Electron delocalization in the S1 and T1 metal-to-ligand charge transfer states of trans-substituted metal quadruply bonded complexes

摘要

The singlet S1 and triplet T1 photoexcited states of the compounds containing MM quadruple bonds trans-M2(TⁱPB)2(O2CC6H4-4-CN)2, where TⁱPB = 2,4,6-triisopropylbenzoate and M = Mo (>I) or M = W (>I^′), and trans-M2(O2CMe)2((N[ⁱ Pr ])2CC ≡ CC6H5)2, where M = Mo (>II) and M = W (>II^′), have been investigated by a variety of spectroscopic techniques including femtosecond time-resolved infrared spectroscopy. The singlet states are shown to be delocalized metal-to-ligand charge transfer (MLCT) states for >I and >I^′ but localized for >II and >II^′ involving the cyanobenzoate or amidinate ligands, respectively. The triplet states are MoMoδδ* for both >I and >II but delocalized ³MLCT for >I^′ and localized ³MLCT for >II^′. These differences arise from consideration of the relative orbital energies of the M2δ or M₂δ* and the ligand π^∗ as well as the magnitudes of orbital overlap.