Structural Analysis of Cs₂HgBr₄ in Normal, Incommensurate and Twinned Phases

X-ray diffraction and Raman spectroscopy have shown that the crystal structure of Cs₂HgBr₄ in the normal, incommensurate and low-temperature phases can be described by disordered models.

Theoretical Prediction of Bond-Valence Networks. II. Comparison of the Graph-Matrix and Resonance-Bond Approaches

The bond-valence and resonance-bond-number methods for calculating interatomic distances are compared for KVO₃, β-Ga₂O₃, TeI₄, Li₂SiO₃, Li₂GeO₃ and CaCrF₅.

Monoclinic and Hexagonal Nepheline Structures of (Na_3/4/K_1/4)AlGeO₄

Hexagonal (Na_3/4K_1/4)AlGeO₄ is isostructural with the mineral nepheline, (Na_3/4K_1/4)AlSiO₄, with a similar split oxygen position and a cation deficiency on the potassium site. In contrast, the alkali sites are fully occupied in the structure of monoclinic (Na_3/4K_1/4)AlGeO₄ and the lower unit-cell symmetry eliminates the oxygen disorder.

Determination of the Bonding and Valence Distribution in Inorganic Solids by the Maximum Entropy Method

The maximum entropy method provides a means of ranking bond graphs in order of symmetry and gives good predictions of the bond valences.

Comparison of Experimental and Theoretical Structure Amplitudes and Valence Charge Densities of GaAs

The valence and difference charge densities of GaAs obtained from experimental and theoretical data (Hartree–Fock and density functional theory) show a charge accumulation between nearest neighbours slightly shifted towards the arsenic site. The disagreement remaining between experimental and theoretical data and between those of both ab initio methods are of the same order of magnitude.

Order and Disorder in Niobium Tungsten Oxides of the Tetragonal Tungsten Bronze Type

Distinct types of diffuse scattering which appear in the electron diffraction patterns of tetragonal tungsten bronze-type (TTB) niobium tungsten oxides are caused by different arrangements of filled pentagonal tunnels. A structural model for a new TTB superstructure (Nb₆W₈O₃₉) has been derived from HRTEM images.

Classification and Distortion in Six-Coordinate Bis(salicylaldiminato)nickel(II) Complexes: Crystal Structure of Bis[2-[[(2-hydroxyphenyl)methylene]amino]-1-phenyl-1,3-propanediolato]nickel(II).2H₂O

A new classification based on the geometry of the coordination polyhedron, especially useful for six-coordinate bis(salicyl- aldiminato) complexes, has been proposed. The distortions of octahedral Ni²⁺ complexes have been analyzed and exemplified by a crystal structure of a complex showing the largest shift of the metal from the geometric center observed so far in similar complexes.

X-ray Studies on Crystalline Complexes Involving Amino Acids and Peptides. XXXIII. Crystal Structures of L- and DL-Arginine Complexed with Oxalic Acid and a Comparative Study of Amino Acid–Oxalic Acid Complexes

The oxalic acid complexes of DL and L forms of basic amino acids exhibit a variety of ionization states and stoichiometries. They demonstrate the tendency of individual molecules to retain their intrinsic aggregation propensities even as they interact with other molecules.

Pseudoacids. II. 2-Acylbenzoic Acid Derivatives

Structures of the cyclic derivatives of o-acylbenzoic acids, including the chloride, endo- and exocyclic amides, the ester and two types anhydride, are described. Former aldehyde/ketone carbon–heteroatom endocyclic and exocyclic bond distances show length variations which correlate with the relative basicities of the attached groups.

Structural, Thermodynamic and Kinetic (Hysteresis) Aspects of the Enantiotropic First-Order Phase Transformations of N-Anilinophthalimide and N-(N'-Methylanilino)phthalimide

Physico-chemical studies of the phase transformations by Chattaway and co-workers (1911–1915) are extended by structure determinations for the four phases involved and DSC measurements on the transformations.

Hypothetical Crystal Structures of Benzene at 0 and 30 kbar

An attempt has been made to unify and extend previous predictions of the possible crystal packings of benzene. Dozens of hypothetical structures were generated, but the two experimentally observed ones still have the lowest enthalpy at their respective pressures.

Structure of Z-(Aib)₉OBu^t

Z-(Aib)₉OBu^t contains the unusual α-aminoisobutyric acid. The structure of this synthetic oligopeptide reveals a rare C-terminal conformation in the form of a disorder of one of the two molecules in the asymmetric unit.

Temperature Dependence of the Rigid-Body Motion of Anthra­quinone

The precision of previous studies may have been limited by twinning. Analyses of data collected at five temperatures show that the temperature dependence of the rigid-body motion is normal and confirm that the out-of-plane motion of the O atoms is large.

Hydrogen Bonding to Thio­cyanate Anions: Statistical and Quantum-Chemical Analyses

A re-investigation of the formation of hydrogen bonds to the thiocyanate anion demonstrates that preferred hydrogen-bond geometries are in the directions of the sulfur and nitrogen lone pairs of the anion.

Carbonyl–Carbonyl Interactions can be Competitive with Hydrogen Bonds

Three C=O⋯C=O interaction motifs are commonly observed in crystal structures: the antiparallel, perpendicular and sheared-parallel motifs. Ab-initio molecular-orbital calculations on a bis-propanone dimer model yield interaction energies of -22 kJ mol⁻¹ for the antiparallel motif, having two short C⋯O interactions, and -7.6 kJ mol⁻¹ for the perpendicular motif, having only one such short dipolar interaction.

Crystal Engineering Using Tris-phenols. Cross-Linked, Pairwise-Interwoven Two-Dimensional Nets in the 2:1 Adduct of 1,1,1-Tris(4-hydroxyphenyl)ethane with 1,2-Di­amino­ethane

Pairwise-interwoven nets built from tris-phenol molecules are cross-linked into two-dimensional bilayers by 1,2-diamino- ethane molecules.

Uric Acid Dihydrate Revisited

Refinement of uric acid dihydrate as both twinned and disordered in space group P2₁/c fully accounts for inconsistencies present in previous orthorhombic descriptions.

Structural Determination of the Hydrofullerene C₆₀D₃₆ by Neutron Diffraction

Five proposed structures are compared with the reduced density function derived from neutron diffraction data. A T symmetry structure provides the best agreement.