Interaction of the thallium cation with 1,3-alternate-25,27-bis(1-octyloxy)calix[4]arene-crown-6: Experimental and theoretical study

Abstract

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Tl+ (aq)+1·Cs+ (nb)⇔1·Tl+ (nb)+Cs+ (aq) taking place in the two–phase water–nitrobenzene system (1=1,3-alternate-25,27-bis(1-octyloxy)calix[4]arene-crown-6; aq=aqueous phase, nb=nitrobenzene phase) was evaluated as logKex (Tl+, 1·Cs+)=−2.1±0.1. Further, the stability constant of the 1·Tl+ complex in nitrobenzene saturated with water was calculated for a temperature of 25°C: logβnb(1·Tl+)=11.6±0.2. Finally, by using quantum mechanical DFT calculations, the most probable structures A and B of the cationic complex species 1·Tl+, which are obviously in a dynamic equilibrium, were indicated. In both of these structures of the resulting 1·Tl+ complex, the “central” cation Tl+ is bound by eight strong bond interactions to six oxygen atoms from the 18-crown-6 moiety and to two carbons of the respective two benzene rings of the parent ligand 1 via cation-π interaction.