Experimental and DFT study on the complexation of with a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium NH 4 + ( aq ) + 1 · Cs + ( nb ) ⇆ 1 · NH 4 + ( nb ) + Cs + ( aq ) taking part in the two-phase water–nitrobenzene system (1 = hexaarylbenzene-based receptor; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K ex ( NH 4 + , 1 · Cs + ) = - 0.4 ± 0.1 . Further, the stability constant of the 1 · NH 4 + complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C as log β nb ( 1 · NH 4 + ) = 6.3 ± 0.2 . By using quantum mechanical DFT calculations, the most probable structures A and B of the 1 · NH 4 + complex species, which are obviously in a dynamic equilibrium, were indicated. In both of these structures of the resulting complex 1 · NH 4 + having C3 symmetry, the cation NH 4 + synergistically interacts with the polar ethereal oxygen fence and with the central hydrophobic benzene bottom via cation–π interaction.