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

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 [CpMen(dppe)RuCNFeLx][A] (A = PF ₆ ^- 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 = PF ₆ ^- , 1Me[PF6], 1Et[PF6], 1Pr[PF6], and 1Bu[PF6]; n = 1, x = Me, Et, Pr, and Bu, and A = PF ₆ ^- , 2Me[PF6], 2Et[PF6], 2Pr[PF6], and 2Bu[PF6]; n = 5, x = Me, Et, Pr, and Bu, and A = I ^- , 3Me[I], 3Et[I], 3Pr[I], and 3Bu[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 CpMe ₅ , 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 ^II CN ( n = 0, 1 and 5) fragment.