(E)-1-(2,4-Dinitrophenyl)-2-(3-ethoxy-4-hydroxybenzylidene)hydrazine

The molecule of the title hydrazine derivative, C15H14N4O6, is essentially planar, the dihedral angle between the substituted benzene rings being 2.25 (9)°. The ethoxy and hydroxy groups are almost coplanar with their bound benzene ring [r.m.s. deviation = 0.0153 (2) Å for the ten non-H atoms]. Intramolecular N—H⋯O and O—H⋯Oethoxy hydrogen bonds generate S(6) and S(5) ring motifs, respectively. In the crystal, molecules are linked by O—H⋯Onitro hydrogen bonds into chains propagating in [010]. Weak aromatic π–π interactions, with centroid–centroid distances of 3.8192 (19) and 4.0491 (19) Å, are also observed.


Comment
As part of our on-going research on diaryl-hydrazones with potential bioactivity, the title compound (I) was synthesized in order to study and compare its antioxidant activity with the other related compounds (Fun et al., 2011;2012;2013). In our antioxidant activity evaluation of (I) by DPPH scavenging (Molyneux, 2004) it was found that (I) possesses strong antioxidant activity with 82.71% inhibition, comparison with L-ascorbic acid as a standard (90.39 % inhibition). Herein we report the synthesis and crystal structure of (I).
In Fig. 1, the molecular structure of (I), C 15 H 14 N 4 O 6 , is essentially planar with the dihedral angle between the two substituted benzene rings being 2.25 (9)°. The mean plane through the bridge fragment (N1/N2/C7) makes the dihedral angles of 2.25 (19) and 2.30 (19)° with the C1-C6 and C8-C13 rings, respectively. Both nitro groups of the 2,4-dinitro-  Table 1) generates an S(6) ring motif whereas another intramolecular O6-H1O6 -O5 hydrogen bond generates S(5) ring motif. These intramolecular hydrogen bonds help to stabilize the planarity of the molecule. Bond distances in (I) are comparable with those observed in the closely related structure (Fun et al., 2013).

Experimental
2,4-dinitrophenylhydrazine (0.40 g, 2 mmol) was dissolved in ethanol (10 ml) and H 2 SO 4 (conc.) (98 %, 0.50 ml) was added slowly with stirring. A solution of 3-ethoxy-4-hydroxybenzaldehyde (0.30 g, 2 mmol) in ethanol (20 ml) was then added to the solution with continuous stirring for 1 hr, yielding an orange solid which was filtered off and washed with methanol. Orange plates of (I) were recrystallized from acetone solution by slow evaporation of the solvent at room temperature over a few weeks, Mp. 515-516 K.

Refinement
Hydrazine and hydroxy H atoms were located from a difference Fourier map and refined freely. The remaining H atoms were positioned geometrically and allowed to ride on their parent atoms, with d(C-H) = 0.93 Å for CH and aromatic, and 0.96 Å for CH 3 atoms. The U iso values were constrained to be 1.5U eq of the carrier atom for methyl H atoms and 1.2U eq supplementary materials for the remaining H atoms. A rotating group model was used for the methyl groups.    The crystal packing of (I) viewed along the c axis. Hydrogen bonds are shown as dashed lines.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O1