Reactions of Fe(CN)(5)L(3-) (L = 4-aminopyridine (4-ampy), pyridine (py), 4,4’-bipyridine (4,4’-bpy), and pyrazine (pz)) with peroxydisulfate, Fe(CN)(5)L(3-) + S2O82- reversible arrow Fe(CN)(5)L(2-) + SO4- + SO42-, have been found to follow an outer-sphere electron transfer mechanism. The specific rate constants of oxidation are 1.45 +/- 0.01, (9.00 +/- 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 constants of oxidation for the corresponding Ru(NH3)(5)L(2+) complexes were 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 corrections for the differences in reduction potentials and in the charges of the 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.