Influence of the electronic effect of an ancillary ligand on MMCT and LMCT in localized cyanide-bridged complexes containing non-innocent ligands

Abstract

Mixed-valence (MV) complexes containing non-innocent ligands are excellent models for the investigation of the electron-transfer process. A series of twelve bimetallic cyanide-bridged complexes [CpMe_n(dppe)RuCNFeL_x][A] (A = PF₆⁻ or I⁻, CpMe_n = alkyl cyclopentadienyl, dppe = 1,2-bis (diphenylphosphino)ethane, and L_X = pentane-2,4-dione-bis (S-alkylisothiosemi-carbazonato); n = 0, x = Methyl (Me), Ethyl (Et), n-Propyl (Pr) and n-Butyl (Bu), and A = PF₆⁻, 1_Me[PF₆], 1_Et[PF₆], 1_Pr[PF₆], and 1_Bu[PF₆]; n = 1, x = Me, Et, Pr, and Bu, and A = PF₆⁻, 2_Me[PF₆], 2_Et[PF₆], 2_Pr[PF₆], and 2_Bu[PF₆]; n = 5, x = Me, Et, Pr, and Bu, and A = I⁻, 3_Me[I], 3_Et[I], 3_Pr[I], and 3_Bu[I]) have been synthesized and well characterized. The investigations demonstrate that all the cations of the complexes could be described with the basic electronic configuration , in which the fragment could be regarded as being delocalized. The ligand to metal charge transfer (LMCT) transition in the fragment and the low-spin Ru^II to the intermediate-spin Fe^III charge transfer (MMCT) transition have been investigated. The UV-vis-NIR spectral analysis results suggest that the energy of the LMCT transition is lower than that of the MMCT transition due to electron delocalization between the non-innocent ligand and the Fe^III ion, which is strongly supported by TDDFT calculations. Furthermore, the Ru^II → Fe^III MMCT energy decreases and the LMCT energy increases with the increasing electron donating ability of the ancillary ligands from Cp, CpMe to CpMe₅, but slightly changes with the variation of the ligand L_x from Me, Et, Pr to Bu. Compared to the MMCT energy change, however, the energy of the LMCT from to Fe^III in the delocalized moiety is less influenced by the electronic effect of the ancillary ligand or the CpMe_n(dppe)Ru^IICN (n = 0, 1 and 5) fragment.