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

The crystal structures of the 1:2 compounds of chloranilic acid (systematic name: 2,5-di-chloro-3,6-dihy-droxy-1,4-benzo-quinone) with 2-pyridone, 3-hy-droxy-pyridine and 4-hyroxypyridine, namely, bis-(2-pyridone) chloranilic acid, 2C5 H5 NO·C6 H2 Cl2 O4 , (I), bis-(3-hy-droxy-pyridinium) chloranilate, 2C5 H6 NO+ ·C6 Cl2 O4 2- , (II), and bis-(4-hy-droxy-pyridinium) chloranilate, 2C5 H6 NO+ ·C6 Cl2 O4 2- , (III), have been determined at 120 K. In the crystal of (I), the base mol-ecule is in the lactam form and no acid-base inter-action involving H-atom transfer is observed. The acid mol-ecule lies on an inversion centre and the asymmetric unit consists of one half-mol-ecule of chloranilic acid and one 2-pyridone mol-ecule, which are linked via a short O-H⋯O hydrogen bond. 2-Pyridone mol-ecules 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 inter-actions 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-hy-droxy-pyridinium cation, while that of (III) comprises two independent halves of anions and two 4-hy-droxy-pyridinium cations. The primary inter-molecular inter-action 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 inter-actions link the cations and the anions into a layer parallel to (301).