Using the inclusion complexation of methylene blue with p-sulfonatocalixarene (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.
- Binding Constant
- Effects of Counter Anions
- Ionic Liquids
ASJC Scopus subject areas
- Physical and Theoretical Chemistry