Structure determination of Mg₃(OH)₅Cl·4H₂O (F5 phase) from laboratory powder diffraction data and its impact on the analysis of problematic magnesia floors

The crystal structure with the idealized formula Mg₃(OH)₅Cl·4H₂O, the so-called F5 phase according to 5Mg(OH)₂·MgCl₂·8H₂O in the system MgCl₂–MgO–H₂O, has been solved ab initio from high-quality laboratory powder diffraction data at room temperature. The F5 phase is of technological importance as the most important binder phase in Sorel cements.

Structural stability and formability of ABO₃-type perovskite compounds

On the basis of the bond-valence model and structure-map technology, the structural stability and formability of ABO₃-type perovskite compounds were investigated in 376 ABO₃-type compounds.

Equilibrium langbeinite-related phosphates Cs_1 + xLn_xZr_2 − x(PO₄)₃ (Ln = Sm–Lu) in the melted systems Cs₂O–P₂O₅–LnF₃–ZrF₄

Members of a series of langbeinite-like compounds incorporating caesium cations inside the crystal cavities have been obtained by the flux technique and have been structurally characterized. Possibilities for the formation of caesium-containing langbeinite-related phosphates in the melted system Cs₂O–P₂O₅–ZrF₄–LnF₃ (Ln = La–Nd, Sm–Lu) are analyzed.

Neutron diffraction investigation of the temperature dependence of crystal structure and thermal motions of red HgI₂

Thermal displacement parameters in red HgI₂ measured by neutron powder diffraction are interpreted in terms of a phonon model and a mechanism for anharmonic contributions.

Temperature dependence of the AV₃O₇ (A = Ca, Sr) structure

The oxovanadates AV₃O₇ (A = Ca, Sr) were synthesized and studied in the temperature ranges 297 down to 100 K, and 315 down to 100 K by means of single-crystal X-ray diffraction.

Reticular merohedral twinning within the La₉Sb₅O₅ structure family: structure of Pr₉Sb₅O₅, Sm₉Sb₅O₅ and Dy₉Sb₅O₅

A single crystal of Pr₉Sb₅O₅ and reticular merohedral twinned crystals of Sm₉Sb₅O₅ and Dy₉Sb₅O₅ have been studied by single-crystal X-ray diffraction.

Structure of calcium aluminate decahydrate (CaAl₂O₄·10D₂O) from neutron and X-ray powder diffraction data

The crystal structure of the high-alumina cement calcium aluminate hydrate is determined by means of neutron and X-ray powder diffraction on deuterated samples.

Experimental and theoretical characterization of the Zn—Zn bond in [Zn₂(η⁵-C₅Me₅)₂]

The experimental electron density obtained from a multipole refinement of the synchrotron X-ray data for the title complex, together with theoretical ab initio calculations of the electron density at the molecular geometry obtained from neutron diffraction data provide a complete characterization of both its Zn—Zn and Zn—Cp^* bonds.

Probabilistic model-based methodology for the conformational study of cyclic systems: application to copper complexes double-bridged by phosphate and related ligands

A methodology for the conformational study of cyclic systems through the statistical analysis of torsion angles is presented. It relies on a combination of different methods based on a probabilistic model which takes into account the topological symmetry of the structures.

Supramolecular structures in N-isonicotinoyl arylaldehydehydrazones: multiple hydrogen-bonding modes in series of geometric isomers

In N-isonicotinoyl arylaldehydehydrazones, the molecules may be linked into supramolecular structures in one, two or three dimensions by various combinations of hydrogen bonds, augmented by π⋯π stacking interactions. The hydrogen-bonded structures can range between one-, two- and three-dimensional within a series of isomers differing only in the location of a single, simple substituent such as F or OMe.

Compressed hydrogen-bond effects in the pressure-frozen chloro­acetic acid

Pressure freezing of dichloroacetic acid yields a crystal structure with interesting multihalogen motifs.

Isobaric and isochoric freezing of CH₂BrCl and isostructural relations between CH₂Cl₂, CH₂Br₂ and CH₂BrCl

It has been shown on a simple compound, CH₂BrCl, that pressure-frozen crystals are dominated by one short contact in the crystal isostructural with the CH₂Cl₂ crystal, space group Pbcn, whereas temperature freezing of CH₂BrCl leads to the crystal isostructural with CH₂Br₂, space group C2/c, with some of the intermolecular contacts electrostatically unfavourable. In both the CH₂BrCl forms the Cl and Br atoms are disordered.

An unexpected co-crystal with a variable degree of order: 1:1 rac-1,2-cyclo­hexanediol/tri­phenylphos­phine oxide

A 1:1 co-crystal of rac-1,2-C₆H₁₀(OH)₂ and (C₆H₅)₃PO has been found that is unusual because there are no strong interactions between the two different kinds of molecules, which are segregated into layers. The degree of ordering of enantiomers within and between the C₆H₁₂O₂ layers seems to depend on the solvent from which the crystal is grown.

Rietveld refinement of a wrong crystal structure

The Rietveld refinement of γ-quinacridone (C₂₀H₁₂N₂O₂) with the crystal structure of β-quinacridone gives a smooth difference curve and a reasonable looking crystal structure; nevertheless, molecular conformation, packing and lattice parameters are definitively wrong. This example shows that a successful Rietveld refinement is not always final proof of the crystal structure.

Monitoring structural transformations in crystals. 11. Yang photocyclizations – one type of reaction, but diversity of structural changes

Variations in the cell constants, the product content in the crystal, the mutual orientation of directly reacting atoms, the orientation of molecules and changes in the hydrogen bonds brought about by an intramolecular photochemical reaction were monitored using X-ray diffraction. The studies provide detailed information about the course of the Yang photocyclization reactions in crystals.