Ligation of Titanium-oxide and {Mo₂} Units for Solar CO₂ Storage

Two Mo-Ti-mixed oxide clusters, TiMo and TiMo, which contain the {Mo₂^V} unit commonly observed in many polyoxomolybdates, were successfully synthesized. The introduction of a {Mo₂^V} dopant into a titanium-oxide cluster (TOC) results in a red shift of the absorption edge, hence leading to a substantial enhancement of visible-light absorption. The band gap electron transition mainly involves the ligand-to-metal charge transfer (LMCT, benzoate-to-Mo) and Mo^V d-d transition. Both clusters show favorable visible-light responsiveness and charge-separation efficiency. Both serve as heterogeneous photocatalysts and exhibit excellent catalytic activity in CO₂/epoxide cycloadditions under very mild conditions. The mechanism study suggests that the catalytically active sites are mainly Mo^V, and the photogenerated electrons and holes are both involved. TiMo exhibits better photocatalytic activity than TiMo, demonstrating the crucial role of the titanium-oxide core, which corresponds to improved light absorption and charge-separation efficiency. Our findings highlight the potential of the {Mo₂^V} unit in constructing Mo-Ti-mixed oxide clusters with interesting topologies and excellent solar-light-harvesting activity.