A series of biscalixarenes (2n) doubly-bridged with oxyethylene chains at the lower rim have been synthesized. As in conventional ionophoric monocalixarene derivatives, these compounds showed ion selectivity towards Na+. The 1H NMR spectroscopic studies established that Na+ and K+ ions complexed with 2n oscillate intramolecularly between two calixarene ionophoric sites. Two coalescence temperatures were found in the temperature-dependent 1H NMR spectra in the presence of these metal cations: the coalescence for the intermolecular metal exchange appears at a high temperature region whereas the coalescence for the intramolecular metal oscillation appears at a low temperature region. These two processes could be discriminated by the difference in the concentration dependence: the intermolecular process is concentration-dependent whereas the intramolecular process is concentration-independent. This is a unique dynamic system in which metal cations jump from one ionophoric site to another ionophoric site in biscalixarenes in the NMR time-scale.
|Number of pages||7|
|Journal||Journal of the Chemical Society, Perkin Transactions 2|
|Publication status||Published - Jan 1 1995|
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