Structural diversity of the Ag coordination sphere in complexes of silver(I) nitrate with 3-halopyridine. Characterization of the complexes in solution and in the solid state

Abstract

Three 1:2 complexes of Ag(I) nitrate with 3-halopyridine of the general formula [Ag(NO3)(3-Xpy)2], X=Cl (1), Br (2), I (3), were prepared and characterized by elemental analysis, IR spectroscopy, mass spectrometry, multinuclear NMR spectroscopy in solution (1H, 13C, 15N, 109Ag) and in the solid state (13C, 15N), by powder and by single-crystal (1 and 3) X-ray analysis. Data showed that in complexes 1 and 3 the Ag atoms are coordinated by two halopyridine ligands through the N atoms and by various number of nitrate groups resulting in three-, four- and five-coordinated Ag atoms. Single point DFT calculations, followed by NPA and QTAIM analyses, were performed to understand the nature of bonding in the crystal structures. Three types of interactions were detected: coordinate Ag–N bonding, weaker Ag–O ionic bonding and in 3 weak Ag–Ag closed-shell bonding with a small covalent contribution. In vitro tests of all complexes gave better antibacterial activity when tested against Gram-negative than Gram-positive strains.