Nucleophilic square-planar substitutions. Part I. Ionic-strength effects on the substitution of chloro- and bromo-diethylenetriamineplatinum(II) complexes by iodide ions

Abstract

The kinetics for the replacement by iodide ions of co-ordinated halogen from chloro- and bromo-diethylenetriamineplatinum(II) cations have been investigated at 25° over a range of concentrations of the nucleophile. At constant ionic strength, the plots of the pseudo first-order rate constants against iodide ion concentration are straight lines which pass virtually through the origin. The apparently large intercepts obtained from data previously reported by Gray are due to the fact that the ionic strength of the medium was not held constant, rather than to a relatively rapid background solvolysis. The second-order rate constants, k₂, calculated from the linear plots, obey the equation log k₂=A+Bµ^½, where A and B are constants at constant temperature, and µ is the ionic strength of the solution.