Chemistry of hexanuclear rhenium chalcohalide clusters.

A general method for accessing the solution chemistry of cluster constituents of solid phases exhibiting extended cluster frameworks is demonstrated. The approach is described in terms of simple metal−anion (M−X) frameworks and involves the formal incorporation of AX into a parent structure, resulting in termination of the X bridges between M centers while balancing the charge of the resulting framework with external cations A. The new structures obtained display frameworks of reduced connectedness and dimensionality. By replacing single metal centers with multinuclear cluster cores, this dimensional reduction approach is extended to cluster-containing frameworks. Its utility is demonstrated via application to the phases Re6Q8Cl2 (Q = S, Se), exhibiting three- and two-dimensional arrays of face-capped octahedral [Re6(μ3-Q)8]2+ cluster cores covalently linked through extremely tight Re2Q2 rhombic interactions of the type common to many intractable cluster frameworks (including the Chevrel phases). Stoichio...

A Solid-State Route to Molecular Clusters: Access to the Solution Chemistry of [Re6Q8]2+ (Q = S, Se) Core-Containing Clusters via Dimensional Reduction

Metal chalcogenide cluster chemistry

The mixed tellurium/selenium Re6 clusters [NMe4]4[Re6(Te8-nSen)(CN)6] (n = 0−8) have been prepared from the reactions of Re6Te15 with the appropriate stoichiometry of NaCN and Se at 600 °C, followed by cation exchange with NMe4Br. A typical anion comprises an Re6 octahedron with its eight faces capped by μ3-chalcogen atoms to form a pseudocube, and each Re atom has a terminal cyanide ligand. These anions have essentially idealized cubic symmetry. In the [Re6Te8(CN)6]4- anion, Re−Re bond distances range from 2.673(1) to 2.690(1) A and Re−(μ3-Te) distances range from 2.683(1) to 2.705(1) A. In the [Re6Se8(CN)6]4- anion the Re−Re and Re−(μ3-Se) distances range from 2.622(2) to 2.638(2) A and 2.520(3) to 2.550(3) A, respectively. The “[Re6Te4.34Se3.66(CN)6]4-” anion, with disordered Se/Te positions, displays intermediate bond distances with Re−Re distances ranging from 2.653(1) to 2.665(1) A and Re−(μ3-Q) (Q = Se, Te) distances ranging from 2.581(1) to 2.673(1) A. Whereas single-crystal X-ray diffraction resu...

Cocrystallized Mixtures and Multiple Geometries: Syntheses, Structures, and NMR Spectroscopy of the Re6 Clusters [NMe4]4[Re6(Te8-nSen)(CN)6] (n = 0−8)

The state-of-the-art and prospects of the development of chemistry of chalcogenide clusters of Group 5–7 metals of the Periodic Table are discussed. The main structural types, methods of synthesis, the reactivity and possible applications of vanadium, niobium, tantalum, chromium, molybdenum, tungsten and rhenium chalcogenide clusters with nuclearity of three and larger are considered.

Chalcogenide clusters of Group 5–7 metals

Nouveaux thiochlorures de molybdène(II): Mo6Cl10Y (Y = S, Se, Te): Structure et propriétés magnétiques et électriques

Rhenium octahedral clusters: Characterization of Re6Se4Cl10 and the parent compound Re6Br10

Compounds with clusters of molybdenum or rhenium: Structure and dielectric behaviour

On propose de completer, dans le cas d'un ferroelectrique du type BaTiO3, l'expression de l'enthalpie libre, pour tenir compte de facteurs propres aux domaines de polarisation: on en deduit une formule reliant la temperature de transition para-ferroelectrique a un parametre caracteristique de cette structure en domaines. Les temperatures generalement donnees pour BaTiO3 correspondraient alors a des domaines de dimensions moyennes superieures a 0,2 μm.



Supplementary terms, related to the domain structure, are introduced into the free energy expression for a ferroelectric of the perovskite type. Formulae are then derived for the associated paraferroelectric transition-temperature dependence. Unusually high values for this temperature (e.g. >135 °C) are predicted for domains less than 0.2 μm in size.

Influence de l'organisation en domaines du titanate de baryum sur sa température de transition

Relations are established between the experimental data epsilon *( omega ) obtained in a limited frequency domain and the first order moments of the distribution function of dielectric relaxation times.

http://iopscience.iop.org/article/10.1088/0022-3719/13/18/015/pdf

F. Le Traon

Papers

Nouveaux thiochlorures de molybdène(II): Mo6Cl10Y (Y = S, Se, Te): Structure et propriétés magnétiques et électriques

Rhenium octahedral clusters: Characterization of Re6Se4Cl10 and the parent compound Re6Br10

Compounds with clusters of molybdenum or rhenium: Structure and dielectric behaviour

Influence de l'organisation en domaines du titanate de baryum sur sa température de transition

Principal moments of the distribution function of relaxation times deduced from experimental plots of the dielectric permittivity versus frequency