The reaction of radiation-generated free radicals with cobalt(II) and cobalt(III) complexes containing macrocyclic ligands

The reactions of radiation-generated free radicals with complexes of cobalt(III) and cobalt(II) containing the tetradentate 14-membered macrocyclic ligands 5,7,7,12,14,14 - hexamethyl - 1,4,8,11 - tetraazacyclotetradeca - 4,11 - diene (4,11 - dieneN₄), 5,7,7,12,12,14 - hexamethyl - 1,4,8,11 - tetraazacyclotetradeca - 4,14 - diene (4,14 - dieneN₄), and 2,3,9,10 - tetramethyl - 1,4,8,11 - tetraazacyclotetradeca - 1,3,8,10 - tetraene (1,3,8,10 - tetraeneN₄) have been studied in aqueous solution using pulse radiolysis. The cobalt(III) complexes can be reduced to cobalt(II) by e_aq⁻, CO₂⁻ and (CH₃)₂$\text{Z.}\text{̇}$COH with the rate constants of the reactions depending upon the nature of the macrocycle and the axial ligand coordinated to the metal center. The rate constants and transient spectra arising from the reactions of the cobalt(II) species with H atoms, CH₃ radicals, and Br₂⁻ radicals have also been determined.