Crystal structure of N-hydroxyquinoline-2-carboxamide monohydrate

The N-hydroxyquinoline-2-carboxamide molecule has a nearly planar structure [maximum deviation = 0.062 (1) Å] and only the hydroxy H atom deviates from the molecule plane.

The title compound, C 10 H 8 N 2 O 2 ÁH 2 O, consists of an N-hydroxyquinoline-2carboxamide molecule in the keto tautomeric form and a water molecule connected through an O-HÁ Á ÁO hydrogen bond. The N-hydroxyquinoline-2carboxamide molecule has a nearly planar structure [maximum deviation = 0.062 (1) Å ] and only the hydroxy H atom deviates significantly from the molecule plane. In the crystal,stacking between the aromatic rings [intercentroid distance = 3.887 (1) Å ] and intermolecular O-HÁ Á ÁO hydrogen bonds organize the crystal components into columns extending along the b-axis direction.
Structural information about the title compound is absent in the literature, however, and this will be useful in controlling the purity of the synthesized ligand and metal complexes by ISSN 2056-9890 powder diffraction. It is well known that the products of such syntheses can be contaminated with impurities that result from hydrolysis or oxidation of the hydroxamic groups to the carboxylic group. In addition, syntheses of polynuclear complexes are often carried out with various metal-to-ligand ratios, so that in some cases an excessive quantity of the hydroxamic ligand can be present in the isolated samples.

Structural commentary
The molecular structure of the title compound is presented in Fig. 1. It consists of an N-hydroxyquinoline-2-carboxamide molecule in the keto tautomeric form {which is supported by the C O [1.227 (2) Å ] and C-N [1.317 (2) Å ] bond lengths} and a water molecule. The carbonyl group possesses a Z conformation against the N1 atom of the quinoline moiety and E conformation against the hydroxy oxygen atom [torsion angles O2-N2-C10-O1 = 0.8 (2) and N1-C9-C10-O1 À177.33 (14) ]. The N-hydroxyquinoline-2-carboxamide molecule has an almost planar structure (non-hydrogen atoms are planar to within 0.03 Å ). Only the H atom of the OH group deviates significantly from the molecular plane: the C-N-O-H torsion angle of À75.1 (13) is defined by the O-HÁ Á ÁO hydrogen bond between hydroxy group and the water molecule. The C-N and C-C bond lengths in the quinoline moiety are typical for 2-substituted pyridine derivatives (Moroz et al., 2012;Strotmeyer et al., 2003;Krä mer & Fritsky, 2000).

Figure 1
The asymmetric unit of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as spheres of arbitrary radius. The dashed line indicates a hydrogen bond.
chloride in the presence of N-methylmorpholine according to the reported procedure (Trivedi et al., 2014). Light-yellow crystals suitable for X-ray diffraction were obtained from aqueous solution by slow evaporation at room temperature (yield 76%).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All hydrogen atoms were found from the difference-Fourier maps and refined isotropically.  (Sheldrick, 2008); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009). 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.