N′-[(E)-4-Benzyloxy-2-hydroxybenzylidene]-4-nitrobenzohydrazide monohydrate

The title compound, C21H17N3O5·H2O, exists in the keto form with an E conformation with respect to the azomethine double bond. The twist angles between the aromatic rings are in the range 4.67 (10)–17.54 (10)°. A water molecule of solvation is present in the lattice. A conventional intramolecular O—H⋯N hydrogen bond increases the rigidity of the molecule. Intermolecular O—H⋯O, N—H⋯O and C—H⋯O hydrogen-bonding interactions establish a supramolecular linkage among the molecules in the crystal structure. There are also C—H⋯π interactions present.

The title compound, C 21 H 17 N 3 O 5 ÁH 2 O, exists in the keto form with an E conformation with respect to the azomethine double bond. The twist angles between the aromatic rings are in the range 4.67 (10)-17.54 (10) . A water molecule of solvation is present in the lattice. A conventional intramolecular O-HÁ Á ÁN hydrogen bond increases the rigidity of the molecule. Intermolecular O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen-bonding interactions establish a supramolecular linkage among the molecules in the crystal structure. There are also C-HÁ Á Á interactions present.  H atoms treated by a mixture of independent and constrained refinement Á max = 0.14 e Å À3 Á min = À0.16 e Å À3 Table 1 Hydrogen-bond geometry (Å , ).

Related literature
Cg is the centroid of the C1-C6 ring  The lattice water molecule plays an essential role in packing of the molecules forming conventional and nonconventional hydrogen bonds between the carbohydrazide and water molecules (Fig. 2). A C-H···π interaction is also observed in the crystal structure between one of the H atoms attached to the C7 carbon atom and the phenyl ring of the adjacent molecule in the crystal system (Fig. 3). Two types of very weak π-π interactions also present with a shortest centroid-centroid distance of 4.9302 (14) Å. In crystal packing, the parallel arrangement of the molecules along a axis is shown in Fig. 4.

Experimental
The title compound was prepared by adapting a reported procedure (Emmanuel et al., 2011) by refluxing a mixture of methanolic solutions of 4-nitrobenzohydrazide (0.181 g, 1 mmol) and 4-(benzyloxy)-2-hydroxybenzaldehyde (0.228 g, 1 mmol) for 4 h. The formed crystals were collected, washed with few drops of methanol and dried over P 4 O 10 in vacuo.
Single crystals of the title compound suitable for X-ray analysis were obtained by slow evaporation from its methanolic solution.

Refinement
All H atoms on C were placed in calculated positions, guided by difference maps, with C-H bond distances 0.93-0.97 Å. H atoms were assigned as U iso =1.2 U eq . N2-H2N and O4-H4O (0.86 Å) H atoms were located from difference maps and restrained using DFIX instructions. The O1S-H1S and O1S-H2S (0.86 Å) H atoms of the water molecule is also located from difference maps and restrained using DFIX and DANG instructions.
In the absence of significant anomalous scattering effects Friedel pairs have been merged.

Figure 1
ORTEP view of the molecular structure of the title compound, along with the atom-labelling, drawn with 50% probability displacement ellipsoids.

Figure 4
Packing arrangement of molecules along a axis.   (7) 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.