Experimental and quantum chemical studies of sulfamethazine complexes with Ni(II) and Cu(II) ions

[Ni(SZ)Cl(H₂O)₃]2H₂O and [Cu(SZ)(NO ₃)(H₂O)₂]2H₂O (HSZ = 4-amino-N-(4,6-dimethyl-2-pyrimidinyl) benzenesulfonamide, sulfamethazine) have been synthesized and characterized by experimental and theoretical methods at the DFT/B3LYP/LANL²DZ level of theory. Ni(II) is coordinated by sulfonamidic (N¹5) and pyrimidic (N23) of the sulfamethazine drug, three water molecules, and one chloride forming a distorted octahedral geometry, while the Cu(II) complex has a square pyramidal geometry with the same ligand N,N active binding sites. Natural bond orbital (NBO) analysis of CuSZ reveals the participation of the coordinated NO^-3 in triple H-bonds of different strengths with hydrated water molecules, LP(2)O ₃3→σ/(O₄5-H₄6), LP(2)O ₄₀→σ/(O₄5-H₄4), and LP(2) O ₃8→σ/(O₄8-H₄7). The voltammogram of NiSZ shows one cathodic and one anodic peak. The complexes and NaSZ were screened for their antibacterial activity.