Synthesis, structural and metal-to-metal charge transfer properties of cyanide-bridged compound [FeII/III-NC-RuII-CN-FeII/III]

Abstract

Cyanide-bridged complexes trans-[Cp(dppe)Fe(NC)Ru^II(^tbupy)₄(CN)Fe(dppe)Cp][PF₆]_n (^tbupy = 4-tert-butylpyridine, n = 2, 3 and 4, respectively, 1–3,) were systematically synthesized and characterized in three distinct redox states. Single-crystal X-ray diffraction analysis, IR, electrochemistry, electronic absorption spectroscopy, EPR and Mössbauer spectroscopy clearly revealed the detailed electronic structures of complexes 1–3, and these findings allowed us to understand the systematic changes in structure and electronic state that accompany the changes in the redox states. The metal-to-metal charge transfer (MMCT) of the one-electron oxidation product 2 is mainly attributed to Ru^II and Fe^II → Fe^III MMCT transitions, and the MMCT of the two-electron oxidation product 3 is mainly attributed to Ru^II → Fe^III MMCT transitions. The IR, EPR, Mössbauer spectroscopy and magnetic properties indicate electron delocalization in complexes 2 and 3, and that of 3 is much stronger than that of 2. The two-electron oxidation product 3 may be localized at low temperatures but delocalized at room temperature regarding the EPR, Mössbauer spectra and magnetic properties.