Selective extraction of Pd(ii) by p-tert-butylcalix[4]arenedicarboxylic acid

Abstract

Solvent extraction of various metal ions has been carried out using p-tert-butylcalix[4]arenedicarboxylic acid (4) as the metal extractant. Compound 4 showed high extraction selectivity toward Pd²⁺ ions. Slope analysis of the solvent extraction and X-ray structural analysis of a Pd²⁺ complex of compound 4 revealed that the selectivity results from the coordination of compound 2 to Pd²⁺ with the carboxy groups directly attached to the calix skeleton, thereby forming a rigid 2 : 2 (M/L) complex.