A T-shaped cyanidometal-bridged tetranuclear Fe3Ru complex with oxidation-driven intramolecular charge transfer between metal centres†

A T-shaped cyanidometal-bridged tetranuclear one-electron oxidized complex [{CpFe^II(dppe)(CN)}₃Ru^III(DMPZ)₂Cl][PF₆]₂ (1⁺, Cp = cyclopentadienyl; dppe = 1,2-bis(diphenylphosphino)ethane; DMPZ = 2,6-dimethylpyrazine), which can be considered as a composition of cis- and trans-configuration trinuclear subunits, was synthesized and well characterized. The FTIR and UV-vis-NIR spectra of products of 1⁺ with different valence states were investigated by spectroelectrochemical measurements on an OTLLE cell in dichloromethane. (TD)DFT calculations were performed to fully understand the metal-to-metal charge transfer (MMCT) transition and delocalization properties of the T-shaped cyanidometal-bridged tetranuclear complexes. Spectral analyses revealed a superior electronic delocalization between the terminal Fe centers positioned in the trans-configuration compared to those in the cis-configuration. Most importantly, this work shows the presence of the oxidation-driven intramolecular charge transfer from the terminal Fe center to the central Ru center during the change from the two-electron oxidized state (1²⁺) to the three-electron oxidized state (1³⁺), as confirmed by electrochemistry, FTIR and UV-vis-NIR spectroscopy, and also strongly supported by theoretical calculations.