Calix[4]pyrrole: A New Ion-Pair Receptor As Demonstrated by Liquid-Liquid Extraction

Journal Article · Tue Jan 01 00:00:00 EST 2008 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja7102179· OSTI ID:1038492

Wintergerst, Mr. Matthieu ^[1]; Levitskaia, Tatiana G. ^[2]; Moyer, Bruce A ^[3]; Sessler, Jonathan L. ^[4]; Delmau, Laetitia Helene ^[3]

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1. Ecole Nationale Superieure de Chimie de Paris
2. Pacific Northwest National Laboratory (PNNL)
3. ORNL
4. University of Texas

Solvent-extraction studies provide confirming evidence that meso-octamethylcalix[4]pyrrole acts as an ion-pair receptor for cesium chloride and cesium bromide in nitrobenzene solution. The stoichiometry of the interaction under extraction conditions from water to nitrobenzene was determined from plots of the cesium distribution ratios vs cesium salt and receptor concentration, indicating the formation of an ionpaired 1:1:1 cesium:calix[4]pyrrole:halide complex. The extraction results were modeled to evaluate the equilibria inherent to the solvent-extraction system, with either chloride or bromide. The binding energy between the halide anion and the calix[4]pyrrole was found to be about 7 kJ/mol larger for cesium chloride than for the cesium bromide. The ion-pairing free energies between the calix[4]pyrrole-halide complex and the cesium cation are nearly the same within experimental uncertainty for either halide, consistent with a structural model in which the Cs+ cation resides in the calix bowl. These results are unexpected since nitrobenzene is a polar solvent that generally leads to dissociated complexes in the organic phase when used as a diluent in extraction studies of univalent ions. Control studies involving nitrate revealed no evidence of ion pairing for CsNO3 under conditions identical to those where it is observed for CsCl and CsBr.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1038492
• Journal Information: Journal of the American Chemical Society, Vol. 130, Issue 12; ISSN 0002--7863
• Country of Publication: United States
• Language: English