Influence of Counter Anions on Inclusion Complexation of p-Sulfonatocalix[6]arene with 1-Butyl-3-methylimidazolium Salts (Ionic Liquids)

Yusaku Honda, Shono Fujitani, Sho Tamaki, Naoya Inazumi, Tadashi Hanaya, Yoshimi Sueishi

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Using the inclusion complexation of methylene blue with p-sulfonatocalix[6]arene (Calix-S6) as a chemical indicator, the association constants of inclusion complexes of Calix-S6 with visible-spectroscopically inert 1-butyl-3-methylimidazolium salts (ionic liquids (IL): counter anions BF4 -, PF6 -, and Cl-) were determined. It was found that the experimentally observed association constants of IL with Calix-S6 in a water-methanol mixture increased in the order of counter anion Cl- < BF4 - < PF6 -. The 19F NMR signals of counter anions BF4 - and PF6 - shift upfield upon addition of Calix-S6. From the 19F NMR chemical shifts, we suggested that Calix-S6 forms weak 1:1 complexes with the BF4 - and PF6 - anions. The binding constants and their thermodynamic parameters for the complexation of the BF4 - and PF6 - anions with Calix-S6 were evaluated in a water-methanol mixture (6:4 (V/V)) at 298 K: KA = 26.2 M-1 for BF4 - and 106 M-1 for PF6 -. Based on the results, the characteristics for the complexation of the counter anions with Calix-S6 were discussed and the inclusion constants of Calix-S6 with the cationic ring moiety of 1-butyl-3-methyl-imidazolium salts were determined.

Original languageEnglish
Pages (from-to)1153-1164
Number of pages12
JournalZeitschrift fur Physikalische Chemie
Issue number8
Publication statusPublished - Aug 28 2016



  • Binding Constant
  • Effects of Counter Anions
  • Ionic Liquids
  • p-Sulfonatocalix[6]arene

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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