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.