4-CYANOPYRIDINE-BRIDGED AND 3-CYANOPYRIDINE-BRIDGED BINUCLEAR COMPLEXES OF PENTACYANOFERRATE AND PENTAAMMINERUTHENIUM

The binuclear complexes (CN)5Fe(PyCN)Ru(NH3)5- (III) (4- and 3-isomers) were prepared by the substitution reactions of Ru(NH3)5NCPy2+ on Fe(CN)5OH2(3-). Complexes III undergo nitrile hydrolysis to give mixed-valence species of the form (CN)5Fe(PyCONH)Ru(NH3)5- (IV) (4- and 3-isomers) when they are subjected to chemical oxidations of 1 equiv of peroxydisulfate. The results of UV-vis, IR, and electrochemical data suggest that complexes IV belong to a valence-trapped formulation containing the localized oxidation states Fe(II) and Ru(III). Rate constants of formation and dissociation of III and IV were measured, and the values of k(f) (approximately 10(3) M-1 s-1) and k(d) (approximately 10(-3) s-1) were consistent with kinetic results expected for the substitution of Fe(CN)5OH23- with the divalent ligands. The kinetics of the nitrile hydrolysis were investigated, and it was found that the oxidized binuclear complexes III hydrolyze at a faster rate than the corresponding mononuclear Ru(III) complexes. Cyclic voltammetry of IV shows that the oxidation proceeds in two one-electron steps corresponding to [III,L,III] + e reversible [II,L,III] and [II,L,III] + e reversible [II,L,II]. The 4-isomer-bridged binuclear complex IV exhibits an intervalence band at 645 nm with molar absorbance 5.70 x 10(2) M-1 cm-1 and a half-width of 5100 cm-1. The properties of the IT band are discussed on the basis of Hush's theory.