Kinetics and Thermodynamics of the Complex-formation of Nickel(II) and Cobalt(II) Ions with Ammonia and Pyridine- 2-azodimethylaniline in Water, at Pressures from 1 bar to 2 kbar

Abstract

Thermodynamic and kinetic measurements have been made at a series of pressures from 1 bar to 2 kbar on the reactions of nickel(IQ and cobalt(II) ions with ammonia and with the large bidentate ligand PADA (pyridine-2-azodimethylaniline) in aqueous solution. The apparatus consisted of a high-pressure cell and a laser temperature-jump apparatus with spectrophotometric detection. A method is described for determining equilibrium constants at high pressures from the amplitude of the optical-density change on reaction. The values found for AK* are all in the region of 4-5 to + 8 cm3 mol-1. The results are consistent with the interpretation that the transition state involves considerable stretching of the cation-water bond, as postulated in the Eigen-Wilkins mechanism.