Kinetics of ternary complex formation between nickel species and 5-nitrosalicylic acid

Abstract

Stopped-flow and temperature-jump relaxation methods have been used to measure rate constants and activation parameters for the formation and dissociation of a 1:1 complex between nickel(II) and 5-nitrosalicylate(2–)(nsa) and of ternary complexes between nsa and nickel(II)–polytriphosphate, –iminodiacetate, –nitrilotriacetate, –ethylenediamine-NN′-diacetate, –diethylenetriamine, –triethylenetetramine, and –2,2′,2″-triaminotriethylamine complexes. Rate constants and activation parameters have also been measured for the reaction between the Ni^II complex of ethylenediamine-NN′-diacetate and pyridine-2-azo-p-dimethylaniline. The results can be rationalized in terms of the normal dissociative model provided the local charge density on the metal species is considered rather than its overall charge. The results provide further evidence that the number of binding nitrogen atoms on the first ligand has a larger influence on ternary complex formation than its charge.