Outer-sphere charge transfer in mixed-metal ion pairs

Article abstract of DOI:10.1021/ic00134a059

Outer-sphere charge-transfer (OSCT) transitions have been observed in water for a series of mixed-metal ion pairs: [M^II(CN₆),Ru^III(NH₃) ₅(L)]^- (M = Fe, Ru, Os; L = pyridine or a substituted pyridine). After developing an appropriate thermochemical cycle it is possible to show that as expected from theory, the energies of the optical transitions vary with ΔH_IP^o′ where ΔH_IP^o′ is the enthalpy difference associated with charge transfer within the ion pair, [M^II(CN)₆,Ru^III(NH₃) ₅(L)]^- → [M^III(CN)₆,Ru^II(NH₃) ₅(L)]^-. A detailed analysis of the OSCT absorption bands leads to a number of important conclusions, including (1) the presence of electronic structure is due to the effects of spin-orbit coupling at the M^III(CN)₆^3- d⁵ core following optical excitation, (2) the extent of electronic coupling between electron-donor and -acceptor sites is only slightly dependent on M in M(CN)₆^4-, and (3) the most probable outer-sphere structure involves contact between M(CN)₆^4- and an ammine face of the complexes Ru(NH₃)₅(L)³⁺.