Reactions of µ-hydroxo dicobalt complexes. Part VI. Equilibrium and kinetic studies on the reaction of chloride ions with the µ-amido-µ-hydroxo-bis[tetra-amminecobalt(III)] complex

Abstract

The cleavage of the hydroxo-bridge of the µ-amido-µ-hydroxo-bis[tetra-amminecobalt(III)] complex by chloride ions in aqueous perchloric acid solutions, µ= 2·0M(NaClO₄), has been studied. From spectrophotometric studies [graphic omitted] (i) at 554 nm, [Cl^–]= 0·2–0·5M and [H⁺]= 0·3 – 2·0M, the equilibrium constant K for (i) at 25° is 10·6 ± 1·4 l² mol^–2. Rate constants k_eq for the equilibration in (i) can be expressed, k_eq(s^–1)=k₁[H⁺][Cl^–]+k₂[Cl^–]+k_b where data for the back reaction k_b have been reported previously. At 25°k₁= 9·6 (± 0·2)× 10^–4 I² mol^–2 s^–1, k₂= 1·2 (± 0·2)× 10^–4 I mol^–1 s^–1, and k₁/k_–1= 11·9 ± 0·6 I² mol^–2, where the latter is in satisfactory agreement with the above value of K. From the temperature dependences ΔH₁‡= 16·2 ± 0·5 kcal mol^–1, ΔS₁‡=–18·1 ± 1·8 e.u., ΔH₂‡= 25·0 ± 3·9 kcal mol^–1 and ΔS₂‡= 7·4 ± 12·7 e.u. The further reaction with a second chloride (ii) is effective [Cl^–] > 0·5M. At 25°K₃= 0·09 ± 0·04 I mol^–1, and from equilibration studies k₃∼ 9 × 10^–5 I mol^–1 s^–1 and k_–3= 2·2 × 10^–3 s^–1 at 1·5° [graphic omitted] (ii)