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 Ag-Ag distance is shorter in 1 (3.152(6) angstrom) than 2 (3.303(9) angstrom). 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 Ag-Ag, Ag-N and Ag center dot center dot center dot O interactions were analyzed using atoms in molecules and natural bond orbital calculations.