Synthesis and structure of the novel anion [AsMo6O15(OH)(3)(SO4)(3)](6-), first example of a reduced molybdo-sulphate cluster

A novel anion derived from the Anderson structure has been obtained in aque ous acid solution by condensation of three pairs of edge-sharing molybdenum octahedra around a central arsenite. This association forms a hexanuclear ring of Ms(V) with three external sulphate groups bridging the binuclear mo lybdenum units. This compound cystallizes in the presence of alkaline ions and its orthorhombic structure was solved by single crystal X-ray diffracti on [Cmca, a = 24.3189(3) Angstrom, b = 12.4454(1) Angstrom, c = 26.9211(3) Angstrom, V = 8147,9 Angstrom(3)] from 4 277 unique reflections [I greater than or equal to 2 sigma(I)], R-1 = 0.0471 and R-w(2) = 0.1429. The solid i s a three-dimensional network built up from cluster anions strongly connect ed to alkaline ions via ionic links. This soluble compound, presenting labi le peripheral sulphates, is predisposed for exchanges to build new anions. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevi er SAS.