Electrochemical and spectroscopic investigation of the influence of acid-base chemistry on the redox properties of 2,5-dimercapto-1,3,4-thiadiazole

The UV-vis spectroscopy and cyclic voltammetry of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) were studied in the absence and presence of pyridine (Py) or triethylamine (TEA) in acetonitrile solutions in order to examine the influence of acid-base processes on the redox behavior of DMcT. In solutions containing Py, DMcT can be singly deprotonated to give the anionic species, DMcT^-. In solutions containing TEA, DMcT can be either singly or doubly deprotonated to give the anionic species, DMcT^-, or the dianion, DMcT^2-, depending on the stoichiometry. These acid-base processes were monitored using UV-vis spectroscopy, and those results are reported here. The cyclic voltammetry of both systems was also examined in the absence and presence of Py or TEA. These experiments clearly showed that deprotonation of DMcT results in facilitation of its electrochemical oxidation, leading either to a disulfide-containing dimer or a disulfide-containing polymer, depending on conditions. The relevance of these results to the use of DMcT as a cathode material in lithium secondary batteries is discussed.