SYNTHESIS AND CHARACTERIZATION OF CYANIDE-BRIDGED HETEROBINUCLEAR MIXED-VALENCE COMPOUNDS BASED ON CYCLOPENTADIENYLORGANOPHOSPHINE-RUTHENIUM(II) AND OSMIUM(II) CYANO AND PENTAAMMINE-RUTHENIUM(III) AND OSMIUM(III) MOIETIES

Six novel cyanide-bridged mixed-valence complexes, [(eta5-C5H5)(PPh3)2 M'(mu-CN)M(NH3)5][CF3SO3]3 (M = Ru, M' = Ru or Os; M = Os, M' = Ru or Os) and [(eta5-C5R5)(PPh3)2Ru(mu-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 b y cyclic voltammetry. They exhibit moderately intense (epsilon(max) al most-equal-to 2000-4000 dm3 mol-1 cm-1), broad (DELTAnu1/2 almost-equa l-to 5000 cm-1) intervalence charge-transfer transitions in the visibl e spectrum, analysis of which reveals Robin-Day Class II behaviour (al pha2 almost-equal-to 0.8-2.0%, H(rp) almost-equal-to 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 sol vent donicity, where appropriate, and simple perturbation arguments. T he weak solvent dependence of the coupling element, H(rp), indicates t hat the charge-transfer mechanism proceeds primarily through an electr on, rather than hole, transfer pathway. The intervalence charge-transf er bands of the cyclopentadienylosmium complexes exhibit a pronounced spin-orbit splitting, the relative intensities of the components also showing solvent dependence.