The vanadium(II) reduction of tris(2,2′-bipyridine)cobalt(III) and the dissociation of the tris(2,2′-bipyridine)cobalt(II) product

Abstract

The rate law for the vanadium(II) reduction of Co(bipy)₃³⁺(bipy = 2,2′-bipyridine), is independent of hydrogen-ion concentration and of the form, rate =k[V²⁺][Co(bipy)₃³⁺]. At 25 °C and µ= 2·0M(LiClO₄), k= 1110 l mol^–1 s^–1ΔH‡= 3·6 ± 0·1 kcal mol^–1, and ΔS‡=–32·6 ± 0·4 e.u. The reaction is of the outer-sphere type. The subsequent dissociation (by aquation) of the product Co(bipy)₃²⁺ has also been studied and the mechanism is discussed. At 25° the rate constant k₁ for cleavage of the first chelate ring is 36·0 s^–1, ΔH‡₁= 12·4 ± 0·4 kcal mol^–1, and ΔS‡₁=–10·0 ± 1·6 e.u., µ= 2·0M(LiClO₄). Activation parameters are compared with those for the corresponding dissociations of Fe(bipy)₃²⁺ and Ni(bipy)₃²⁺.