Is there a future for topological analysis in experimental charge-density research?

Investigations are critically discussed where a toplogical analysis of the experimental charge density from single-crystal X-ray diffraction is the main result.

The future of topological analysis in experimental charge-density research

The state of the art and the future of the topological analysis of experimental electron charge density is the topic of this perspective article, within a debate stimulated by a recent communication.

Temperature-induced reversible structural phase transition and X-ray diffuse scattering in 2-amino-3-nitropyridinium hydrogen sulfate

A novel polar material, C₅H₆N₃O₂(HSO₄), was synthesized, and its structure was determined in two phases. The origin of the X-ray diffuse scattering in a high-temperature disordered phase is explained as a precursor effect of the long-range ordered low-temperature phase.

Growth, crystal structure, Hirshfeld surface, optical, piezoelectric, dielectric and mechanical properties of bis­(L-asparaginium hydrogensquarate) single crystal

Intermolecular interactions in the bis­(L-asparaginium hydrogensquarate) monohydrate crystal are analyzed using Hirshfeld surface. The title compound has shown promising nonlinear optical and piezoelectric properties.

Identification of a deleterious phase in photo­catalyst based on Cd_1 − xZn_xS/Zn(OH)₂ by simulated XRD patterns

The XRD pattern of a deleterious phase in the photocatalyst based on Cd_1 − xZn_xS/Zn(OH)₂ contains two relatively intensive asymmetric peaks with d-spacings of 2.72 and 1.56 Å. To identify this phase, the XRD patterns were calculated for three models: sheet-like β-Zn(OH)₂, sheet-like hydrozincite, Zn₅(CO₃)₂(OH)₆, and turbostratic hydrozincite. Simulations revealed the formation of a nanocrystalline turbostratic hydrozincite-like phase.

Could incommensurability in sulfosalts be more common than thought? The case of meneghinite, CuPb₁₃Sb₇S₂₄

The crystal structure of the mineral meneghinite, CuPb₁₃Sb₇S₂₄, has been solved and refined as an incommensurate structure from X-ray single-crystal diffraction data in four-dimensional superspace. The very small departure from the commensurate value of the modulation raises the question of whether incommensurability in sulfosalts could be much more frequent than previously thought.

Ordered vacancy distribution in 2/1 mullite: a superspace model

A superspace model with complete vacancy ordering is presented based on X-ray diffraction of a 2/1 mullite sample with sharp satellite reflections. The results allow different conclusions of previous investigations of the last decades to be consolidated.

The impact of anion ordering on octahedra distortion and phase transitions in SrTaO₂N and BaTaO₂N

Anion (O/N) ordering was observed in BaTaO₂N and SrTaO₂N. A further Ta—O/N octahedra displacement (rotation about the c axis) distortion was observed in SrTaO₂N.

Synthesis, crystallization, X-ray structural characterization and solid-state assembly of a cyclic hexapeptoid with propargyl and methoxyethyl side chains

The synthesis and the structural characterization of a cyclic hexapeptoid with four meth­oxy­ethyl and two propargyl side chains allows a discussion of the solid-state assembly of a hydrate crystal form (I) and an anhydrous crystal form (II). The relative amounts of forms (I) and (II) in the as-purified product were determined by Rietveld refinement and depend on the purification procedures.

An ordering phase transition, short hydrogen bonds and high Z′ in the structure of Ni(Hpydc)₂·3H₂O

The frequently reported structure of Ni(Hpydc)₂·3H₂O (H₂pydc = pyridine-2,6-dicarboxylic acid, also known as dipicolinic acid) is reinvestigated at temperatures ranging from 298 to 90 K. Strong hydrogen bonds are indicated.

Structural and Raman spectroscopic characterization of pyroxene-type compounds in the CaCu_1−xZn_xGe₂O₆ solid-solution series

The clinopyroxene CaCuGe₂O₆ transforms from P2₁/c ↔ C2/c with increasing replacement of Cu²⁺ by Zn²⁺. The structural phase change is characterized using single-crystal X-ray diffraction and temperature-dependent Raman spectroscopy.

Formation and distortion of iodido­antimonates(III): the first isolated [SbI₆]³⁻ octahedron

Two iodidoantimonates(III), (C₄H₁₂N₂)₃[SbI₆]₂·5H₂O and (C₄H₁₂N₂)[SbI₄]₂·4H₂O, obtained by reacting Sb₂O₃ and piperazine in hydroiodic acid, show different schemes of interactions: the hydrogen bonds in (C₄H₁₂N₂)₃[SbI₆]₂·5H₂O form a network that favours the formation of significantly distorted isolated [SbI₆]^3– octahedra.

Die Symmetrie von Spiralketten

The relationship between the chemical designation for helical polymeric molecules and the corresponding Hermann–Mauguin rod group symbols is analyzed, including interlocked multiple helices and helices of joined coordination polyhedra. The crystallographic rod subgroups of non-crystallographic rod groups are given.

Searching for stereoisomerism in crystallographic databases: algorithm, analysis and chiral curiosities

A computational approach for determining the chirality and stereoisomerism of chemical residues in crystallographic data entries is presented. The method is demonstrated for a dataset of 254 354 organic entries from the Cambridge Structural Database, revealing 409 kryptoracemates and 133 diastereomeric cocrystals.

Sr_1/2Ce_5/14□_1/7WO₄: a new modulated ternary scheelite compound

A new ternary scheelite tungstate (Sr, Ce)WO₄ phase was synthesized, with a two-dimensional incommensurately modulated structure linked to partial ordering of Sr and Ce cations and vacancies as seen using high-resolution electron microscopy. A band gap of 3.2 eV makes it a promising violet-emitting compound.

The hydrogen bond between N—H or O—H and organic fluorine: favourable yes, competitive no

The interaction between strong donors (N—H, O—H) and carbon-bound fluorine is energetically favourable but very uncompetitive, a donor's last resort.

Synthesis and crystal structure of pyrrolo­quinoline quinol (PQQH₂) and pyrrolo­quinoline quinone (PQQ)

Pyrroloquinoline quinol (PQQH₂) and pyrroloquinoline quinone (PQQ) molecules play an important role as a cofactor in alcohol- and glucose-dehydrogenase reactions in bacteria. In the present study, the crystal structure analyses of PQQ and PQQH₂ have been successfully elucidated for the first time.

Crystallographic and optical study of LiNb_1 − xTa_xO₃

The structure of lithium niobate-tantalate has been studied using powder and single-crystal X-ray diffraction focusing on the composition and temperature induced zero-birefringence points.

Chiral and achiral crystals, charge-assisted hydrogen-bond patterns and self-organization of selected solid diaminium thio­sulfates

The formation of chiral crystals from achiral components, strong hydrogen-bond schemes and other structural properties of diaminium thio­sulfates are investigated and described. The conformations of α,ω-alkyl­diaminium cations in the solid state are analysed.