The aquation of trans-bis(ethylenediamine)difluorochromium(III) and related lons in aqueous solutions of strong acids

Abstract

The hydrolysis of a series of fluoro-complexes in aqueous solutions of strong acids has been studied over a wide range of acid concentrations. The kinetic results have been analysed by the treatments of Hammett and Zucker, Bunnett, and Bunnett and Olsen. Analysis of the results indicates that hydroxonium ion acts as a proton-transfer agent in the rate-determining step. The mechanism involves attack by hydroxonium ion adjacent to the leaving protonated fluoro-ligand and should lead to retention of configuration. The hydrolysis of trans-[Cr(en)₂F₂]⁺(en = ethylenediamine) ion in perchloric acid is catalysed by added sodium fluoride, maximum catalysis being effected by only a five-fold excess of fluoride ion over complex-ion concentration. Addition of other salts has no effect on the rate constants, demonstrating that general acid–base catalysis is not involved.