Influence of the Substitution of the Ligand on MM′CT Properties of Mixed Valence Heterometallic Cyanido-Bridged Ru–Fe Complexes

We investigated how substitution of the ligand around the lower valent metal ion influences the electron transfer properties from the lower valent metal ion to the higher valent metal ion in heterometallic complexes. A series of new binuclear cyanido-bridged Ru/Fe complexes [TpmRu(L)(μ-CN)Fe(dppe)Cp][PF6]n (n = 2, 3) (Tpm = Tris(1-pyrazolyl)methane, dppe = bis(diphenylphosphino)ethane, L = 1,10-phenanthroline (phen), 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (4,4′-(CH3)2-bpy)) were synthesized and characterized. In the one-electron oxidized [TpmRuII(L)(μ-CN)FeIII(dppe)Cp][PF6]3 binuclear system, the cyanide bridge promotes the electron transfer from the RuII ion to the FeIII ion. As the substitution of L changes from 1,10-phenanthroline to 4,4′-dimethyl-2,2′-bipyridine, their molecular structure, cyclic voltammetry, IR and UV present obvious changing trends. Moreover, the assignment of MM′CT transition and the differences of electronic properties in the different mixed complexes with different L ligands can be reasonably elucidated via time-dependent density functional theory/density functional theory calculations.