Crystal structure of N-(quinolin-6-yl)hydroxylamine

The title compound crystallized with four independent molecules in the asymmetric unit. They are linked via two N—H⋯O and one O—H⋯N hydrogen bond, forming a tetramer-like unit.


Structural commentary
The title compound, C 9 H 8 N 2 O, crystallized with four independent molecules (A, B, C, and D) in the asymmetric unit (Fig. 1). The O atoms of the hydroxylamino groups in the four ISSN 1600-5368 independent molecules A, B, C, and D are displaced from the aromatic ring planes by 0.745 (5), 0.550 (5), 0.971 (6) and 0.293 (5) Å , respectively. The four molecules are linked via one O-HÁ Á ÁN and two N-HÁ Á ÁN hydrogen bonds, forming a tetramer-like unit ( Fig. 1 and Table 1).

Supramolecular features
In the crystal, the tetramer-like units are linked by O-HÁ Á ÁN and N-HÁ Á ÁO hydrogen bonds, forming layers parallel to (001); see Table 1 and Fig. 2. These layers are linked via C-HÁ Á ÁO hydrogen bonds and a number of C-HÁ Á Á interactions (Table 1), forming a three-dimensional structure.

Synthesis and crystallization
To a stirred solution of 6-nitroquinoline [(1); 0.5 g, 2.87 mmol] in EtOH/CH 2 Cl 2 (1:1 v/v, 20 ml) at 273 K was added a slurry of Raney nickel (0.5 ml). To this mixture, hydrazine hydrate (10 equivalents) was added dropwise with stirring over the course of 1 h while keeping the solution under an inert atmosphere of nitrogen gas. The solid was removed by filtration and the resulting solution diluted with water (2 ml) and then extracted with ethyl acetate (2 Â 10 ml). The combined organic extracts were washed with brine and dried over sodium sulfate. Column chromatography on silica gel, eluted with ethyl acetate and MeOH/CH 2 Cl 2 , gave the title compound as a yellow solid (yield: 100 mg, 25% yield, R F = 0.1 in MeOH/ CH 2 Cl 2 4:96). It was found to be unstable upon standing in organic solvents. Crystals of the title compound were obtained by dissolving pure product in warm ethyl acetate followed by  Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
A view of the molecular structure of the four independent molecules (suffixes A, B, C and D) of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 50% probability level. Hydrogen bonds are shown as dashed lines (see Table 1 for details).

Figure 2
A view along the a axis of the crystal packing of the title compound. Hydrogen bonds are shown as dashed lines (see Table 1

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The NH H atoms were located in a difference Fourier map and freely refined. The OH and Cbound H atoms were included in calculated positions and treated as riding: O-H = 0.84, C-H = 0.95 Å with U iso (H) = 1.2U eq (O,C). Several crystals examined proved to have multiple domains. The final data crystal, while still a multiple, could be described having primarily two domains and was treated as such. Orientation matrices for the two domains were determined using the program CELL_NOW (Bruker, 2008) and the data were processed further using TWINABS (Bruker, 2008). The model converged well using the HKLF5 data but the final difference map shows several peaks of 0.4 to 0.96 e Å À3 near two of the four independent molecules. While this residual electron density could be interpreted as disorder of parts of those molecules, attempts to model such disorder were unsatisfactory, requiring considerable restraints/constraints to achieve convergence, and were not included in the final model. An alternative explanation of this residual electron density is a possible contribution from crystalline domains not included in the twinning description.   Computer programs: APEX2 and SAINT (Bruker, 2008), SHELXS97 and SHELXL97 (Sheldrick, 2008), ORTEPIII (Burnett & Johnson, 1996), PLATON (Spek, 2009) and publCIF (Westrip, 2010).

Special details
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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. The data crystal was a two-domain pseudo-merohedral twin. Data was processed using TWINABS and the final refinement was carried out with the HKLF 5 data. The H atoms on the N2 atoms were located and refined with isotropic thermal parameters. The H atoms on the OH groups appeared in difference maps, but were placed at calculated positions and allowed to find maximum overlap with the electron density in a riding model. Residual electron density near two of the four independent molecules was not amenable to reasonable modelling as disorder and may indicate contribution of an additional minor crystalline domain.