A calix[4]arene strapped calix[4]pyrrole: An ion-pair receptor displaying three different cesium cation recognition modes

Sung Kuk Kim, Jonathan L. Sessler, Dustin E. Gross, Chang Hee Lee, Jong Seung Kim, Vincent M. Lynch, Lætitia H. Delmau, Benjamin P. Hay

Research output: Contribution to journalArticle

131 Citations (Scopus)

Abstract

An ion-pair receptor, the calix[4]pyrrole-calix[4]arene pseudodimer 2, bearing a strong anion-recognition site but not a weak cation-recognition site, has been synthesized and characterized by standard spectroscopic means and via single-crystal X-ray diffraction analysis. In 10% CD3OD in CDCl 3 (v/v), this new receptor binds neither the Cs+ cation nor the F- anion when exposed to these species in the presence of other counterions; however, it forms a stable 1:1 solvent-separated CsF complex when exposed to these two ions in concert with one another in this same solvent mixture. In contrast to what is seen in the case of a previously reported crown ether "strapped" calixarene-calixpyrrole ion-pair receptor 1 (J. Am. Chem. Soc. 2008, 130, 13162 -13166), where Cs+ cation recognition takes place within the crown, in 2CsF cation recognition takes place within the receptor cavity itself, as inferred from both single-crystal X-ray diffraction analyses and 1H NMR spectroscopic studies. This binding mode is supported by calculations carried out using the MMFF94 force field model. In 10% CD3OD in CDCl3 (v/v), receptor 2 shows selectivity for CsF over the Cs+ salts of Cl-, Br-, and NO 3- but will bind these other cesium salts in the absence of fluoride, both in solution and in the solid state. In the case of CsCl, an unprecedented 2:2 complex is observed in the solid state that is characterized by two different ion-pair binding modes. One of these consists of a contact ion pair with the cesium cation and chloride anion both being bound within the central binding pocket and in direct contact with one another. The other mode involves a chloride anion bound to the pyrrole NH protons of a calixpyrrole subunit and a cesium cation sandwiched between two cone shaped calix[4]pyrroles originating from separate receptor units. In contrast to what is seen for CsF and CsCl, single-crystal X-ray structural analyses and 1H NMR spectroscopic studies reveal that receptor 2 forms a 1:1 complex with CsNO 3, with the ions bound in the form of a contact ion pair. Thus, depending on the counteranion, receptor 2 is able to stabilize three different ion-pair binding modes with Cs+, namely solvent-bridged, contact, and host-separated.

Original languageEnglish
Pages (from-to)5827-5836
Number of pages10
JournalJournal of the American Chemical Society
Volume132
Issue number16
DOIs
Publication statusPublished - 2010 Apr 28

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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