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

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium CH3NH3+(aq) + 1 · Cs+(nb) ↔ 1 · CH3NH3+nb) + Cs+(aq) taking place in the two-phase water-nitrobenzene system (1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log Kex (CH3NH3+, 1· Cs+) = -0.4 ± 0.1. Further, the stability constant of the 1 · CH3NH3+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 deg C: log βnb (1 · CH3NH3+) = 5.2 ± 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structures A and B of the 1 · CH3NH3+ cationic complex species, which are obviously in a dynamic equilibrium, were indicated. In both of these structures of the resulting complex 1 · CH3NH3+, the cation CH3NH3+ synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom of the parent receptor 1 via cation -π interaction. (author)