Metal ion recognition: The story of an oxa-aza macrocycle
Pure and Applied Chemistry
Abstraa -The interaction of a pyridine-derived dioxa-triaza-macrocycle with divalent first row transition metal cations is discussed. Selected crystal structures and speciation studies are presented together with information on application to metal extraction and transport. The recovery of metals from sulfide-rich ores by pyrometallurgical processes is regarded as environmentally unsatisfactory due to the accompanying production of sulfur dioxide which leads to an enhanced acidity in rainfall.
... idity in rainfall. Particulate matter from smoke effluents can also be dispersed and dispensed onto nearby land and, if toxic, give rise to further problems. Therefore it is important to establish processes by which metals of interest can be extracted from what are often low-grade ores by an alternative technology. Consequently there has been much interest in the application of hydrometallurgical techniques which involve a leaching process to dissolve the metals followed by solvent extraction processes to separate and recover the metal ions of interest. Solvent extraction has been used as one of the major techniques in the industrial hydrometallurgy of non-ferrous metals, particularly in the recovery of copper, in cobalt-nickel separation and in the concentration of uranium.1J Macrocycles, and macrobicyclic, ligands have been shown to be effective in alkali, and alkaline earth, selectivity.3 This may be related to a cation radius:macrocyclic cavity radius control in which the cation having the 'best fit' for the cavity will be the cation strongest complexed by that macrocycle. As there is a clear and steady increase in ionic radius between the alkali metals as the group is progressed then it becomes possible to discriminate between by careful ligand cavity control. In the example given (Table) evidence can