The most fundamental and lasting objective of synthesis is not production of new compounds but production of properties

George S. Hammond Norris Award Lecture, 1968

The development of new reagents for selective binding and separation of metal ions in solutions represents a real challenge because of the complexities of intra-and intermolecular interactions associated with metal ion (M)-ligand (L) binding in the liquid phase.1 In solution, the stability of complexes depends on the number and type of the coordination centers of L, its topology and exibility/rigidity and solvent effects. In some cases, complexation is accompanied by proton dissociation or association, as well as by the formation of contact-or solvent-separated ion pairs with a counterion. Compared with complexation in homogeneous solutions, extraction processes are more complex because they involve various chemical and physical interactions of molecular species (extractant, coextractant, and counterions) situated in two immiscible liquid phases.2 Even in the simplest case, an extraction process involves the formation of a metal-ligand complex in one of the phases or at the liquid-liquid interface, followed by its diffusion into the organic phase. The formation of more complex species like inverse micelles, vesicles, etc., also affects extraction equilibria.