MIXED-VALENCE CHEMISTRY OF PYRIMIDINE BRIDGED BINUCLEAR COMPLEX OF PENTACYANOFERRATE AND PENTAAMMINERUTHENIUM

The pyrimidine bridged binuclear complex (CN)5FepymRu(NH3)5- (I) was p repared in aqueous solution by mixing equimolar of Fe(CN)5OH23- and Ru (NH3)5pym2+. Its mixed valence state molecule (CN)5FepymRu(NH3)-5(II) was obtained upon oxidation of I by one equivalent of peroxydisulfate ion. Both binuclear complexes and corresponding Fe(II) and Ru(II) mono nuclear complexes displayed a metal-to-ligand charge transfer absorpti on in 400-450 nm region. Rate constants of formation and dissociation of I and II were measured, and the values of k(f) (approximately 10(3) M-1 s-1) and k(d) (approximately 10(-3)-10(-4) s-1) were consistent w ith kinetic results expected for the substitution of Fe(CN)5OH23- with di- and trivalent ligands. Cyclic voltammetry of I exhibited two one- electron steps of oxidation corresponding to [III, L, II] + e --> [II, L, II] and [III, L, III] + e --> [III, L, II], respectively. The mixe d valence binuclear complex II showed an intervalence band at 955 nm w ith a molar extinction coefficient 5.80 x 10(2) M-1 cm-1 and a half-wi dth 5 100 cm-1. The properties of the IT band conform to Hush's theory . Spectroscopic, electrochemical and kinetic results of II suggest tha t the mixed valence complex features a trapped - valence formulation w ith localized oxidation states of Fe(II) and Ru(III).