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 γ-activity measurements, the exchange extraction constant corresponding to the equilibrium Ag⁺ (aq) + 1·Cs⁺(org) ? 1·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·Cs⁺) = ?1.5 ± 0.1. Further, the stability constant of the 1·Ag⁺ complex in FS 13 saturated with water was calculated for a temperature of 25 °C: log β _org(1·Ag⁺) = 10.1 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structure of the cationic complex species 1·Ag⁺ was derived. In the resulting 1·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-π interaction.