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

Cyanide-bridged complexes trans-[Cp(dppe)Fe(NC)Ru-II((t)bupy)(4)(CN)Fe(dppe)Cp][PF6](n) ((t)bupy = 4-tert-butyl-pyridine, 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 Mossbauer 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, Mossbauer 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, Mossbauer spectra and magnetic properties.

Automated summary

A series of cyanide-bridged complexes were synthesized and characterized in three different redox states, revealing systematic changes in electronic structure and properties. The metal-to-metal charge transfer in the one-electron oxidation product 2 is attributed to Ru-II and Fe-II -> Fe-III transitions, while that in the two-electron oxidation product 3 is mainly attributed to Ru-II -> Fe-III transitions. Electron delocalization was observed in complexes 2 and 3, with stronger conjugation present in 3.