Syntheses, Structural Characterization, and Catalytic Properties of Di- and Trinickel Polyoxometalates

The syntheses, structural characterization, and catalytic properties of two different nickel-containing polyoxometalates (POMs) are presented. The dinickel-containing sandwich-type POM [Ni2(P2W15O56)2]20– (Ni2) exhibits an unusual αααα geometry. The trinickel-containing Wells–Dawson POM [Ni3(OH)3(H2O)3P2W16O59]9– (Ni3) shows a unique structure where the [α-P2W15O56]12– ligand is capped by a triangular Ni3O13 unit and a WO6 octahedron. Ni3 shows a high catalytic activity for visible-light-driven hydrogen evolution, while the activity for Ni2 is minimal. An analysis of the structures of multinickel-containing POMs and their hydrogen evolution activity is given.