Twinning and intergrowth of rare earth boride carbides

Metal-atom square nets occur in many rare earth boride carbides and account for their tendency to form twins and intergrown crystals of different phases. The possibilities of structure determinations via X-ray diffraction and electron microscopy on intergrown crystals are discussed.

Investigation of the structure and phase transitions in the novel A-site substituted distorted perovskite compound Na_0.5Bi_0.5TiO₃

Rietveld neutron powder profile analysis of the A-site substituted distorted perovskite compound Na_0.5Bi_0.5TiO₃ (NBT) is reported over the temperature range 5–873 K. Detailed characterization of the phase transition sequence occurring in this compound has been made. The general trends of cation displacements and the deviations of the octahedral network from the prototypic cubic perovskite structure have been established and their systematic behaviour with temperature is reported. The second harmonic generation as a function of temperature has also been made.

Intersubsystem chemical bonds in the misfit layer compounds (LaS)_1.13TaS₂ and (LaS)_1.14NbS₂

High-resolution X-ray scattering experiments provide detailed information on the intersubsystem bonding in (LaS)_1.13TaS₂ and (LaS)_1.14NbS₂. A correlation is revealed between relative positions of the mutually incommensurate subsystems, the displacement modulation and the modulation of the temperature parameters.

Single-crystal study of the m = 2 tubular cobalt oxide, Bi₄Sr₁₂Co₈O_30−δ

A detailed description of the tubular oxide Bi₄Sr₁₂Co₈O_30−δ is given. [Co₄O₁₃] clusters are present and their particular structure is determined; they are one of the basic elements for building [Sr₄Co₄O₁₃]_∞ pillars, well known in this type of phase. A comparison between pillars in the Co and the related Mn tubular oxide, Bi_3.6Sr_12.4Mn₈O_30−δ, is given.

Crystal chemistry of zirconosilicates and their analogs: topological classification of MT frameworks and suprapolyhedral invariants

Zirconosilicates and their MT analogs with the frameworks of M octahedra and T tetrahedra (60 minerals and 34 synthetic phases) were first arranged into 41 topological types using coordination sequences of M and T atoms. A procedure is proposed of hierarchical analysis of MT framework structure organization on three levels (atomic, polyhedral and suprapolyhedral), which is based on the concept of polyhedral microensemble.

A new set of molecular descriptors

A new set of criteria for quantitative analysis of molecular interactions is proposed, which is based on the conceptions of atomic and molecular Voronoi–Dirichlet polyhedra. The set was used to study the influence of steric factors on the stability of complex groups as well as on the presence or absence of agostic contacts in crystal structures of 808 rare-earth π-complexes.

Modified photoreactivity due to mixed crystal formation. I. Three mixed crystals between isostructural cobaloxime complexes

The different rate constants of photoisomerization from the 2-cyanoethyl group to the 1-cyanoethyl group among three mixed cobaloxime complex crystals with the 2-cyanoethyl group and different pyridine derivatives as axial positions are explained well by the volumes of the reaction cavities. The reaction pathway was directly observed since the isomerization in one of the crystals proceeded with retention of the single-crystal form.

Structure prediction as a tool for solution of the crystal structures of metallo-organic complexes using powder X-ray diffraction data

Prediction provides sets of energetically reasonable crystal structures, from which the actual structure may be deduced by recourse to powder X-ray diffraction data. In this manner, structure prediction becomes a powerful tool for structure solution.

Structures of trans-[PtCl₂(PBz₃)₂], trans-[PtI₂(PBz₃)₂], trans-[Pt(NCS)₂(PBz₃)₂]·0.5C₆H₆ and trans-[PdI₂(PBz₃)₂]

The complexes trans-[PtCl₂(PBz₃)₂], trans-[PtI₂(PBz₃)₂], trans-[Pt(NCS)₂(PBz₃)₂] and trans-[PdI₂(PBz₃)₂] have been structurally characterized and the differences or similarities in geometry are analysed by half-normal probability plots and RMS calculations.

Inclusion compounds of a diol host with xylidines: controlled stoichiometries

A series of inclusion compounds of a diol host with a number of xylidine isomers as guests gave rise to various host:guest ratios controlled by crystallization temperatures. The crystal structures were elucidated by X-ray diffraction. Their thermal characteristics, selectivities of enclathration by the host and kinetics of decomposition were measured.

Structure and pseudosymmetry of cholesterol at 310 K

The structure of cholesterol above the (304.8 K) phase transition, previously published in preliminary form, has been fully refined using augmented X-ray data.

Isostructuralism in a series of methylester/methyl­amide derivatives of (R,R)-O,O′-di­benzoyl tartaric acid; inclusion properties and guest-dependent homeotypism of the crystals of (R,R)-O,O′-di­benzoyltartaric acid di­amide

In the series of methylester/N-methylamide derivatives of (R,R)-O,O′-dibenzoyl tartaric acid, which utilize the twofold symmetry site in their crystals, the methylester group shows the ability to mimic the N-methylamide substituent. This leads to static disorder and the isostructuralism phenomenon, as well as to the replacement of N—H⋯O by C—H⋯O hydrogen bonds. The molecules of (R,R)-O,O′-dibenzoyltartaric acid diamide form hydrogen-bond patterns typical for amides, but at the expense of their packing efficiency, which results in a series of homeotypic inclusion compounds.

Chiral versus racemic building blocks in supra­molecular chemistry: tartrate salts of organic di­amines

In salt-type adducts of organic diamines with chiral or racemic tartaric acids, the hard hydrogen bonds can generate sheets, bilayers or three-dimensional frameworks: the supramolecular structures formed by the chiral acid can closely mimic centrosymmetry

Polymorphs and pseudopolymorphs of N,N′-di­thiobisphthalimide

The title compound (I) forms a wide variety of polymorphs and solvates: some of the polymorphs are solvent free, while the solvates may have solvent molecules hydrogen bonded to (I) or simply encapsulated within a framework structure. In some solvates the framework formed by (I) contains continuous channels and solvent molecules may be localized within the channels or intractably disordered within them.

Amino-substituted O⁶-benzyl-5-nitroso­pyrimidines: interplay of molecular, molecular-electronic and supramolecular structures

Highly polarized molecular electronic structures in 2,4,6-trisubstituted-5-nitrosopyrimidines lead to extensive charge-assisted hydrogen bonding.

[Ni(cyclam)(OCOR)₂], a finite molecular complex: hydrogen-bonded supramolecular aggregation in one, two and three dimensions, and coordination polymers in one and two dimensions. Erratum

Erratum to Acta Cryst. (2002), B58, 78–93.

Structurally ferroelectric SrMgF₄. Erratum

Erratum to Acta Cryst. (2002), B58, 34–37.