Kinetics of the oxidation of chloride ions by tris(2,2′-bipyridine)nickel(III) ions in aqueous perchlorate media
Abstract
The kinetics of oxidation of chloride ions by the tris(2,2′-bipyridine)nickel(III) ion, [Ni(bipy)3]3+, have been investigated in aqueous media. Using conventional spectrophotometry, the orders in the reactant concentrations were found to be variable at an ionic strength of 5.00 mol dm–3. However, using stopped-flow spectrophotometry to investigate the oxidation at an ionic strength of 2.50 mol dm–3 at high [Cl–], the order in [NiIII] was always unity and plots of the pseudo-first-order rate constants ×[Cl–]–1 with [Cl–] at constant acidity were linear with an intercept on the ordinate, and invariant with changes in the acidity. This is interpreted in terms of the involvement of outer-sphere complexes of Cl– and [Ni(bipy)3]3+ in the mechanism in two parallel pathways. The enthalpies and entropies of activation are compared with those for the oxidation of other substrates by [Ni(bipy)3]3+.