The kinetics of the decomposition of amido- and superoxo-bridged binuclear complexes of cobalt

Abstract

The kinetics of the decomposition of the single-bridged decammine µ-amido- and µ-superoxo-dicobalt complexes (NH₃)₅Co·NH₂·Co(NH₃)₅⁵⁺ [graphic omitted] Co(NH₃)₆³⁺+ Co(NH₃)₅H₂O³⁺, and (NH₃)₅Co·O₂·Co(NH₃)₅⁵⁺ [graphic omitted] Co(NH₃)₅H₂O³⁺+ Co²⁺+ 5NH₄⁺+ O₂, have been studied in aqueous perchloric acid, µ= 2·0M, in the range 47·3–80°. Both reactions are first-order in complex and independent of hydrogen-ion concentration in the range 0·02–2·0M. At 64·6°k₁= 13·5 × 10^–5 sec.^–1 and k₂= 6·65 × 10^–5 sec.^–1; the activation parameters are ΔH₁^‡= 31·5 ± 1·2 kcal. mole^–1, ΔS₁^‡= 5·6 ± 3 e.u., ΔH₂^‡= 28·1 ± 1·2 kcal, mole^–1, and ΔS₂^‡= 17 ± 3·5 e.u. respectively.

In the decomposition of the double-bridged complex (NH₃)₄Co·µ(NH₂,O₂)·Co(NH₃)₄⁴⁺ at 85° and µ= 2·0M, the rate constant for the disappearance of complex is ca. 4·1 × 10^–5 sec.^–1. Evidence for the formation of a single-bridged intermediate is considered.