Crystal structure and Hirshfeld surface analysis of N-[(Z)-(2-hydroxyphenyl)methylidene]aniline N-oxide

The conformation of the title compound is partially determined by a strong, intramolecular O—H⋯O hydrogen bond. In the crystal, C—H⋯O hydrogen bonds link the molecules, forming chains along the a-axis direction, which are linked into strongly corrugated sheets parallel to the ac plane by C—H⋯O hydrogen bonds and C—H⋯π(ring) interactions. The sheets are associated through additional C—H⋯π(ring) interactions.


Chemical context
Nitrones are a very important class of organic compounds as a result of their medicinal and pharmaceutical applications. They show antifungal (Salman et al., 2013), antibacterial (Chakraborty et al., 2010), neuroprotective (Chioua et al., 2012) and anticancer (Floyd et al., 2011) activities. In addition, nitrone compounds are widely used as antioxidant agents (Al-Mowali et al., 2014) because of their ability to scavenge free radicals. Based on these findings and following our interest in this area, we report herein the crystal structure of the title compound.

Supramolecular features
In the crystal, C7-H7Á Á ÁO2 i hydrogen bonds (Table 1) link the molecules, forming chains along the a-axis direction. The chains are linked into strongly corrugated sheets parallel to the ac plane by C10-H10Á Á ÁO2 ii hydrogen bonds and C11-H11Á Á ÁCg1 iii interactions (Cg1 is the centroid of the C1-C6 hydroxyphenyl ring; Table 1 and Fig. 2). The sheets are stacked along the b-axis direction by C4-H4Á Á ÁCg2 iv interactions (Cg2 is the centroid of the C8-C13 phenyl ring; Table 1 and Figs. 2 and 3).

Hirshfeld surface analysis
A Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was carried out using CrystalExplorer17.5 (Turner et al., 2017) to visualize the intermolecular interactions in the title compound. The Hirshfeld surface mapped over d norm (Fig. 4) shows the expected bright-red spots near atoms O1, O2, H7 and H10, which are involved in the C-HÁ Á ÁO hydrogenbonding interactions. The bright-red spot near O1 indicates its role as a hydrogen-bond acceptor to (C10)H10 (Fig. 4) and another red region near O2 correlates with the C7-H7Á Á ÁO2 interaction.
The two-dimensional fingerprint plots show the relative contributions of the various types of contacts to the Hirshfeld surface for the title compound (McKinnon et al., 2007). The plots ( Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
Detail of the intermolecular C-HÁ Á ÁO hydrogen bonds and the C-HÁ Á Á(ring) interactions (black and green dashed lines, respectively) viewed along the b-axis direction.

Figure 3
Packing viewed along the (120) direction with intermolecular interactions shown as in Fig. 2.

Figure 1
The title molecule with labelling scheme and 50% probability ellipsoids. The intramolecular hydrogen bond is shown by a dashed line. Table 2 Summary of short interatomic contacts (Å ) in the title compound.

Database survey
The In the crystal of DEPVOM, (101) layers are generated by C-HÁ Á ÁO hydrogen bonds coupled with C-HÁ Á Á(ring) and offsetstacking interactions. In the crystal of SIYHAK01, C-HÁ Á ÁO and C-HÁ Á ÁBr hydrogen bonds together with offsetinteractions stack the molecules along the a-axis direction. In the crystal of JELQOJ, the organic and peroxide molecules are linked through both peroxide O-H donor groups to oxide O-atom acceptors, giving one-dimensional chains extending along the b-axis direction. Weak intermolecular C-HÁ Á ÁO hydrogen-bonding interactions are also present. In the crystal of ERIXEJ, the molecule is stabilized by an intramolecular C-HÁ Á ÁO hydrogen bond. The geometry about the C N bond is Z [C-C-N-O torsion angle = À4.2 (3) ] and the phenyl and benzene rings are transoriented around the C N bond. The phenyl and benzene rings make a dihedral angle of 56.99 (2) .    N-phenylhydroxyamine in ethanol followed by stirring for 5 minutes, then standing at room temperature in the dark overnight gave the nitrone, which was recrystallized from ethanol in 53% yield; m.p. 387-388 K.

Refinement
Crystal and refinement details are presented in Table 4. The H atom of the OH group was found in difference-Fourier maps, and its positional parameters were fixed using the AFIX 3 instruction in SHELXL and were refined with the isotropic displacement parameter U iso (H) = 1.5U eq (O). The C-bound H atoms were positioned geometrically, with C-H = 0.95 Å , and constrained to ride on their parent atoms, withU iso (H) = 1.2U eq (C). Attempts to determine the absolute structure did not produce a definitive result, viz.: Flack x = 0.2 (3) by classical fit to all intensities 0.30 (14) from 611 selected quotients (Parsons' method). A round of TWIN/BASF refinement gave BASF = 0.2 (4) with no improvement in the model.

Funding information
The support of NSF-MRI grant No. 1228232 for the purchase of the diffractometer and Tulane University for support of the Tulane Crystallography Laboratory are gratefully acknowledged.

N-[(Z)-(2-Hydroxyphenyl)methylidene]aniline N-oxide
Crystal data  (Parsons et al., 2013). Absolute structure parameter: 0.30 (13) 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 )