Effect of crown ring size and upper moiety on the extraction of s-block metals by ionizable calixcrown nano-baskets

Abstract

Eight ionizable nano-baskets of cone 25,26-di(carboxymethoxy)calix[4]arene- crown-3,4,5,6 were synthesized and were verified by 1H and 13C NMR spectroscopy, IR spectroscopy and elemental analysis. The competitive solvent extractions of alkali and alkaline earth metal cations were studied using such nano-baskets. The novelty of this study is including three binding units of calixarene's bowl, crown ether's ring and electron-donor ionizable moieties in a unique scaffold to assess the binding tendency towards the cations. The objective of this work is to study the extraction efficiency, selectivity and pH1/2 of such complexes. The result of solvent extraction experiments indicated that these compounds were effective extractants of alkali and alkaline earth metal cations. Their selectivities were greatly influenced by the acidity of solution and the conformations of the calixcrown. One conformer was selective to Na+ in pH ≥ 4, while the other was highly selective to Ba2+ in pH 6 and upper. Copyright © 2005 KCSNET.