Characterization of molecular oxygen binding to [CoII(1,4,8,11-tetraazacyclotetradecane)] in aqueous solutions

1, 4, 8,11-tetraazacyclotetradecane (cyclam), a cyclic tetramine, binds various metal cations among which Co2+ is of a particular importance as its complex can bind molecular oxygen and help separate it from nitrogen of air. The stability constants of the O2 complexes have been the subject of many works but, due to kinetic complications, none of these studies yielded satisfactory results. In the present work spectrophotometry has been used to investigate the acid-base properties of the various species as well as the kinetic and thermodynamic aspects of their formation. For kinetic reasons the superoxo complex is formed primarily which then evolves to the mu -peroxo derivative, the most stable species. This study reveals why the many previous experiments conducted to measure the stability constants of the oxygen complexes have failed.