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

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs+ (aq) + I− (aq) + 1 (org) ⇔ 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 Kex (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 °C: log βorg (1⋅Cs+) = 9.9 ± 0.1. Finally, by using quantum mechanical DFT 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–π interaction.