H2O2 activation by heteropolyacids with defect structures: the case of gamma-[(XO4)W10O32](n-) (X = Si, Ge, n=8; X = P, n=7)

DFT calculations including relativistic and solvent effects have been carried out for elucidating geometries and energies of tetra-protonated, site-defective, polyoxotungstates with general formula gamma-(XO4)W10O32](n-) [X = Si, Ge, n-8; X=P, n=7). Converging spectroscopic and computational evidence point to a unique role played by the lacunary structure, and allow to address the electronic and structural factors dictating the protonation sites and equilibria of these complexes, as well as their impact on H2O2 activation. In all cases, the evolution of the four terminal W - O functions, bordering the site defect on the polyoxotungstate surface, towards a bis-aquo, bis-oxo structure is preferred over the formation of four terminal hydroxo ligands. Substitution of these W - OH2 functions with peroxo ligands and their involvement in the oxygen transfer to an alkene acceptor is also supported by DFT calculations.