Effects of Different Substituents on the Crystal Structures and Antimicrobial Activities of Six Ag(I) Quinoline Compounds

The syntheses and single crystal X-ray structures of [Ag(5-nitroquinoline)(2)]NO3 (1), [Ag(8-nitroquinoline)(2)]NO3 center dot H2O (2), [Ag(6-methoxy-8-nitroquinoline)(NO3)](n) (3), [Ag(3-quinolinecarbonitrile)(NO3)](n) (4), [Ag(3-quinolinecarbonitrile)(2)]NO3 (5), and [Ag(6-quinolinecarboxylic acid)(2)]NO3 (6) are described. As an alternative to solution chemistry, solid-state grinding could be used to prepare compounds 1 and 3, but the preparation of 4 and 5 in this way failed. The Ag(I) ions in the monomeric compounds 1, 2, 5, and 6 are coordinated to two ligands via the nitrogen atoms of the quinoline rings, thereby forming a distorted linear coordination geometry with Ag-N bond distances of 2.142(2)-2.336(2) angstrom and N-Ag-N bond angles of 163.62(13)degrees-172.25(13)degrees. The 1D coordination polymers 3 and 4 contain Ag(I) centers coordinating one ligand and two bridging nitrate groups, thereby forming a distorted trigonal planar coordination geometry with Ag-N bond distances of 2.2700(14) and 2.224(5) angstrom, Ag-O bond distances of 2.261(4)-2.536(5) angstrom, and N-Ag-O bond angles of 115.23(5)degrees-155.56(5)degrees. Hirshfeld surface analyses of compounds 1-6 are presented as d(norm) and curvedness maps. The d(norm) maps show different interaction sites around the Ag(I) ions, i.e., Ag center dot center dot center dot Ag interactions and possible O-H center dot center dot center dot O, C-H center dot center dot center dot O, C-H center dot center dot center dot N, and C-H center dot center dot center dot C hydrogen bonds. Curvedness maps are a good way of visualizing pi-pi tacking interactions between molecules. The antimicrobial activities of compounds 1, 2, and 6 were screened against 15 different multidrug-resistant strains of bacteria isolated from diabetic foot ulcers and compared to the antimicrobial activities of the clinically used silver sulfadiazine (SS). Compound 2 showed activity similar to SS against this set of test organisms, being active against all strains and having slightly better average silver efficiency than SS (5 vs 6 mu g Ag/mL). Against the standard nonresistant bacterial strains of Staphylococcus aureus, Pseudomonas aeruginosa, Proteus mirabilis, and Streptococcus pyogenes, compound 1 performed better than silver nitrate, with an average MIC of 6 mu g Ag/mL versus 18 mu g Ag/mL for the reference AgNO3. Electrospray ionization mass spectrometry (ESI-MS) analyses of compounds 3 and 6 in DMSO/MeOH confirm the two-coordinated Ag+ complexes in solution, and the results of the H-1 NMR titrations of DMSO solutions of 5-nitroquinoline and 8-nitroquinoline with AgNO3 in DMSO suggest that 5-nitroquinoline is more strongly coordinated to the silver ion.