Kaolin polytypes revisited ab initio

Re-examination and quantum optimization of kaolin layer stackings allow the construction of a rough enthalpy versus pressure graph with 36 stackings where kaolinite and dickite are low-energy solutions, whereas nacrite and HP-dickite are low-enthalpy solutions at moderate pressures; minor temperature dependence of this calculated 0 K graph would explain the bulk of the current observations for synthesis, diagenesis and transformation of kaolin minerals. The ideal model of nacrite is one member of a homometric but energy-distinguishable pair, whereas its literature-printed structure is correctly that of the stable member.

Disordered misfit [Ca₂CoO₃][CoO₂]_1.62 structure revisited via a new intrinsic modulation

A new structural model has been determined for the [Ca₂CoO₃][CoO₂]_1.62 misfit lamellar cobalt oxide compound. It can be described with a new commensurable modulation implied by a partial ordering within the [CoO] layer.

Structures of 6H perovskites Ba₃CaSb₂O₉ and Ba₃SrSb₂O₉ determined by synchrotron X-ray diffraction, neutron powder diffraction and ab initio calculations

Ba₃CaSb₂O₉ and Ba₃SrSb₂O₉ are 6H perovskites with monoclinic C2/c and triclinic symmetries, respectively. Their distortions from the ideal hexagonal P6₃/mmc symmetry of Ba₃MgSb₂O₉ are due to the increasing size of the alkaline-earth cation in the perovskite B site from Mg²⁺ to Ca²⁺ to Sr²⁺.

KSm(MoO₄)₂, an incommensurately modulated and partially disordered scheelite-like structure

The new incommensurately modulated scheelite-like structure of KSm(MoO₄)₂ with partially disordered K and Sm has been refined by the Rietveld method. Anisotropic microstrain line-broadening has been applied to the profile refinement of the powder diffraction measurement. The fit is greatly improved in comparison with standard isotropic line-broadening.

Crystal architecture of R₂SnS₅ (R = Pr, Nd, Gd and Tb): crystal structure relationships in chalcogenides

The crystal architecture of R₂SnS₅ (R = Pr, Nd, Gd and Tb) is discussed.

Sr_4 + nMn³⁺₄Mn⁴⁺_nO_10 + 3n: a new homologous series of oxygen-vacancy-ordered perovskites built from Mn³⁺O₅ pyramids and Mn⁴⁺O₆ octahedra

A new homologous series of oxygen-vacancy-ordered perovskite compounds with the formula SrMnMnO is described. Rules for generating these compounds are given in the form of simple building blocks formed by Mn³⁺O₅ pyramids and Mn⁴⁺O₆ octahedra. Related compounds in the CaMnO_x and LaCuO_x systems have also been identified as members of the proposed series.

Cis/trans isomers of PtX₂L₂ (X = halogen, L = neutral ligand); the crystal structures of two polymorphs of cis-di­chlorobis(di­benzyl sulfido-κS)platinum(II) in the temperature range 100–295 K

The crystal structures of two polymorphs of cis-PtCl₂(Bz₂S)₂ at 295, 250, 200, 150 and 100 K are reported with emphasis on crystal packing. The structural class distribution for cis-PtX₂L₂ (X = halogen, L = neutral ligand) is given together with an analysis of the trans and cis influence in cis/trans-PtCl₂L₂ complexes.

Structure-directing weak phosphoryl XH⋯O=P (X = C, N) hydrogen bonds in cyclic oxazaphos­pholidines and oxazaphosphinanes

Cyclic oxazaphospholidines and oxazaphosphinanes develop linear molecular chains bonded by relatively weak XH⋯O=P interactions (X = C, N); the chains themselves are sometimes weakly linked by CH or other CH⋯O interactions.

Conformations of substituted benzo­phenones

The inclinations of the two aryl rings (ring twists) in a series of 104 benzophenone molecules have been examined. Six new benzophenone structures are incorporated into the study including 2,2′-dihydroxy-4,4′-dimethoxybenzophenone that appears to have the smallest reported twist angle of any substituted benzophenone reported to date.

Molecular and crystalline structure of cyclo­heptane­spiro-3′(4′H)-6′,7′,8′,9′-tetra­hydro­cyclo­hexa[b][1,4]thiazole-2′(5′H)-thione from powder synchrotron X-ray diffraction data

The molecular and crystal structure of a new nitrogen–sulfur pro-ligand used in the design of metal organic compounds with potential applications in inorganic biomimetic catalysis, cycloheptanespiro-3′(4′H)-6′,7′,8′,9′-tetrahydrocyclohexa[b][1,4]thiazole-2′(5′H)-thione, was solved and refined using synchrotron powder X-ray diffraction data.

Pseudopolymorphism of N-acetyl-L-phenylalanine methyl ester

Two pseudopolymorphs of N-acetyl-L-phenylalanine methyl ester were obtained, namely an anhydrous orthorhombic phase and a hemihydrate tetragonal phase. Spontaneous re-crystallization of the anhydrous compound to the hemihydrate is observed in the presence of a trace amount of water.

Deuterated γ-malonic acid: its neutron crystal structure in relationship to other polymorphs of aliphatic di­carboxylic acids

Three complete neutron diffraction datasets have been collected on deuterated malonic acid single crystals, DOOC(CD₂)COOD, above (153 K), just below (56 K) and further below (50 K) the low-temperature phase transition (T_c = 56.5 K). The full structural details, determined from refinements including higher-order displacement tensors, are related to those from other aliphatic dicarboxylic acids subject to polymorphism.

Structures of mono-unsaturated tri­acylglycerols. III. The β-2 polymorphs of trans-mono-unsaturated tri­acylglycerols and related fully saturated tri­acylglycerols

The β-2 crystal structures of a series of saturated and trans-mono-unsaturated triacylglycerols have been solved from high-resolution powder synchrotron diffraction data. Most postulations about the packing of these polymorphs are confirmed.

Structures of mono-unsaturated tri­acylglycerols. IV. The highest melting β′-2 polymorphs of trans-mono-unsaturated tri­acylglycerols and related saturated TAGs and their polymorphic stability

The crystal structures of the β-2 polymorph of a series of mixed-chain saturated and trans-mono-unsaturated triacylglycerols have been solved from high-resolution powder diffraction data. A novel β′-2 polymorph of PSS has been found and its structure has been solved.