Kinetics of ternary complex formation between cobalt(II) species and 5-nitrosalicylic acid: the effect of charge

The temperature-jump relaxation method has been used to measure rate constants and activation parameters for the formation and dissociation of a 1:1 complex between cobalt(II) and 5-nitrosalicylate-(2–)(nsa2–), and of ternary complexes between nsa2– and cobalt(II)–nitrilotriacetate, –ethylenediamine N,N-diacetate, –ethylenediamine-N,N′-diacetate, and –triethylenetetramine; also, rate constants for the formation and dissociation of ternary complexes between nsa and cobalt(II)–polytriphosphate, –iminodiacetate and –diethylenetriamine. Independently determined equilibrium constants are reported for [Co(nsa)] and for the ternary complexes involving polytriphosphate, nitrilotriacetate, ethylenediamine-N,N-diacetate and -N,N′-diacetate. The rate parameters are compared with those for the corresponding nickel(II) reactions and for the corresponding reactions of both metals with the neutral ligand N,N-dimethyl(p-pyridin-2-ylazo)aniline. The results for nsa are only partly explicable in terms of the Fuoss equation.