(3 + 2)-Dimensional superspace approach to the structure of the stage-2 misfit layer compound (SbS)_1.15(TiS₂)₂

The composite crystal (SbS)_1.15(TiS₂)₂ was prepared, which is built up of alternatingly interface-modulated SbS double layers and paired sandwiches of (TiS₂)₂.

Vacancies and electron localization in the incommensurate intergrowth compound (La_0.95Se)_1.21VSe₂

The structure of (La_0.95Se)_1.21VSe₂, a misfit layer chalcogenide, was determined. It is built of an alternating stack of LaSe double layers, which contain La vacancies, and VSe₂ sandwiches.

A synchrotron X-ray study of the electron density in SmFeO₃

The deformation electron density (Δρ) has been determined for synthetic samarium orthoferrite, SmFeO₃, using focused λ = 0.7 Å synchrotron X-radiation. The approximate Δρ map symmetry indicates that the electron density is perturbed significantly by the cation-cation interactions.

A synchrotron X-ray study of the electron density in C-type rare earth oxides

Deformation electron densities for synthetic C-type Y₂O₃, Dy₂O₃ and Ho₂O₃ were determined using focused synchrotron (λ = 0.7 Å) and Mo Kα (λ = 0.71073 Å) X-radiation. Approximate symmetry in the Δρ maps indicates that the cations deform more strongly by interaction with other cations than with O atoms, unless the symmetry of the O-defined crystal field is low.

Distance limits of OH⋯Y hydrogen bonds (Y = Cl, Br, I) in solid hydroxides, structure refinement of laurionite-type Ba(OD)I, Sr(OD)I and Sr(OH)I by neutron and synchrotron X-ray powder diffraction

ynchrotron X-ray and neutron powder diffraction experiments on M(OH)I (M = Sr, Ba). The longest H⋯Y distances (Y = Cl, Br, I), for which hydrogen bonds have been established, are 2.80, 2.90 and 3.25 Å, respectively.

Occurrence of a monoclinic distortion in β-Fe₂PO₅

High-resolution synchrotron powder diffraction reveals a monoclinic distortion in β-Fe₂PO₅ at room temperature. A Rietveld refinement is performed and the description of the structure shows that the two iron sites are very similar.

Cation disorder in ferroelectric PbBi₂Nb₂O₉

Changes in the ferroelectric transition temperature in PbBi₂-Nb₂O₉ have been shown by Raman and neutron diffraction studies to relate to Pb-Bi ordering.

Structural chemistry of NaCoPO₄

The crystal structures of both polymorphs of NaCoPO₄ have been determined by single crystal X-ray diffraction. Bond-valence analysis reveals that the polymorphism is due in part to the bonding around the Na atoms.

Temperature dependence of structure parameters in natural magnetite: single crystal X-ray studies from 126 to 773 K

Structural parameters and their thermal changes in magnetite have been studied and the following have been observed: the oxygen coordinate remained almost constant at temperatures below ca 600 K, but it began to increase above ca 600 K; the thermal vibrational ellipsoid at the B site was prolate and oblate at temperatures below and above 630 K, respectively.

Charge density studies in NH₄[Ti(C₂O₄)₂].2H₂O crystals at two wavelengths

Charge density studies of NH₄[Ti(C₂O₄)₂].2H₂O are presented using Mo Kα and Ag Kα radiation. The asphericity in density around Ti and the bonding feature of C₂O₄²⁻ as well as hydrogen bonding are clearly demonstrated.

A tri­benzyl­idene­methane–tantalum compound: some experiences with `inversion twinning'

Inversion twinning was observed in crystals of (η⁵-cyclopenta-dienyl)(η⁴-tribenzylidenediide)dimethyltantalum; the molecules have threefold symmetry imposed on them, which also requires that they will be disordered. A satisfactory model was developed and refined, but the problems of data reduction with inversion twinning present were not completely resolved.

