Evidence of a stable charge-transfer adduct between 2-mercaptoethanol and cobalt-polytetraaminophthalocyanine

The electro-oxidation of 2-mercaptoethanol by poly-Co-tetraaminophthalocyan ine (p-CoTAPc) and poly-metal-free-tetraarainophthalocyanine (p-H(2)TAPc), absorbed on electrode surfaces has been investigated by UV-visible spectroe lectrochemistry and electrochemical techniques. In the case of p-CoTAPc, an irreversible oxidation wave is obtained by cyclic voltammetry, whereas p-H (2)PcTA practically does not show activity. The foot of the oxidation, as t he open circuit potential measurements indicate that the responsible redox couple is Co(II)/Co(I). The p-CoTAPc modified-electrode loses its activity after a first potential cycle. UV-visible spectroelectrochemical measuremen ts show a charge transfer band (metal to ligand) for the p-CoTAPc between Q and Soret bands when negative potentials are applied and Co(I) is obtained . The presence of 2-mercaptoethanol promotes the appearance of the charge t ransfer band at open circuit potential and retain this band even at potenti als as positive as +0.2V where normally the Co center is in +2 oxidation st ate. The permanence of a stable charge transfer band indicates the formatio n of a stable charge-transfer adduct between Co(I) and the thiol. This addu ct would be responsible for the loss of catalytic activity for p-CoTAPc aft er the first oxidation cycle.