NMR relaxation studies in solutions of transition metal complexes. IX. Dynamics of equilibria in aqueous solutions of some copper(II)nitrilotriacetate–B ligand mixed ligand complexes

Abstract

The formation constants of the complexes formed in the copper(II)-nitrilotriacetate (NTA 3− parent and in the copper(II)-NTA 3−-glycinate, copper(II)-NTA 3−-ammonia and copper(II)-NTA 3−-methylamine mixed ligand equilibrium systems in aqueous solution have been determined by pH-metry at 25°C in 1 M KCl. The dynamics of equilibria have been studied using the NMR relaxation technique. The glycinate ligand is thought to be more loosely bound to the central copper(II) ion in the mixed complex than in the parent one. In spite of this the ligand exchange rate is much slower, thus the thermodynamic stabilization is reflected in the increase of the kinetic stability of the mixed ligand complex also. The surprisingly high molar relaxation coefficient of the CuNTANH 3 mixed complex is interpreted by the fast formation and dissociation of the mixed ligand complex, ▪ with a forward rate constant of 2.1 × 10 8 M −1 s 1̄.