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.