X-ray structure determination of the monoclinic (121 K) and orthorhombic (85 K) phases of langbeinite-type dithallium dicadmium sulfate

The twinned low-temperature monoclinic (P2₁) and orthorhombic (P2₁2₁2₁) phases of the type I langbeinite Tl₂Cd₂(SO₄)₃ have been determined. The monoclinic phase shows pseudo-orthorhombic symmetry. The rotation of the SO₄ tetrahedra in the orthorhombic phase seems to be continuous with that of the monoclinic one.

Application of graph theory to detect disconnected structures in a crystallographic database: copper oxide perovskites as a case study

A method is proposed for determining erroneous crystal structures with a disconnected topology. This method was tested on a sample of structures from the Inorganic Crystal Structure Database.

Structure and complex twinning of dysprosium disilicate (Dy₂Si₂O₇), Type B

Crystals of the triclinic type B structure of dysprosium disilicate are complexly twinned and dimensionally monoclinic. The type B structure has a linear cluster of triple [SiO₄] tetrahedra and individual tetrahedra are moderately distorted, in agreement with revised structural data for holmium disilicate.

Localized defects in radiation-damaged zircon

-Decay radiation-damaged natural zircon is compared to the undamaged material. The anisotropy of the unit-cell swelling originating from localized defects is explained in terms of the anisotropic expansion of ZrO polyhedra.

Structure of the β form of calcium pyrophosphate tetrahydrate

Calcium pyrophosphate hydrates contribute to the disease chondrocalcinosis (pseudogout). Here a new crystal structure of the second polymorph of the tetrahydrate has been determined. It has been shown to be monoclinic, not orthorhombic as earlier supposed, and to have specific features which contribute to the autoinhibition of growth in supersaturated solutions at pH 7.

Modulated structure of La₂Co_1.7 from neutron and X-ray diffraction data

The incommensurately modulated structure of the compound La₂Co_1.7, lanthanum cobaltide, was determined from neutron and X-ray single-crystal diffraction data collected at 15 K and room temperature. Two descriptions in the superspace formalism using the sawtooth function and the composite model were used to describe the periodicity of cobalt. The chemical composition was newly determined as La₂Co_{1.8 (1)}.

Structures and phase transitions of the A₇PSe₆ (A = Ag, Cu) argyrodite-type ionic conductors. III. α-Cu₇PSe₆

The crystal structure of α-Cu₇PSe₆, one of the three polymorphic forms of the argyrodite Cu₇PSe₆ compound, is determined by means of single-crystal diffraction from twinned crystals and powder X-ray diffraction, with the help of NMR measurements. The analysis reveals a complete localization of copper in different low coordination selenium sites. The copper environment is examined and compared to the situation in β-Cu₇PSe₆ and the environment of silver in Ag₇PSe₆.

Dopant positions in strontium/chromium- and barium-doped KTP, determined with synchrotron X-radiation

The synchrotron X-ray diffraction measurement of Sr/Cr- and Ba-doped KTP crystals show that the Ba dopant is positioned in the larger of the two K cavities while Sr is located in both cavities, whereas Cr^III and Cr^VI are found inside the TiO₆ octahedra.

Anharmonicity of potentials of atoms in potassium hydrogensulfide (KDS) determined by neutron single-crystal diffraction

The crystal structure of the rhombohedral modification of potassium hydrogensulfide which is stable between T = 101 and 426 K was investigated with neutron single-crystal diffraction at ambient temperature on the fully deuterated compound. A considerable anharmonicity of the deuterium atom potential was detected using a Gram-Charlier series to describe the thermal displacement of the atoms.

X-ray diffraction study of copper(I) thiourea complexes formed in sulfate-containing acid solutions

The crystal and molecular structure of a new copper(I) thiourea complex, [Cu(SC(NH))](SO)HO, was determined. It is arranged as centrosymmetric [Cu(tu)] ions with a crown-like conformation.

Powder and single-crystal X-ray diffraction study of the structure of [Y(H₂O)]₂(C₂O₄)(CO₃)₂

The structure of [Y(H₂O)]₂(C₂O₄)(CO₃)₂ is solved ab initio from powder and single-crystal diffraction data. The structure is compared to that of the related gadolinium compound with half a unit-cell volume.

Orientational disorder as a function of temperature in the clathrate structure of hydro­quinone and C₆₀

The molecular rigid-body translations and librations in the structure of (hydroquinone)₃C₆₀ at four temperatures are determined from X-ray diffraction data.

Crystallographic and molecular mechanics investigation of an order–disorder transition and dimorphism in 5H,10H-di­thiolo[2,3-b]-2,5-benzodi­thiocine-2-thione

An order–disorder transition and dimorphism in the title compound have been studied by X-ray crystallography. The molecules adopt U-shaped conformations which molecular mechanics confirm as the most stable.

