High yield synthesis of mixed-metal keggin polyoxoanions in non-aqueous solvents: Preparation of (n-Bu4N)4[PMW11O40] (M = V, Nb, Ta)

The synthesis of (n-Bu4N)4[PMW11O40] (M = V, Nb, Ta) in non-aqueous solvents is described using the lacunary compound (n-Bu4N)4H3[PW11O39] and commercially available VOCl3, NbCl5 and TaCl5. The yield and purity of the product vary depending on the solvent and the presence of base. 183W NMR spectroscopy of the title compounds reveal six resonances in the ratio 2:2:2:1:2:2 (M, Nb, Ta) consistent withtheir formulation as monosubstituted tungstophosphates with the Keggin structure. Their FAB mass spectra display protonated molecular ions in the positive ion mode and monoanionic fragments MOx and MWnOx(n ⪖ 1, x ⪖ n) (M = Nb, Ta) in the negative ion mode.