Synthesis, spectroscopic characterization, crystal structure, Hirshfeld surface analysis and antimicrobial activities of two triazole Schiff bases and their silver complexes

Abstract

The present work describes the synthesis, structural characterization, Hirshfeld analysis, and antibacterial assays of two hydroxy Schiff bases with triazole moiety: N-[(E)-(3-hydroxy)methylidene]-4H-1-2-4 triazol-4-amine (L1) and N-[(E)-(2,4-dihydroxy)methylidene]-4H-1-2-4 triazol-4-amine (L2). The interaction of these two Schiff bases with AgNO3 leads to Ag(I) dimer [Ag(L1)](NO3) in the case of the first ligand (L1) and polymer [Ag(L2)]n(NO3)n(H2O) for (L2). Crystal structure determination and Hirshfeld analysis reveal the presence of two important hydrogen bond interactions in the four compounds, O…H and H…N, involving nitrogen atoms of triazole ring. Contribution of these two types of hydrogen bonds evolves inversely from (L1) which contains one –OH, to (L2) containing two –OH, then to [Ag(L1)](NO3) dimer and finally to [Ag(L2)]n(NO3)n(H2O) polymer. Indeed, we observed an increase of the percentage to the Hirshfeld surfaces of O…H contribution from (L1) to [Ag(L2)]n(NO3)n(H2O) passing by (L2) and [Ag(L1)](NO3), while the percentage of N…H decrease in the same way. Antibacterial activity of the free ligands (L1), (L2) and their silver complexes [Ag(L1)](NO3) and [Ag(L2)]n(NO3)n(H2O) were evaluated against four Gram-negative (E. coli, Salmonella typhimurium, Klebsiella pneumoniae and Serratia marcescens) and two Gram-positive (Staphylococcus aureus, streptococcus) bacteria strains, using the standard antibiotics, Colistin, Fosfomycin, Gentamycin, Erythromycin, Rifampicin, Amikacin, Ofloxacin and Amoxicillin as positive controls. AgNO3 salt was also used as second control test. The results of this evaluation reveal that, while the two Schiff bases inhibit the growth of the Serratia Marcescens bacterium only, the two Ag(I) complexes are active for all bacteria, with activities comparable to the ones of silver nitrate. However, [Ag(L2)]n(NO3)n(H2O) complex appears significantly more efficient than the AgNO3 salt against Klebsiella Pneumoniae.