The tris(picolinate)vanadate(II) ion: Redox properties and electron transfer kinetics with cobalt(III) amines

Abstract

Vanadium(II) ions form with the pyridine-2-carboxylate ligand a deep blue, tris-substituted complex absorbing at 660 nm (ε = 7.2 × 10 3 M −1) cm −1) with a shoulder at 450 nm. Reversible spectroelectrochemistry and cyclic voltammetry were observed for this complex, with E 1 2 = −0.448 V vs NHE, and Δ S rc θ = −6 cal · mol −1 · deg −1. Electron transfer kinetics with [CO(en) 3] 3+ led to k 12 = 3100 M −1 s −, Δ H ≠ = 12.4 kcal · mol −1 and Δ S ≠ = −0.9 cal · mol −1 · deg −1 ( I = 0.10 M). For the related [Co(NH 3) 6] 3+ complex, k 13 = 1.9 × 10 4 M −1 s −1. The self-exchange rate constant and activation parameters were analysed in terms of relative Marcus theory.