Design, synthesis and evaluation of silver-specific ligands
Complexes of the malonamide ligands with copper(II) and silver(I) have been synthesised, and examination of these complexes has revealed distinct differences in their co-ordination preferences towards silver(I) and copper(II). Tentative, computer-modelled structures for the complexes have been proposed using the available spectroscopic and elemental analysis data. Computer modelling, at the Molecular Mechanics level, has also been used to assess the capacity of the ligand systems to adopt conformations suitable for the chelation of tetrahedral silver(I).
Solvent extraction studies have been undertaken using aqueous metal ion solutions and various organic solvents. The dithiodiamide derivatives typically presented solubility problems, but one of the ligands, N,N´-bis(3-chlorophenyl)-3,6-dithiaoctanediamide, exhibited significant but slow extraction of silver(I) into toluene. The malonamide derivatives, however, proved to be readily soluble in ethyl acetate and, in some cases, exhibited good to excellent selectivity for silver(I) in the presence of the base metals copper and lead. Atomic absorption analysis revealed rapid equilibration times (<15 min) and high extraction efficiencies over a wide pH range (2.78 - 9.0). Metal selectivity has been determined by ICP-MS analysis of the residual silver, copper and lead present in the aqueous phase after 15 min, and one of the ligands, N,N´-bis(2-benzylsulfanylethyl)malonamide, exhibits excellent (>= 96 %) silver(I) specificity.
School Location:South Africa
Source Type:Master's Thesis
Date of Publication:01/01/2001