Intervalence charge transfer in a “chain-like” ruthenium trinuclear assembly based on the bridging ligand 4,7-phenanthrolino-5,6:5′,6′-pyrazine (ppz)

Abstract

The IVCT characteristics of the mixed valence forms of the trinuclear complex [{Δ-Ru(bpy)₂}₂{Δ^t-Ru(bpy)(µ-ppz)₂}]ⁿ⁺ (n = 7, 8; t = trans), and the diastereoisomers (meso and rac) of the dinuclear complex [{Ru(bpy)₂}₂(µ-ppz)]⁵⁺, display a marked dependence on the nuclearity and extent of oxidation of the assemblies. The dinuclear species are classified as borderline localised–delocalised mixed valence species while the two mixed valence states of the trinuclear complex exhibit localised behaviour. One-electron oxidation of a terminal Ru centre in the trinuclear case gives rise to a broad, low intensity IVCT band for the +7 mixed valence species which is composed of two underlying Gaussian-shaped bands. The transitions are identified as adjacent and remote IVCT transitions, with the former dominating the intensity of the IVCT manifold. The +8 mixed valence species exhibits a single dominant IVCT band arising from the equivalent IVCT transitions from the central Ru^II to peripheral Ru^III centres.