STABILITY-CONSTANTS OF THORIUM(IV) COMPLEXES WITH ARYL-BIS-(5-HYDROXY-3-METHYL-1-PHENYL-4-PYRAZOLYL) METHANE LIGANDS

Stability constants of complexes of aryl-bis-(5-hydroxy-3-methyl-1-phe nyl-4-pyrazolyl) methane [ArBPyM] derivatives with thorium(IV) ions we re determined by the potentiometric method at 30 degrees C and an ioni c strength of 0.1 mol.dm(-3) (KNO3) in 75% (v/v) dioxane-water. The ev aluation of the titration data indicated that four kinds of complexes ([ThL](2+), [ThLOH](+), [ThL(2)], and [ThL(OH)(2)](2-)) were formed. T he formation constants for all [ThL](2+) and [ThL(2)] complexes have b een calculated to compare these values with those previously reported [1,2] with Ln(3+) and UO22+ metal ions [2,3]. The probable ligand-bond ing sites of the complexes are proposed. In addition, the applicabilit y of the Hammett equation for the correlation of the stability constan ts of [Th(IV)-ArBPyM] complexes are discussed.