3-Carboxyquinolin-1-ium-2-carboxylate monohydrate

The title compound, C11H7NO4·H2O, contains a 3-carboxyquinolin-1-ium-2-carboxylate (qda) zwitterion and one water molecule. In the crystal, pairs of N—H⋯O hydrogen bonds link the molecules into inversion dimers, and these dimers are further connected by O—H⋯O hydrogen bonds into a three-dimensional supramolecular architecture. In addition, π–π interactions occur between pyridine and benzene rings from different qda ligands [centroid–centroid distance = 3.749 (1) Å] and the dihedral angles of the –CO2H and –CO2 groups to the quinoline system are 8.47 (3) and 88.16 (6)°, respectively.

The title compound, C 11 H 7 NO 4 ÁH 2 O, contains a 3-carboxyquinolin-1-ium-2-carboxylate (qda) zwitterion and one water molecule. In the crystal, pairs of N-HÁ Á ÁO hydrogen bonds link the molecules into inversion dimers, and these dimers are further connected by O-HÁ Á ÁO hydrogen bonds into a threedimensional supramolecular architecture. In addition,interactions occur between pyridine and benzene rings from different qda ligands [centroid-centroid distance = 3.749 (1) Å ] and the dihedral angles of the -CO 2 H and -CO 2 groups to the quinoline system are 8.47 (3) and 88.16 (6) , respectively.
Data collection: CrystalClear (Rigaku, 2007); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Crys-talClear (Rigaku, 2007) and DIAMOND (Brandenburg, 1998) Quinoline carboxylic acid derivatives have been explored in the synthesis of metal organic frameworks due to their abundant coordination modes which lead to the construction of metal organic frameworks with intriguing structures and functional properties (Dobrzyńska et al. 2004;Hu et al. 2007;Dobrzyńska et al. 2005;Li & Liu 2010). It is well known that noncovalent intermolecular interactions such as hydrogen bonding interactions and π-π interactions, play crucial role in the design and construction of supramolecular architecture (Wang et al. 2011). Taking quinoline-2-carboxylic acid for example, the crystal structures of its metal complexes have been determined for several metal ions, including Cu II (Zurowska et al. 2007), Mn II (Dobrzyńska & Jerzykiewicz, 2008), Ni II (Odoko et al. 2001), Co II and Fe II (Dobrzyńska et al. 2004). Of these complexes, the magnetic properties of Cu II , Co II and Fe II complexes have also been investigated.
Herein, the structurally similar quinoline-2,3-dicarboxylic acid (qda) is a good choice for constructing a framework with novel physical properties, and the crystal structure of its monohydrate is reported now.
In this report, the title compound was prepared by using quinoline-2,3-dicarboxylic acid (qda) ligand under hydrothermal conditions. The analysis of crystal structure shows that one proton of carboxyl group of qda is transferred to N atom from pyridine ring, and one water molecule exists in the crystal lattice (Fig. 1). As shown in Fig. 2, the N-H···O hydrogen bond (yellow dotted line) links the molecules into dimers, and these dimers are further connected by O-H···O hydrogen bond (black dotted line) to a 3D supramolecular architecture. In addition, the π-π interactions (blue dotted line) occur between pyridine ring and benzene ring from different qda ligands with the distance of 3.749 (1) Å, making the supramolecular network more stable (Fig. 3).

Experimental
The quinoline-2,3-dicarboxylic acid (qda) was purchased commercially and used without further purification. A mixture of ZnCl 2 (13.4 mg, 0.1 mmol), and qda (43.8 mg, 0.2 mmol) was dissolved in a 15 mL of water, and the pH was adjusted to 7 by 1 mol L -1 sodium hydroxide solution. Then the mixture was placed in a 25 mL autoclave with Teflon-liner. The autoclave was heated to 433 K and held at this temperature for three days. It was then cooled to room temperature under spontaneous conditions. The colourless block crystals were obtained with a yield of 60 %, however, X-ray crystallographic study shows that this crystal is not zinc complex but the title compound.

Refinement
All H atoms on C atoms were placed in an ideal position using a riding model th with C-H distances of 0.93 Å and SHELXL97 (Sheldrick, 2008); molecular graphics: CrystalClear (Rigaku, 2007) and DIAMOND (Brandenburg, 1998); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figure 1
The crystal structure of the title compound with atom-labelling scheme, showing 30% probability displacement ellipsoids. H atoms are presented as a small spheres of arbitrary radius.    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. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.