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ABSTRACT
Predicting the effectiveness of liquid-liquid extraction of metal chelates and choosing optimal extraction reagents requires several characteristics of the components of the extraction system to be taken into consideration. This paper provides an analysis of the factors that affect the value of the partition constant of a chelate and the possibilities to predict the value of the partition constant from the nature of the metal ion, the structure of the chelating reagent, and the organogenic elements, one might have expected these techniques to be capable to predict the partition constants of chelates as well. However, the problem of determining the increments of metals turned out to be very difficult even in the case of relatively simple complexes. An analysis of the partition constants of coordinatively-saturated metal acetylacetonates has shown that the values depend on a large number of parameters, some of which are correlated. The central metal atom modifies the donor properties of the heteroatoms in the extraction reagent molecule to such a great extent that one cannot assign them the increments valid for the free reagent molecule.
Obviously, much more sophisticated models are needed for properly determining the contribution of each fragment in this complex system with numerous inner relations. Such models cannot ignore various intermolecular interactions occurring in the extration systems and will inevitably use the theories that describe them quantitatively, some of which have been reviewed in this paper.