Spectroscopic and electrochemical studies on linkage isomerism in iron(II) complexes of benzotriazole, a corrosion inhibitor

Benzotriazole reacts with the aquapentacyanoferrate(II) complex, at pH 4.5, producing a mixture of N-coordinated isomers. Characterization based on 1H and 13C nmr spectroscopy yielded an equilibrium constant K = 1.9 ± 0.3, favoring the less symmetric N1-isomer. Two reversible peaks of oxidation, corresponding to the N1 and N2 isomers, were observed in the cyclic voltammograms at high scan rates, with E1/2 = 0.43 and 0.53 V versus NHE, respectively. The cyclic voltammograms at intermediate scan rates were successfully analysed in terms of an isomerization reaction preceding reversible charge-transfer. The kinetic constants of isomerization, kf and kb, were 1.5 and 0.65 s−1, respectively. The limiting dissociative rates, k−L = 5.3 × 10−3 s−1, measured in the presence of dimethyl sulfoxide, support an intramolecular mechanism for the isomerization reaction.