Significant progress in predicting the crystal structures of small organic molecules – a report on the fourth blind test

The findings of the fourth blind test of crystal structure prediction, which have demonstrated important progress in computational methods, are presented and discussed.

Ln₃M_1 − δTX₇ – quasi-isostructural compounds: stereochemistry and silver-ion motion in the Ln₃Ag_1 − δGeS₇ (Ln = La–Nd, Sm, Gd–Er and Y; δ = 0.11–0.50) compounds

The crystal structures of the Ln₃Ag_1 − δGeS₇ (Ln = La–Nd, Sm, Gd–Er, Y; δ = 0.11–0.50) compounds were determined. Structural relationships, stereochemistry and silver-ion motion in the Ln₃M_1 − δTX₇ compounds are discussed.

Symmetry rules and strain/order-parameter relationships for coupling between octahedral tilting and cooperative Jahn–Teller transitions in ABX₃ perovskites. I. Theory

The symmetry and transformation behaviour of ABX₃ perovskites with Jahn–Teller and octahedral tilting transitions are analysed using group theory and Landau theory. Selected well known perovskite structures occur among the structure types predicted on this basis, but there are also many more which have not yet been reported. General expressions are given for the lattice geometry of the Jahn–Teller/tilted structures, and symmetry hierarchies are derived to describe the possible phase transitions which can occur between them.

Symmetry rules and strain/order-parameter relationships for coupling between octahedral tilting and cooperative Jahn–Teller transitions in ABX₃ perovskites. II. Application

The thermodynamic and structural evolution of selected vanadate, manganite, aluminate and cobaltate perovskites which undergo both octahedral tilting transitions and Jahn–Teller cooperative distortion transitions have been determined from observed variations in lattice parameters. Analysis of the lattice-parameter data in terms of symmetry-adapted strains confirms the importance of strain/order-parameter coupling and reveals the separate evolution of Jahn–Teller and tilting components in these materials.

X-ray powder diffraction and electron diffraction studies of the thortveitite-related L phase, (Zn,Mn)₂V₂O₇

A phase found as a minor second phase in zinc oxide-based varistor materials doped with vanadium oxide and manganese oxide is shown to be the L phase in the pseudobinary Mn₂V₂O₇–Zn₂V₂O₇ system. Rietveld refinement of the L phase shows that it has a thortveitite supercell structure.

Polymorphism of CaTeO₃ and solid solutions Ca_xSr_1 − xTeO₃

Compounds in the family Ca_1 − xSr_xTeO₃ crystallize in at least five different structure types. Whereas the structures of β-, β′-, γ-CaTeO and the solid solutions Ca_0.55Sr_0.45O₃ and Ca_0.77Sr_0.33TeO₃ are closely related, the thermodynamically stable α-CaTeO₃ shows unique structural features.

Polymorphism in iodotris(tri-p-tolylphosphine)silver(I)

The synthesis and characterization of a new polymorph of the complex [AgI{P(4-MeC₆H₄)₃}₃] is described. The molecular structure was determined by single-crystal X-ray diffraction. The current polymorph was compared with a previously reported polymorph using r.m.s. overlay as well as half-normal probability plot analysis.

Electron diffraction, X-ray powder diffraction and pair-distribution-function analyses to determine the crystal structures of Pigment Yellow 213, C₂₃H₂₁N₅O₉

The crystal structure of the α phase of this azo pigment was investigated by various methods and finally solved from X-ray powder data. Pair-distribution-function analysis was used to obtain structural information on the nanocrystalline β phase.

Structures of six industrial benzimidazolone pigments from laboratory powder diffraction data

The first six structures of commercially produced benzimidazolone pigments were solved from laboratory powder diffraction data. All six structures are very different but have strong intermolecular hydrogen bonding in common.

Structure determination of seven phases and solvates of Pigment Yellow 183 and Pigment Yellow 191 from X-ray powder and single-crystal data

Laboratory X-ray powder data were sufficient to solve the crystal structures of Ca(C₁₆H₁₀Cl₂N₄O₇S₂)·H₂O (α-P.Y. 183) and Ca(C₁₇H₁₃ClN₄O₇S₂)·3H₂O (β-P.Y. 191) using real-space and Rietveld methods. Structures of other phases and solvates were determined from Rietveld refinement on isostructural compounds or from single-crystal data.

An aza-cyclophane stacked in racemic columnar assemblies: whole-molecule disorder in a two-dimensional solid solution

A ten-membered N-acetyl macrocyclic amide crystallizes as a solid solution of racemic columnar assemblies consisting of alternating enantiomers in a stacked-cup array, each as a chloroform monosolvate, but with a random distribution of the columns within the crystal leading to whole-molecule disorder within the crystal.

Trans-cinnamic acid and coumarin-3-carboxylic acid: experimental charge-density studies to shed light on [2 + 2] cycloaddition reactions

Experimental charge-density studies have been used to obtain insights into the intra- and intermolecular interactions present in coumarin-3-carboxylic acid and trans-cinnamic acid, both of which undergo [2 + 2] cycloaddition reactions upon irradiation.

X-ray crystal structures of di­acetates of 6-s-cis and 6-s-trans astaxanthin and of 7,8-dide­hydroastaxanthin and 7,8,7′,8′-tetrade­hydroastaxanthin: comparison with free and protein-bound astaxanthins

The crystal structures of diacetates of 6-s-cis and 6-s-trans astaxanthin, and the diols 7,8-didehydroastaxanthin and 7,8,7′,8′-tetradehydroastaxanthin provide an ensemble of end-ring conformations which are compared with those of unbound astaxanthin and the protein-bound astaxanthin in lobster β-crustacyanin. The effect of these end-ring conformations on the colour of the crystals and their solid- and solution-state UV–vis spectra are discussed with reference to the large bathochromic shift seen between the unbound and protein-bound forms of astaxanthin.