Electronic spectroscopy and photophysics of d4 clusters

The electronic structural analogies between (d4)2 M2X84− and (d4)6 (M6X8)X62− (M=Mo, W; X=Cl, Br, I) clusters are outlined. Metal-localized δ-type orbitals play an important role in the ground state and the lowest excited states of each complex. All evidence suggests that the splitting between the emissive δδ*-singlet and the δδ*-triplet excited states of M2X84− and related species is greater than 1 eV, whereas the ∼2-eV emissive excited state of (M6X8)X62− is a spin triplet.