Synthesis, structure and in vitro biological activity of pyridoxal N(4)-substituted thiosemicarbazone cobalt(III) complexes

Cobalt(III) complexes containing pyridoxal N(4)-substituted thiosemicarbazone ligands with the composition [Co(HL^1-2·Cl) (HL^1-2·H₂O)] (1-2) have been synthesized from the reaction of [CoCl₂(PPh₃)₂] and pyridoxal N-methyl-thiosemicarbazone hydrochloride (H₃L¹·Cl)/ pyridoxal N-phenyl-thiosemicarbazone hydrochloride (H₃L ²·Cl). The richness of the coordination chemistry of this ligand is highlighted by the modulation of its charge from neutral (H ₃L·Cl) (L) to dianionic (HL·Cl) (L^2-) and monoanionic forms (HL·H₂O) (L^-) and coordinated as tridentate binegative mode around cobalt(III) ion by forming neutral complex. The new complexes were characterized by various analytical and spectroscopic techniques (IR, electronic, ¹H NMR and ESI-Mass). The X-ray crystal structure of the complex 2, demonstrated distorted octahedral coordination geometry around the metal centre. Further, the investigation of effect of substitution (CH₃ or C₆H₅) on terminal N(4)-nitrogen of thiosemicarbazone exhibited its influence on the potential binding and cleavage ability with DNA, BSA binding, free radical scavenging and cytotoxicity.