Formation constants of trivalent lanthanide metal ions and hydrazone β-diketones in 75% dioxane – water solvent

Abstract

A new series of hydrazone β-diketone organic ligands were prepared: 3-(2-acetylphenylhydrazone)pentane-2,4-dione (2-APHA), 2-(2-acetylphenylhydrazone)-1-phenyl-1,3-butane dione (2-APHB), 2-(2-acetylphenylhydrazone)-1,3-diphenyl-1,3-propane dione (2-APHDB), 3-(2-acetylphenylhydrazone) 1,1,1-trifluoropentane-2,4-dione (2-APHTA) and 2-(2-acetyl-phenylhydrazone)-5,5-dimethyl-1,3-cyclohexane dione (2-APHDm). The step formation constants of their 1:1 and 1:2 rare-earth complexes were determined at 30 °C by pH titration in 75% (v/v) dioxane–water solvent. The ionization constant of ligands were also measured. A curious odd–even stability differential was apparent in the (2-APHDm) ligand with the heavier rare earths Gd–Lu. The differential was apparent in both log K1 and log β values and may be sufficient to cause reversal of the usual ion-exchange elution sequence.