Absolute structure determination: pushing the limits

The historical context of the paper by Watkin & Cooper [(2016), Acta Cryst. B72, 661–683] is sketched.

Why direct and post-refinement determinations of absolute structure may give different results

Comparison of direct and post-refinement methods for determining the Flack absolute structure parameter provides a mechanism for exposing deficiencies in a structure analysis. A substantial discrepancy is often indicative of underlying problems with the data and/or structural model.

Two rhodamine 6G derivative compounds: a structural and fluorescence single-crystal study

The synthesis, characterization, structural analysis and fluorescence properties of two rhodamine 6G derivatives are described. A single-crystal in-situ reaction study is presented, carried out by fluorescence methods, which enabled the `opening' of the spiro­lactam ring in the solid phase.

Br⋯Br and van der Waals interactions along a homologous series: crystal packing of 1,2-di­bromo-4,5-di­alkoxybenzenes

The crystalline structures of four homologues of the 1,2-dibromo-4,5-dialkoxybenzene series [Br₂C₆H₂(OC_nH_2n + 1)₂ for n = 2, 12, 14 and 18] have been solved by means of single-crystal crystallography.

Effect of Al and Ca co-doping, in the presence of Te, in superconducting YBCO whiskers growth

In view of future exploitation of intrinsic Josephson junctions (IJJs) for solid-state THz applications, we synthesized high-quality superconducting YBCO tape-like single crystals (whiskers) from Ca–Al-doped precursors in the presence of Te. Firstly, we aim to carry out the importance of the simultaneous use of Ca, Te and Al in promoting YBCO whiskers growth with superconducting properties, then to fill the lack of YBCO structure investigations in the literature by reporting single-crystal X-ray diffraction refinements of tetragonal YBCO.

Bis-(1-(2-amino­ethyl)piperidino), (2-(2-amino­ethyl)pyridino) and (1-(2-amino­ethyl)pyrrolidino)-substituted di­cyanoquinodi­methanes: consequences of flexible ethylene spacers with heterocyclic moieties and amine functionalities

Synthesis and characterization of new functional molecular materials based on disubstituted tetracyanoquinodimethanes

CH₃NH₃PbI₃: precise structural consequences of water absorption at ambient conditions

Structure, symmetry and hydrogen bonds have been determined for pristine and aged tetragonal CH₃NH₃PbI₃ crystals upon H₂O absorption from air at room temperature. Single-crystal X-ray diffraction data obtained on a synchrotron light source was used for the study. H₂O insertion into the structure changes hydrogen bonds and, consequently, the space group from I422 (pristine crystal) to P4₂2₁2 (aged crystal).

Structures and physicochemical properties of vortioxetine salts

Eight salts of vortioxetine were synthesized and structurally elucidated by single-crystal structure analysis. Physical and chemical properties were evaluated by a variety of analytical techniques. Vortioxetine aspartate dihydrate shows a higher solubility than the corresponding anhydrate.

Mutual transformation between crystalline phases in silicon after treatment in a planetary mill: HRTEM studies

Silicon particles after treatment in a planetary mill have been examined in transmission electron microscopy. It is shown that along with the initial phase of silicon, Si-I, the sample also contains some high-pressure phases: Si-III (Kasper phase) and Si-IV (lonsdaleite). We studied the orientation relationship between the particles of different phases.

Accurate unrestrained DDM refinement of crystal structures from highly distorted and low-resolution powder diffraction data

Crystal structures of the benzene:ethane co-crystal and 2-aminopyridinium fumarate–fumaric acid are refined without geometric restraints using the derivative difference method from strongly distorted synchrotron and low-resolution laboratory X-ray powder diffraction data. The results are compared with density functional theory calculations and former restrained Rietveld refinements for the same datasets.

Towards a revisitation of vesuvianite-group nomenclature: the crystal structure of Ti-rich vesuvianite from Alchuri, Shigar Valley

Vesuvianite containing 5.85 wt% TiO₂ from an Alpine-cleft-type assemblage outcropped near Alchuri, Shigar Valley, Northern Areas, has been studied. The role of the Y1 site in the diversity of vesuvianite-group minerals is discussed.

Crystal chemistry of tri­alkylsilyl-capped (3Z)-4-(methylthio)-3-penten-1-yne: polymorphism, twinning and ambiguity of order–disorder descriptions

Silyl-capped ene-yne compounds crystallize in layers and feature polymorphism and twinning.

Variable-temperature X-ray diffraction study of structural parameters of NH---S hydrogen bonds in tri­ethylammonium and pyridinium silane­thiolates

Hydrogen bonds in triethylammonium and pyridinium silanethiolate salts have been characterized by X-ray, FT–IR and NMR spectroscopies. DFT calculations reveal strongly asymmetric double-well minima at the potential energy curves of the studied compounds.

The orthorhombic pseudopolymorph of tacrine hydrochloride

The orthorhombic pseudopolymorph of the acetylcholinesterase inhibitor tacrine hydrochloride was obtained after recrystallization from a water:ethanol mixture.

Topological characterization of electron density, electrostatic potential and intermolecular interactions of 2-nitro­imidazole: an experimental and theoretical study

In this paper we present a detailed investigation of experimental and theoretical charge density analysis and electrostatic properties of the 2-nitroimidazole molecule. The topological properties of electron density reveal the charge density distribution of the molecule and non-bonding regions.

Communication between cation environments in aluminosilicate frameworks: incommensurately modulated crystal structure of an e-plagioclase

Plagioclase is known as one of the most common mineral exhibits in the earth's crust, but is also noted for its complicated crystal structure. In this article we present a full detailed analysis of the incommensurately modulated structure of intermediate e-plagioclase (An₄₄), and highlight how it originates from the coupling between the coordination environments of its cations.

Highlights in Mineralogical Crystallography