Synthesis, characterisation and extraction behaviour of calix[4]arene-based phosphonic acids

Abstract

Three new bis(phosphonic) acids were prepared by derivatization of p-tert-butylcalix[4]arene on the lower rim by –(CH₂)_xPO₃H₂ groups and were fully characterized by NMR spectroscopy; some of them were further investigated by X-ray analysis. The compounds obtained were tested as extractants for La³⁺, Eu³⁺, Yb³⁺ and Th⁴⁺ in 0.1–1 M HNO₃. Structural details of the complex HLn(H₂L¹)₂ where Ln = Y, La, Eu were elucidated by NMR techniques in solution. The extraction efficiencies decrease with increasing length of the CH₂ spacer; the dependence is not monotonic, and an extraordinary selectivity was observed for Yb. The extraction efficiency of Ln³⁺ for all of the ligands studied increased significantly with decreasing ionic radius.