A new thiourea ligand (HL), namely N-(4-chlorophenyl)morpholine-4-carbothioamide and its Co(III), Ni(II) and Ag(I) complexes (1a, 1b and 1c) were synthesized and investigated by Fourier-transform infrared, 1H NMR and UV-visible spectroscopies. The compounds HL and 1c were characterized by single-crystal X-ray crystallography revealing the triclinic space group P[Formula: see text] for both compounds. The inhibitory effect of HL ligand, 1a, 1b, and 1c complexes was investigated with in vitro tests on Gram-positive and Gram-negative bacteria. For the 1c complex, the results showed that the coordination of the HL to Ag(I) ion increased its antibacterial effect especially against E. coli. The assays also indicated that for the same bacteria strains, the new complexes showed higher activity than the ligand, with the relative activity 1c > 1b > 1a > HL. Moreover, all samples were more suitable antimicrobial agents against the Gram-negative than those of the Gram-positive bacteria. Eventually, the relationship between the structure and bactericidal activities of these specimens was examined by calculating frontier molecular orbital (HOMO and LUMO) energies using density functional theory method at the 6-31 G*/LANL2DZ level of theory.