6-[(2-Hydroxy-5-methylanilino)methylidene]-4-nitrocyclohexa-2,4-dien-1-one

The title compound is nearly planar with a dihedral angle between the aromatic rings of 1.41 (8)°. The phenolic O atom is deprotonated and the N atom of the azomethine unit carries the proton, thereby forming an intramolecular N—H⋯O hydrogen bond. In the crystal, the molecules form inversion dimers via pairwise O—H⋯O hydrogen bonds.

The title compound was prepared in order to extend the series of available ligands. Its preparation was performed according to methods described in the literature for the parent compound salicyclidene-o-aminophenol (salopH 2 ; Freeman & White, 1956;Pettinari et al., 2001) by the reaction of 2-hydroxy-5-nitrobenzaldehyde and 2-amino-4methylphenol in ethanol.
The molecule is nearly planar with a dihedral angle between the aromatic rings of 1.41 (8) . Atom H2 forms an intramolecular hydrogen bond (Table 1, Fig. 1) between the phenolic oxygen atom O1 and N1 of the azomethine unit: the hydrogen atom is localized at a distance of 0.93 (2) Å from N1, indicating the presence of the keto-amine form. The presence of a quinoidal structure is further supported by the shortening of the bond C3-O1 to 1.2734 (19) Å and the lengthening of the adjacent C-C bonds in the phenyl ring [C2-C3 = 1.446 (2), C3-C4 = 1.420 (2) Å ] (Nazır et al., 2000;Warncke et al., 2016). There are several structure reports of Schiff bases with an oxygen atom in the ortho-data reports position where the intramolecular bridging hydrogen atom is localized at the nitrogen atom (e.g. Pradeep, 2005;Dubs et al., 2000;Hö pfl et al., 1998;Bö hme & Fels, 2008a,b). The stabilization of salicylidene-imines by 'resonance-assisted hydrogen bonding' has been discussed previously (Hö kelek et al., 2004).
In the crystal, the molecule forms dimers via pairwise O2-H9Á Á ÁO1 hydrogen bonds. An intermolecular C-HÁ Á ÁO short contact (HÁ Á ÁO = 2.32 Å ) to one of the O atoms of the nitro group is also present.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. The methyl group at C14 is rota-tionally disordered over two orientations in a 0.59 (5):0.41 (5) ratio.

Funding information
Funding for this research was provided by: Open Access Funding by the Publication Fund of the TU Bergakademie Freiberg.

data-1
IUCrData ( where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.16 e Å −3 Δρ min = −0.17 e Å −3 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. Hydrogen atoms bonded to C were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.93 Å for Csp 2 , and 0.96 Å for CH 3 . U iso (H) = xU eq (C), where x = 1.2 for Csp 2 and 1.5 for CH 3 . The hydrogen atoms at N1 and O2 (H2 and H9) were located by difference Fourier synthesis and freely refined.