Charge distribution in metal to ligand charge transfer states of quadruply bonded metal complexes

•We report electronic structures of quadruply metal-metal bonded carboxylate complexes.•Photophysical studies reveal the dynamics of the singlet and triplet excited states.•Time-resolved infrared femtosecond spectroscopy reveals the location of charge.•Examples of localized and delocalized metal to ligand charge transfer states are reported.

The application of fs time resolved infrared, TRIR spectroscopy to complexes of the form M2L4, M2L3L1 and M2L2L21 where M = Mo or W and L or L1 = a carboxylate or amidinate has allowed the nature of 1MLCT S1 states to be probed with respect to the location of charge on the ligands. The 3MLCT states, which are formed by intersystem crossing, have similarly been probed in a few instances where M = W but for M = Mo the T1 states are typically 3MoMoδδ*. Examples of localized, valence trapped and delocalized ligand excited states have been found with the latter being favored by strong ligand–ligand coupling via the M2δ orbital.