Photoelectron Spectroscopy of Doubly and Singly Charged Group VIB Dimetalate Anions:  M₂O₇^2-, MM‘O₇^2-, and M₂O₇^- (M, M‘ = Cr, Mo, W)

We produced both doubly and singly charged Group VIB dimetalate speciesM₂O₇^2-, MM‘O₇^2-, and M₂O₇^- (M, M‘ = Cr, Mo, W)using two different experimental techniques (electrospray ionization for the doubly charged anions and laser vaporization for the singly charged anions) and investigated their electronic and geometric structures using photoelectron spectroscopy and density functional calculations. Distinct changes in the electronic and geometric structures were observed as a function of the metal and charge state. The electron binding energies of the heteronuclear dianions MM‘O₇^2- were observed to be roughly the average of those of their homonuclear counterparts (M₂O₇^2- and M‘₂O₇^2-). Density functional calculations indicated that W₂O₇^2-, W₂O₇^-, and W₂O₇ possess different ground-state structures:  the dianion is highly symmetric (D_3d,A_1g) with a single bridging oxo ligand, the monoanion is a doublet (C₁, ²A) with two bridging oxo ligands and a radical terminal oxo ligand, whereas the neutral is a singlet (C₁, ¹A) with two bridging oxo ligands and a terminal peroxo ligand. The combined experimental and theoretical study provides insights into the evolution of geometric and electronic structures as a function of charge state. The clusters identified might provide insights into the possible structures of reactive species present in early transition-metal oxide catalysts that are relevant to their reactivity and catalytic function.