Competitive bulk liquid membrane transport and solvent extraction of some transition and post-transition metal ions using acylthiourea ligands as ionophores

Abstract

Competitive transport experiments involving metal ions from an aqueous source phase through a chloroform membrane into an aqueous receiving phase have been carried out using a series of acylthiourea ligands as the ionophore present in the organic phase. The source phase contained equimolar concentrations of cobalt(II), nickel(II), copper(II), zinc(II), silver(I), cadmium(II) and lead(II) with the source and receiving phases being buffered at a number of different pHs. Transport selectivity was observed for silver(I) in all but one case. Selectivity for silver(I) was also observed in a series of parallel solvent extraction experiments carried out under similar source and membrane phase conditions. An X-ray diffraction study of the silver(I) complex of the N,N-dibutyl-N′-benzoylthiourea from this series is reported. There are two crystallographically independent molecules in the asymmetric unit and each molecule consists of four silver(I) ligand complex units, hence giving rise to Z = 8. In each molecule, both chelate and monodentate co-ordination modes of complexation to silver(I) are evident. Hence, each silver is co-ordinated to a sulfur and oxygen atom from one ligand and to a shared (bridging) sulfur from another ligand. Each silver atom is thus co-ordinated to three donor atoms.