Cluster approach to the Ti₂Ni structure type

The Ti₂Ni structure type emerges as a consequence of the competition between face-centred cubic translational and icosahedral-face orientational ordering of the 16(c) first coordination clusters along regular tetrahedron edge directions.

Review of polyhedral distortions as a multi-scale minimization of the electric polarization and their correlations with physical properties

The Jahn–Teller and non-Jahn–Teller distortions are reviewed within the same context. The origin and the influence of the magnitude of polyhedral elongations on physical properties are discussed for the superconductor cuprates and the CMR manganites.

Structure model for the τ(μ) phase in Al–Cr–Si alloys deduced from the λ phase by the strong-reflections approach

Two closely related quasicrystal approximants are expected to have similar crystallographic structure-factor amplitudes and phases for the strong reflections so the structure of an unknown quasicrystal approximant can be solved from a related known quasicrystal approximant. This strong-reflections approach is applied to the new τ(μ)-AlCrSi phase and a structure model of τ(μ) is deduced from the structure of the related λ-Al₄Mn phase.

Systematic prediction of new ferroelectrics in space group R3. I

Eighteen of a total 52 inorganic structure types with R3 symmetry are shown to satisfy the criteria for ferroelectricity. As many as 46% of those initially reported in the space group R3, 35% of those currently assigned, most likely exhibit higher symmetry.

Structural disorder of a new zeolite-like lithosilicate, K_2.6Li_5.4[Li₄Si₁₆O₃₈]·4.3H₂O

Hydrothermal synthesis and structural analysis of the zeolite-like lithosilicate RUB-30 (K_2.6Li_5.4[Li₄Si₁₆O₃₈]·4.3H₂O) are reported. Two different structure types are proposed based on the observation of unusual superstructure reflections and diffuse streaks.

Getting more out of an incommensurately modulated structure: the example of K₅Yb(MoO₄)₄

Based on the superspace approach we present a method to generate a family of modular structures, provided that one of its members exhibits an incommensurately modulated (i.e. aperiodic) structure. This approach, which relies on the variation of the modulation vector q, is illustrated with the generation of the K₅Yb(MoO₄)₄ family and the analysis of its temperature-dependent phase transformations.

Structures of the cation-deficient perovskite Nd_0.7Ti_0.9Al_0.1O₃ from high-resolution neutron powder diffraction in combination with group-theoretical analysis

The room-temperature structure of the cation-deficient perovskite, Nd_0.7Ti_0.9Al_0.1O₃, with layered ordering of cations/vacancies on the A-site, involves octahedral tilting around two axes. Tilting around the axis parallel to the direction of the layered cation/vacancy ordering disappears above ca 750 K, the only tilt persisting at higher temperature being about a single axis perpendicular to this direction.

Temperature-resolved study of three [M(M′O₄)₄(TBPO)₄] complexes (MM′ = URe, ThRe, ThTc)

Crystals of the three actinide complexes [M(M′O₄)₄(TBPO)₄], where MM′ = URe, ThRe, ThTc, respectively, studied between 293 and 100 K, show a number of reversible crystal-to-crystal phase transitions. The increase of order and differences in conformations of the complexes seen at the lower temperatures arise from a combination of the freezing of the ⁿBu groups, the differing packing constraints of the various space groups and the network of weak C—H⋯O intra- and intermolecular hydrogen bonds.

Absence of halogen⋯halogen interactions in chlorotri­methylsilane polymorphs

A new β-phase of (CH₃)₃SiCl obtained by pressure freezing is strikingly similar to the α-phase obtained by cooling. In neither of these structures are Cl⋯Cl contacts shorter than 4.9 Å.

Pressure-frozen benzene I revisited

The crystal structure of benzene in phase I, space group Pbca, has been determined at 0.30, 0.70 and 1.10 GPa, and 296 K. Short H⋯C contacts explain the exceptional resistance of benzene to polymerization.

Structure of N⁶-furfurylaminopurine (kinetin) di­hydrogenphosphate

The crystal structure of kinetin dihydrogenphosphate has been determined at various temperatures providing evidence for the polymorphic phase transition at 291.1 K. The dynamic equilibrium between the different tautomeric forms of the adenosine residue is observed in the low-temperature phase.

3,5-Dihalo-4-hydroxybenzo­nitriles: isostructures, polymorphs and solvates

Seven 3,5-dihalo-4-hydroxybenzonitrile compounds form chains as a consequence of OH⋯NC interactions. In the case of the bromo and iodo compounds the chains assemble into layers through X⋯X contacts with two-dimensional isostructurality among the compounds.

Five varieties of hydrogen bond in 1-formyl-3-thiosemicarbazide: an electron density study

The crystal structure of 1-formyl-3-thiosemicarbazide was re-elucidated at room temperature, 100 and 90 K, and all the intermolecular interactions were characterized by the topological analysis of the electron density.

Monitoring structural transformations in crystals. 8. Monitoring molecules and a reaction center during a solid-state Yang photocyclization

Changes in the crystal structure were monitored throughout the course of an intramolecular single-crystal to single-crystal Yang photocyclization reaction by means of X-ray diffraction. The results are compared with analogous data for intermolecular solid-state reactions.

Relationship between structure and photoinitiating abilities of selected bromide salts of 2-oxo-2,3-di­hydro-1H-imidazo[1,2-a]pyridine (IMP): influence of the solvent and the substitution in benzaldehyde on the course of its reaction with IMP

Structural X-ray and ¹H NMR investigations as well as DFT calculations provide evidence that the course of the reaction of substituted benzaldehyde with 2-oxo-2,3-dihydro-1H-imidazo[1,2-a]pyridinium cation is different in protic and polar aprotic solvents, and depends on the character and the position of the substituent in the benzaldehyde. Both theory and experiment point to the benzylidene derivatives as possessing higher photoinitiating ability than their benzyl analogues.

Polymorphs of p-nitrophenol as studied by variable-temperature X-ray diffraction and calorimetry: comparison with m-nitrophenol

Variable-temperature X-ray diffraction and differential scanning calorimetry experiments have been performed for p-nitrophenol polymorphs. Crystal structures, interactions and thermodynamics in the polymorphs of p-nitrophenol have been compared with those corresponding to the polymorphs of m-nitrophenol.

Neutron diffraction analysis of deuterium transfer in chiral β-thiolactam formation in the crystalline state

The neutron diffraction analysis of the photoisomerization of a partially deuterated achiral α,β-unsaturated thioamide to form a chiral β-thiolactam in the crystalline state revealed the direction and the process of deuterium transfer by determination of an absolute configuration of a produced chiral methylene, —C^*HD—.

Structures and the oxygen deficiency of tetragonal and monoclinic zirconium oxide nanoparticles

Synchrotron X-ray powder diffraction work demonstrated that there existed two phases of oxygen-deficient tetragonal ZrO_2 − δ [average particle size: 11 ± 2 nm, δ = 0.031 (7)] and monoclinic ZrO₂ (average particle size: 24 ± 4 nm) in a nano-sized zirconium oxide sample. MEM electron-density distribution was investigated for the tetragonal ZrO_2 − δ phase.

Hydrated metal(II) complexes of N-(6-amino-3,4-di­hydro-3-methyl-5-nitroso-4-oxopyrimidin-2-yl) derivatives of glycine, glycylglycine, threonine, serine, valine and me­thionine: a monomeric complex and coordination polymers in one, two and three dimensions linked by hydrogen bonding. Corrigendum

Correction to data collection details for compound (VIII) in Acta Cryst. (2004). B60, 46–64.

Notes for authors 2006