Synthesis, characterization and antimicrobial activity of a bidentate NS Schiff base containing S-allyl dithiocarbazate and its complexes

Reaction of S-allyl dithiocarbazate (SADTC) with 2,4,5-trimethoxy benzaldehyde afforded a bidentate NS Schiff base (1) (allyl-3-N-(2,4,5-trimethoxyphenylmethylenehydrazine carbodithioate), which on subsequent reaction with M(II) (M = nickel (II), zinc(II) and copper (II)) ions in methanol yielded bis-chelated inner complexes, ML₂ (2,3,5), while it formed a tris-chelated ML₃ (4) complex with Co(III) with deprotonated ligand (L). All the compounds were characterized by physico-chemical techniques, viz., molar conductance, magnetic susceptibility measurement, IR, NMR, UV/Vis spectroscopy and mass spectroscopic techniques. The crystal structure of 1 and 2 was also determined by single crystal X-ray crystallography. The crystal structure analyses showed that 1 exists in its thione tautomeric form, which underwent deprotonation of its imide (NH) proton via thiol form (SH) in its nickel (II) complex 2. The complex exhibited a trans-planar geometry. In the complexes (2,3,5), each of the two deprotonated ligands chelated the metal ions through the azomethine nitrogen and thiolate sulfur atom forming five membered rings. In contrast, a six coordinated octahedral complex 4 was obtained with Co(II) with three deprotonated ligands where Co(II) was oxidized to Co(III) during reaction. Among the test compounds, only the ligand and its cobalt (III) complex showed significantly strong antibacterial activity against S.-β -haemolyticus, K. pneumoni and E. coli respectively. In contrast, solely the cobalt (III) complex exhibited potential antifungal activity against A. fumigates, A. niger and C. albicans respectively. Overall, the complex showed strong activity than the corresponding ligand.