N′-[(Z)-4-(Dimethylamino)benzylidene]-4-nitrobenzohydrazide monohydrate

In the asymmetric unit of the title compound, C16H16N4O3·H2O, there are two symmetry-independent hydrazide molecules with almost identical geometries, and two independent water molecules. The dihedral angles between the two benzene rings in the two hydrazide molecules are 0.11 (5) and 0.77 (5)°. In one molecule, an intramolecular C—H⋯O hydrogen bond generates a ring of graph-set motif S(5). Intermolecular N—H⋯O, O—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds and π–π stacking interactions between the benzene rings [centroid–centroid distances in the range 3.5021 (6)–3.6403 (6) Å] are observed, together with O⋯O [2.7226 (11) Å], O⋯N [2.7072 (10) Å] and N⋯O [2.7072 (10)–2.8582 (12) Å] short contacts. The hydrazine molecules are stacked along the b axis and adjacent molecules are linked by water molecules.


Comment
Hydrazones possessing an azometine -NHN═CH-proton constitute an important class of compounds for new drug development. Therefore, many researchers have synthesized these compounds as target structures and evaluated their biological activities. These observations have been the guides for the development of new hydrazones. Hydrazones containing an azometine -NHN═CH-proton are synthesized by heating the appropriate substituted hydrazines/hydrazides with aldehydes and ketones in solvents like ethanol, methanol, tetrahydrofuran, butanol, glacial acetic acid, ethanol-glacial acetic acid. Another synthetic route for the synthesis of hydrazones is the coupling of aryldiazonium salts with active hydrogen compounds (Rollas & Küçükgüzel, 2007). Hydrazide-hydrazones compounds are not only intermediates but they are also very effective organic compounds in their own right. When they are used as intermediates, coupling products can be synthesized by using the active hydrogen component of the -CONHN═CH-azometine group (Singh et al., 1992). N-Alkyl hydrazides can be synthesized by reduction of hydrazones with NaBH 4 (Ergenç & Günay, 1998), substituted 1,3,4-oxadiazolines can be synthesized when hydrazones are heated in the presence of acetic anhydride (Durgun et al., 1993). Prompted by these review and in continuation of our work (Fun et al., 2008), we herein report the crystal structure of the title compound, (I).
There are two independent molecules (A and B) in the asymmetric unit of (I), with similar geometries (Fig. 1.) The bond lengths and angles are found to have normal values (Allen et al., 1987). The dihedral angle formed by the benzene (C1A-C6A) and (C9A-C14A) rings is 0.11 (5)° in molecule A and that between the benzene (C1B-C6B) and (C9B-C14B) rings is 0.77 (5)° in molecule B, indicating that they are coplanar. In molecule B, an intramolecular C-H···O hydrogen bond generates an S(5) ring motif (Bernstein et al., 1995).

Experimental
The title compound was obtained by refluxing 4-nitrrophenyl hydrazide (0.01 mol) and 4-(dimethylamino)benzaldehyde (0.01 mol) in ethanol (30 ml) with the addition of 3 drops of concentrated Sulfuric acid for 3 h. Excess ethanol was removed from the reaction mixture under reduced pressure. The solid product obtained was filtered, washed with water and dried.
Crystals suitable for X-ray analysis were obtained from ethanol by slow evaporation.

Refinement
The amino and water H atoms were located in a difference map and refined with restraints of N-H = 0.85 (1) and O-H = 0.84 (1) Å. The remaining H atoms were positioned geometrically [C-H = 0.93 (aromatic) or 0.96 Å (methyl)] and refined using a riding model, with U iso (H) = 1.2U eq (aromatic C) and 1.5U eq (methyl C). A rotating-group model was used for the methyl groups. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom numbering scheme.

Special details
Experimental. The data was collected with the Oxford Cyrosystem Cobra low-temperature attachment. 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.