In‐Situ Growth of Metallocluster Inside Heterometal‐Organic Cage to Switch Electron Transfer for Targeted CO₂ Photoreduction

Construction of metal-organic cages (MOCs) with internal modifications is a promising avenue to build enzyme-like cavities and unlocking the mystery of highly catalytic activity and selectivity of enzymes. However, current interests are mainly focused on single-metal-node cages, little achievement has been expended to metallocluster-based architectures, and the in situ endogenous generation of metal clusters. Herein, based on the hard-soft-acids-bases (HSAB), the metallocluster-based heterometallic MOC (Cu₃VMOP) constructed of [Cu₃OPz₃]⁺ and [V₆O₆(OCH₃)₉(SO₄)(CO₂)₃]^2- clusters was obtained by one-pot method. In addition, Cu₄I₄ was generated in situ in the cage to form Cu₄I₄@Cu₃VMOP by the coordination-driven hierarchical self-assembly strategy. As catalysts for CO₂ reduction, Cu₃VMOP produces HCOOH and CH₃COOH as the main reduction product with yield of CH₃COOH up to 0.9 mmol g^-1, ranking among the highest value of reported materials, whereas Cu₄I₄@Cu₃VMOP exhibited targeted CO₂-to-HCOOH conversion with 100 % formic acid selectivity and the yield outperforms that of Cu₃VMOP by 5 fold. Theoretical calculations and femtosecond time-resolved transient absorption reveal that endogenous Cu₄I₄ not only regulates orbital arrangements and enhances localized electron states to generate a long-lived charge-separated state, but also raises *CO coupling energy barrier, resulting in the targeted conversion of CO₂ to formic acid.