Different delocalized ranges in mixed valence cyanido–metal-bridged Fe–Ru–Fe complexes controlled by terminal ligand substitution modification

Abstract

In order to investigate the properties of metal to metal charge transfer (MMCT) influenced by the relative energy level between the bridging unit and the terminal unit, two groups of heterotrimetallic cyanido–metal-bridged complexes, trans-[Cp(dppe)Fe-CN-Ru(MeOpy)₄-NC-Fe(dppe)Cp][X]_n (1[X]_n; n = 2, 3, or 4; X = PF₆ or BF₄) (Cp = cyclopentadiene, dppe = 1,2-bis(diphenylphosphino)ethane, MeOpy = 4-methoxypyridine) and [Cp*(dppe)Fe-CN-Ru(MeOpy)₄-NC-Fe(dppe)Cp*] [X]_n (2[X]_n; Cp* = 1,2,3,4,5-pentamethylcyclopentadiene; n = 2, 3, or 4; X = PF₆ or BF₄) were synthesized and fully characterized. The crystallography data suggest different oxidation sites in the ground state for one-electron oxidation products 1³⁺ and 2³⁺, and the electrochemical and Mössbauer spectra suggest that in the one-electron oxidation compounds 1³⁺, the charge is delocalized all along the trimetal backbone Fe–Ru–Fe, while in 2³⁺, the charge is rather delocalized between the two metal parts Fe–Ru. Further oxidation of N³⁺ gives N⁴⁺ (N = 1 or 2), during which a spin transfer towards the terminal units is observed in both series.