2-Carboxy-6-(quinolin-1-ium-8-yloxy)benzoate

In the zwitterionic title compound, C17H11NO5, the dihedral angle between the two aromatic rings is 76.90 (7)°. The dihedral angles between the carboxyl groups and the benzene ring are 64.02 (9) and 21.67 (9)°, the larger angle being associated with an intramolecular N—H⋯Ocarboxyl hydrogen bond, resulting from proton transfer from the carboxylic acid group to the quinoline N atom and giving an S(9) ring motif. In the crystal, molecules are connected by O—H⋯O hydrogen bonds into chains extending along the b-axis direction. An overall two-dimensional network structure is formed through π–π interactions between the quinoline rings [minimum ring-centroid separation = 3.6068 (6) Å].


Related literature
For the use of phthalic acid derivatives in the construction of coordination polymers, see: Su et al. (2007);Zhang, Su, Li et al. (2006). For their potential applications, see: Wang et al. (2009);Zhang, Su, Song et al. (2006). For graph-set analysis, see: Etter et al. (1990).  Table 1 Hydrogen-bond geometry (Å , ). supplementary materials Acta Cryst. (2012). E68, o1351 [doi:10.1107/S1600536812013980] 2-Carboxy-6-(quinolin-1-ium-8-yloxy)benzoate Li-Mao Cai, Xin Fang, Mei-Jin Lin, Jin Xie and Jun-Dong Wang Comment Phthalic acid derivatives have proved useful as ligands for the construction of coordination polymers which have a number of potential applications (Zhang, Su, Song et al., 2006;Zhang, Su, Li et al., 2006;Su et al., 2007;Wang et al., 2009). As a part of our investigation of the rare earth coordination networks based on these phthalic acid derivatives, we report here the crystal structure of the title compound, the zwitterionic substituted phthalic acid C 17 H 11 NO 5 (Fig. 1). In this molecule, the carboxylic acid substituent group at C15 has protonated the quinoline N-atom, giving an intramolecular N-H···O carboxyl hydrogen-bonding association [graph set S9 (Etter et al., 1990)]. The dihedral angles between the carboxyl groups and the benzene ring are 64.02 (9)° and 21.67 (9)°, the larger angle being associated with the intramolecular hydrogen bond. The molecules are connected by intermolecular carboxylic acid O-H···O hydrogen bonds (Table 1) giving one-dimensional chains which extend along the b axial direction and give an overall two-dimensional network structure through π-π interactions between the quinoline rings [minimum ring centroid separation, 3.6068 (6) Å] (Fig. 2).

Experimental
3-Nitropthalonitrile (1.73 g, 10.0 mmol), 8-hydroxyquinoline (1.45 g, 10.0 mmol) and K 2 CO 3 (4.14 g, 30.0 mmol) were suspended in dry DMF (20 ml) and stirred at room temperature under a nitrogen atmosphere for 4 h. The reaction mixture was then poured into water (200 ml), and the crude product was separated by filtration and purified by column chromatography on silica gel using CH 2 Cl 2 as an eluent. After removal of the solvent by rotary evaporation, 2.25 g of 3-(quinolin-8-yloxy)-phthalonitrile was obtained in a yield of 83%. Under nitrogen, 2.71 g, 10.0 mmol) of this compound and KOH (1.20 g, 30.0 mmol) were suspended in 30 ml of distilled water and refluxed until the solution turned clear.
After being cooled to room temperature, the pH of the reaction mixture was slowly adjusted to about 5-6 using HCl (6.0 mol/L) with stirring. The solid product was separated by filtration, and then washed successively with water (3 times 30 ml). After drying under vacuum, 2.78 g of final produc was obtained in a yield of 91%. The solid was dissolved in methyl alcohol and the filtered solution was evaporated slowly at room temperature for 5-10 days, giving colorless crystals suitable for X-ray structure analysis.

Refinement
Carboxylic acid H atoms were located in a difference-Fourier analysis and their positional and isotropic displacement parameters were refined. Other H-atoms were placed in geometrically determined positions and were treated as riding, with C-H = 0.93 Å and with U iso (H) = 1.2U eq (C).

Figure 1
The molecular structure of the title compound, showing the atom-labelling scheme, with the intramolecular hydrogen bond shown as a dashed line. Displacement ellipsoids are drawn at the 30% probability level.