemic agent

The electrostatic properties and bond orders of metformin chloride are analyzed experimentally and theoretically.

A priori checking of the light-response and data quality before extended data collection in pump–probe photocrystallography experiments

In picosecond and slower pump–probe diffraction experiments the collection of response–ratio correlation sets prior to full data collection provides an invaluable confirmation of the existence of a light-induced signal prior to full data collection. If a response to light exposure is observed, the quality of the data being collected can be assessed.

Deformations of the α-Fe₂O₃ rhombohedral lattice across the Néel temperature

Synchrotron radiation powder diffraction studies of synthetic hematite, α-Fe₂O₃, show that its crystal structure symmetry is monoclinic both below and above the Néel temperature, T_N = 950 K.

Isothermal equation of state and high-pressure phase transitions of synthetic meridianiite (MgSO₄·11D₂O) determined by neutron powder diffraction and quasielastic neutron spectroscopy

We report high-pressure neutron powder diffraction measurements of the most hydrated phase in the MgSO₄–H₂O system, magnesium sulfate undecahydrate, including an analysis of the elastic strain tensor and observations concerning phase changes that occur at high pressure.

Structure, thermal expansion and incompressibility of MgSO₄·9H₂O, its relationship to meridianiite (MgSO₄·11H₂O) and possible natural occurrences

We have employed neutron and X-ray powder diffraction and density functional theory calculations to determine the structure and thermoelastic properties of a new hydrate in the MgSO₄–H₂O binary system, magnesium sulfate enneahydrate. We show that this 9-hydrate could occur naturally in certain hypersaline lakes on Earth and indicate where it may be formed as a more persistent mineral elsewhere in the solar system.

An unusual case of OD-allotwinning: 9,9′-(2,5-di­bromo-1,4-phenylene)bis­[9H-carbazole]

The title compound crystallizes as allotwins made up of two OD-polytypes with a maximum degree of order.

Crystal structure prediction by ionic network analysis: the example of (p–T–X)-structure relationships in olivines

A predictive method for the unit-cell parameters and atomic coordinates of ionic crystals is described. It is based on crystal structures known at systematically varying values of pressure, temperature or chemical composition, and applied to olivines

Neutron and X-ray investigations of the Jahn–Teller switch in partially deuterated ammonium copper Tutton salt, (NH₄)₂[Cu(H₂O)₆](SO₄)₂

Pressure, temperature and deuteration-dependent phase transition in the ammonium copper salt, (NH₄)₂[Cu(H₂O)₆](SO₄)₂, was studied using neutron and X-ray diffraction on single crystal and powder samples.

A revised interpretation of the structure of (NH₄)₂Ge₇O₁₅ in the light of the Extended Zintl–Klemm Concept

The Extended Zint–Klemm Concept accounts for the tetrahedral and octahedral coordination of Ge atoms in (NH₄₂Ge₇O₁₅

Formation of co-racemic uranyl chromate constructed from chiral layers of different topology

A unique uranyl-based structural architecture formed by chiral layers of different topology is described. Layer pairs of different topology can be considered as racemic pairs and the whole structure is a co-racemate built by a combination of two racemates.

Synchrotron X-ray diffuse scattering from a stable polymorphic material: terephthalic acid, C₈H₆O₄

A model for the X-ray diffuse scattering from terephthalic acid (C₈H₆O₄) is presented, and used to explore the sensitivity of diffuse scattering to polymorphic interconversion, and to demonstrate the relative ease with which the harmonic (`thermal') component of the diffuse scattering can be modelled.

Structures and thermal stability of the α-LiNH₄SO₄ polytypes doped with Er³⁺ and Yb³⁺

We present new results about the polymorphism of LiNH₄SO₄. Two new α-polytypes have been obtained, thanks to doping effects. The thermal stability of the α-modification is clarified and the coexistence of α- and β-polytypes and the mechanism of the α → β phase transition is proposed.