Neutral and ion-pair silver(I) complexes of Schiff bases derived from methyl and ethyl carbazates with glyoxylic acid: Synthesis, structure, thermal behavior and cytotoxic activity

Abstract New hydrazone ligands methoxycarbonyl-hydrazono-acetic acid, (HL1) and ethoxycarbonyl-hydrazono-acetic acid, (HL2) generated from methyl and ethyl carbazates with glyoxylic acid, and their respective silver(I) complexes [Ag(HL1)(L1)].H2O (1) and [Ag(HL2)2]+1[Ag(L2)2]−1 (2) were synthesized and characterized by various physico-chemical techniques. Single crystal X-ray structures of the ligand, HL1 and complexes (1 & 2) were determined. In complex 1, the five coordination sites around silver are occupied by one each of a neutral bidentate (N, O) HL1 ligand, with a free carboxyl group and an anionic tridentate (O, N, O) L1 carboxylate ligand, while complex 2 is unique with a homo nuclear ion-pair nature. In the cationic moiety, the silver ion is hexa-coordinated to two neutral tridentate (O, N, O) hydrazone ligands with the binding carboxyl groups protonated; whereas in the anionic moiety, the silver ion is penta-coordinated with two negatively charged carboxylate ligands with one of them as bidentate (N, O) and the other as tridentate (O, N, O). Thermal data for the prepared complexes 1 and 2 show a low temperature endo-followed by an exothermic decomposition pattern as that of the Schiff base ligands (HL1 & HL2), in the range 175–350 °C to give metallic silver as the end residue, which was confirmed by PXRD, FTIR and FESEM analyses. All of the compounds are water soluble and hence used for biological studies, such as antimicrobial (antibacterial and antifungal stains) and anticancer activities (Hela, MCF-7, and compared with a normal cell HBL-100). From a biological screening test, the silver complexes tend to be a potential applicant expandable as efficient cytotoxic agents. Further, the path of cell death (apoptosis) was also examined through fluorescence staining methods (AO/EtBr and DAPI).