Spectroelectrochemical studies on mixed-valence states in a cyanide-bridged molecular square, [RuII2FeII2(μ-CN)4(bpy)8](PF6)4•CHCl3•-H2O

A cyanide-bridged molecular square of [(Ru2Fe2II)-Fe-II(mu-CN)(4)(bpy)(8)]-(PF6)(4).CHCl3.H2O, abbreviated as [(Ru2Fe2II)-Fe-II](PF6)(4), has been synthesised and electrochemically generated mixed-valence states have been studied by spectroelectrochemical methods. The complex cation of [(Ru2Fe2II)-Fe-II](4+) is nearly a square and is composed of alternate Ru-II and Fe-II ions bridged by four cyanide ions. The cyclic voltammogram (CV) of [(Ru2Fe2II)-Fe-II](PF6)(4) in acetonitrile showed four quasireversible waves at 0.69, 0.94, 1.42 and 1.70V (vs. SSCE), which correspond to the four one-electron redox processes of [(Ru2Fe2II)-Fe-II](4+) reversible arrow [(Ru2FeFe)-Fe-II-Fe-II (III)] (5+)reversible arrow[(Ru2Fe2III)-Fe-II](6+) reversible arrow [(RuRuFe2III)-Ru-II-Fe-III](7+) reversible arrow[(Ru2Fe2III)-Fe-III](8+). Electrochemically generated [(Ru2FeFeIII)-Fe-II-Fe-II](5+) and [(Ru2Fe2III)-Fe-II](6+) showed new absorption bands at 2350 nm (epsilon = 5500m(-1) cm(-1)) and 1560 nm (epsilon = 10500 m(-1) cm(-1)), respectively, which were assigned to the intramolecular IT (intervalence transfer) bands from Fell to Fe-III and from Ru-II to Fe-III ions, respectively. The electronic interaction matrix elements (H-AB) and the degrees of electronic delocalisation (alpha(2)) were estimated to be 1090 cm(-1) and 0.065 for the [(Ru2FeFe2III)-Fe-II-Fe-II](5+) state and 1990 cm(-1) and 0.065 for the [(Ru2Fe2III)-Fe-II](6+) states.