Theoretical and experimental (113 K) electron-density study of lithium bis­(tetra­methylammonium) hexa­nitrocobaltate(III)

Topological analysis of the experimental and theoretical electron density of lithium bis(tetramethylammonium) hexanitrocobaltate(III) crystals sheds light on the nature of the ligand-transition metal interaction and on the asphericity of nonbonding 3d-electrons around the Co atom.

Anomalous dispersion analyses of the Ni-atom site in an aluminophosphate test crystal including the use of tuned synchrotron radiation

The use of anomalous dispersion, including synchrotron radiation, to determine the metal-atom substitution sites for the test case of NiAPO is described. Optimization of the experimental protocols is discussed for cases of partial occupancy and for more than one metal atom of similar atomic number.

Hydrogen-bond patterns in 1,4-di­hydro-2,3-quinoxalinediones: ligands for the glycine modulatory site on the NMDA receptor

The crystal structures of five 1,4-dihydro-2,3-quinoxalinedione antagonists of the NMDA modulatory glycine binding site have been determined and the hydrogen-bonding graph sets of all quinoxalinedione crystal structures have been analyzed. Two types of hydrogen-bonding motifs are found: a centrosymmetric dimeric ring and an infinite chain; this analysis suggests biological activity requires one donor and two hydrogen-bond acceptors for receptor recognition.

Structure of 1,5-bis­(di­methylamino)-1,5-di­phenylpentadienylium perchlorate and modelling of pentadienylium salts (cyanine dyes)

The X-ray structure and molecular modelling of 1,5-bis-(dimethylamino)-1,5-diphenylpentadienylium perchlorate are studied. Modelling of two other related cyanine dyes reproduces the solid state structure with good accuracy.

Chemistry of the S=O bond. 13. Structures of isomers 1 (I) and 2 (II) of 4-methyl-1,3,2-dioxa­thiane 2-oxide and 1,3,2-dioxathiepane 2-oxide (III) at 256, 240 and 228 K

The crystal and molecular structures of isomers 1 and 2 of 4-methyl-1,3,2-dioxathiane 2-oxide and 1,3,2-dioxathiepane 2-oxide have been determined by single crystal X-ray diffraction methods at low temperatures.

Stereochemistry of serotonin receptor ligands from crystallographic data. Crystal structures of NAN-190.HBr, 1-phenylbiguanide, MDL 72222 and mianserin.HCl and selectivity criteria towards 5-HT₁, 5-HT₂ and 5-HT₃ receptor subtypes

A systematic structural analysis of serotonin receptor ligands has identified their similarities with the endogenous ligand serotonin (5-hydroxytryptamine or 5-HT) and the stereochemical differences which determine selectivity for the various receptor subtypes: 5-HT₁, 5-HT₂ and 5-HT₃.

Electron density study of a new non-linear optical material: L-arginine phosphate monohydrate (LAP). Comparison between X–X and X–(X + N) refinements

(X-X) and X-(X + N) charge densities of LAP are compared together with the corresponding topology and electrostatic potentials. Reliable results may be obtained from (X-X) data only.

Conformational analysis from crystallographic data using conceptual clustering

Conceptual clustering, a machine learning technique, is applied to the determination of conformational preferences from crystal structure data.

Crystal and molecular structure of 1,25-di­hydroxycholecalciferol

The solid-state conformation of the biologically active form of vitamin D₃ is discussed.

Crystal packing calculations and Rietveld refinement in elucidating the crystal structures of two modifications of 4-amidinoindanone guanylhydrazone

Two modifications of 4-amidinoindanone guanylhydrazone have been elucidated. The generality of a combination of high-precision computational chemistry and Rietveld refinement is demonstrated for one modification where no single crystals were available.

Benzene-1,2-di­sulfonate dianion: another compound with meshed cogwheel substituents?

Two crystal structures of benzene-1,2-disulfonic acid salts have been determined and the cogging of the sulfonate groups as well as the possible pathways of conformational isomerization of the dianion are discussed, based on a PM3 enthalpy hypersurface and compared with known molecules containing adjacent threefold substituents -XY₃.