Effect of the stability of 1,3-bis(diphenylphosphoryl)-2-oxapropane complexes on the separation of lanthanide ions and their detection†

Abstract

Phosphoryl podands of neutral type with a flexible ethylene glycol chain and diphenylphosphorylmethyl end groups are known for their complexation properties towards various cations. In this work, the complexation process between 1,3-bis(diphenylphosphoryl)-2-oxapropane (L) and lanthanide ions was studied. Namely, the stability constants of lanthanide complexes with L in acetonitrile were estimated by the method of spectrophotometric titration. It was found that the stability constants of Ln³⁺ complexes with L increase in the lanthanide series, which is consistent with the extraction and ion-selective properties of L. The extraction ability of L and this ligand in the presence of ionic liquids (ILs) such as methyltrioctylammonium nitrate (MTOAN) and bis[(trifluoromethyl)sulfonyl]imide 1-butyl-3-methylimidazolium (C₄mimTf₂N) was studied. It was found that in the presence of ILs, L extracts the elements of the yttrium subgroup of lanthanides much better than those of the cerium subgroup: SF_Lu/Ce(L–MTOAN) = 2.29; SF_Lu/Ce(L–C₄mimTf₂N) = 110.38. The use of the L–C₄mimTf₂N mixture in the processes of lanthanide separation into subgroups is much more efficient than the use of L without the addition of ILs or the use of the L–MTOAN mixture. The ion-selective properties of L towards Ln³⁺ ions were studied. Podand L exhibits potentiometric selectivity to Lu³⁺ ions.