Tripodal organophosphorus ligands as synergistic agents in the solvent extraction of lanthanides(III). Structure of mixed complexes and effect of diluents

The solvent extraction of lanthanides (III) (except for Pm) from chloride medium (at mu = 0.1) into an organic phase containing 4-benzoyl-3-methyl-1-phenyl-5-pyrazolone (HPy) and neutral tripodal ligands on the triphenylphosphine oxide platform with anchored carbamoyl side arms (2-R2NC(O)CH2OC6H4)(3)PO, where R = Bu (L1) and cyclo-Hex (L2) has been studied. A considerable synergistic effect (up to 10(7)) has been observed in the presence of neutral ligands L1 or L2 in the organic phase containing HPy. The stoichiometry of the Ln(III) extracted species has been determined by slope analysis and the equilibrium constants have been calculated. It has been found that the lanthanides(III) ions are extracted with mixtures of HPy and neutral ligands L1 or L2 in toluene as LnPy(3)L species. The [LaPy3(H2O)(2)], and new [LaPy3(L1)] and [LaPy3(L2)] complexes have been synthesized and characterized via elemental analysis and IR spectroscopy. Solution structure of the above complexes has been examined by IR and multinuclear (H-1, C-13, and P-31) NMR spectroscopy in toluene-d(8) and CDCl3. The effect of diluents on synergistic extraction and the solution structure of mixed complexes are discussed. (C) 2019 Elsevier Ltd. All rights reserved.