Experimental and theoretical study on the cooperative interaction of the ethanolammonium cation with a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium HL+(aq) + 1 · Cs+(nb) ⇔ 1 · HL+(nb) + Cs+(aq) taking place in the two-phase water-nitrobenzene system (HL+ = ethanolammonium, 1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (HL+,1 · Cs+) = −1.1 ± 0.1. Further, the stability constant of the 1 · HL+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb (1 · HL+) = 5.4 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structures A and B of the 1 · HL+ complex species, which are obviously in a dynamic equilibrium, were indicated. In both of these structures of the resulting complex 1 · HL+, the cation HL+ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom of the parent receptor 1 via cation-π interaction.

Highlights► Stability of the ethanolammonium · HAB-based receptor complex was determined. ► Quantum mechanical DFT calculations were used. ► The structures A and B of the resulting complex species were predicted.