Extraction and DFT study on the complexation of the cesium cation with a hexaarylbenzene-based receptor

Abstract

Abstract From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Cs+(aq) + A−(aq) + 1(nb) ⇆ 1·Cs+(nb) + A− (nb) taking part in the two-phase water–nitrobenzene system (A− = picrate, 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ex (1·Cs+, A−) = 2.8 ± 0.1. Further, the stability constant of the hexaarylbenzene-based receptor·Cs+ complex (abbrev. 1·Cs+) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log β nb (1·Cs+) = 4.7 ± 0.1. By using quantum mechanical DFT calculations, the most probable structure of the 1·Cs+ complex species was solved. In this complex having C 3 symmetry, the cation Cs+ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom via cation–π interaction. Finally, the calculated binding energy of the resulting complex 1·Cs+ is −220.0 kJ/mol, confirming relatively high stability of the con...