On the mechanism of some first-order enantiotropic solid-state phase transitions: from Simon through Ubbelohde to Mnyukh

An integrated and comparative study of more than 20 enantiotropic solid-state phase transitions shows that these are all first-order and proceed by a `nucleation and growth' mechanism in accordance with the description set out especially by Yuri Mnyukh.

Structure determination of A₂M³⁺TaO₆ and A₂M³⁺NbO₆ ordered perovskites: octahedral tilting and pseudosymmetry

The crystal structures of six A₂M³⁺M⁵⁺O₆ ordered perovskites as determined from X-ray and neutron powder diffraction data are reported here. These samples show a high degree of pseudosymmetry that complicates the interpretation of the powder diffraction data. Correct space-group assignments were made through the systematic analysis of the supercell reflections, splitting of the fundamental perovskite peaks and crystal chemical considerations.

Structure prediction of ordered and disordered multiple octahedral cation perovskites using SPuDS

The capabilities of the program SPuDS have been extended to predict crystal structures of A₂MM′X₆ ordered double perovskites. Its accuracy and potential applications are discussed.

`Ionic' size differences from bond-valence parameters and from ionic radii

Expectation values for size differences between pairs of `ions' (atoms in oxidation states ≠ 0) embedded into similar coordination environments are calculated from bond-valence parameter and ionic radii tables.

Experimental versus expected halide-ion size differences; structural changes in three series of isotypic bis­muth chalcogenide halides

Experimentally determined, halide-ion size differences are compared with expected sizes in the three series of isotypic bismuth chalcogenide halide compounds KBi₆O₉X, BiOX and BiSX.

Compressibility of the nitridosilicate SrYb[Si₄N₇] and the oxonitridoaluminosilicates MYb[Si_4−xAl_xO_xN_7−x] (x = 2; M = Sr, Ba)

In situ high-pressure X-ray powder diffraction up to 42 GPa was performed in order to explore the compressibilities of the title compounds. The results show that the sialons MYb[Si_4−xAl_xO_xN_7−x] (x = 2; M = Sr, Ba) are more compressible than the nitridosilicate SrYb[Si₄N₇], while all phases are stable up to the highest pressures reached.

Estimation of polyhedral compressibilities and structural evolution of GdFeO₃-type perovskites at high pressures

A new approach based on the bond-valence matching relation is developed to predict the detailed structural evolution of GeFeO₃-type perovskites at high pressure from knowledge of the room-pressure structure and the high-pressure unit-cell parameters alone.

Na₂Si₃O₇: an incommensurate structure with crenel-type modulation functions, refined from a twinned crystal

A (3 + 1)-dimensional superspace model for the incommensurate structure of Na₂Si₃O₇ is presented and refined from twinned X-ray diffraction data.

Structural complexity in minerals: twinning, polytypism and disorder in the crystal structure of polybasite, (Ag,Cu)₁₆(Sb,As)₂S₁₁

The atomic structures of 222- and 221-polybasite have been solved and refined from X-ray diffraction data from twinned crystals at 100 and 120 K, respectively. A possible mechanism regulating the type of unit cell that is stabilized is proposed.

A comparative crystallochemical analysis of binary compounds and simple anhydrous salts containing pyramidal anions LO₃ (L = S, Se, Te, Cl, Br, I)

A comparative analysis of simple anhydrous salts M_y(LO₃)_z (L = S, Se, Te, Cl, Br, I) showed their relationships to six types of binary compounds (NaCl, NiAs, PoCl₂, Tl₂S₂, ZnTe, rutile). It has been established that in 36 out of the 61 salts at least one ion array has the topology of close packing or the body-centred cubic lattice.

Crystal structures of the tri­fluoro­methyl sulfonates M(SO₃CF₃)₂ (M = Mg, Ca, Ba, Zn, Cu) from synchrotron X-ray powder diffraction data

The crystal structures of M(SO₃CF₃)₂ (M = Mg, Ca, Ba, Zn, Cu) were determined using high-resolution X-ray powder diffraction data.

Cis/trans isomers of PtX₂L₂ (X = halogen, L = neutral ligand); the crystal structure of trans-di­chlorobis(di­methyl sulfide)platinum(II) and the pressure dependence of its unit-cell dimensions

The crystal structure of trans-PtCl₂(dms)₂ (dms is dimethyl sulfide) has been determined from single-crystal diffraction data and the pressure dependence of its unit-cell dimensions has been studied with diamond–anvil cells up to 8.0 GPa using powder diffraction. trans-PtCl₂(dms)₂ adopts the molecular point group C_i, which is the most frequently occurring point group for trans-PtX₂L₂ complexes (78%) as observed in the Cambridge Structural Database (CSD), followed by C₁ (16%). No preference for either trans- or cis-PtX₂L₂ is found in the CSD.

X-ray crystallographic structures of enamine and amine Schiff bases of pyridoxal and its 1:1 hydrogen-bonded complexes with benzoic acid derivatives: evidence for coupled inter- and intramolecular proton transfer

Schiff base structures containing pyridoxal (PL) and their 1:1 acid–base adducts are reported and serve as models for the coenzyme pyridoxal-5′-phosphate (PLP) in the dependent enzymes. They allow the study of the intramolecular OHN hydrogen bond of PL/PLP Schiff bases and the H-acceptor properties of their pyridine rings.

S,S-1,2-Di­cyclo­hexylethane-1,2-diol and its racemic compound: a striking exception to Wallach's rule

Analyses of the crystal structures of enantiopure S,S-1,2-dicyclohexylethane-1,2-diol and its racemic compound suggest a reason why crystals of any enantiopure material might be expected to be less dense than crystals of the corresponding racemic compound and to be more likely to have Z′ > 1.

17 salts of ephedrine: crystal structures and packing analysis

The structures of anhydrous ephedrine and ephedrine hemihydrate together with 17 salts of the base are reported. It is evident that the observed packings are in most cases related to those of the neutral molecule, incorporating both bilayer and conformational elements.

The incommensurately modulated structure of a tricyclic natural-product-like compound of empirical formula C₂₂H₂₀O₃

The single-crystal incommensurately modulated structure of 3,4-diphenyl-2a,5a,6,7,8,8a,8b-heptahydrofuro[4,3,2-de]chromen-2-one, C₂₂H₂₀O₃, is presented.

Chemical bonding in pentaerythritol at very low temperature or at high pressure: an experimental and theoretical study

Atomic interactions in the pentaerythritol crystal based on the experimental electron density at 15 K, and theoretical calculations based on the experimental molecular geometries obtained at room and low (15 K) temperatures, as well as at high pressure (1.15 GPa) have been analyzed and compared.