Polyoxometalate Complexes of Anatase-Titanium Dioxide Cores in Water

Polyoxometalate (POM) cluster anions are shown to serve as covalently coordinated ligands for anatase-TiO₂ nanocrystals, giving isolable assemblies uniquely positioned between molecular macroanions and traditional colloidal nanoparticles. Na⁺ salts of the water-soluble polyanionic structures are obtained by reacting amorphous TiO₂ with the 1nm lacunary ion, Na₇[α-XW₁₁O₃₉] (X=P⁵⁺), at 170 °C, after which an average of 55 α-PW₁₁O₃₉^7- clusters are found as pentadentate ligands for Ti^IV ions covalently linked to 6nm single-crystal anatase cores. The attached POMs are reversible electron acceptors, the reduction potentials of which shift in a predictable fashion by changing the central heteroatom, X, directly influencing a model catalytic reaction. Just as POM cluster anions control the reactivities of metal centers in molecular complexes, directly coordinated POM ligands with tunable redox potentials now provide new options for rationally controlling the reactions of semiconductor nanocrystals. Redox-active ligands for TiO₂: Polyoxometalate (POM) electron acceptors serve as covalently coordinated inorganic ligands for anatase-TiO₂ nanocrystals, giving assemblies positioned between molecular macroanions and traditional colloidal nanoparticles. The POM ligands have tunable redox potentials, providing options for controlling reactions of soluble metal oxide semiconductor nanocrystals.