Interaction of the cesium cation with calix[4]arene-bis(t-octylbenzo-18-crown-6): Extraction and DFT study

From extraction experiments and gamma-activity measurements, the extraction constant corresponding to the equilibrium Cs+ (aq) + I- (aq) + 1 (org) double left right arrow 1.Cs+ (org) + I- (org) taking place in the two-phase water-phenyltrifluoromethyl sulfone (abbrev. FS 13) system (1 = calix[4]arene-bis(t-octylbenzo-18-crown-6); aq = aqueous phase, org = FS 13 phase) was evaluated as log K-ex (1-Cs+, I-) = 2.1 +/- 0.1. Further, the stability constant of the 1.Cs+ complex in FS 13 saturated with water was calculated for a temperature of 25 degrees C: log beta(org) (1.Cs+) = 9.9 +/- 0.1. Finally, by using quantum mechanical OFT calculations, the most probable structure of the cationic complex species 1.Cs+ was derived. In the resulting 1.Cs+ complex, the "central" cation Cs+ is bound by eight bond interactions to six oxygen atoms of the respective 18-crown-6 moiety and to two carbons of the corresponding two benzene rings of the parent ligand 1 via cation-pi interaction. (C) 2012 Elsevier B.V. All rights reserved.