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

Crystal structures of hydrogen-bonded 1:2 compounds of chloranilic acid with 2-pyridone, 3-hydroxypyridine and 4-hyroxypyridine have been determined at 120 K. In each crystal structure, the acid and base molecules are linked by short O—H⋯O and N—H⋯O hydrogen bonds.

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 NOÁC 6 H 2 Cl 2 O 4 , (I), bis(3-hydroxypyridinium) chloranilate, 2C 5 H 6 NO + Á-C 6 Cl 2 O 4 2À , (II), and bis(4-hydroxypyridinium) chloranilate, 2C 5 H 6 NO + Á-C 6 Cl 2 O 4 2À , (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-HÁ Á ÁO hydrogen bond. 2-Pyridone molecules form a head-to-head dimer via a pair of N-HÁ Á ÁO 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-HÁ Á Á(O,O) hydrogen bond between the cation and the anion. The hydrogen-bonded units are further linked via N-HÁ Á ÁO hydrogen bonds, forming a layer parallel to the bc plane. In (III), one anion is surrounded by four cations via O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, while the other is surrounded by four cations via N-HÁ Á ÁO and C-HÁ Á ÁCl hydrogen bonds. These interactions link the cations and the anions into a layer parallel to (301).

Chemical context
Chloranilic acid, a dibasic acid with hydrogen-bond donor and acceptor groups, appears particularly attractive as a template for generating tightly bound self-assemblies with various pyridine derivatives, as well as a model compound for investigating hydrogen transfer motions in O-HÁ Á ÁN and N-HÁ Á ÁO hydrogen-bond systems (Zaman et al., 2004;Seliger et al., 2009;Asaji et al. 2010). In the present study, we have prepared three 1:2 compounds of chloranilic acid with 2-pyridone, 3-hydroxypyridine and 4-hydroxypyridine in order to extend our study of D-HÁ Á ÁA hydrogen bonding (D = N, O or C; A = N, O or Cl) in chloranilic acid-substitutedpyridine systems (Gotoh et al., 2009a(Gotoh et al., ,b, 2010. The crystal structure of the 1:1 compound of chloranilic acid with 3-hydroxypyridine, namely, 3-hydroxypyridinium hydrogen chloranilate monohydrate, has been reported . ISSN 2056-9890

Structural commentary
In compound (I), the base molecule is in the lactam form and no acid-base interaction involving H-atom transfer is observed (Fig. 1). The acid molecule lies on an inversion centre and the asymmetric unit consists of one-half acid molecule and one base molecule, which are linked via a short O-HÁ Á ÁO hydrogen bond (O2-H2Á Á ÁO3; Table 1). The dihedral angle between the acid ring and the base ring is 37.82 (5) .
In compound (II), an acid-base interaction involving H-atom transfer is observed. The chloranilate anion is located on an inversion centre and the asymmetric unit contains onehalf anion molecule and one cation molecule. The primary intermolecular interaction between the cation and the anion is a bifurcated O-HÁ Á Á(O,O) hydrogen bond (O3-H3Á Á ÁO2 and O3-H3Á Á ÁO1 i ; symmetry code as in Table 2) to afford a centrosymmetric 1:2 aggregate of the anion and the cation (Fig. 2). The dihedral angle between the acid ring and the base ring is 72.69 (5) .

Supramolecular features
In the crystal of compound (I), two adjacent 2-pyridone molecules, which are related by a twofold rotation axis, form a head-to-head dimer via a pair of N-HÁ Á ÁO hydrogen bonds (N1-H1Á Á ÁO3 i ; symmetry code as in Table 1), as observed in various cocrystals of 2-pyridone (Odani & Matsumoto, 2002).
The acid and base molecules form an undulating tape structure running along [201] through the above-mentioned O-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds (Fig. 5). The tapes are stacked along the b axis into a layer structure through ainteraction between the pyridine rings [centroid-to-centroid distance = 3.7005 (6) Å and interplanar spacing = 3.4239 (4) Å ] and a short CÁ Á ÁC contact [C2Á Á ÁC3 iv = 3.3056 (13) Å ; symmetry code: (iv) x, y + 1, z]. A weak C-HÁ Á ÁCl interaction formed between the acid and base molecules (C7-H7Á Á ÁCl1 ii ; Table 1) links the layers. The O-HÁ Á ÁO hydrogen bond between the acid and base molecules is short [O2Á Á ÁO3 = 2.4989 (11) Å ], suggesting possible disorder of the H atom in the hydrogen bond, but no distinct evidence of the disorder was observed in the difference Fourier map, nor from the molecular geometry.

Synthesis and crystallization
Single crystals of compound (I) were obtained by slow evaporation from an ethanol solution (120 ml) of chloranilic acid (350 mg

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Bis(3-hyroxypyridinium) 2,5-dichloro-3,6-dioxocyclohexa-1,4-diene-1,4-diolate (II)
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.75 e Å −3 Δρ min = −0.34 e Å −3 Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq