Metal-Ion Recognition—Selective Bulk Membrane Transport of Silver(I) Using Thioether Donor Macrocycles as Ionophores, and X-Ray Structure of the Silver Complex of an S4-Donor Ring

Abstract

Competitive metal-ion transport experiments, each involving transport from an aqueous source phase containing equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), cadmium(II), silver(i), and lead(II) across a chloroform membrane phase to an aqueous receiving phase have been carried out. The membrane phase incorporated an ionophore chosen from a series of thioether-containing macrocycles. For those systems that displayed transport behaviour, sole selectivity for silver(I) was observed under the conditions employed. The effect of variation in the macrocyclic sulfur atom donor set and the presence of hydrophilic ring substituents on transport efficiency is presented. An X-ray structure of the 1 : 1 silver(I) nitrate complex of a 16-membered, S₄-donor macrocycle shows the presence of four crystallographically independent macrocycles displaying conformational isomerism. Each silver(I) has an approximate tetrahedral geometry, being bound to three sulfur atoms from three different macrocycles and to one nitrato ligand to yield a three-dimensional network.