Supramolecular structure of 1H-pyrazoles in the solid state: a crystallographic and ab initio study

A semi-quantitative bimodal model accounts for most cases of the N—H⋯N hydrogen-bond networks in 1H-unsubstituted pyrazoles (dimers, trimers, tetramers and chains). Ab initio calculations provided a basis for the model.

Structural characterization of protonated benzeneseleninic acid, the di­hydroxyselenonium ion

The dihydroxyselenonium ion has been structurally characterized in two aryl sulfonium salts and its pK value determined from ⁷⁷Se chemical shifts.

Topology of molecular packings in organic crystals

The topological properties of molecular packings and molecular coordination numbers (MCNs) were determined in the crystal structures of 33 575 monosystem organic compounds. It is found that within the first coordination sphere most of the molecules tend to arrange with MCN = 14, but molecular packings as a whole tend to be constructed according to one of the close packings.

Comparison of the structural motifs of aceto­acetanilides and related azo pigments

The structures of three acetoacetanilides and one related monoazo pigment are presented. Relationships and differences in terms of torsion angles, hydrogen bonding and steric factors are discussed.

Adducts of meso and racemic 5,5,7,12,12,14-hexa­methyl-1,4,8,11-tetra­aza­cyclo­tetra­decane with trigonally tris­ubstituted benzene carboxylic acids: supramolecular structures in one and two dimensions

Salt-like adducts of meso and racemic 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (tet-a and tet-b, respectively) with 5-hydroxyisophthalic acid contain very similar hydrogen-bonded sheet structures, despite the different configurations and conformations of the cations (meso versus racemic) and the different space groups. The salt-like adduct of tet-a with 3,5-dinitrobenzoic acid has a one-dimensional structure, a chain of rings.

Crystal engineering in the gem-alkynol family: interplay between strong and weak interactions in structures of 2,3,5,6-tetrahalo[F,Cl,Br]-trans-1,4-diethynylcyclohexa-2,5-diene-1,4-diols

In common with the parent molecule, structures of the tetrahalogenated derivatives are mediated by O—H⋯O hydrogen bonds, which form hexameric synthons in the fluoro compound, but tetrameric synthons in the chloro and bromo analogues. Differences in the overall structural architectures are due to the interplay between these strong interactions and a variety of weaker interactions involving the halogens, C—H donors and the ethynyl π-system.

Crystal engineering in the gem-alkynol family; synthon repetitivity and topological similarity in di­phenylethynylmethanols: structures that lack O—­H⋯O hydrogen bonds

Structures of four derivatives of diphenylethynylmethanol fail to form the expected strong O—H⋯O hydrogen bonds. Instead, the structures are mediated by weaker interactions involving O—H and C—H donors and hydroxy-O and π-acceptors, together with halogen⋯halogen interactions in the dichloro and dibromo derivatives.

Halogen trimer synthons in crystal engineering: low-temperature X-ray and neutron diffraction study of the 1:1 complex of 2,4,6-tris­(4-chloro­phen­oxy)-1,3,5-triazine with tri­bromo­benzene

The host triazine molecules form a two-dimensional hexagonal network via the Cl⋯Cl interactions of a triangular Cl₃ synthon. Guest molecules are located in the hexagonal channels using C—Br⋯π and C—H⋯π interactions.

Qu­antitative analysis of hydrogen bonding and atomic thermal motion in the organic non-linear optical material DCNP using X-ray and neutron diffraction

The crystal structure of the organic non-linear optical material 3-(1,1-dicyanoethenyl)-1-phenyl-4,5-dihydro-1H-pyrazole, DCNP, deduced by single-crystal neutron diffraction and variable-temperature X-ray diffraction studies, is presented. The hydrogen bonding and atomic thermal motion thus characterized are related to the physical properties of the material and the thermal expansivity coefficients of the material are evaluated.

Selective solvent inclusion as a tool for mapping molecular properties in crystal structures: a di­ethylstilbestrol example

Intermolecular interactions and molecular conformations are compared for diethylstilbestrol molecules in nine different solvate structures.

Structure of C_nC_n+2C_n-type (n = even) β′-tri­acylglycerols

The crystal structures of β′-CLC and β′-MPM have been determined from single-crystal and high-resolution X-ray powder diffraction data, respectively. Furthermore, a comparison is made with existing models of β′-C_nC_n+2C_n triacylglycerols and with stable C_nC_nC_n triacylclycerols

Conformational transformation coupled with the order–disorder phase transition in 2-methyl-1,3-cyclo­hexanedione crystals. Erratum

Erratum to Acta Cryst. (2000). B56, 872–542.

Scintag X'TRA: new X-ray diffraction system