Polyoxometalates from heteropoly "brown" precursors. A new structural class of mixed valence heteropolytungstates, [(XO4)W3IVW17VIO 62Hx]n- - Dickman, M.H.; Ozeki, T.; Evans Jr., H.; Rong, C.; Jameson, G.B.; Pope, M.T. (Journal of the Chemical Society, Dalton Transactions, 2000)