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-dihydroxycyclohexa-2,5-diene-1,4-dione) with pyrrolidin-2-one and piperidin-2-one, namely, chloranilic acid-pyrrolidin-2-one (1/1), C(6)H(2)Cl(2)O(4)·C(4)H(7)NO, (I), chloranilic acid-pyrrolidin-2-one (1/2), C(6)H(2)Cl(2)O(4)·2C(4)H(7)NO, (II), chloranilic acid-piperidin-2-one (1/1), C(6)H(2)Cl(2)O(4)·C(5)H(9)NO, (III), and chloranilic acid-piperidin-2-one (1/2), C(6)H(2)Cl(2)O(4)·2C(5)H(9)NO, (IV), the shortest interactions between the two components are O-H...O hydrogen bonds, which act as the primary intermolecular interaction in the crystal structures. In (II), (III) and (IV), the chloranilic acid molecules 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 intermolecular interactions, connect the pyrrolidin-2-one molecules 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.