Equilibria and ligand-substitution kinetics of the five-co-ordinate cobalt(II) complex of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane with unidentate ligands
Abstract
Cobalt(II) reacts with 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmc) to give the five-co-ordinate complex, [Co(tmc)(H2O)]2+, in which the water molecule can be replaced by unidentate ligands L such as OH–, OCN–, SCN– and N3–. The stability constants of the complexes [Co(tmc)L]+, determined by spectrophotometric titrations, decrease in the order OH– > OCN– > SCN– > N3–. The kinetics of formation and dissociation of [Co(tmc)L]+ were measured by the stopped-flow technique. A reaction scheme is proposed to explain the kinetic data.