Medium controlled redox activity and coordination behavior of a triazole indolinone ligand with vanadyl lons.

The electrochemical behavior of 3-(2-(4-amino-5-mercapto-4 H-1,2,4-triazol-3-yl)hydrazono)indolin-2-one (H2TIS) was investigated by cyclic voltammetry at a glassy carbon electrode at 303.15 K. The redox response of H2TIS was found to be strongly medium dependent. In acidic medium (0.1 M HNO3), the anodic process is attributed to a ligand centered oxidation involving proton-coupled electron transfer, while the cathodic response corresponds to reduction of the indolin-2-one carbonyl group. In neutral medium (0.1 M KCl), the carbonyl moiety displays a quasi-reversible redox couple. Conversely, in an alkaline medium (0.1 M NaOH), only a single irreversible anodic peak is observed, which is attributed to the oxidation of the deprotonated thiolate moiety, plausibly leading to the formation of disulfide linked dimeric species. The electrochemical behavior of vanadyl ions (VO2+) was also studied in 0.1 M KCl, both in the absence and presence of H2TIS. The VO2+ system exhibits a quasi-reversible redox reaction under near-neutral conditions, while coordination with H2TIS induces potential shifts and increases the electrochemical stability of the metal center. Stoichiometric analysis based on cyclic voltammetry, Job’s method and molar ratio plots suggest formation of 1:1 and 1:2 VO2+-H2TIS complexes in solution. These findings highlight the medium-dependent redox versatility of H2TIS and the promising electrochemical properties of the VO2+ complexes.