Anderson-type heteropolyanions of molybdenum(VI) and tungsten(VI)

The previously reported preparation of some Anderson-type molybdopolyanions containing divalent metal ions (Zn, Cu, Co or Mn) as a heteroatom has been reinvestigated. The molybdopolyanions of Zn(II) and Cu(II) were confirmed, although the Cu(II) polyanion was not stable and could not be recrystallized. On the other hand, the polyanions of Co(II) and Mn(II) could not be reproduced. Another type of heteropoly compound, [X(H2O)6-x(Mo7O24)]4− [X = Cu(II), Co(II) or Mn(II)], was isolated as solids, which are not stable thermally. The mixed-type Anderson polyanions, [Ni(II)Mo6-xWx,O24H6]4−, which have been questioned as mixtures of species with different x values, were also reinvestigated using IR, UV absorption and MCD spectra. They are single species, but not mixtures, although some positional isomers may be present for the compounds where x = 2-4. The possibility of oxidation of the heteroatom with the Anderson structure maintained was examined. The oxidation of [Ni(II)Mo6O24H6]4− by the S2O2−8 ion in aqueous solution gave the Waugh-type [Ni(IV)Mo9O32]6− polyanion, whereas the oxidation of [Ni(II)W6O24H6]4− gave no heteropoly compound.