Extraction and DFT study on the complexation of k+ with a hexaarylbenzene - based polyaromatic receptor

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium K+ (aq) + 1•Cs+(nb)sipky ⇄ 1•K+ (nb) + Cs+(aq) taking part in the two-phase water-nitrobenzene system (1 = hexaarylbenzene - based polyaromatic receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (K+, 1•Cs+) = -1.0 ± 0.1. Further, the stability constant of the hexaarylbenzene - based polyaromatic receptor • K+ complex (abbrev. 1•K+) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb (1•K+) = 5.1 ± 0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1•K+ complex species was solved. In this complex having C3 symmetry, the cation K+ 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•K+ is -282.8 kJ mol-1, confirming the relatively high stability of the considered cationic complex species.