Kinetics of Ternary Complex-Formation Between Cobalt (II) Species and N,N-Dimethyl (P-Pyridin-2-Ylazo) Aniline

The temperature-jump relaxation method has been used to measure the rate constants and the activation enthalpies and entropies for the formation and dissociation of the ternary complexes between N,N'-dimethyl(p-pyridin-2-ylazo)aniline (pada) and cobalt(II)-N-methyliminodiacetate, -ethylenediamine-N.N'-diacetate, -ethylenediamine-N,N'-diacetate, -diethylenetriamine, and -triethylenetetramine complexes. Independently determined equilibrium constants are also reported for the complexes involving ethylenediamine-N,N-diacetate, -N,N'-diacetate and triethylenetetramine. The rate parameters reported here, and previously for four related cobalt(II) systems, are compared with those for the corresponding nickel(II) reactions. It is confirmed that some of the factors influencing reactivity are the same for the two metals (notably the number of bound nitrogen atoms) but there are also significant differences.