Kinetics of ternary complex formation between cobalt(II) species and 2,2′-bipyridine: parametrization of bound-ligand effects

Abstract

Temperature-jump and stopped-flow relaxation methods have been used to measure rate constants (and in some cases activation enthalpies and entropies) for the formation and dissociation of the 1 : 1 complex between cobalt(II) and 2,2′-bipyridine (bipy), and of ternary complexes between bipy and cobalt(II)-polytriphosphate, -nitrilotriacetate, -ethylenediamine-N,N-diacetate, -ethylenediamine-N,N′-diacetate, -triethylenetetramine and -2,2′,2″-triaminotriethylamine complexes. The rate constants kf for the three series involving, respectively, bipy, N,N-dimethyl(p-pyridin-2-ylazo)aniline and the dianion from 5-nitrosalicylic acid have been compared. The data are found to fit the simple parametrization scheme recently developed for analogous reactions of nickel(II) in which the terms are linked directly to structural features of the reactants. The relative behaviour of the two metals is discussed.