Chiral determination: direct interpretation of convergent-beam electron diffraction patterns using the series expansion of Cowley and Moodie

A simple formula is derived for the analysis of chirally sensitive convergent-beam electron diffraction (CBED) patterns based on second-order scattering between all visible beams. The results agree with experiment and the limits of the formula are explored. Comparisons are made between patterns taken near major zone axes and those exactly at minor zone axes. The experimental aspects of chiral CBED are discussed.

Complex disorder in β-NH₄Fe₂(PO₄)₂: deciphering from a five-dimensional formalism

The structure of β-NH₄Fe₂(PO₄)₂ exhibits complex disorder phenomena preventing an accurate structural description. An artificially ordered structure has been generated using a five-dimensional approach and the diffuse streaks observed on the diffraction patterns. The analysis of this artificial model allows a description of the actual compound and opens the route to the synthesis of polytype compounds.

Atomvolumen, Packungsdichte der Atome und chemische Bindung in nichtmetallischen Elementen

The atomic volume of non-metallic elements depends on the packing density of atoms as a feature of the crystal structure, and on a reduced atomic volume which is characteristic of each element and its valence. Different valences of one element are recognized by different reduced atomic volumes.

Atomic displacements in BiFeO₃ as a function of temperature: neutron diffraction study

The structural parameters of BiFeO₃ have been determined by high-resolution neutron powder diffraction for temperatures between 293 and 923 K. It was found that there is a local minimum for the rhombohedral angle α_rh, near the Néel temperature T_N ≃ 640 K, a gradual rotation of the FeO₆ octahedra and an increase of the Fe—O—Fe angle.

A structural phase transition in NaTaOGeO₄ and its relation to phase transitions in titanite

The structure of NaTaOGeO₄ at T = 98 K has been determined. It is of the distorted titanite type with space-group symmetry P2₁/c. A phase transition to the titanite aristotype structure with space-group symmetry C2/c occurs close to T = 116 K. Anisotropic diffuse scattering in layers of constant l = 2n is observed above T_c and up to ambient temperatures.

Crystal structure and local order in Co₆Al_11−xSi_6+x

The crystal structure and local ordering of Co₆Al_11−xSi_6+x was determined by single-crystal X-ray diffraction and transmission electron microscopy. The crystal structure consists of planar layers with the composition [Co₆Al₁₀Si₄], which are penetrated by perpendicular (Si—Si—Al) chains.

Structure of unsolvated magnesium borohydride Mg(BH₄)₂

The structures of two phases of unsolvated Mg(BH₄)₂, a material of interest for hydrogen storage, were solved by synchrotron powder diffraction. Both structures are more complicated than other similar metal hydrides and theoretical predictions.

Structure of oxidized bis­muth nanoclusters

Synchrotron X-ray diffraction has determined that β-Bi₂O₃ is the dominant oxide phase covering hexagonal bismuth nanoclusters produced in an inert gas aggregation source. High-resolution transmission electron microscopy of bismuth nanoclusters has shown the oxide thickness and orientation, and has been compared with the synchrotron diffraction measurements.

Probability density analyses of guest ions in hollandite A_xMg_x/2Ti_{8 − x/2}O₁₆ (A = K, Rb)

Probability density functions of mobile ions in hollandite ionic conductors were obtained from a new structure model considering the local structure around a vacancy.

Synthesis, structure, and stability of the high-temperature 6H-type perovskite phase Ba₃BaSb₂O₉

The high-temperature structure of Ba₃BaSb₂O₉ has been solved and Rietveld-refined as an ideal (P6₃/mmc) 6H perovskite, using synchrotron X-ray powder diffraction data. The size difference between SbO₆ and BaO₆ octahedra is greater than for any other reported 6H perovskite.

New oxybromide cobaltites with layered perovskite-related structures: 18R-Ba₆Co₅BrO₁₄ and 14H-Ba₇Co₆BrO₁₇

The crystal structures of two new cobaltites, Ba₆Co₅BrO₁₄ and Ba₇Co₆BrO₁₇, have been solved. They are built by the stacking of [BaO₃] and new [BaOBr] layers. Disorder has been observed in the vicinity of the [BaOBr] layers and characterized by the maximum entropy method for the two compounds.

