Metal–metal charge transfer and solvatochromism in cyanomanganese carbonyl complexes of ruthenium and osmium

Abstract

The complexes [(H₃N)₅Ru^II(µ-NC)Mn^IL_x]²⁺, prepared from [Ru(OH₂)(NH₃)₅]²⁺ and [Mn(CN)L_x] {L_x = trans-(CO)₂{P(OPh)₃}(dppm); cis-(CO)₂(PR₃)(dppm), R = OEt or OPh; (PR₃)(NO)(η-C₅H₄Me), R = Ph or OPh}, undergo two sequential one-electron oxidations, the first at the ruthenium centre to give [(H₃N)₅Ru^III(µ-NC)Mn^IL_x]³⁺; the osmium(III) analogues [(H₃N)₅Os^III(µ-NC)Mn^IL_x]³⁺ were prepared directly from [Os(NH₃)₅(O₃SCF₃)]²⁺ and [Mn(CN)L_x]. Cyclic voltammetry and electronic spectroscopy show that the strong solvatochromism of the trications depends on the hydrogen-bond accepting properties of the solvent. Extensive hydrogen bonding is also observed in the crystal structures of [(H₃N)₅Ru^III(µ-NC)Mn^I(PPh₃)(NO)(η-C₅H₄Me)][PF₆]₃·2Me₂CO·1.5Et₂O, [(H₃N)₅Ru^III(µ-NC)Mn^I(CO)(dppm)₂-trans][PF₆]₃·5Me₂CO and [(H₃N)₅Ru^III(µ-NC)Mn^I(CO)₂{P(OEt)₃}(dppm)-trans][PF₆]₃·4Me₂CO, between the ammine groups (the H-bond donors) at the Ru(III) site and the oxygen atoms of solvent molecules or the fluorine atoms of the [PF₆]⁻ counterions (the H-bond acceptors).