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This paper deals with the electrochemical properties of three iso-structural compounds of general formula [SiW$_{10}$ O$_{36}$(M$_{2}$O$_{2}$E$_{2}$)]$^{6-}$ (M $=$ Mo or W; E $=$ S or O). A first part is focused on their electrochemical behaviors in aqueous medium. A second part concerns the electrocatalytic properties of these compounds in aqueous medium and the preparation of modified glassy carbon electrodes through a layer-by-layer methodology. This method allowed preparing a multilayer system, which was applied to the electroanalysis of iodate anions in aqueous medium with a limit detection of $6.2~\mu \mbox {M}$.

Host–guest assemblies open up opportunities for developing novel functional CLUSPOM multicomponent systems based on transition metal clusters (CLUS), polyoxometalates (POMs) and macrocyclic organic ligands. In water–ethanol solution γ-cyclodextrin (γ-CD) interacts with halide metal clusters [M6Cl14]2– (M = Mo, W) to form sandwich-type structures. The supramolecular association between the clusters and CDs, however, remains weak in solution, and the interactions are not strong enough to prevent the hydrolysis of the inorganic guest. Although analysis of the resulting crystal structures reveals inclusion complexation, 1H NMR experiments in solution show no specific affinity between the two components. The luminescent properties of the host–guest compounds in comparison with the initial cluster complexes are also studied to evaluate the influence of CD. [ABSTRACT FROM AUTHOR]

Abstract: Reaction of the [Mo2O2S2(OH2)6]2+ aqua cation and [WO4]2− with the trivacant ion [α-B-AsW9O33]9− in acidic condition (pH=1.4) leads to the formation of a {Mo2S2O2}-supported polyoxotungstate. The mixed salt NMe4K12[(α–AsW9O33)3(WO(OH2))3(Mo2O2S2(H2O)4)]•20H2O (noted TMAK 12 –1) has been obtained as single crystals and structurally characterized by X-ray diffraction analysis. The structural analysis of TMAK 12 -1 reveals a molecular polyoxotungsto-arsenate (III) framework consisting of three α-{AsW9O33} subunits mutually linked by three {O=W-OH2}4+ groups. The resulting triangular arrangement delimits a large “open-space”, lined on the periphery by six terminal oxygen atoms. The central cavity is partially filled by a single {Mo2O2S2(OH2)4}2+ which spans two {AsW9O33} subunits. Furthermore, three potassium ions have been located, one being embedded within the central cavity and the other two, symmetrically distributed at the periphery of the central cavity. In the solid state, two anions 1 interact through hydrogen bonds and ionic contacts to give a large dimeric arrangement bordered by two TMA+ cations. 1 has been characterized in solution (Li+ salt) by its 183W NMR spectrum which contains 16 lines in agreement with the C s idealized symmetry assumed for the isolated anion 1. Infrared data and elemental analysis are also supplied. [Copyright &y& Elsevier]

Abstract: The self-condensation of the [Mo2O2E2]2+ precursors is at the origin of a family of discrete cyclic species. The condensation can be performed in the presence or not of guest species. With E=O, the resulting cycles delimit an anionic open cavity, which can be filled by neutral polar molecules such as aquo ligands, or by alkaline cations. With E=S, the resulting cycles delimit a cationic cavity, which can be filled with neutral molecules, or anions like halides or more sophisticated groups like caboxylates. The flexibility of the rings is at the origin of striking host–guest properties: the symmetry and the nuclearity of the inorganic backbone are directed by the size and shape of the encapsulated guest. The metal coordination versatility confers to the ring unusual dynamic properties. In the solid state, molecular rings arrange in striking 3-D networks in which alkaline cations organize in pillars or layers decorated with anionic rings. The control of the partial occupancy of the cationic pillars permits to synthesize very good ionic conductors. To cite this article: F. Sécheresse et al., C. R. Chimie. 8 (2005) . [Copyright &y& Elsevier]