polyoxometalates

Polyoxometalates are large inorganic anions formed via condensation-addition reactions of simple oxoanions of early transition elements such as V, Mo and W.

e.g.      7 MoO₄^2- + 8 H⁺   =     [Mo₇O₂₄]^6- + 4 H₂O        an isopolymolybdate

            12 WO₄^2- + SiO₃^2- + 22 H⁺   =     [SiW₁₂O₄₀]^4- + 11 H₂O     a heteropolytungstate