Tuning the metal-to-metal charge transfer energy of cyano-bridged dinuclear complexes

Abstract

The metal-to-metal charge transfer (MMCT) transitions of a series of Class II mixed valence dinuclear complexes bearing cyano bridging ligands may be varied systematically by variations to either the hexacyanometallate(II) donor or Co^III acceptor moieties. Specifically, the new dinuclear species trans-[L^14SCoNCFe(CN)₅]⁻ (L^14S = 6-methyl-1,11-diaza-4,8-dithia-cyclotetradecane-6-amine) and trans-[L¹⁴CoNCRu(CN)₅]⁻ (L¹⁴ = 6-methyl-1,4,8,11-tetraazacyclotetradecane-6-amine) have been prepared and their spectroscopic and electrochemical properties are compared with the relative trans-[L¹⁴CoNCFe(CN)₅]⁻. The crystal structures of Na{trans-[L^14SCoNCFe(CN)₅]}·5½H₂O·½EtOH, Na{trans-[L¹⁴CoNCRu(CN)₅]}·3H₂O and Na{trans-[L¹⁴CoNCRu(CN)₅]}·8H₂O are also reported. The ensuing changes to the MMCT energy have been examined within the framework of Hush theory, and it was found that the free energy change between the redox isomers was the dominant effect in altering the energy of the MMCT transition.