Incommensurately modulated lanthanide coinage-metal diarsenides. I. CeAu_1−δAs₂ [δ = 0.015 (2)] – a new distortion variant of the HfCuSi₂ type with irregularly stacked cis–trans chains of arsenic atoms

The modulated structure CeAu_1−δAs₂, a new distortion variant of the HfCuSi₂ type, is described.

Incommensurately modulated lanthanide coinage-metal diarsenides. II. GdCuAs₂, GdAu_1−δAs₂ and TbAu_1−δAs₂ – new distortion variants of the HfCuSi₂ type with irregularly stacked zigzag chains of arsenic atoms

Three modulated structures of lanthanide coinage-metal diarsenides are presented and discussed as new distortion variants of the HfCuSi₂ type.

Modulation of atomic positions in CaCu_xMn_7−xO₁₂ (x ≤ 0.1)

It is shown that there is a close relationship between the modulation of the atomic positions and the modulation of the magnetic moments of Mn ions in CaCu_xMn_7−xO₁₂ compounds for x = 0 and x = 0.1 at low temperatures.

Modulated crystal structure of incommensurate low tridymite

Wavefunctions with up to third-order harmonics were refined in order to describe the positional modulation of incommensurate low tridymite. The structural modulation is accompanied by an additional modulation of the anisotropic displacement parameters.

Structure of caesium di­sulfate at 120 and 273 K

Caesium disulfate represents a new structure type with a uniquely high number of independent formula units at 120 K. Between 230 and 250 K it shows an order–disorder transition. The Cs⁺-ion arrangement shows a remarkable similarity to the high-pressure Rb^IV metal structure.

Order–disorder of oxygen anions and vacancies in solid solutions of La₂TiO₅ and La₄Ga₂O₉

Solid solutions of La₂TiO₅ and La₄Ga₂O₉ were structurally characterized by X-ray powder diffraction. The structural relationship between end members – orthorhombic La₂TiO₅ and monoclinic La₄Ga₂O₉ – was elucidated.

Eu₃Si_15 − xAl_1 + xO_xN_23 − x (x ≃ 5/3) as a commensurate composite crystal

A new Eu-SiAlON crystal, Eu₃Si_15 − xAl_1 + xO_xN_23 − x (x ≃ 5/3), was grown. Its structure is considered to be that of a commensurate composite crystal. A structure model in (3 + 1)-dimensional superspace is also proposed.

Ternary fluorides BaMF₄ (M = Zn, Mg and Mn) at low temperatures

Ternary fluorides BaMF₄ (M = Zn, Mg, Mn) have been studied in the temperature range from 300 to 10 K.

Modulated structure and phase transitions of Sr₁₀Ga₆O₁₉

The modulated structure of Sr₁₀Ga₆O₁₉ at ambient temperature has been investigated. At high temperature, two phase transitions (one between 453 and 503 K and the other between 503 and 673 K) have been found.

Superspace description of the modulated structure of the metal-salt-hybrid Bi_7 − δNi₂Br_{5 − 2δ} (δ = 1/9)

The sub-bromide Bi_7 − δNi₂Br_{5 − 2δ} contains Bi₃Ni rods, which are isolated by a bromido-bismuthate matrix. A structure model is developed in (3 + 1)-dimensional superspace.

Weak interactions in chain polymers [M(μ-X)₂L₂]_∞ (M = Zn, Cd; X = Cl, Br; L = substituted pyridine) – an electron density study

Topological analyses of the experimental electron-density distributions in crystals of five chain polymers [M(μ-X)₂(py)₂] (M = Zn, Cd; X = Cl, Br; py = 3,5-substituted pyridine) confirmed the existence of (3, −1) critical points both for intuitively strong chemical bonds and for secondary interactions. The latter comprise intra- and inter-strand C—H⋯X—M hydrogen bonds and C—X⋯X—C interhalogen contacts and stabilize the polymeric structures unusual for Zn as the metal center.

[Ru(py)₄Cl(NO)](PF₆)₂·0.5H₂O: a model system for structural determination and ab initio calculations of photo-induced linkage NO isomers

Structure analysis of GS (ground state) and two light-induced (SI and SII) metastable linkage NO isomers of [Ru(py)₄Cl(NO)](PF₆)₂·0.5H₂O is presented. The experimental results are compared with solid-state calculations based on density functional theory (DFT). The influence of the different occupancies of the metastable isomer SI and GS on the refinement results was solved by a simulation procedure.

Topological properties of hydrogen bonds and covalent bonds from charge densities obtained by the maximum entropy method (MEM)

The maximum-entropy charge densities of six amino acids and peptides reveal systematic dependencies of the properties at bond critical points on bond lengths. MEM densities demonstrate that low-order multipoles (l_max = 1) and isotropic atomic displacement parameters for H atoms in the multipole model are insufficient for capturing all the features of charge densities in hydrogen bonds.

Structure and conformational analysis of a bidentate pro-ligand, C₂₁H₃₄N₂S₂, from powder synchrotron diffraction data and solid-state DFTB calculations

The crystalline structure of ethyl 1′,2′,3′,4′,4a′,5′,6′,7′-octahydrodispiro[cyclohexane-1,2′-quinazoline-4′,1′′-cyclohexane]-8′-carbodithioate, C₂₁H₃₄N₂S₂, a bidentate pro-ligand with a coordination sphere of the type [NS]¹⁻, was solved and refined from synchrotron powder diffraction data, and compared with in-vacuum density-functional theory (DFT) B3LYP/6-311G* and solid-state density-functional tight-binding (DFTB) theoretical calculations.

The experimental and theoretical QTAIMC study of the atomic and molecular interactions in di­nitrogen tetroxide

Quantum-topological analysis of electron density and density-based functions is used to reveal the role of the Lewis-type molecular complementarity, the electrostatic force field and the features of the exchange and correlation energy density in forming the observed three-dimensional structure of the α-N₂O₄ crystal.