Synthesis and structural and spectroscopic properties of a cyanido-bridged mixed-valence compound [Fe–NC–Ru–CN–Fe]

Abstract

The cyanide-bridged compounds trans-[Cp(dppe)Fe^II(NC)Ru^II(py)₄(CN)Fe^II(dppe)Cp][PF₆]₂ (1, py = pyridine, dppe = bis (diphenylphosphino) ethane, Cp = cyclopentadienyl anion), trans-[Cp(dppe)Fe^II(NC)Ru^II(py)₄(CN)Fe^III(dppe)Cp][PF₆]₃ (2), trans-[Cp(dppe)Fe^III(NC)Ru^II(py)₄(CN)Fe^III(dppe)Cp][PF₆]₄ (3), trans-[Cp(dppe)Fe^II(NC)Ru^II(MeOpy)₄(CN)Fe^II(dppe)Cp][PF₆]₂ (4, MeOpy = 4-methoxypyridine) and trans-[Cp(dppe)Fe^III(NC)Ru^II(MeOpy)₄(CN)Fe^II(dppe)Cp][PF₆]₃ (5) were systematically synthesized and characterized by IR spectroscopy, electronic absorption spectroscopy, elemental analysis, mass spectrometry and cyclic voltammetry. Fortunately, crystals of 1, 2, 4, trans-Ru^II(MeOpy)₄(CN)₂ and [CpFe^III(dppe)Br](PF₆) suitable for single-crystal X-ray diffraction analysis were obtained. The metal-to-metal charge transfer (MMCT) of the one-electron oxidation products 2 and 5 is mainly attributed to the Ru^II and Fe^II to Fe^III MMCT transitions, and the MMCT of the two-electron oxidation product 3 is mainly attributed to the Ru^II→Fe^III MMCT transitions. According to the classification of Robin and Day, compounds 2, 3 and 5 belong to the class II mixed-valence compounds. The IR spectra, MMCT band and redox splitting of compounds 2 and 5 indicate that replacing the py ligand in the central unit with MeOpy shows better electronic communication properties.