CMP0-calix[4]arenes with spacer containing intramolecular hydrogen bonding: Effect of local rigidification on solvent extraction toward f-block elements

摘要

To understand intramolecular hydrogen bonding in effecting liquid-liquid extraction behavior of CMPO-calixarenes, three CMPO-modified calix@@[4]arenes (CMPO-CA) 5a-5c with hydrogen-bonded spacer were designed and synthesized. The impact of spacer rotation that is hindered by introduction of intramolecular hydrogen bonding upon extraction of La~(3+), Eu~(3+), Yb~(3+), Th~(4+), and UO_2~(2+) has been examined. The results show that 5b and 5c containing only one hydrogen bond with a less hindered rotation spacer extract La~(3+) more efficiently than 5a containing two hydrogen bonds with a more hindered rotation spacer, demonstrating the importance of local rigidification of spacer in the design of extractants in influencing the coordination environment, The large difference in extractability between La~(3+) and Yb~(3+) (or Eu~(3+)) by 5b (or 5c), and the small difference by 5a, suggests intramolecular hydrogen bonding do exert pronounced influence upon selective extraction of light and heavy lanthanides. Log-log plot analysis indicates a 1∶1, 2∶1 and 1∶1 stoichiometry (ligand/metal) for the extracted complex formed between 5b and La~(3+), Th~(4+), UO_2~(2+), respectively. Additionally, their corresponding acyclic analogs 7a-7c exhibit negligible extraction toward these metal ions. These results reveal the possibility of selective extraction via tuning local chelating surroundings of CMPO-CA by aid of intramolecular hydrogen bonding.