Abstract

The redox behavior of the ligand 2-​mercaptonicotinic acid and its chromium(III) complex is studied in DMSO. The oxidn. of this compd. to the corresponding disulfide at +0.90 V vs. SCE is displaced at +0.20 V vs. SCE and -​0.05 V vs. SCE upon addn. of one and two equiv. of base resp. The addn. of chromium(III) to the ligand, both in its neutral and mono-​anionic form, does not produce any change in the spectrum or in the cyclic voltammograms, which indicates that there is very weak or no interaction from chromium. If the proton mercapto group is neutralized, a 1:3 complex is formed and the dimerization does not occur. This complex is characterized by polarog., cyclic voltammetry, controlled-​potential electrolysis, UV-​visible spectrometry and magnetic susceptibility measurements. The conditional formation const. is detd. by polarog. and spectroscopic methods, giving the values of 2.5×1014 and 1.5×1014 (25°C)​, resp.