Concerning the Ground State and S1 and T1 Photoexcited States of the Homoleptic Quadruply Bonded Complexes Mo2(O2CC6H4‑p‑X)4, where X = CC–H or CN

The preparation of the homoleptic MM quadruply bonded complexes Mo2(O2CC6H4-p-X)4, where X = CC–H (I) or CN (II), is reported along with the solution characterization data and electronic structure calculations employing density functional theory. The compounds are colored orange (I) and red (II) due to the metal-to-ligand charge transfer involving the HOMO, Mo2δ, and LUMO, which is a ligand-based π* combination. Studies of the S1 state, 1MLCT, by femtosecond time-resolved infrared spectroscopy indicate that the negative charge is distributed principally over two trans ligands. The T1 states are 3MoMoδδ* as determined by NIR emission and nanosecond transient absorption.