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.
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