Comparison between the inter- and intra-molecular kinetics of reduction of penta-ammine(ligand)cobalt(III) complexes by the para-nitrobenzoate radical: A pulse-radiolytic study

Second-order rate constants for reduction by the p-nitrobenzoate radical of the complexes [Co^III(NH₃)₅X] [X = NH₃, PhCO₂^-, p-O₂NC₆H₄CO₂^-, Br^-, pyridine (py), and m-H₂NCOC₅H₄N] have been measured and are in the range 10⁵-10⁷ I mol^-1 s^-1. The rates of the first three reactions are considerably faster than those expected from the intramolecular rate of electron transfer in [Co^III(NH₃)₅(O₂CC₆H ₄NO₂^-p)]⁺ and suggest poor 'electron permeability' of the carboxylate group.