A series of 2-(4-sulfamethazine)hydrazono-5,5-dimethylcyclohexane-1,3-dione (HL) and its complexes of Co(II), Ni(II) and Cu(II) (1–3) were synthesized. Elemental measurements, FTIR, 1H NMR, 13C NMR, UV–Visible, X-ray diffraction analysis, and magnetic measurements have characterized the ligand and its complexes. By coordinating with the oxygen atom of the carbonyl group (C=O) and through the hydrazone moiety nitrogen atom(-NH-) with deprotonation, the ligand (HL) functions as amonobasic bidentate ligand. The coordination geometry of the complexes Co(II) andNi(II) is octahedral, where the complex Cu(II) is square planar. The ligand and its complexes were determined with the optimized bond lengths, bond angles and quantum chemical parameters. The ligand and its complexes calfs thymus DNA linking activity was examined through absorption spectra and viscosity measurements. Results of the evaluation of synthesized compounds against the Sections of MCF-7 and HepG-2 active tumor cells have been published in the viability assay for vinblastine and colchicine, relative to positive controls. The DPPH free radical-scavenging assay specifies the in vitro anti-oxidant function of all complexes. Finally, fungal (Candida albicans), gram-negative (Escherichia coli) and gram-positive (Staphylococcus aureus) bacteria have been investigated for the anti-microbial activities of the complexes using the disc diffusion process. Molecular docking was used to predict the binding of SARS-CoV-2 key protease in complex COVID-19 (5REA) between the ligand and breast cancer mutant (3hb5) receptor and the crystal structure.