Framework `interstitial' oxygen in La₁₀(GeO₄)₅(GeO₅)O₂ apatite electrolyte

Framework oxygens in La₁₀(GeO₄)₅(GeO₅)O₂ apatite provide a reservoir of ions that migrate between the large channels in a process that converts some GeO₄ tetrahedra to GeO₅ distorted trigonal bipyramids.

Ligand and coordination-plane distortions in platinum(II) complexes of isomers of di­methyl-2,2′-bi­pyridine

Distortions in M = Pt and Pd complexes of planar aromatic bidentate ligands (L) coordinating by two pyridyl ring N atoms are caused by repulsive interligand interactions involving the substituents on the pyridyl C atoms adjacent to these N atoms. Whereas the highly distorted structures observed for LMCl₂ with bulky L (e.g. 6,6′-dimethyl-2,2′-bipyridine) are generally similar, the nearly equal occurrence of two different types of distortions (canting and bow-incline) for [L₂M]X₂ complexes suggests that these distortions have similar energy and that subtle solid-state effects dictate which type of distortion occurs.

Using cluster analysis to study transition-metal geometries: four-coordinate complexes with two salicylaldiminato or related ligands

Cluster analysis is used to analyse and classify metal coordination geometry in four-coordinate bis-salicylaldimato transition-metal complexes available in the Cambridge Structural Database. Structures are automatically clustered into groups based purely on the geometric similarity of the fragments and these groups can then be interpreted by the structural chemist.

Structural systematics of 4,4′-disubstituted benzenesulfonamido­benzenes. 1. Overview and dimer-based isostructures

The systematic variation of two substituents results in a set of 100 related compounds and 133 crystal structures whose interrelations are analysed. A subset of 22 isostructures is discussed in detail.

Accurate charge density of the tripeptide Ala-Pro-Ala with the maximum entropy method (MEM): influence of data resolution

The dependence of electron densities obtained by the maximum entropy method on the measurement temperature (100 versus 20 K) and the resolution of X-ray diffraction data are analysed for the tripeptides Ala-Pro-Ala and trialanine.

Single-crystal-to-single-crystal E → Z isomerization of tiglic acid in a supramolecular framework

The single-crystal-to-single-crystal E → Z photoisomerization of tiglic acid occurs in the supramolecular crystals CECR–HTA·2MeOH·1.5H₂O (1) (where HTA = tiglic acid, CECR = C-ethylcalix[4]resorcinarene) with the preservation of the crystal lattice, indicating the `scaffolding effect' of the molecular framework, which holds the crystal together notwithstanding the change in shape of the embedded guest molecules.

Comparison of the proton-transfer path in hydrogen bonds from theoretical potential-energy surfaces and the concept of conservation of bond order. II. (N—H⋯N)⁺ hydrogen bonds

The quantum-mechanically derived reaction coordinates (QMRC) for the proton transfer in (N—H⋯N)⁺ hydrogen bonds have been derived from ab initio calculations of potential-energy surfaces. A comparison is made between QMRC and the corresponding bond-order reaction coordinates derived by applying the Pauling bond-order concept together with the principle of conservation of bond order.

Disorder in penta­chloro­nitro­benzene, C₆Cl₅NO₂: a diffuse scattering study

Monte Carlo computer simulation has been used to interpret and model observed single-crystal diffuse X-ray scattering data for pentachloronitrobenzene, C₆Cl₅NO₂. The strong, detailed and very distinctive diffraction patterns can be accounted for almost entirely on the assumption of the random occupancy of each molecular site, but with very large local relaxation displacements that tend to increase the neighbouring distances for contacts involving NO₂⋯NO₂ and NO₂⋯Cl with a corresponding reduction for those involving Cl⋯Cl.

Analysis of structures with saturated hydrogen bonding. Corrigendum

A corrigendum to the paper by Loehlin & Okasako (2007), Acta Cryst. B63, 132–141.