Crown ether derivatives of calix[5]arenes: synthesis and complexation properties

Abstract

Several crown ether derivatives of calix[5]- and tert-butylcalix[5]-arene have been synthesized and converted into their trimethyl ethers as neutral ligands. For selected examples extraction studies have been carried out with alkali metal picrates in the system water–dichloromethane and stability constants have been determined by UV spectroscopy in methanol. All ligands show a more or less pronounced preference for the larger alkali cations. The selectivity for Cs⁺ over Na⁺ is highest for the crown-5 derivative of tert-butylcalix[5]arene (S= 630). Calorimetric titrations show that the complexation is e, nthalpically and entropically driven.