Hydrogen-bonded structures of the isomeric 2-, 3- and 4-carbamoylpyridinium hydrogen chloranilates.

In the three isomeric salts, all C(6)H(7)N(2)O(+).C(6)HCl(2)O(4)(-), of chloranilic acid (2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone) with 2-, 3- and 4-carbamoylpyridine, namely, 2-carbamoylpyridinium hydrogen chloranilate (systematic name: 2-carbamoylpyridinium 2,5-dichloro-4-hydroxy-3,6-dioxocyclohexa-1,4-dienolate), (I), 3-carbamoylpyridinium hydrogen chloranilate, (II), and 4-carbamoylpyridinium hydrogen chloranilate, (III), acid-base interactions involving H-atom transfer are observed. The shortest interactions between the cation and the anion in (I) and (II) are pyridinium N-H...(O,O) bifurcated hydrogen bonds, which act as the primary intermolecular interaction in each crystal structure. In (III), an amide N-H...(O,O) bifurcated hydrogen bond, which is much weaker than the bifurcated hydrogen bonds in (I) and (II), connects the cation and the anion.