Chromium(II) and vanadium(II) reductions of µ-amido-µ-chloro- and µ-amido-µ-bromo-bis[tetra-amminecobalt(III)] complexes

Abstract

Intermediate formation of Co(NH₃)₅H₂O²⁺ is observed in the Cr²⁺ reductions of the title complexes in aqueous solutions, I= 2·0M(LiClO₄), [H⁺]= 0·1–1·97M, but is not detected (<6%) in the corresponding V²⁺ reductions. Intermediate formation of Co(NH₃)₅X²⁺(X^–= Cl^–, Br^–) is observed in the latter with a 1 : 1 ratio of reactants. From pH and n.m.r. measurements it is concluded that (I) and not (II), equation (i), is predominant under the conditions [graphic omitted] investigated. The Cr²⁺ reactions are inner sphere and involve (I). The V²⁺ reactions proceed with outer-sphere reduction of (I) to give Co(NH₃)₅X²⁺ which reacts at about the same rate with a second V²⁺. Under pseudo-first-order conditions, with V²⁺ in large excess, build-up of Co(NH₃)₅X²⁺ as an intermediate is not therefore observed. Full kinetic data including activation parameters are reported.