A synchrotron X-ray study of the electron density in Y₂BaCuO₅

The features in a synchrotron radiation Δρ image for Y₂BaCuO₅ are predominantly due to exchange depletion of the electron density between second nearest-neighbour cations.

Synchrotron X-ray electron density in the layered LaOCl structure

The deformation electron density in LaOCl measured with synchrotron X-radiation accumulates in the inter-layer region stabilizing the structure that contains layers of positively charged Cl atoms.

Structure of Ce₂Pt₆Ga₁₅: interplanar disorder from the Ce₂Ga₃ layers

The structure of the heavy fermion compound Ce₂Pt₆Ga₁₅ has been determined from neutron powder and X-ray/neutron single-crystal diffraction. The structure is unusual in that Ce layers have 1/3 of the Ce atoms replaced by groups of three Ga atoms. Weak diffuse scattering suggests that disorder arises from a lack of registration of successive Ce₂Ga₃ layers.

Ab initio Hartree–Fock study of the electronic charge density of the cubic boron nitride and its comparison with experiments

The electronic charge density of cubic BN and structure factors are calculated at the ab initio Hartree-Fock level. It reveals the semi-covalent character of the BN bond and a charge transfer from B to N close to unity. Comparison with experiments leads to a satisfactory agreement.

A critical review of the experimental valence charge density of GaAs

The valence charge and difference densities of GaAs were calculated without foregoing refinements of a charge density model using six different data sets published until now. Only four of these describe the covalent bond as well as the partial charge transfer between neighboring atoms in qualitative agreement with the theoretical prediction.

Kristallstruktur und zwillingsbildung der intermetallischen phase β-Bi₂Rh

A new triclinic structure type adopted by the high-temperature polymorph of an intermetallic phase was prepared.

Antiferroelectric modulations in Sb₂WO₆ and Sb₂MoO₆

The structure of Sb₂WO₆, previously reported in the space group P1, is re-refined in P-1 as a 2a x 2b x 2c superstructure, improving the residual R from 0.12 to 0.04. Synthesis of the isostructural phase Sb₂MoO₆ is also reported.

Sodalite, Na₄Si₃Al₃O₁₂Cl: structure and ionic mobility at high temperatures by neutron diffraction

Refinement of the high-temperature structures of sodalite (295-1200 K) based on single-crystal neutron diffraction and an anharmonic thermal vibration model for Na⁺, Cl⁻ and O indicate (i) the thermal expansion from an untwisting of the aluminosilicate framework due to increasing translational motions of Na⁺ coupled with librations of SiO₄/AlO₄ tetrahedra and (ii) Na⁺-Cl⁻ diffusion along <111> channels.

Static disorder in the incommensurate structure of the high T_c superconductor Bi₂Sr₂CaCu₂O_8+δ

The incommensurate modulated structure of the high T_c superconductor Bi₂Sr₂CaCu₂O_8+δ has been explained on the basis of a disorder of the Bi atom.

Structure of the polytypic β-form of P₃N₃(OCH₂CF₂CF₂CH₂O)F₄

The structure of the polytypic form of the title compound can be described in terms of a layer structure which contains an ⋯ABAABA⋯ repeat pattern of layers. The A and B layers have pseudoslab symmetries pc2a and p2₁/c11, respectively.

Structural studies on monofluorinated derivatives of the phytohormone indole-3-acetic acid (auxin)

s part of the molecular recognition studies on auxins, a series of indole-3-acetic acids fluorinated at the phenyl ring positions 4, 5, 6 and 7 has been examined. Structural studies based on X-ray structure analysis, computational chemistry methods and some physico-chemical properties are presented and correlated with bioassays performed on the Avena and Pisum sativum.

Experimental and theoretical morphologies of diuron, N'-(3,4-di­chloro­phenyl)-N,N-di­methylurea

The experimental morphology of diuron crystals, a weed killer, is compared with the theoretical morphology determined using both a geometrical observation law and molecular mechanics calculations.

