Experimental and DFT study on the complexation of the silver cation with calix[4]arene-bis(t-octylbenzo-18-crown-6)

From extraction experiments and gamma-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag+ (aq) + 1 center dot Cs+(org) a double dagger" 1 center dot Ag+ (org) + Cs+ (aq) taking place in the two-phase water-phenyltrifluoromethyl sulfone (FS 13) system (1 = calix[4]arene-bis(t-octylbenzo-18-crown-6); aq = aqueous phase, org = FS 13 phase) was evaluated as logK (ex) (Ag+, 1 center dot Cs+) = -1.5 +/- A 0.1. Further, the stability constant of the 1 center dot Ag+ complex in FS 13 saturated with water was calculated for a temperature of 25 A degrees C: log beta (org)(1 center dot Ag+) = 10.1 +/- A 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1 center dot Ag+ was derived. In the resulting 1 center dot Ag+ complex, the "central" cation Ag+ is bound by eight bond interactions to six oxygen atoms from 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.