Selectivity in transport
Abstract
A series of bis benzimidazole ligands, bridged by additional donor groups (ether, thioether) and with pendant carboxylic amide groups, was prepared. In three-phase transport experiments using one quadridentate ligand and metal nitrates, the sequence Ag+≈ Cu2+ > Cd2+ > Zn2+ > Pb2+ was observed for rates of single-ion transport. In pairwise comparisons of mixtures of two salts, potentially useful discriminations between Ag+ and Pb2+, Ag+/Cu2+, Ag+/Zn2+, Ag+/Cd2+, Cu2+/Zn2+, and Cd2+/Zn2+ were also observed. The complexation behaviour of several ligands with Pb2+ and Ag+ in a single phase was further screened in an attempt to explain the observed discrimination between these cations, either in solid or solution, with 1H and 13C n.m.r., i.r., and fast atom bombardment (f.a.b.) mass spectrometric techniques. Evidence for complexes of Ag+ was found for each ligand, with each technique. However for Pb2+ only the ligands with benzimidazole plus ether donors showed any tendency to complex; although solids with a 1:1 ligand: metal salt composition could be isolated, only one could be verified as a complex in the f.a.b. experiment. Solid complexes with a 1:1 composition were isolated for the nitrate salts of Cd2+, Cu2+, and Zn2+.