(E)-2,4-Dihydroxy-N′-(2-hydroxy-3-methoxy-5-nitrobenzylidene)benzohydrazide dihydrate

The asymmetric unit of the title compound, C15H13N3O7·2H2O, consists of a hydrazone molecule and two solvent water molecules. The molecule adopts an E configuration with respect to the C=N bond. It is relatively planar, with a dihedral angle between the two benzene rings of 2.6 (1)°. There are intramolecular O—H⋯N and O—H⋯O hydrogen bonds in the hydrazone molecule. In the crystal structure, symmetry-related molecules are linked through intermolecular N—H⋯O and O—H⋯O hydrogen bonds to form a three-dimensional network.

The asymmetric unit of the title compound, C 15 H 13 N 3 O 7 Á-2H 2 O, consists of a hydrazone molecule and two solvent water molecules. The molecule adopts an E configuration with respect to the C N bond. It is relatively planar, with a dihedral angle between the two benzene rings of 2.6 (1) . There are intramolecular O-HÁ Á ÁN and O-HÁ Á ÁO hydrogen bonds in the hydrazone molecule. In the crystal structure, symmetry-related molecules are linked through intermolecular N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds to form a three-dimensional network.

Comment
Hydrazone compounds have been widely investigated for their biological properties (Patil et al., 2010;Cukurovali et al., 2006). Furthermore, the crystal structures of the hydrazone compounds have also attracted much attention in recent years (Mohd Lair et al., 2009;Lin & Sang, 2009;Suleiman Gwaram et al., 2010). As a continuation of our work on the structural characterization of such compounds (Han & Zhao, 2010a,b), we report herein on the synthesis and crystal structure of the new title hydrazone compound.
The title compound, Fig. 1, consists of a hydrazone molecule and two water molecules of crystallization. The hydrazone molecule adopts an E configuration with respect to the C═N bond. The dihedral angle between the two benzene rings in the hydrazone molecule is 2.6 (1)°. There are intramolecular O-H···N and O-H···O hydrogen bonds in the hydrazone molecule ( Fig. 1 and Table 1). All the bond lengths are within normal ranges (Allen et al., 1987), and are comparable with those in similar compounds (Li & Ban, 2009;Lo & Ng, 2009;Ning & Xu, 2009;Zhu et al., 2009).
In the crystal structure of the title compound symmetry related molecules are linked through intermolecular N-H···O and O-H···O hydrogen bonds to form a three-dimensional network (Table 1 and Fig. 2).

Experimental
A mixture of 3-methoxy-5-nitrosalicylaldehyde (0.197 g, 1 mmol) and 2,4-dihydroxybenzohydrazide (0.168 g, 1 mmol) in 50 ml methanol was stirred at room temperature for 1 h. The mixture was then filtered to remove any impurities, and the filtrate left at room temperature for slow evaporation of the solvent. After a few days colourless block-like crystals of the title compound, suitable for X-ray diffraction, were formed.

Refinement
Amino H and water H atoms were located from a difference Fourier map and refined isotropically, with N-H, O-H, and H···H distances restrained to 0.90 (1), 0.85 (1), and 1.37 (2) Å, respectively. The C-bound H atoms were positioned geometrically and refined using the riding-model approximation, with C-H = 0.93 and 0.96 Å for CH and methyl H atoms, respectively, O-H(hydroxyl) = 0.82 Å, with U iso (H) = k × U eq (parent C or O atom), where k = 1.2 for CH H atoms and k = 1.5 for O(hydroxyl) and methyl H atoms. Fig. 1. The molecular structure of the title compound, with atom labels and displacement ellipsoids drawn at the 30% probability level. Intramolecular O-H···O and O-H···N hydrogen bonds are shown as dashed lines.  Table 1 for details).

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 > σ(F 2 ) is used only for calculating Rfactors(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.