Synthesis, X-ray structure, DFT and antimicrobial studies of Ag(I) complexes with nicotinic acid derivatives

The [Ag(Menic)₂(ClO₄)]₂, (1) and [Ag(NA)₂]ClO₄, (2) complexes, where Menic; methylnicotinate and NA; nicotinamide, were synthesized and characterized using elemental analysis, FTIR, NMR and single crystal X-ray diffraction combined with DFT calculations. The Ag(I) is coordinated with two organic ligand molecules in both complexes. In 1, the coordination sphere is completed by one ClO₄¯ anion as a monodentate ligand while in 2, the ClO₄¯ anion is in the outer sphere. Both complexes showed some argentophilic interactions where the AgAg distance is shorter in 1 (3.152(6) Å) than 2 (3.303(9) Å). The organic ligands showed no antimicrobial activity up to 15 mmole/L while both silver(I) complexes are biologically active against different bacterial strains and the fungus Candida albicans. The minimal inhibition concentrations (MICs) of the Ag(I) complexes are in the range of 4-8 mmol/L depending on the nature of microorganism. Complex 2 showed slightly better antifungal action than 1. In contrast, complex 1 showed higher antibacterial potency against P. aeruginosa, C. perfringens, Sh. sonnei and Str. pneumonia compared to 2. The antibacterial action of 2 is slightly higher or equal against the rest of microorganisms compared to 1. The strength and nature of the AgAg, AgN and Ag…O interactions were analyzed using atoms in molecules and natural bond orbital calculations.