Reactions of metal complexes in solution. Part II. The effect of chloride ion on the rate of the acid-catalysed aquation of trans-dinitrotetramminecobalt(III) nitrate

Abstract

The acid-catalysed aquation of trans-dinitrotetramminecobalt(III) nitrate has been studied in the presence of chloride ions over a temperature range 25–40° at an ionic strength of 2·5M. In the acid range [H⁺]= 0·1–1·5M at [Cl^–]= 2·0M, the increase in the rate may be interpreted in terms of the reactions of the ion-pairs [Co(NH₃)₄(NO₂)₂]⁺Cl^–, [Co(NH₃)₄(NO₂)(NO₂H)]²⁺Cl^–, and [Co(NH₃)₄(NO₂H)₂]³⁺Cl^–. Rate constants for each reaction have been obtained and thermodynamic parameters derived. The results are consistent with a reaction scheme involving a solvent-assisted dissociative mechanism.