Experimental charge density study of 7-di­spiro[2.0.2.1]heptane carboxylic acid

The effect of substitution on the bonding in the polyspirocyclopropane frame and chemical behaviour of the title compound is discussed in terms of the topological analysis of experimental multipole charge density distributions.

Statistical analysis of noncovalent interactions of anion groups in crystal structures. I. Hydrogen bonding of sulfate anions

The high capacity of the sulfate dianion to form multiple hydrogen bonds has been analyzed, using the Cambridge Structural Database.

Statistical analysis of noncovalent interactions of anion groups in crystal structures. II. Hydrogen bonding of thio­cyanate anions

The first systematic analysis of the hydrogen-bonding properties of the (SCN)⁻ anion was performed. The bidentate acceptor function of thiocyanate was observed.

Neutron diffraction of a complex of 1,8-bis­(di­methylamino)naphthalene with 1,2-di­chloromaleic acid

Neutron single-crystal data of a complex of 1,8-bis(dimethylamino)naphthalene with 1,2-dichloromaleic acid were collected at 100 K at ISIS and have been compared with single crystal data from X-ray diffraction.

Structural, kinetic and thermodynamic aspects of the conformational dimorphism of di­ethyl 3,6-di­bromo-2,5-di­hydroxyterephthalate

The crystal structures of diethyl 3,6-dibromo-2,5-dihydroxyterephthalate have been determined and the structural, kinetic and thermodynamic aspects of the conformational dimorphism in the title compound investigated.

Simple averaging procedure for aromatic ring system: mean molecular fragment of tryptophan metabolites

A simple averaging procedure for bond lengths and angles applicable to an aromatic ring system was applied to the crystal structures of tryptophan metabolites, and mean values for the indole ring were proposed.

Planarity of nitro-substituted pheno­thiazines

The structures of three 2- and 3-nitrophenothiazine derivatives, which are all bright red, have been determined. One of them forms stacks in which donor and acceptor regions of the almost planar ring system alternate.

A database study of the bonding and conformation of bis-sulfonylamide/-imide moieties

Analysis of 44 structures containing R-SO₂-NQ-SO₂-R^' (Q = e⁻, H, alkyl, aryl, O or S; R, R^' = Me, Et or Ph) units retrieved from the Cambridge Structural Database reveals marked differences between the archetypes of the S-N bonds (i.e. nitrogen charged or neutral) in the range 1.57-1.76 Å. The S^VI-X bonds of the type S^VI[O,O^',N,C] tetrahedra are characterized and correlated with the bond angles and torsion angles formed around the S atoms. It is shown that the interdependence of the S-X bonds and their interbond angles is principally governed by the environment of the N atoms.

Structures of three inclusion compounds of cholanamide with either (S)-enantiomer, (R)-enantiomer or an optically resolved mixture of butan-2-ol

Crystal structures of three inclusion compounds of cholanamide obtained from the solutions of (S)-butan-2-ol, (R)-butan-2-ol and racemic butan-2-ol have been determined. The host cholanamide molecules form the same layered arrangements providing channel spaces for the guest butan-2-ol molecules, where the pure (S)-and (R)-enantiomers of butan-2-ol and the (S)-enriched mixture of enantiomers are accommodated, respectively.

The hydrogen-bond C–H donor and π-acceptor characteristics of three-membered rings

Three-membered ring C-H donors are shown to form hydrogen bonds to oxygen acceptors that are of similar strength to Csp²-H⋯O bonds. The existence of O,N-H⋯π(ring) bonding, predicted from spectroscopic results, is confirmed by analysis of the available crystallographic data.

Tautomerism in 3{5}-(di­methoxyphenyl)pyrazoles

The single crystal structure of 3{5}-(2^',5^'-dimethoxyphenyl)pyrazole contains purely the 5-substituted tautomer, while 3{5}-(3^',4^'-dimethoxyphenyl)pyrazole crystallizes as a prototropically disordered hemihydrate. These observations are supported by solid-state and solution NMR measurements.