Inferring planar disorder in close-packed structures via ∊-machine spectral reconstruction theory: structure and intrinsic computation in zinc sulfide

A structural analysis from X-ray diffraction spectra of four planar disordered ZnS specimens is presented using ∊-machine spectral reconstruction theory. Physical and computational measures, such as stacking entropy, configurational energy and hexagonality as well as characteristic length parameters, are calculated for each specimen.

Superspace description of the crystal structures of Ca_n(Nb,Ti)_nO_3n + 2 (n = 5 and 6)

The crystal structures of Ca₅Nb₄TiO₁₇ (n = 5) and Ca₆(Nb,Ti)₆O₂₀ (n = 6) are described in a unified superspace approach as commensurately modulated structures with discontinuous atomic domains given by occupational crenel functions. Displacive modulation functions of the two compounds exhibit similarities, but they also show that the idea of a unified superspace model does not extend toward the precise atomic positions.

Qu­antitative description of the tilt of distorted octahedra in ABX₃ structures

A method describing perovskite-related ABX₃ structures via distorted octahedral parameters and tilting angles is developed. An analysis of monoclinic I2/c, orthorhombic Pbnm and Immm structures, and their transformations in terms of octahedral parameters and tilting angles is carried out.

Structures of CsEuBr₃ and its degradation product Cs₂EuBr₅·10H₂O

The GdFeO₃-type crystal structure of CsEuBr₃ is reported together with the crystal structure of one of its degradation products in air, Cs₂EuBr₅·10H₂O.

Octahedral As in M⁺ arsenates – architecture and seven new members

The present paper presents an overview of all known M⁺ arsenates(V) containing octahedrally coordinated arsenic (M⁺ = Li, Na, K, Rb, Cs, Ag) and the crystal structures of the following seven new hydrothermally synthesized members belonging to four novel and two known structure types: LiH₂As₃O₉, LiH₃As₂O₇, KHAs₂O₆, KH₃As₄O₁₂ and isotypic RbH₃As₄O₁₂, CsAs₃O₈ and AgH₂As₃O₉. The overall mean As—O distance for all known AsO₆ octahedra in inorganic compounds (with R factors < 0.072) is 1.830 (2) Å.

Influence of polyhedron distortions on calculated bond-valence sums for cations with one lone electron pair

Bond-valence sums (BVS) of cations that have one lone electron pair deviate more from the stoichiometric valence the more eccentric their coordination polyhedra. This suggests that BVS values describe a structural valence that is different from the stoichiometric valence.

LTN-type zeolite framework as an interpenetrating net of KFI- and SOD-type parts homeomorphic to cuprite, Cu₂O

The complex LTN-type zeolite framework is described as consisting of two interpenetrating parts in order to understand the connectivities of their underlying nets. Both parts are homeomorphic to diamond-type tetrahedral frameworks.

Structures of three dehydration products of bis­chofite from in situ synchrotron powder diffraction data (MgCl₂·nH₂O; n = 1, 2, 4)

In the course of the thermal decomposition of bischofite MgCl₂·6H₂O to MgCl₂, the crystal structures of three low hydrate magnesium chlorides, MgCl₂·nH₂O (n = 1, 2, 4), have been determined from in situ temperature-dependent synchrotron powder diffraction data. The release of water molecules is reflected in the coordination spheres of the Mg atoms, starting from discrete Mg(H₂O)₆ octahedra in bischofite to infinite layers of MgCl₆ octahedra in chloromagnesite (MgCl₂).

Order and disorder among the layered double hydroxides: combined Rietveld and DIFFaX approach

Rietveld and DIFFaX techniques used in conjugation with one another provide evidence to show the ubiquitous nature of stacking faults in the layered double hydroxides. Stacking faults can be eliminated by altering the nucleation conditions.

Triclinic apatites

A combination of selected area diffraction, neutron and X-ray powder diffraction show that Ca₁₀(AsO₄)₆F₂ and Ca₁₀(VO₄)₆F₂ are the first fully stoichiometric triclinic apatites. These results are supported by ab initio calculations which also predict that Cd₁₀(PO₄)₆F₂ and Ca₁₀(CrO₄)₆F₂ are isostructural.

Systematic prediction of new ferroelectrics in space group R3. II

Coordinate analysis of the 71 structure determinations in Part II of the space group R3 reveals six structure types that are new potential ferroelectrics, eight that more likely belong or may undergo a transition to crystal class 3m, 14 that are more likely or may undergo a transition to nonpolar, ten with reduced predictive properties, and nine others for which the space group is more likely to remain R3 over the full thermal stability range.

Synthesis and structural characterization of BaV₄O₉

The new barium oxovanadate BaV₄O₉ was synthesized and studied between room temperature and 100 K by means of single-crystal X-ray diffraction.

Optimal partitioning of molecular properties into additive contributions: the case of crystal volumes

Taking advantage of geometrical considerations, the densities of 42 880 molecular crystals are predicted with an average absolute deviation from experiment close to 2%, for various temperatures and using remarkably few empirical parameters.

Accurate charge density of trialanine: a comparison of the multipole formalism and the maximum entropy method (MEM)

An improved approach to charge-density refinements with the MEM is proposed. The resulting electron density maps resemble the corresponding multipole derived maps in most aspects.

Polymorphism of 4-bromobenzo­phenone

The structure of a new polymorph (triclinic ) of 4-bromobenzophenone has been determined. Its physical properties and the relevant growth procedure are compared with those of the known monoclinic P2₁/c polymorph. The unusually large and anisotropic thermal expansion is ascribed to the peculiarities of the structure of the title compound.

Structure and hydrogen bonding in 2,4-di­hydroxybenzoic acid at 90, 100, 110 and 150 K; a theoretical and single-crystal X-ray diffraction study

A new polymorph of 2,4-dihydroxybenzoic acid is characterized by multiple-temperature X-ray diffraction and solid-state computations. The possibility of cooperative disorder in the hydrogen-bonding scheme in this system is discounted by the computational results.

Chemical bonding and intermolecular interactions in energetic materials: 1,3,4-tri­nitro-7,8-di­aza­pentalene

The electron density and related properties of 1,3,4-trinitro-7,8-diazapentalene (space group Pca2₁) have been determined from low-temperature X-ray diffraction data and compared with theoretical calculations.

Influence of fluoro-substitution on the planarity of 4-chlorobi­phenyl (PCB 3)

Using X-ray structure analysis and semi-empirical computations we have employed a novel approach using fluorine tagging to investigate the structural effects of PCBs that have strong implications for biological activity. Fluorine tagging provides information about the geometry of the PCBs themselves and will open new levels of understanding of QSARs and will support the increasing interest in fluorine as a valuable label in toxicologic research.

Unravelling the chemical basis of the bathochromic shift in the lobster carapace; new crystal structures of unbound astaxanthin, canthaxanthin and zeaxanthin

An ensemble of six crystal structures of free carotenoids allows several key parameters, thought to influence the colour tuning of the bathochromatic shift of astaxanthin in the blue protein crustacyanin, to be varied. That the crystals are red and not the blue of crustacyanin is therefore significant.