Complexes of Cd(II) with Nicotinamide, Nitrate, and Oxalate as Mixed Ligands: Synthesis, Characterization, and Biological Activity

Three complexes of Cd(II), [Cd(NA)2(NO3)2(H2O)2] (1), [Cd(NA)2(NO3)2(H2O)2]·2NA (2), and [Cd(ox)(NA)(H2O)]·H2O (3) (NA = nicotinamide, ox = oxalate) were synthesized and characterized. Complexes (1) and (2) are mononuclear, while complex (3) is a bidimensional polymeric coordination compound, with oxalate anions bridging metal ions in two different ways: µ2 bis-bidentate chelating manner and µ4 bis-bidentate bis-monodentate manner. The stereochemistry of Cd(II) in compounds (1) and (3) is a distorted pentagonal bipyramid, while in compound (2) it is a regular octahedron. Complexes (1) and (2) demonstrated significant activity against Enterococcus faecalis and Escherichia coli, showcasing their potential as effective antibacterial agents and inhibitors of microbial adhesion. The complexes were characterized by means of single-crystal X-ray diffraction, elemental analysis, FTIR (all complexes), 1H NMR, 13C NMR, fluorescence spectroscopy, and antimicrobial activity (complexes (1) and (2)).