Synthesis, spectroscopic characterization, DFT calculations and antimicrobial properties of silver(I) complexes of 2,2′-bipyridine and 1,10-phenanthroline

Silver(I) complexes of 2,2′-bipyridine (bpy) and 1,10-phenanthroline (phen), namely [Ag(bpy)₂]NO₃, [Ag(bpy)(CN)]·bpy, [Ag(phen)₂]NO₃, [Ag(phen)(CN)] and [Ag(phen)(CN)]·phen, were prepared and characterized by elemental analysis and IR, ¹H and ¹³C NMR spectroscopies. In the nitrate complexes, both the bpy or phen ligands were bound to the Ag(I) ion, whereas in the cyanide complexes only one N,N′-chelating ligand was found in the inner coordination sphere. For a reliable interpretation of the experimental IR and NMR spectra of the complexes studied, molecular modelling and the corresponding spectral calculations were performed using density functional theory (DFT). The spectroscopic data were consistent with the presence of N,N′-bidentate linked bpy and phen ligands in the complexes and indicated coordination of the cyanido group to the Ag(I) ion. The antimicrobial activities for two of the complexes were evaluated by minimum inhibitory concentration experiments and the results showed that the complexes (especially [Ag(phen)₂]NO₃) exhibited significant activities against gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) and molds (Aspergillus Niger, Penicillium citrinum), while their activity against yeasts (Candida albicans, Saccharomyces cerevisiae) was poor.