An NMR Study on Complexation of Cesium Ion by p-tert-Butylcalix[6]arene Ethyl Ester

摘要

Complexation of cesium ion by p-tert-butylcalix[6]arene ethyl ester was studied by NMR spectroscopy in nonpolar CDCl_3 and polar acetone-d_6 and the results were compared with each other.Analysis of temperature dependent ~1H spectra and titration curves reveals that both solvents result in a 1:1 cone-form complex with nonpolar CDCl_3 yielding a more tightly bound one than acetone-d_6.Unexpectedly,at very low temperature,we have found that two phenyl ring proton peaks of equal intensity appear both in CDCl_3 and in acetone-d_6 solution which gradually collapse and eventually coalesce into a single line as temperature is raised.This observation could be interpreted in terms of the chemical exchange through direct and/or indirect interconversion between two equivalent conformations possible the complex in both solvents over the temperature range observed.And broadening of ~(133)Cs (I=7/2) nmr line with increasing temperature has also been observed,indicating the exchange of ~(133)Cs ion between the complex and the solvent.From numerical fitting of lineshape changes for one-dimensional ~1H and ~(133)Cs spectra,the exchange rate constants and other relevant parameters for this conformational interconversion and the complex-solvent exchange were deduced.