A Combined Experimental and DFT Study on the Complexation of the Hydrazinium Cation with a Hexaarylbenzene – Based Receptor

From extraction experiments and γ-activity measurements, the exchange extraction constant corresponding to the equilibrium N2H+ 5 (aq) + 1.Cs+(nb) _1.N2H+ 5 (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 (N2H+ 5, 1.Cs+) = –1.2 ± 0.1. Further, the stability constant of the hexaarylbenzene – based receptor .N2H+ 5 complex (abbrev. 1.N2H+ 5) in nitrobenzene saturated with water was calculated for a temperature of 25 °C: log βnb (1.N2H+ 5) = 5.6 ± 0.2. By using quantum mechanical DFT calculations, the most probable structure of the 1.N2H+ 5 complex species was solved. In this complex, the cation N2H+ 5 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.N2H+ 5 is –270.5 kJ/mol, confirming the relatively high stability of the considered cationic complex species.