Metal ion recognition. Selective interaction of silver(i) with tri-linked N2S2-donor macrocycles and their single-ring analogues

Abstract

The interaction of four tri-linked N₂S₂-donor macrocyclic ligands and their single ring analogues with silver(I) has been investigated. The 3 ∶ 1 (metal ∶ ligand) stoichiometries of the silver(I) complexes of the tri-linked species in dimethyl sulfoxide-d⁶/CDCl₃ were confirmed by means of NMR titrations involving the incremental addition of silver(I) nitrate to the respective ligands in the above solvent mixture and following the corresponding induced shifts in the ¹H NMR spectrum. Solid 3 ∶ 1 (metal ∶ ligand) complexes were isolated for each of the parent (unsubstituted) tri-linked ligands. Competitive solvent extraction experiments (water/chloroform) and related bulk membrane transport (water/chloroform/water) experiments have been performed in which each of the four tri-linked ligands as well as their single ring analogues were employed as the extractant/ionophore in the chloroform phase. In both sets of experiments the respective aqueous source phases (buffered at pH 4.9) contained an equimolar mixture of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(I) and lead(II) nitrates. For membrane transport the aqueous receiving phase was buffered at pH 3. Under the conditions employed, both the solvent extraction and the bulk membrane transport experiments resulted in high extraction/transport selectivity for silver(I) relative to the other six metal ions present.