Kinetics of ternary complex formation between nickel species and 2,2′-bipyridine: parameterization of bound ligand effects

Abstract

Stopped-flow and temperature-jump relaxation methods have been used to measure rate constants k_f for the formation of ternary complexes between 2,2′-bipyridine (bipy) and nickel(II)–nitrilotriacetate, –ethylenediamine-N,N-diacetate, –ethylenediamine-N,N′-diacetate, –diethylenetriamine, – triethylene-tetramine, and -2,2′,2″-triaminotriethylamine complexes. Rate and equilibrium constants are also reported for the reaction of the nickel(II)–ethylenediamine-N,N-diacetate complex with pyridine-2-azo-p-dimethylaniline (pada) and the dianion from 5-nitrosalicyclic acid (nsa). Comparison of the rate constants k_f for the three series involving, respectively, bipy, pada and nsa suggests a simple parametrization scheme in which the terms are linked directly to structural features of the reactants. Major factors involved are the charges on the two ligands and the number of bound nitrogen atoms. The mechanistic interpretation of the terms is also considered.