Analysis of the environment of beryllium, magnesium and alkaline earth atoms in oxygen-containing compounds

The coordination numbers of Be, Mg and alkaline earth atoms were determined using Voronoi–Dirichlet polyhedra in the crystal structures of about 2100 inorganic and organometallic compounds. The volume of the domains of Mg, Ca, Sr and Ba atoms was found to be independent of their coordination numbers.

Concerning inorganic crystal structure types

A program and database to find crystal structure types of inorganic compounds has been developed.

Solution and refinement of the crystal structure of Bi₇Ta₃O₁₈

The crystal structure of heptabismuth tritantalum octadecaoxide, Bi₇Ta₃O₁₈, has been solved and refined using single-crystal X-ray data and corroborated by powder neutron diffraction data. The structure is based on dislocated layers of the fluorite type. The metal populations are fully ordered, with TaO₆ octahedra forming columns amid variously coordinated Bi and O atoms in distorted fluorite positions.

Iodo-oxyapatite, the first example from a new class of modulated apatites

Iodo-oxyapatite, Ca₁₅(PO₄)₉IO, was synthesized by a flux method. The unit cell is tripled owing to ordering of the iodide and oxide ions.

Elucidation of the crystal structure of oxyapatite by high-resolution electron microscopy

The projection symmetry observed in high-resolution electron micrographs of hydroxyapatite is p3 and not p6, which would be compatible with the accepted space group . This is attributed to dehydration of hydroxyapatite in the microscope under the electron beam, giving rise to oxyapatite. The crystal structure of oxyapatite was elucidated from the electron micrographs.

Search for Pnma materials with high-temperature structural phase transitions

A systematic search over the Pnma structures in the Inorganic Crystal Structure Database results in the detection of 58 substances with very strong pseudosymmetric features that suggest the existence of a Landau-type phase transition at higher temperatures.

Crystallographic disorder in mixed-valent dioxo-bridged Mn^III,IV complexes. [Mn₂O₂(bpy)₄][Ce(NO₃)₆].5H₂O

The mixed-valent Mn^III,IV complex ion in the title compound has crystallographically equivalent Mn sites because of disorder about a crystallographic twofold axis passing through the bridging oxo ligands.

Charge and momentum densities of cubic tetra­cyano­ethylene and its insertion compounds

The complementary views of chemical bonding provided by charge and momentum densities are described and their application to the possible mechanism of insertion of metal atoms in molecular crystals is considered.

Conformational behaviour of bridging di­phenylphosphido ligands

The conformational behaviour of [M₂{μ-PPh₂}] species, studied by database and computational methods, shows that experimental geometries lie within 8 kJ mol⁻¹ of the global minimum. Phenyl ring rotations occur by both coupled disrotatory and uncoupled conrotatory motions of the two P—Ph rotors.

Experimental evidence for the amino-group non-planarity in nitroanilines: neutron diffraction study of 2-methyl-5-nitroaniline at 100 K

A single-crystal neutron diffraction study of 2-methyl-5-nitroaniline at 100 K has been performed at ISIS in order to establish the degree of planarity of the amino group and to add to the understanding of the role of hydrogen bonds in the molecular organization of nitroanilines.

Hydrogen-bonding interactions in the crystalline-phase structures of cinnamic acid derivatives

Crystals of cinnamic acids and esters were found to consist of almost planar layers kept together by intermolecular C—H⋯O hydrogen bonds of various types. Intramolecular C—H⋯O hydrogen bonds render synperiplanar and antiperiplanar C=C—C=O arrangements equally possible in the acids, but fix exclusively a synperiplanar conformation in the esters.

Interaction of lysine with iodic acid

The crystal structure and spectral data for a new compound, Lys.3HIO₃, are reported.

Charge density study of N-acetyl-L-tyrosine ethyl ester monohydrate derived from CCD area detector data

The crystal structure, thermal vibrations and electron density of N-acetyl-L-tyrosine ethyl ester monohydrate, C₁₃H₁₇NO₄.H₂O, have been analysed using single-crystal 110 K X-ray diffraction data collected using a CCD area detector during one week. This work shows that area detectors permit charge density studies in a more routine way than is possible with conventional diffractometers.

TEMPO radicals showing magnetic interactions. I. 4-(4-Halo­benzyl­idene­amino)TEMPO and related compounds

The structural features of 4-(4-halobenzylideneamino)TEMPO radical crystals and related compounds can be classified into three groups. The relationships between the crystal structures and the mechanism of the intermolecular magnetic interactions are discussed.

Anhydrous ammonioguanidinium(2+) and dihydrated bis­[aminoguanidinium(1+)] hexa­fluoro­silicates: new co-products of preparing ferroelectric ammonioguanidinium(2+) hexa­fluoro­zirconate

The structures of CH₈N₄SiF₆ and (CH₇N₄)₂SiF₆·2H₂O, new materials formed as by-products in the course of preparing ferroelectric CH₈N₄ZrF₆ in the presence of glassware, are reported for comparison with the corresponding hexafluorozirconates. The packing efficiency in CH₈N₄SiF₆ is appreciably higher than in the dihydrate, which has an ∼8% increase in void space.

Identification of a new trace 114R SiC by HREM

A new trace 114R SiC in commercial α-SiC powder has been identified by HREM. Its stacking sequence is [(33)₄(34)₂]₃, belonging to the structural series (33)_{>n34(33)>m34 predicted theoretically by Pandy & Krishna [Mater. Sci. Eng. (1975), 20, 243–249].}

Energetic study of the disordered solvent in the crystal structure of an isoxazole derivative. Erratum

An error in printing in the paper by Pani et al. [Acta Cryst. (1998), B54, 872–876] is reported.

Intermolecular interactions