Ligation of Titanium-oxide and {Mo 2 } Units for Solar CO 2 Storage.

Two Mo-Ti-mixed oxide clusters, Ti 6 Mo 4 and Ti 4 Mo 4 , which contain the {Mo 2 V } unit commonly observed in many polyoxomolybdates, were successfully synthesized. The introduction of a {Mo 2 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 CO 2 /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. Ti 6 Mo 4 exhibits better photocatalytic activity than Ti 4 Mo 4 , 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 {Mo 2 V } unit in constructing Mo-Ti-mixed oxide clusters with interesting topologies and excellent solar-light-harvesting activity.