Green Protocol for Design, Synthesis, and Biological Evaluation of New Schiff Base Complexes of Co(II), Ni(II), Zn(II), and Cd(II) Metal Ions

ABSTRACT New Schiff base ligands, benzyl‐2‐((4‐bromothiophen‐2‐yl)methylene)hydrazine‐1‐carbodithioate (L 1 ), and 2‐((4‐bromothiophen‐2‐yl)methylene)hydrazine‐1‐carbothioamide (L 2 ) were prepared by condensation of respective 4‐bromothiophene‐2‐carbaldehyde with s‐benzyldithiocarbazate and thiosemicarbazide. Their Co(II), Ni(II) Zn(II), and Cd(II) complexes were synthesized by conventional as well as microwave irradiation methods. Metal salts react with the ligands in 1:2 M ratio to give colored products. The compounds were characterized by elemental analyses, magnetic measurements, and spectroscopic techniques (FT‐IR, UV–Vis, mass, powder XRD, 1 H NMR, and 13 C NMR). Based on the magnetic measurement and spectral data, an octahedral environment for Co(II) and Ni(II) complexes and a tetrahedral structure for Zn(II) and Cd(II) complexes have been proposed. The ligands and their Co(II), Ni(II), Zn(II), and Cd(II) complexes were screened for antibacterial, antifungal, antioxidant, antimycobacterial, and anticancer activities. The synthesized metal(II) complexes were active toward bacterial ( E. coli , B. subtilis ) and fungal ( A. niger , P. chrysogenum ) strains. Antioxidant studies indicate that the Zn(II) and Cd(II) complexes possess maximum radical scavenging activity. The synthesized ligand (L 1 ) and metal(II) complexes were screened for their antimycobacterial properties against Mycobacterium tuberculosis using the BD BACTEC™ MGIT™ DST method. One of the compounds, Ni(L 1 ) 2 ·2H 2 O, rested the growth of Mycobacterial tuberculosis bacteria. The anticancer activity of the compounds against cancer cell lines MCF‐7 and HeLa was performed using the MTT cell viability method. The results showed that M(II) complexes are more sensitive towards the cancer cell line in comparison to the free ligand.