Activation volumes for the ligand-substitution reactions of nickel(II) and cobalt(II) cations with pyridine-2-azo-4-dimethylaniline in various solvents

Abstract

The rates of the ligand-substitution reactions of the neutral ligand pada (pyridine-2-azo-4-dimethyl-aniline) with Ni²⁺ and Co²⁺ have been determined by a laser-flash relaxation method, at pressures from 1 to 2000 bar, in water, DMF and DMSO. The results at 1 bar agree with those from stopped-flow experiments. Activation volumes ΔV^≠_L have been derived. Variation of the anion (ClO^–₄, BPh^–₄, NO^–₃) appears to produce no systematic change in ΔV^≠_L. The values of ΔV^≠_L in the non-aqueous aprotic solvents DMF and DMSO are fairly close to those in water. Comparison with the value of ΔV^≠_L, the activation volume for solvent exchange, is possible in a few cases; the differences are small.