{Mo2O2S2}2+-directed synthesis of a polyoxotungstoarsenate(III). Structure and 183W NMR studies of the [α-AsW9O33)3(WO(OH2))3 (Mo2O2S2(H2O)4)]13- anion

Reaction of the [Mo2O2S2(OH2)(6)](2+) aqua cation and [WO4](2-) with the trivacant ion [alpha-B-AsW9O33](9-) in acidic condition (pH = 1.4) leads to the formation of a (Mo2S2O2)-supported polyoxotungstate. The mixed salt NMe4K12[(alpha-AsW9O33)(3)(WO(OH2))(3)(Mo2O2S2 (H2O)(4))]center dot 20H(2)O (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 alpha-(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 W-183 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. (C) 2011 Published by Elsevier Masson SAS on behalf of Academie des sciences.