Two new members of the niobium-substituted polytungstophosphate family based on hexalacunary [H2P2W12O48](12-) building blocks

Two structurally novel nanoscale clusters [{Nb-6(O-2)(4)P2W12O57}(2)](20-) (1) and [{P2W12Nb7O63(H2O)(2)}(4)-{Nb4O4(OH)(6)}](30-) (2) were synthesized under specific reaction conditions. Cluster 1 displays an unprecedented di-Nb O Nb-linked Wells-Dawson dimer, whilst cluster 2 contains the highest nuclearity niobium containing heteropolyoxometalate to date. Furthermore, P-31 and W-183 NMR spectra indicate that the polyanion 2 remains stable in solution. The photocatalytic activities of the respective salts 1a, 2a and K-6[alpha-P2W18O62]center dot 14H(2)O for H-2 evolution were evaluated. The enhanced photocatalytic activity of 2a may be attributed to the incorporation of Nb into the polyoxotungstate framework.