One-electron reduction of tris(2,2'-bipyridine) and tris(1,10-phenanthroline) complexes of cobalt(III) in aqueous solution

The reaction of Co(2,2'-bipyridine)33+ with radiation-generated reducing radicals (e/sub aq/-, CO2-, (CH3)2COH, and CH2OH) in aqueous solution quantitatively and rapidly (k = 108 - 1010 M-1 s-1) yields high-spin (t/sub 2g/5 e/sub g/2) Co(bpy)32+ (lambda/sub max/ 300 nm, epsilon/sub max/ 4.2 x 104 M-1 cm-1) which slowly (k = 3.4 s-1 at pH 0.5-10.5; 8.0 s-1 at pH 0.3) equilibrates with the loss of bpy; Co(bpy)32+ does not transfer an electron to O2 or p-benzoquinone. Equilibrium mixtures of Co(bpy)/sub n/2+ react with e/sub aq/- (k > 1010 M-1 s-1) to produce Co(bpy)/sub n/+ (lambda/sub max/ 620 nm, epsilon/sub max/ 5.1 x 103 M-1 cm-1). Reduction of Co(phen)33+ yields Co(phen)32+ (lambda/sub max/ 270 nm, epsilon/sub max 5.6 x 104 M-1 cm-1); conversion to the equilibrium mixture (Co(phen)/sub n/2+) occurs in a time frame (>1 s) too long to be detected by pulse radiolysis. The relationship of these results to those of the Waltz and Pearson and Baxendale and Fiti is discussed. 38 references, 4 figures