Synthesis, structure diversity, and antimicrobial studies of Ag(i) complexes with quinoline-type ligands

Abstract

Compounds [Ag(5NO₂Qu)₂]BF₄ (1) and [Ag(Qu3CN)(H₂O)]BF₄ (2) were prepared and studied from a structural perspective and screened for antimicrobial activity. The Ag(I) in the monomeric complex 1 is coordinated to two 5-nitroquinoline (5NO₂Qu) ligands via the N-atoms of the quinoline rings with equidistant Ag–N bonds (2.146(2) Å) and a N–Ag–N^# bond angle of 171.42(8)°. The 2D coordination polymer 2 contains tetracoordinated Ag(I) with two N-atoms (N1 and N2^#1) from two quinoline-3-carbonitrile (Qu3CN) ligands and two O-atoms (O1 and O1^#1) from two water molecules. The Qu3CN ligand acts as a connector between the Ag(I) sites along the b-direction via two short Ag1–N1 (2.185(4) Å) and Ag1–N2^#1 (2.204(4) Å) bonds. In addition, the Ag(I) is coordinated with two symmetry related water molecules which are also acting as connectors between the Ag(I) sites along the a-direction via two longer Ag1–O1 (2.470(4) Å) and Ag1–O1^#2 (2.546(4) Å) bonds. Hirshfeld surface analysis confirmed the significance of the polar F⋯H contacts in the molecular packing of 1 (25.9%) and 2 (39.9%). In addition, the crystal packing of 1 showed a significant amount of polar O⋯H (23.5%) contacts. Also, both complexes displayed π–π stacking interactions. The Ag(I) complexes and the free ligand were assessed for their antimicrobial activities. It was found that 1 (MIC = 7.8 μg mL⁻¹) and 2 (MIC = 31.25 μg mL⁻¹) have higher antifungal potency against C. albicans than their free ligands (MIC = 125 μg mL⁻¹). Interestingly, 1 has better antifungal activity than the standard nystatin (15.6 μg mL⁻¹). Also, both Ag(I) complexes and the free ligands as well have better activity against P. mirabilis than the common antibiotic amoxicillin.