Activation volume as evidence for a dissociative-interchange mechanism of nickel(II) ion complexation with isoquinoline in water, N,N-dimethylformamide, acetonitrile, methanol, and ethanol

Activation volumes for the complexation of nickel(II) ion with isoquinoline in various solvents were determined by a high-pressure stopped-flow technique. Values of activation volume for formation and dissociation of the (isoquinoline)nickel(II) complex are respectively 7.4 ± 1.3 and 8.9 ± 0.8 cm³ mol^-1 in water, 9.3 ± 0.3 and 12.2 ± 0.3 cm³ mol^-1 in N,N-dimethylformamide, 12.8 ± 0.6 and 9.9 ± 0.5 cm³ mol^-1 in methanol, and 12.6 ± 0.5 and 15.7 ± 1.1 cm³ mol^-1 in ethanol. The activation volume of the complex formation in acetonitrile is 9.4 ± 0.1 cm³ mol^-1. All the positive values of the activation volume strongly indicate that the ligand substitution reactions on nickel(II) ion proceed via a dissociative-interchange mechanism in these solvents.