Abstract
The extraction of the alkaline-earth metal ions by 25,27-dicarboxymethyl-26,28-dimethoxy-5,11,17,23-tetra- tert-butylcalix [4]arene(L IH 2) and 25,27-dicarboxymethyl-26,28-dimethoxyethoxy-5,11,17,23-tetra- tert-butylcalix [4]arene (L IIH 2) in 1,2-dichloroethane is shown to be pH dependent. The analysis of the extraction equilibrium results indicates that the extraction process takes place via the formation of ML 2 IH 2 (M 2 = Ca 2, Sr 2 and Ba 2), ML 2 IIH 2 (M 2 = Ca 2 and Sr 2) and ML II (M 2 = Ba 2) complexes. Both ligands show a high selectivity for calcium. The existence of the ML 2H 2 complexes is supported by 1H-NMR and FAB + experiments on the corresponding Ca 2 complexes. 1H-NMR investigations show that the calcium ion is located outside the calixarene cavity. Competitive extraction of Mg, Ca, Sr and Ba suggests the formation of mixed complexes.
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