The Use of Ethers as Effective Ligands for the Extraction of Metal Ions by Ion Exchange

Abstract A quantum chemical calculation of complexation energies of a series of substituted aza-18-crown-6-ethers with Li + – Na + – K + ions has been carried out and influence of the substituent in the ether molecule on the strength of the “complexing agent – ligand” bond has been shown. The geometry optimization of substituted aza-18-crown-6 ethers and their complexes was carried out by the RHF method with 6 31G(d, p) basis; using the Firefly freeware product. The cavity diameter in the studied compounds was calculated as the value of the average distance between two most distant heteroatoms in the ether molecule. It was established that the introduction of large radical into the molecule leads to significant change in the structure of the ether cycle. The change in the structure of the macrocycle is accompanied by a significant decrease in the cavity size; this causes effective complexation with ions having a small van der Waals radius. The complexation selectivity increases in the series Li + > Na + > K + . According to the performed quantum chemical calculation, it was found that changing the steric hindrance in the macrocycle provides the possibility to manage the complexation selectivity. The obtained results are an intermediate stage in the development of new types of ion-exchange materials capable of selectively removing certain types of cations from solutions containing their mixtures or from wastewater.