Full Paper

Induction-Driven Stabilization of the Anion–π Interaction in Electron-Rich Aromatics as the Key to Fluoride Inclusion in Imidazolium-Cage Receptors

  1. Dr. Zhaochao Xu1,2,4,
  2. Dr. N. Jiten Singh3,4,
  3. Dr. Sook Kyung Kim1,
  4. Dr. David R. Spring2,*,
  5. Prof. Kwang S. Kim3,*,
  6. Prof. Juyoung Yoon1,*

Article first published online: 13 DEC 2010

DOI: 10.1002/chem.201002105

Issue

Chemistry - A European Journal

Chemistry - A European Journal

Volume 17, Issue 4, pages 1163–1170, January 24, 2011

Additional Information

How to Cite

Xu, Z., Singh, N. J., Kim, S. K., Spring, D. R., Kim, K. S. and Yoon, J. (2011), Induction-Driven Stabilization of the Anion–π Interaction in Electron-Rich Aromatics as the Key to Fluoride Inclusion in Imidazolium-Cage Receptors. Chemistry - A European Journal, 17: 1163–1170. doi: 10.1002/chem.201002105

Author Information

  1. 1

    Department of Chemistry and Nanoscience and Department of Bioinspired Science (WCU), Ewha Womans University, Seoul, 120-750 (Korea), Fax: (+82) 232772384

  2. 2

    Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW (UK), Fax: (+44) 1223336362

  3. 3

    Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology (China), Fax: (+82) 542798137

  4. 4

    Contributed equally to this work.

*Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW (UK), Fax: (+44) 1223336362

Publication History

  1. Issue published online: 18 JAN 2011
  2. Article first published online: 13 DEC 2010
  3. Manuscript Received: 23 JUL 2010

Funded by

  • Basic Science Research Program. Grant Number: 2010-0018895
  • Converging Research Center Program. Grant Number: 2009-0093677
  • WCU. Grant Number: R31-2008-000-10010-0
  • National Research Foundation
  • National Honor Scientist Program
  • WCU. Grant Number: R32-2008-000-10180-0
  • EPB Center. Grant Number: 2009-0063312
  • KISTI. Grant Number: KSC-2008K08-0002
  • Herchel Smith Postdoctoral Fellowship Fund
  • Newman Trust

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Keywords:

  • anions;
  • electron-rich aromatics;
  • fluorides;
  • hydrogen bonds;
  • pi interactions

Graphical Abstract

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Easy as π: The first concrete theoretical and experimental evidence of the anion–π interaction between an electron-rich alkylbenzene ring and a fluoride ion in CH3CN is reported (see graphic). The cyclophane cavity, bridged with three naphthoimidazolium groups, selectively complexes an F ion by means of anion–π interactions and ionic hydrogen bonds.

Abstract

Intermolecular interactions that involve aromatic rings are key processes in both chemical and biological recognition. It is common knowledge that the existence of anion–π interactions between anions and electron-deficient (π-acidic) aromatics indicates that electron-rich (π-basic) aromatics are expected to be repulsive to anions due to their electron-donating character. Here we report the first concrete theoretical and experimental evidence of the anion–π interaction between electron-rich alkylbenzene rings and a fluoride ion in CH3CN. The cyclophane cavity bridged with three naphthoimidazolium groups selectively complexes a fluoride ion by means of a combination of anion–π interactions and (C[BOND]H)+⋅⋅⋅F−-type ionic hydrogen bonds. 1H NMR, 19F NMR, and fluorescence spectra of 1 and 2 with fluoride ions are examined to show that only 2 can host a fluoride ion in the cavity between two alkylbenzene rings to form a sandwich complex. In addition, the cage compounds can serve as highly selective and ratiometric fluorescent sensors for a fluoride ion. With the addition of 1 equiv of F−, a strongly increased fluorescence emission centered at 385 nm appears at the expense of the fluorescence emission of 2 centered at 474 nm. Finally, isothermal titration calorimetry (ITC) experiments were performed to obtain the binding constants of the compounds 1 and 2 with F− as well as Gibbs free energy. The 2-F− complex is more stable than the 1-F− complex by 1.87 kcal mol−1, which is attributable to the stronger anion–π interaction between F− and triethylbenzene.

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