Palladium (II) complexes with thione and thioalkylated thiosemicarbazones: Electrochemical, antimicrobial and thermogravimetric investigations

Four methoxy substitute salicylidene thiosemicarbazones were synthesized. The reaction of both thione and thioalkylated thiosemicarbazones with PdCl2 in ethanol yields ONS-coordinated chelate complexes with general formula [Pd(L)Cl]. The structures of eight compounds were characterized by using analytical and spectroscopic methods. Electrochemistry of the Pd(II) complexes was studied using cyclic voltammetric technique. The CVs of the complexes were quite complicate because of some oxidative responses of the ligands which proceed by forming conjugated –N=CH–, –HC=CH– and –N=CH–HC=CH– groups. Two cathodic responses attributed to one electron reduction of Pd(II)/(I) and Pd(I)/(0) were observed for the central ion coordinated with S atom of H3C–S– group whereas only one reduction peak appeared when the Pd(II) coordinated with S atom of >C=S group of thiosemicarbazone ligand. The latter also showed an additional anodic response assigned to Pd(II)/(III) oxidation. Thermogravimetric analysis (TGA) technique was used to investigate and compare the thermal properties of the ligands and their metal complexes. In vitro antimicrobial activity of thiosemicarbazones and their complexes was evaluated against four Gram-negative bacteria, three Gram-positive bacteria, and antifungal activity against three fungi. [Display omitted] •Four ONS-type palladium(II) complexes of both thione and thioalkylated thiosemicarbazones were synthesized.•The Pd(II) ion coordinated with thione thiosemicarbazones can be oxidized to Pd(III), but not with thioalkylated ones.•The Pd(II) complexes exhibited higher inhibitory activity than the corresponding ligands.•The thermogravimetric analysis of the ligands and Pd(II) complexes was studied in order to evaluate their thermal behavior.