METAL-EXCHANGE REACTIONS BETWEEN "POLYAMINOPOLYCARBOXYLATOZINCATE(II) AND COPPER(II)

The kinetics of the metal-exchange reactions between polyaminopolycarboxylate complexes of Zn2+ and Cu2+ has been studied over the pH range of 4.25-5.75, at different copper concentrations, at ionic strength 0.10 M, and at different temperatures. The reaction is first order in the displaced complex, while the order with respect to copper ranges between one and zero, depending on the ligand nature and on pH. Individual reaction steps taking place for each system, with different copper concentration and pH dependence, are discussed. The experimental results indicate that the exchange reactions proceed through a dinuclear intermediate whose dissociation is the rate-determining step for the less coordinating ligands; increased chelating ability of the ligand shifts the rate-determining step to bond formation with the entering metal rather than bond breakage in the intermediate. © 1978, American Chemical Society. All rights reserved.