Synthesis, crystal structures and competitive complexation property of a family of calix-crown hybrid molecules and their application in extraction of potassium from bittern

Abstract

<div><p>A family of calix-crown hybrid molecules containing calix[4]arene and crown-5/6, either at lower rim or at both upper and lower rims, have been synthesised, characterised and their competitive complexation property towards alkali and alkaline earth metal ions in aqueous media have been investigated. The competitive metal ion extraction study, carried out with equimolar mixture of Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺ and Sr²⁺ in aqueous media, revealed that the amount of K⁺ extracted is remarkably high compared to other metal ions. Complexation with K⁺ has been investigated by ¹H NMR, association constants and thermodynamic parameters have been determined by isothermal calorimetric study. The molecular structures of one of the receptors and two of the K⁺ complexes have been established by single crystal X-ray study. One of the receptors formed bimetallic complex and it exhibited interesting polymeric network structure with bridged picrate anion. These receptors have been applied for extraction of metal ions from bittern.</p></div