Hydrogen-bonded structures of the 1:1 and 1:2 compounds of chloranilic acid with pyrrolidin-2-one and piperidin-2-one

In the four compounds of chloranilic acid (2,5-dichloro-3,6-dihy-droxy- cyclo-hexa-2,5-diene-1,4-dione) with pyrrolidin-2-one and piperidin-2-one, namely, chloranilic acid-pyrrolidin-2-one (1/1), C₆H ₂Cl₂O₄·C₄H₇NO, (I), chloranilic acid-pyrrolidin-2-one (1/2), C₆H₂Cl ₂O1·2C₄H7NO, (II), chloranilic acid-piperidin-2-one (1/1), C₆H₂Cl₂O₄·C ₅H₉NO, (III), and chloranilic acid-piperidin-2-one (1/2), C₆H₂Cl₂O₄·2C ₅H₉NO, (IV), the shortest inter-actions between the two components are O - H⋯O hydrogen bonds, which act as the primary inter-molecular inter-action in the crystal structures. In (II), (III) and (IV), the chloranilic acid mol-ecules lie about inversion centres. For (III), this necessitates the presence of two independent acid molecules. In (I), there are two formula units in the asymmetric unit. The O⋯O distances are 2.4728 (11) and 2.4978 (11) Å in (I), 2.5845 (11) Å in (II), 2.6223 (11) and 2.5909 (10) Å in (III), and 2.4484 (10) Å in (IV). In the hydrogen bond of (IV), the H atom is disordered over two positions with site occupancies of 0.44 (3) and 0.56 (3). This indicates that proton transfer between the acid and base has partly taken place to form ion pairs. In (I) and (II), N - H⋯O hydrogen bonds, the secondary inter-molecular inter-actions, connect the pyrrolidin-2-one mol-ecules into a dimer, while in (III) and (IV) these hydrogen bonds link the acid and base to afford three- and two-dimensional hydrogen-bonded networks, respectively.