The influence of the structure of chelating agents on the complexity and distribution constants of thorium complexes

This paper deals with results obtained by the distribution method described in the preceding paper Margareta Dyrssen, The application of solvent extraction to the study of chelate complexes of thorium, p. 748. . This work still being in progress and new data may considerably change the present picture. For those interested in the chemistry of coordination compounds the value of the acid dissociation constants pka and the mean complexity constants a of ThA4 are of the greatest interest. For those interested in metal extraction log K is very important Definitions of the complexity constants ka, a, and K: cf. M. Dyrssen, p. 750, eqs (8), (2), (11) respectively. . It has been generally recognised that when comparing the reaction of a series of chelate ligand ions A− with hydrogen ion and with a metal ion MN+ the respective equilibrium constants ka and k1 show the same trend; i.e. there appears to be a correlation between acid strength and chelate stability H. Rossotti, this volume page 763. . Furthermore it has been observed that 5‐membered chelate rings are more stable than 6‐ or 4‐membered ones. Such generalisations are however not sufficient to explain the behaviour of so different chelating agents as e.g. oxine, cupferron and acetylacetone. Some properties which at the present time seem relevant to the stability of the chelate‐complexes of H+ and Th4+ will be discussed here.