Kinetics of formation of mixed ligand complexes. I. Copper(II)-2,2'-bipyridyl-glycine system in aqueous solution

The temperature-jump technique has been used to determine the rate constants for the formation and dissociation of the mixed complex Cu(2,2′-bipyridyl)(glycinate)+. Under the conditions of these experiments (temperature = 25°, μ = 0.1 M) it was shown that, within experimental error, the rate constant for attack by the glycine zwitterion is zero. For the reaction Cu(bipy)2+ + gly– ⇋ Cu(bipy)(gly)+ (k12, forward; k21, reverse), the rate constants are k12 = 1.6 × 109 M–1 sec–1 and k21 = 19 sec–1. These rate constants are compared with literature values for the reactions Cu2+ + gly– ⇋ Cu(gly)+ and Cu(gly)+ + gly– ⇋ Cu(gly)2. It is suggested that differences in forward and reverse rate constants can be accounted for in terms of statistical factors, charge effects, and an enhancement term due to the presence of 2,2′-bipyridyl in the inner coordination sphere of the copper ion.