Syntheses, structures and antimicrobial activities of water-soluble silver(i)–oxygen bonding complexes with chiral and racemic camphanic acid (Hca) ligands

Abstract

Water-soluble, relatively light-stable, chiral and achiral silver(I) complexes {[Ag₂(ca)₂]}_n and {[Ag₂(ca)₂(Hca)₂]}_n (R- and S-Hca = (1R,4S)- and (1S,4R)-4,7,7-trimethyl-3-oxo-2-oxabicyclo[2.2.1]heptane-1-carboxylic acid, respectively) prepared from the reaction of Ag₂O with chiral and racemic Hca in 1 ∶ 2 and 1 ∶ 4 molar ratios were characterized by elemental analysis, TG/DTA, FTIR, and solution (¹H, ¹³C and ¹⁰⁹Ag) and solid-state (¹³C) NMR spectroscopy. Crystallography revealed that unique 2₁ helical polymer and zigzag structures were formed on self-assembly of the dimeric units in the crystals of {[Ag₂(S-ca)₂]}_n and three {[Ag₂(ca)₂(Hca)₂]}_n. In the crystal of {[Ag₂(S-ca)₂]}_n two 2₁ helices and a loop were observed in the stair-like polymer structure, whereas zigzag and a loop were seen in the crystals of three {[Ag₂(ca)₂(Hca)₂]}_n. Carbon NMR spectra in the solid state and in D₂O indicated that these polymeric structures were loosely bound and fast ligand-exchange reactions took place in aqueous solution. The complexes, {[Ag₂(ca)₂]}_n and {[Ag₂(ca)₂(Hca)₂]}_n, showed a wide spectrum of effective antimicrobial activity as anticipated for weak silver(I)–O bonding complexes. Similar antimicrobial activity of {[Ag₂(ca)₂]}_n and {[Ag₂(ca)₂(Hca)₂]}_n against selected microorganisms suggested that ligand exchangeability played an important role as well as the coordination geometry of the silver(I) ion.