Cerium [III], thorium [IV] and dioxo-uranium [VI] complexes of 6,7-dihydroxy-4methyl-coumarin: acid dissociation constants in ethanol-water mixtures

ABSTRACT

The successive stability constants of Ce [III], Th [IV] and UO2, [VI] chelates with 6,7-dihydroxy-4-methylcoumarin have been determined pH- metrically at different temperatures and ionic strengths in 60% [by volume] ethanol-water mixture. A 1 1 and 1 2 complexes are formed and evidenced by conductometric studies. The thermodynamic parameters for these chelates have been determined. Smaller values of delta H show the predominance of the entropy effect in the formation of these chelates. The structure of the solid complexes of UO2 [VI] has been assigned on the basis of elemental, thermogravimetric analysis and IR- spectroscopy. The pK-a values of 6,7-dihydroxy-4-methylcoumarin in ethanol-water mixtures have been determined pH-metrically at different temperatures and ionic strengths. The thermodynamic parameters delta G, delta H and delta S have also been evaluated