Reactions of metal complexes in solution. Part IV. Medium effects in the acid-catalysed aquation of the tetranitrodiamminecobaltate(III) ion

Abstract

The acid-catalysed aquation of the tetranitrodiamminecobaltate(III) ion has been investigated over the temperature range 25–35° at an ionic strength of 2·5M in hydrochloric, nitric, and perchloric acid media. In the acid concentration range 0·5–2·5M, the increase in rate may be interpreted in all cases in terms of the reactions of the complex ions Co(NH₃)₂(NO₂)₄^–, Co(NH₃)₂(NO₂H), and Co(NH₃)₂(NO₂)₂(NO₂H)₂⁺. The retardation of the rate in hydrochloric and nitric acid media has been shown to involve the formation of ion-pairs. Reaction rate constants and thermodynamic parameters have been derived. Mechanisms of the reactions are discussed.