KINETIC-STUDIES OF THE REACTIONS OF PENTACYANOFERRATE(II) COMPLEXES WITH PEROXYDISULFATE

Reactions of Fe(CN)(5)L(3-) (L = 4-aminopyridine (4-ampy), pyridine (p y), 4,4'-bipyridine (4,4'-bpy), and pyrazine (pz)) with peroxydisulfat e, Fe(CN)(5)L(3-) + S2O82- reversible arrow Fe(CN)(5)L(2-) + SO4- + SO 42-, have been found to follow an outer-sphere electron transfer mecha nism. The specific rate constants of oxidation are 1.45 +/- 0.01, (9.0 0 +/- 0.02) x 10(-2), (5.60 +/- 0.01) x 10(-2), and (2.89 +/- 0.01) x 10(-2) M(-1) s(-1), for L = 4-ampy, py, 4,4'-bpy, and pz, respectively , at mu = 0.50 M LiClO4, T = 25 degrees C, pH = 4.4-8.8. The rate cons tants of oxidation for the corresponding Ru(NH3)(5)L(2+) complexes wer e also measured and were found to be faster than those of Fe(CN)(5)L(3 -) complexes by a factor of similar to 10(2) even after the correction s for the differences in reduction potentials and in the charges of th e complexes. The difference in reactivity may arise from the hydrogen bonding between peroxydisulfate and the ammonia ligands of Ru(NH3)(5)L (2+) and nonadiabaticity observed in the Fe(CN)(5)L(3-) complexes.