Crystal structures of three hydrogen-bonded 1:2 compounds of chloranilic acid with 2-pyridone, 3-hy­droxy­pyridine and 4-hyroxypyridine

The crystal structures of the 1:2 compounds of chloranilic acid (systematic name: 2,5-di­chloro-3,6-dihy­droxy-1,4-benzo­quinone) with 2-pyridone, 3-hy­droxy­pyridine and 4-hyroxypyridine, namely, bis­(2-pyridone) chloranilic acid, 2C(5)H(5)NO·C(6)H(2)Cl(2)O(4), (I), bis­(3-hy­droxy­pyridinium) chloranilate, 2C(5)H(6)NO(+)·C(6)Cl(2)O(4) (2−), (II), and bis­(4-hy­droxy­pyridinium) chloranilate, 2C(5)H(6)NO(+)·C(6)Cl(2)O(4) (2−), (III), have been determined at 120 K. In the crystal of (I), the base mol­ecule is in the lactam form and no acid–base inter­action involving H-atom transfer is observed. The acid mol­ecule lies on an inversion centre and the asymmetric unit consists of one half-mol­ecule of chloranilic acid and one 2-pyridone mol­ecule, which are linked via a short O—H⋯O hydrogen bond. 2-Pyridone mol­ecules form a head-to-head dimer via a pair of N—H⋯O hydrogen bonds, resulting in a tape structure along [201]. In the crystals of (II) and (III), acid–base inter­actions involving H-atom transfer are observed and the divalent cations lie on an inversion centre. The asymmetric unit of (II) consists of one half of a chloranilate anion and one 3-hy­droxy­pyridinium cation, while that of (III) comprises two independent halves of anions and two 4-hy­droxy­pyridinium cations. The primary inter­molecular inter­action in (II) is a bifurcated O—H⋯(O,O) hydrogen bond between the cation and the anion. The hydrogen-bonded units are further linked via N—H⋯O hydrogen bonds, forming a layer parallel to the bc plane. In (III), one anion is surrounded by four cations via O—H⋯O and C—H⋯O hydrogen bonds, while the other is surrounded by four cations via N—H⋯O and C—H⋯Cl hydrogen bonds. These inter­actions link the cations and the anions into a layer parallel to (301).