The anion [AsIII5MoVI4O20(OCH3)]2−: a new heteropolyoxometalate containing an unusual As5O4 chain

The heteropolyoxometalate [HAsIIIAsVMoVMoVI8O34]6− reacts in aqueous solution with an excess of sodium metaarsenite to give a new arsenomolybdate [AsIII5MoVI4O20(OCH3)]2− which crystallize as the tetrabutylammonium salt. The single-crystal X-ray structure analysis reveals a heteropolyoxometalate anion containing an unusual chain of five arsenic atoms linked to each other by bridging oxygen atoms.