Metal ions, extraction using ligand applications

Extractive separation of metals is usually based on complex formation with inorganic and organic ligands. Therefore the use of the ideas, approaches, and methods of coordination chemistry has always been a most fruitful approach to the extraction of the elements. History shows that many problems of selectivity of separation or enhanced isolation have been successively solved by the rational application of coordination chemistry, e.g., the concept of hard and soft acids and bases. The efficiency of extraction depends on, inter alia, the ratio of charge and coordination number of metal ion. Study of this effect permitted the development of ways to improve separation due to changes in hydration of the species to be extracted. 

We recently reported on the application of combinatorial methods to selection of stable and chloroform-soluble Schiff-base metal complexes from a dynamic library in order to improve the extraction of metal ions (18). In this study, we built a dynamic library of Schiff-base complexes to capitalize on the reversible nature of metal-catalyzed imine bond formation. Library components were chosen to optimize stability and chloroform solubility of metal complexes. By utilizing the template effect, metal ions promote the assembly of a group of ligands, which then undergo a condensation reaction to form a metal complex. Therefore, aldehydes containing a metal ion-binding site were used to facilitate metal ion templated formation of the Schiff-base ligands (Fig. 1). 

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