October 2013 issue
Cover illustration: Reduction of volumes of the voids in the crystal structures of DL-alanine and L-alanine on application of 6 GPa of pressure. Yellow voids are shown within the ball-and-stick structure models. The molecules as well as the topologies and symmetries of their packings are preserved over the whole pressure range of 0-6 GPa. See Fig. 4 in Tumanov & Boldyreva [(2012), Acta Cryst. B68, 412-423].
Acta Cryst. (2013). B69, 419-425
The bond-valence model used previously only for common ionic solids was adapted to (TM)6-chalcohalides, Mx(TM)6Ly (TM = transition metal in the cluster: Nb, Mo, W and Re; L = chalcogen and/or halogen ligands; M = counter-cation). This paper is devoted to the strains around M cations as one of the sources of the valence violations in cluster compounds.
Acta Cryst. (2013). B69, 426-438
The bond-valence model used previously only for common ionic solids was adapted to (TM)6-chalcohalides, Mx(TM)6Ly (TM = transition metal in the cluster: Nb, Mo, W and Re; L = the chalcogen and/or halogen ligands; M = counter-cation). This paper gives a detailed description of the matrix effect.
Acta Cryst. (2013). B69, 439-445
In this work we discuss the concept of tolerance factors for pyrochlores and related structures. We proposed a new form to calculate the tolerance factors for these structures and correlated the tolerance factor with some physical properties.
Acta Cryst. (2013). B69, 446-456
Effect of lone-pair stereoactivity on polyhedral volume and structural flexibility: application to TeIVO6 octahedra
The volumes of 40 TeIVO6 coordination polyhedra studied are 10.3–23.7 Å3, compared with the 12.83 Å3 expected for a regular octahedron. The anions lie close to a spherical surface whose radius varies with the degree of lone-pair localization; 95% of the variation in polyhedron volume is due to a change in both sphere radius and the uniformity of oxygen distribution over the sphere.
Acta Cryst. (2013). B69, 457-464
By the use of Rmerge factors on Friedel-difference intensities and the D-Patterson function, the structure of the intermetallic compound TiGePt is shown to be non-centrosymmetric.
Acta Cryst. (2013). B69, 465-473
X-ray diffraction: a powerful tool to probe and understand the structure of nanocrystalline calcium silicate hydrates
The structure of nanocrystalline calcium silicate hydrates (C-S-H) was studied using X-ray diffraction and literature data. It is proposed that C-S-H of Ca/Si ratio ranging between ∼ 0.6 and ∼ 1.7 can be described as nanocrystalline tobermorite affected by turbostratic disorder. The broadening and shift of the basal reflection positioned between ∼ 13.5 and ∼ 11.2 Å (depending on the Ca/Si ratio) arises from nanocrystallinity and possibly from an interstratification phenomenon.
Acta Cryst. (2013). B69, 474-479
Polytypes and twins in the diamond–lonsdaleite system formed by high-pressure and high-temperature treatment of graphite
Twins and polytypes in diamond and lonsdaleite nanoparticles were studied by high-resolution transmission electron microscopy, and the mechanisms of their appearance were proposed. Coherent and incoherent twin boundaries were observed in nanoparticles.
Acta Cryst. (2013). B69, 480-489
Two- and three-dimensional assembled structures constructed from amidate-bridged paddlewheel complexes with group 6 oxometallate ions
Monocationic amidate-bridged dimetal complexes reacted with dianionic group 6 metallate ions to form two-dimensional square-sheet or three-dimensional diamondoid structures depending on the alkyl group of the amidate ligands.
Acta Cryst. (2013). B69, 490-495
The three-dimensional structure of a hydrothermally synthesized new iron citrate compound, [Fe(H2cit)(H2O)]n, which is built up from the chains of corner-sharing FeO6 octahedra that are further connected through citrate anions, was solved by single-crystal X-ray diffraction. Thermal and magnetic properties of material were investigated by TG, HT-XRD, Mossbauer and magnetic susceptibility analyses.
Acta Cryst. (2013). B69, 496-508
C6H4S2AsCl: description and interpretation of an incommensurately modulated molecular crystal structure
A modulated molecular structure has been refined in (3 + 1)-dimensional superspace and also as two different Z′ = 17 commensurate approximations. The incommensurate modulation can be understood as relieving packing problems in several different directions.
B-IncStrDB reference: 8082ERT5uS
Acta Cryst. (2013). B69, 509-513
The crystal structures of two modifications of (1R,3S)-dimethyl 2-oxocyclohexane-1,3-dicarboxylate were solved simultaneously from a single crystal using X-ray diffraction.
Acta Cryst. (2013). B69, 514-523
Hydrogen-bond landscapes, geometry and energetics of squaric acid and its mono- and dianions: a Cambridge Structural Database, IsoStar and computational study
Hydrogen bonds involving squaric acid and its monoanion are similar in length and strength to those made by carboxylic acid donors and carboxylate COO− acceptors, while hydrogen bonds accepted by the squarate dianion are somewhat stronger. The mono- and dianions have been added as new central groups to the Cambridge Crystallographic Data Centre's (CCDC) IsoStar knowledge base of intermolecular interactions.
Acta Cryst. (2013). B69, 524-526