Reactions of µ-hydroxo-dicobalt complexes. Part VII. The decomposition of the µ-amido-µ-hydroxo-bis[tetra-amminecobalt(III)] complex in aqueous perchlorate solutions and related studies

Abstract

The decomposition of the µ-amido-µ-hydroxo-complex (NH₃)₄Co·µ(NH₂,OH)·Co(NH₃)₄⁴⁺ occurs in two stages. Two steps are involved in the first stage, (i), and the product is the bisaquo-complex (NH₃)₃(H₂O)Co·µ(NH₂,OH)·Co(H₂O)(NH₃)₃⁴⁺, which is present in different isomeric forms. With the assumption that k′₀∼k₀/2, and that [graphic omitted](i) similar spectrophotometric changes are observed, k₀= 4·3 × 10^–5 s^–1, (at 35°), ΔH₀^‡= 25·2 ± 0·4 kcal mol^–1 and ΔS₀^‡= 3·3 ± 1·4 e.u., µ= 2·0M(LiClO₄). The Cr²⁺ reduction of the bisaquo-complex follows the rate law (k₁+k₂[H⁺]^–1)[Cr²⁺][Complex], and with V²⁺ the rate law is k₃[V²⁺][Complex]. At 35° and with µ= 2·0M(LiClO₄)k₁= 0·07 l mol^–1 s^–1, k₂= 0·18 s^–1 and k₃= 0·104 l mol^–1 s^–1. Rate constants for the equilibration of the µ-amido-di-µ-hydroxo- and symmetrical bisaquo-complexes at 25° are k₄= 30 ± 2 l mol^–1 s^–1 and k_–4= 0·41 ± [graphic omitted](ii) 0·07 s^–1, [µ= 2·0M(LiClO₄)]. From spectrophotometric measurements K₄(=k₄/k_–4) is 66 ± 1 l mol^–1 at 25°. Final products following the second stage of the decomposition are ca. 75% cobalt(II) and ca. 25% mononuclear cobalt(III). The mechanism of the second stage is at present uncertain.