Re-Refinement of Composite Modulated Nb₂Zr_x−2O_2x+1 (x = 8) Using Synchrotron Radiation Data

The structure refinement of composite modulated Nb₂Zr_x-2O_2x+1 (x = 8) has been carried out in superspace group Amma(α10)0s0. The equivalence of this present result to an earlier published refinement of the x = 12 member is established.

Structure Refinements of the Layered Intergrowth Phases Sb^IIISb^{V x}A_1−xTiO₆ (x≃0, A = Ta, Nb) Using Synchrotron X-ray Powder Diffraction Data

The structures of the layered intergrowth phases Sb^IIISb_x^VA_1-xTiO₆ (x≃0, A = Ta, Nb) have been refined by the Rietveld method, using synchrotron X-ray diffraction data. Starting models were proposed on the basis that the phases represented n = 1 in the series Sb_n^IIISb_x^VA_n-xTiO_4n+2, for which the n = 3 structures (x = 1.26, A = Ta and x = 0.89, A = Nb) had been previously solved by single crystal X-ray diffraction. The models were found to be essentially correct.

Electron Density Distribution in LiB₃O₅ at 293 K

The σ–π bonding is analysed using the Hansen–Coppens multipole model and compared with Hartree–Fock calculations. The amount of transfer of π electrons from the O atoms to the triangularly coordinated B atoms is specified.

Neutron Diffraction Study of the Ambient-Pressure, Rutile-Type and the High-Pressure, CaCl₂-Type Phases of Ruthenium Dioxide

Compression of the RuO₆ octahedron is anisotropic. In the high-pressure phase the octahedra are rotated by 1.1° with respect to the ambient-pressure phase.

New Bond-Valence Sum Model

A new model is proposed to accommodate zero and some negative oxidation states of a central atom in the bond-valence sum formalism.

Three New Polymorphic Forms of Molybdenum Pentachloride

Three new polymorphic modifications of MoCl₅ have been obtained as single crystals by solvothermal syntheses using CCl₄ and SbCl₅ as solvents. All structures consist of double octahedral Mo₂Cl₁₀ molecules and are derived from the closest packings of Cl atoms with different stacking sequences.

Statistical Analysis of Noncovalent Interactions of Anion Groups in Crystal Structures. III. Metal Complexes of Thio­cyanate and their Hydrogen-Donor Accepting Function

The bidentate function of the thiocyanate anion with respect to metals and/or hydrogen-donor groups was systematically studied using the Cambridge Structural Database.

Multi-Solution Genetic Algorithm Approach to Surface Structure Determination Using Direct Methods

Models of two-dimensional centrosymmetric and non- centrosymmetric structures have been generated and used to test genetic algorithms for direct phasing of surface diffraction data.

Structure and Motion of Tetra­kis­(tri­chlorophosphazeno)phosphonium Hexa­chlorophosphate, [P(NPCl₃)₄]⁺PCl₆⁻, at 93 K

The crystal structure of [P(NPCl₃)₄]⁺PCl₆⁻, determined at 93 K, and the thermal motion of the highly flexible cation, analysed in terms of the rigid-body model with allowances for intramolecular torsions, are reported.

Rigid-Body Disorder Models for the High-Temperature Phase of Ferrocene

The 164 K phase transition of ferrocene is not a simple order–disorder transition.

Phase Transitions in Tris(3,5-di­methylpyrazol-1-yl)methane. The Structure of the High-Temperature Phase from X-ray Powder Diffraction

The effectiveness of the Patterson search method has been demonstrated by determining the crystal structure of the high-temperature phase of C₁₆H₂₂N₆ from laboratory X-ray powder diffraction data. Phase transitions between two isomers of the title compound have been investigated.

Crystallographic and Molecular Mechanics Study of Imido­oxy Anticonvulsants

The results of conformational analysis of seven imidooxy derivatives and the molecular structures found in the crystal for five of them are reported and examined in relation to their activity as anticonvulsants.

Structures of the Phosphazenes [ClC(NPCl₃)₂]⁺PCl₆⁻ and [CH₃C(NPCl₃)₂]⁺SbCl₆⁻ at 90 K

The first crystal structures of compounds in which two NPCl₃ groups are bonded to a single C atom are reported. The cations show the same cis–trans conformations of the backbone; the extremely flexible C-N-P angles can be attributed to intramolecular contacts.

Di­ethyl 2-Benzimidazol-1-ylsuccinate–Picric Acid (1/1) – An Inclusion Molecular Complex

The crystal structure of diethyl 2-benzimidazol-1-ylsuccinate–picric acid (1/1) has been determined by X-ray diffraction analysis. The benzimidazole moiety of the molecules forms channels along the a axis in which the picric acid molecules are located, forming an inclusion molecular complex.

Recognizing the (False Symmetry) Triclinic (aP) to (True Symmetry) Centred Monoclinic (mC) Pathology

Examination of the published data for about fifty crystals where the originally reported triclinic unit cell has been corrected to centred monoclinic re-affirms the importance of calculating the Niggli matrix (metric tensor) as early as possible in a crystal structure analysis.

Structure and Serotonin 5-HT_2C Receptor Activity of ortho- and meta-Substituted Phenylpiperazines

X-ray diffraction and molecular mechanics calculations are used to determine the 5-HT_2C receptor activating conformation of phenylpiperazines. The conclusions are supported by preliminary biological studies on two novel 5-HT_2C ligands.

Packing Modes in Nitro­benzene Derivatives. I. The Single Stacks

Crystal packing modes of nitrobenzene derivatives are pre- sented. The different types of `single stack' modes are described in terms of geometrical parameters.

Packing Modes in Nitro­benzene Derivatives. II. The `Pseudo-Herringbone' Mode

The `pseudo-herringbone' mode of packing for nitrobenzene derivatives is analysed. The mode is divided into four motifs, according to geometrical parameters.

Halogen⋯O(Nitro) Supramolecular Synthon in Crystal Engineering: A Combined Crystallographic Database and Ab Initio Molecular Orbital Study

Analysis of crystallographic data indicates that C-X⋯O(nitro) interactions increase in strength in the order Cl > Br > I, and that the frequency of formation of `bifurcated' motifs, involving X approach between the nitro-O atoms, increases in the same order. Intermolecular pertubation theory calculations on Cl⋯O and Br⋯O interactions agree with these geometrical observations and yield a Cl⋯O interaction energy of ca -6 kJ mol⁻¹ at the 6-31G^* basis set level.

Hydrogen-Bond Acceptor Properties of Nitro-O Atoms: A Combined Crystallographic Database and Ab Initio Molecular Orbital Study

Analysis of crystallographic data shows that nitro-O⋯H-N,O hydrogen bonds are significantly longer (weaker) than their counterparts that involve >C=O acceptors and prefer to form asymmetric motifs with respect to the nitro-O atoms. Intermolecular perturbation theory calculations agree with these experimental observations and indicate a hydrogen-bond energy of -15 kJ mol⁻¹ at the 6-31G^** basis set level.

Disorder in cyclodextrin clathrates: X-ray diffuse scattering analysis of α-cyclodextrin cyclo­pentanone hydrate. Erratum

Correction to Acta Cryst. (1997). B53, 673-679.

Structures and magnetic properties of dimeric copper(II) benzoylformates. Erratum

Correction to Acta Cryst. (1997). B53, 654-661.

Organic molecular crystals: interaction, localization and transport phenimena by E. A. Silinsh and V. Čápek

Physics and chemistry at oxide surfaces by C. Noguera

Synchrotron radiation techniques in industrial, chemical and materials science edited by K. L. D'Amico, L. J. Terminello and D. K. Shuh

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