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• A series of mixed-ligand complexes was synthesized by using a Schiff base as main ligand and nicotinamide as secondary ligand. • The Schiff base was prepared by the interaction of ampicillin drug and 4-chlorobenzophenone. • The DFT calculations and molecular docking analysis were carried out. • The synthesized complexes exhibited significant antimicrobial activity. • The drug-likeness and toxicity of the compounds were also performed. A novel series of mixed-ligand complexes of the type, [ML 1 (L 2) 3 Cl x [M= Cr(III), Fe(III), Co(II),Ni(II), Cu(II), Cd(II) and Hg(II), n = 2, 3], was synthesized using Schiff base (HL 1) as main ligand, nicotinamide (L 2) as secondary ligand, and the corresponding metal ions in 1:3:1 molar ratio. The main ligand, HL 1 was prepared by the interaction of ampicillin drug and 4-chlorobenzophenone. The synthesized mixed ligand complexes were characterized by elemental analysis, UV-Vis, FT-IR,1H-NMR,13C-NMR and TG/DTG studies. In the mixed-ligand complexes, the Schiff base ligand, HL 1 showed coordination to the central metal ion in tridentate manner via azomethine nitrogen, β-lactam ring oxygen and deprotonated carboxylic oxygen atoms, whereas the secondary ligand L 2 (nicotinamide, Nam) coordinated through pyridine nitrogen atoms. The synthesized complexes exhibited significant antimicrobial activity when evaluated against P. pseudomonas, E. coli, S. aureus and B. subtilis microbes. The DFT calculations were also carried out to ascertain the bonding insights into the structure. In addition, molecular docking analysis was performed carried out to know the interactions between complexes and their probable binding sites in penicillin binding protein (PBP2). Moreover, drug-likeness and toxicity of the compounds were also performed to predict the suitability of the complexes as drugs. Image, graphical abstract [ABSTRACT FROM AUTHOR]