Silver(I) complexes of N,N′-diarylformamidine ligands: Synthesis, crystal structures, and in vitro antibacterial studies

Nine silver(I) N,N '-diarylformamidine complexes of type [Ag (Ln)(2)X] (where X = NO3-, CF3COO-, and CF3SO3-, n = 1-5) were synthesised and characterised by physiochemical and spectroscopic techniques. Further confirmation for the formation of the complexes was provided by single-crystal X-ray crystallography. All complexes (but one) adopted linear geometry in which coordination was via two N atoms of two formamidine ligands with the anion (X) displaced from coordination sphere. In the structure of the exception, the anion is part of the coordination sphere and a T-shaped geometry was adopted. The antimicrobial activity of the Ag(I) complexes were investigated against two Gram-positive bacteria, that is, S. aureus ATCC 25923 and Methicillin-resistant S. aureus ATCC 700699 (MRSA) and four Gram-negative bacteria, that is, K. pneumoniae ATCC 31488, S. typhimurium ATCC 14026, P. aeruginosa ATCC 27853 and E. coli ATCC 25922 and they were evaluated based on ciprofloxacin and silver nitrate standards. The newly synthesised target complexes demonstrated promising antibacterial activity against Gram-positive bacteria although less than the reference drug ciprofloxacin. The best active silver(I) complex contains a nitrate counter-ion.

Automated summary

Nine silver(I) complexes with N,N'-diarylformamidine ligands and different anions were synthesized and characterized. The structures of these complexes were confirmed by single-crystal X-ray crystallography. All complexes except one showed linear geometry with coordination of two N atoms from the formamidine ligands and displacement of the anions from the coordination sphere. The exception adopted a T-shaped geometry with the anion included in the coordination sphere. The antibacterial activity of the complexes was evaluated against Gram-positive and Gram-negative bacteria, and the best activity was observed for the complex with a nitrate counter-ion.