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

Abstract

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, 2C5H5NO·C6H2Cl2O4, (I), bis(3-hydroxypyridinium) chloranilate, 2C5H6NO+·C6Cl2O42−, (II), and bis(4-hydroxypyridinium) chloranilate, 2C5H6NO+·C6Cl2O42−, (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 linkedviaa short O—H...O hydrogen bond. 2-Pyridone molecules form a head-to-head dimerviaa 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 linkedviaN—H...O hydrogen bonds, forming a layer parallel to thebcplane. In (III), one anion is surrounded by four cationsviaO—H...O and C—H...O hydrogen bonds, while the other is surrounded by four cationsviaN—H...O and C—H...Cl hydrogen bonds. These interactions link the cations and the anions into a layer parallel to (301).