Trivalent lanthanide and actinide extraction by calixarenes with different ring sizes and different molecular flexibility

Abstract

The binding properties of [1n]metacyclophane-based cation exchangers (n = 5, 6, 7) towards trivalent lanthanides and americium were investigated by means of solvent extraction from water to chloroform and xylene. Extraction constants for four ligands were calculated for Ln(III) and Am(III). Three of the ligands lack But groups in 4-position, giving them higher molecular flexibility compared with the corresponding t-butylcalixarenes. Due to this reason, changing the cavity size lead to small changes in metal extractabilities compared with series of But analogue, while the metal extractabilities themselves are very high. The order of extractability, being Am3+ > Nd3+ > Eu3+ > Tb3+ > Dy3+ > Er3+ > Yb3+ is not influenced by the molecular structure. In the series of t-butylcalix[n]arenes (n = 4-7) the extraction of Am(III) improves with n, the improvement is significantly higher for CHCl3 than for xylene as diluent. The crystal structure of one of these ligands (n = 7) shows a distorted cone conformation. Dimerization in the crystal occurs due to the formation of 8 intermolecular and 4 intramolecular hydrogen bonds, two dimers form a cavity which contains 10 molecules of CDCl3.