Electronic Structure and CO2 Reactivity of Group IV/V/VI Tetraperoxometalates

Tetraperoxo metal complexes are a category of dioxygen compounds with novel properties. One of their underconsidered applications is in direct air capture (DAC) reactions, whose study is of great interest in order to slow the effects of climate change. Through computational modelling, the present work considers a family of tetraperoxometalate complexes of the form [M(O2)4]^x- that capture atmospheric CO2 to produce [MO(O2)2(CO3)]^x- and O2. This reaction was experimentally documented with vanadium and serves as a model for analogous reactions with Group IV (x = -4; M = Ti, Zr, Hf), Group V (x = -3; M = V, Nb, Ta), and Group VI (x = -2; M = Cr, Mo, W) metal centers. Descriptors from density-functional theory (DFT) calculations--including optimized structures, partial charges, and frontier orbital interactions--provide rationalization for predicted differences in reactivity. Of the nine complexes studied, [Ti(O2)4]^4- and [W(O2)4]^2- respectively represent the most and least efficient DAC reagents from their differing abilities to stabilize a bidentate peroxycarbonate (CO4^2-) intermediate in the proposed reaction mechanism.