Cr-Ti Mixed Oxide Molecular Cages: Synthesis, Structure, Photoresponse, and Photocatalytic Properties.

The solvothermal reaction of titanium isopropoxide and chromate in the presence of benzoate produced two novel host-guest clusters encapsulating Cs + or H 3 O + , (H 3 O)@Ti 7 Cr 14 and Cs@Ti 7 Cr 14 . The most remarkable feature is that the Ti 7 O 7 ring is concentrically embraced by a Cr 14 O 14 ring to form a rigid Ti 7 Cr 14 host. ESI-MS and 133 Cs NMR revealed that the overall framework structures are preserved, whereas the benzoate ligands on the two clusters may be labile in solutions. Both (H 3 O)@Ti 7 Cr 14 and Cs@Ti 7 Cr 14 exhibit good UV-vis light-responsive properties and photocatalytic activities, with absorption edges extending up to 780 nm. Cs@Ti 7 Cr 14 is an effective visible-light-responsive photocatalyst in both the heterogeneous methylene dye degradation and homogeneous CO 2 cycloaddition reaction under mild conditions like room temperature and 1 bar of CO 2 . According to the mechanism studies, Cs + , as a rigid guest, can significantly improve the photogenerated charge separation efficiency of the Ti 7 Cr 14 host, thereby improving its interface charge separation properties, photocurrent, and photocatalytic activities. Our findings not only provide new members of heterometallic titanium oxide clusters to enrich the metal oxide cluster family but also open up new possibilities for their photoresponses, which may play an important role in solar energy harvesting for sustainable chemistry.