Crystal structures of 3-chloro-2-nitrobenzoic acid with quinoline derivatives: 3-chloro-2-nitrobenzoic acid–5-nitroquinoline (1/1), 3-chloro-2-nitrobenzoic acid–6-nitroquinoline (1/1) and 8-hydroxyquinolinium 3-chloro-2-nitrobenzoate

The structures of the two isomeric hydrogen-bonded 1:1 co-crystals of 3-chloro-2-nitrobenzoic acid with 5-nitroquinoline and 6-nitroquinoline, and the 1:1 salt of 3-chloro-2-nitrobenzoic acid with 8-hydroxyqunoline have been determined at 190 K. In each crystal, the acid and base molecules are linked by a short O—H⋯N or N—H⋯O hydrogen bond.

The structures of three compounds of 3-chloro-2-nitrobenzoic acid with 5-nitroquinoline, (I), 6-nitroquinoline, (II), and 8-hydroxyquinoline, (III), have been determined at 190 K. In each of the two isomeric compounds, (I) and (II), C 7 H 4 ClNO 4 ÁC 9 H 6 N 2 O 2 , the acid and base molecules are held together by O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds. In compound (III), C 9 H 8 NO + Á-C 7 H 3 ClNO 4 À , an acid-base interaction involving H-atom transfer occurs and the H atom is located at the N site of the base molecule. In the crystal of (I), the hydrogen-bonded acid-base units are linked by C-HÁ Á ÁO hydrogen bonds, forming a tape structure along the b-axis direction. Adjacent tapes, which are related by a twofold rotation axis, are linked by a third C-HÁ Á ÁO hydrogen bond, forming wide ribbons parallel to the (103) plane. These ribbons are stacked viainteractions between the quinoline ring systems [centroidcentroid distances = 3.4935 (5)-3.7721 (6) Å ], forming layers parallel to the ab plane. In the crystal of (II), the hydrogen-bonded acid-base units are also linked into a tape structure along the b-axis direction via C-HÁ Á ÁO hydrogen bonds. Inversion-related tapes are linked by further C-HÁ Á ÁO hydrogen bonds to form wide ribbons parallel to the (308) plane. The ribbons are linked by weakinteractions [centroid-centroid distances = 3.8016 (8)-3.9247 (9) Å ], forming a three-dimensional structure. In the crystal of (III), the cations and the anions are alternately linked via N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, forming a 2 1 helix running along the b-axis direction. The cations and the anions are further stacked alternately in columns along the a-axis direction viainteractions [centroid-centroid distances = 3.8016 (8)-3.9247 (9) Å ], and the molecular chains are linked into layers parallel to the ab plane through these interactions.

Chemical context
The hydrogen bonds formed between organic acids and organic bases vary from an O-HÁ Á ÁN type to an O À Á Á ÁH-N + type depending on the pK a values of the acids and bases as well as intermolecular interactions in the crystals, and at an appropriate ÁpK a [pKa(base) À pKa(acid)] value, a short strong hydrogen bond with a broad single minimum potential energy curve for the H atom or a double-minimum potential is observed (Schmidtmann & Wilson, 2008;Gilli & Gilli, 2009). For the system of quinoline-chloro-and nitro-substituted benzoic acids, we have shown that three compounds of quinoline with 3-chloro-2-nitrobenzoic acid, 4-chloro-2-nitrobenzoic acid and 5-chloro-2-nitrobenzoic acid, the ÁpK a values of which are 3.08, 2.93 and 3.04, respectively, have a ISSN 2056-9890 short double-well OÁ Á ÁHÁ Á ÁN hydrogen bond between the carboxy O atom and the aromatic N atom (Gotoh & Ishida, 2009). Similar OÁ Á ÁHÁ Á ÁN hydrogen bonds have been also observed in compounds of phthalazine with 3-chloro-2-nitrobenzoic acid and 4-chloro-2-nitrobenzoic acid with ÁpK a values of 1.65 and 1.50, respectively (Gotoh & Ishida, 2011), and of isoquinoline with 3-chloro-2-nitrobenzoic acid with ÁpK a = 3.58 (Gotoh & Ishida, 2015).

Structural commentary
The molecular structure of (I) is shown in Fig. 1. The acid and base molecules are held together by an O-HÁ Á ÁN hydrogen bond between the carboxy group and the N atom of the base. In addition, a weak C-HÁ Á ÁO interaction is formed between the acid and base molecules (Table 1). In the hydrogenbonded acid-base unit, the quinoline ring system (N2/C8-C16), the carboxy group (O1/C7/O2) and the benzene ring (C1-C6) are almost coplanar with each other; the carboxy group makes dihedral angles of 9.95 (12) and 9.45 (12) , respectively, with the quinoline ring system and the benzene ring, and the dihedral angle between the quinoline ring system and the benzene ring is 2.59 (4) . On the other hand, the benzene ring and the nitro group (O3/N1/O4) in the acid molecule is almost perpendicular, with a dihedral angle of 86.14 (13) . The quinoline ring system and the attached nitro group (O5/N3/O6) are somewhat twisted with a dihedral angle of 31.67 (11) .
The molecular structure of (II) is shown in Fig. 2. Similar to (I), the acid and base molecules are held together by an O-HÁ Á ÁN hydrogen bond and an additional C-HÁ Á ÁO interaction (Table 2). In the acid-base unit, the quinoline ring The molecular structure of (II), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. The O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds are indicated by dashed lines (Table 2).
system, the carboxy group and the benzene ring of the acid are slightly twisted to each other; the carboxy group makes dihedral angles of 12.08 (13) and 2.40 (13) , respectively, with the quinoline ring system and the benzene ring, and the dihedral angle between the quinoline ring system and the benzene ring is 10.99 (4) . In the acid molecule, the benzene ring and the nitro group (O3/N1/O4) are almost perpendicular with a dihedral angle of 88.54 (13) . On the other hand, in the base molecule the quinoline ring system and the nitro group (O5/N3/O6) are almost coplanar with a dihedral angle of 5.58 (12) . The molecular structure of (III) is shown in Fig. 3. An acidbase interaction involving H-atom transfer occurs and the acid and base molecules are linked by an N + -HÁ Á ÁO À hydrogen bond (Table 3). In the hydrogen-bonded unit, the quinoline ring system makes dihedral angles of 34.96 (13) and 30.80 (14) , respectively, with the carboxylate group and the benzene ring of the acid. In the acid molecule, the benzene ring makes dihedral angles of 4.71 (13) and 86.12 (11) , respectively, with the carboxylate and nitro groups.

Figure 6
A packing diagram of (II), showing the ribbon structure along the b-axis direction formed by O-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds (dashed lines). H atoms not involved in the hydrogen bonds have been omitted.

Figure 5
A partial packing diagram of (I), showing the ribbons linked bystacking interactions (magenta dashed lines).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. All H atoms in compounds (I)- For all structures, data collection: RAPID-AUTO (Rigaku, 2006); cell refinement: RAPID-AUTO (Rigaku, 2006); data reduction: RAPID-AUTO (Rigaku, 2006); program(s) used to solve structure: SHELXT2018/2 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and Mercury (Macrae et al., 2006); software used to prepare material for publication: CrystalStructure (Rigaku, 2018) and PLATON (Spek, 2015). 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.

3-Chloro-2-nitrobenzoicacid-6-nitroquinoline (1/1) (II)
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.50 e Å −3 Δρ min = −0.33 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   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.001 Δρ max = 0.39 e Å −3 Δρ min = −0.29 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