Possible tests for the mechanisms of ligand exchange in solids: The deaquation-anation of [Cr(NH 3) 5(H 2O)]X 3 salts

Abstract

The possibility of using correlations of Δ H + and Δ H, and of Δ H + and Δ S + to gain insight into the mechanisms of ligand-exchange reactions in solids are discussed. These correlations are tested using literature values for the deaquation-anation reactions of [Cr(NH 3) 5(H 2O)]X 3, where X − = Cl −, Br −, I − or NO − 3. The poor agreement in the activation parameters reported in the literature precluded a meaningful test of the Δ H−Δ H * correlation. This poor agreement suggests that these activation parameters are strongly influenced by experimental factors that have not been controlled in studies to date. nevertheless, there is a linear correlation of Δ H † and Δ S † which gives an isokinetic temperature of 367 ± 11 K. This isokinetic behavior suggests that the same mechanism is operative throughout the series.