Interaction of the polyfunctional 2-mercaptonicotinic acid with the ruthenium(III)-edta complex

Abstract

Ruthenium(III)-edta reacts with the 2-mercaptonicotinic ligand in aqueous solution yielding a red product ( λ max = 530 nm) coordinated at the S atom. This species undergoes deprotanation with an apparent pK a = 3.80, generating a blue complex in which the ligand is ( S, N)-bidentate. In the presence of two times excess of ruthenium(III)-edta a binuclear species is formed, involving two bidentate ( N, S) and ( S, O) coordination modes for the bridging ligand. The corresponding mixed-valence species exhibits a strong intervalence band at 8000 cm −1, involving an electronic coupling energy of 990 cm −1. An extensive investigation is reported for the complexes, based on kinetics, cyclic voltammetry and spectroelectrochemistry.