New type of heteropoly anion. Tetramolybdo complexes of dialkyl- and diarylarsinates

Synthesis and characterization of several salts of the heteropoly complexes (R2AsMo4O14(OH))(2-), R = CH3, C2H5, C6H5, are described. These are some of the first examples of stable organic derivatives of heteropoly anions. The crystal structure of (CN3H6)2((CH3)2AsMo4O14(OH))-H2O shows the anion to consist of a compact cluster of edge- and face-shared MoO6 octahedra capped by the (CH3)2AsO2 tetrahedron. The new complexes have two other unusual features. First, a uniquely low charge (2-) for a polyanion that is stable in aqueous solution (pH 2-6) and second, a proton characterized by nmr and ir, that appears to be localized on the oxygen atom that bridges the four molybdenums.