A new class of homogeneous visible-light photocatalysts: molecular cerium vanadium oxide clusters.

Abstract

The first systematic access to molecular cerium vanadium oxides is presented. A family of structurally related, di-cerium-functionalized vanadium oxide clusters and their use as visible-light-driven photooxidation catalysts is reported. Comparative analyses show that photocatalytic activity is controlled by the cluster architecture. Increased photoreactivity of the cerium vanadium oxides in the visible range compared with nonfunctionalized vanadates is observed. Based on the recent discovery of the first molecular cerium vanadate cluster, (nBu4 N)2 [(Ce(dmso)3 )2 V12 O33 Cl]⋅2 DMSO (1), two new di-cerium-containing vanadium oxide clusters [(Ce(dmso)4 )2 V11 O30 Cl]⋅DMSO (2) and [(Ce(nmp)4 )2 V12 O32 Cl]⋅NMP⋅Me2 CO (3; NMP=N-methyl-2-pyrrolidone) were obtained by using a novel fragmentation and reassembly route. Pentagonal building units {(V)M5 } (M=V, Ce) reminiscent of "Müller-type" pentagons are observed in 2 and 3. Compounds 1-3 feature high visible-light photooxidative activity, and quantum efficiencies >10 % for indigo photooxidation are observed. Photocatalytic performance increases in the order 1<3<2. Mechanistic studies show that the irradiation wavelength and the presence of oxygen strongly affect photoreactivity. Initial findings suggest that the photooxidation mechanism proceeds by intermediate formation of hydroxyl radicals. The findings open new avenues for the bottom-up design of sunlight-driven photocatalysts.