Synthesis and characterisation of cyanide-bridged heterobinuclear mixed-valence compounds based on cyclopentadienylorganophosphine-ruthenium(II) and -osmium(II) cyano and pentaammine-ruthenium(III) and -osmium(III) moieties

Abstract

Six novel cyanide-bridged mixed-valence complexes. [(η⁵-C₅H₅)(PPh₃)₂M′(µ-CN)M(NH₃)₅][CF₃SO₃]₃(M = Ru, M′= Ru or Os; M = Os, M′= Ru or Os) and [(η⁵-C₅R₅)(PPh₃)₂Ru(η-CN)Ru(NH₃)₅][CF₃SO₃]₃(C₅R₅= C₅H₄Me or C₅Me₅), have been synthesised using a simple coupling reaction and characterised by electronic and infrared absorption spectroscopy and by cyclic voltammetry. They exhibit moderately intense (ε_max≈ 2000–4000 dm³ mol^–1 cm^–1), broad (Δν_½≈ 5000 cm^–1) intervalence charge-transfer transitions in the visible spectrum, analysis of which reveals Robin–Day Class II behaviour (α²≈ 0.8–2.0%, H_rp≈ 1700–2000 cm^–1). Outer-sphere effects upon the cyanide-bridge stretching frequency and all the intervalence charge-transfer band characteristics are reported and interpreted using linear correlations with respect to Gutmann solvent donicity, where appropriate, and simple perturbation arguments. The weak solvent dependence of the coupling element, H_rp, indicates that the charge-transfer mechanism proceeds primarily through an electron, rather than hole, transfer pathway. The intervalence charge-transfer bands of the cyclopentadienylosmium complexes exhibit a pronounced spin-orbit splitting, the relative intensities of the components also showing solvent dependence.