N′-[4-(Dimethylamino)benzylidene]-3-hydroxy-2-naphthohydrazide

The title compound, C20H19N3O2, was obtained by the condensation of 4-(dimethylamino)benzaldehyde with 3-hydroxy-2-naphthohydrazide. The molecule is approximately planar, with an intramolecular N—H⋯O hydrogen bond involving the imino H atom and the hydroxy O atom. The dihedral angle between the benzene ring and the naphthyl mean plane is 2.72 (13)°. In the crystal structure, symmetry-related molecules are linked by intermolecular O—H⋯O hydrogen bonds, forming chains propagating in the c-axis direction.

The title compound, C 20 H 19 N 3 O 2 , was obtained by the condensation of 4-(dimethylamino)benzaldehyde with 3-hydroxy-2-naphthohydrazide. The molecule is approximately planar, with an intramolecular N-HÁ Á ÁO hydrogen bond involving the imino H atom and the hydroxy O atom. The dihedral angle between the benzene ring and the naphthyl mean plane is 2.72 (13) . In the crystal structure, symmetryrelated molecules are linked by intermolecular O-HÁ Á ÁO hydrogen bonds, forming chains propagating in the c-axis direction.   Table 1 Hydrogen-bond geometry (Å , ). H.-T. Huang

Comment
In recent years compounds derived from the condensation of aldehydes with benzohydrazides have been widely investigated, either for their structures (Qiu & Zhao, 2008;Yathirajan et al., 2007;Salhin et al., 2007) or for their biological properties (Küçükgüzel et al., 2003);Charkoudian et al., 2007). The author reports herein the crystal structure of the title compound, obtained by the condensation of 4-dimethylaminobenzaldehyde with 3-hydroxy-2-naphthohydrazide.
The molecular structure of the title compound is illustrated in Fig. 1. The bond lengths are within normal values (Allen et al., 1987), and are comparable to the values in similar compounds (Fun et al., 2008;Liu & Li, 2004;Lei et al., 2008).
The molecule is approximately coplanar, with the dihedral angle between the benzene ring and the naphthyl mean-plane being 2.72 (13)°. There is an intramolecular N-H···O hydrogen bond, involving the imino H-atom and the hydroxyl O-atom (Table 1).
In the crystal structure symmetry related molecules are linked via intermolecular O-H···O hydrogen bonds to form onedimensional chains propagating in the c direction ( Fig. 2 and Table 1).

Experimental
The title compound was prepared by the condensation of 4-dimethylaminobenzaldehyde (0.1 mol) and 3-hydroxy-2-naphthohydrazide (0.1 mmol) in ethanol (20 ml). The excess ethanol was removed by distillation. The colorless solid obtained was filtered and washed with ethanol. Single crystals, suitable for X-ray diffraction, were obtained on slow evaporation of a solution of the title compound in ethanol.

Refinement
The imino H-atom was located in a difference Fourier map and refined with the N-H distance restrained to 0.90 (1) Å. The remainder of the H-atoms were positioned geometrically (C-H = 0.93-0.96 Å, O-H = 0.82 Å) and refined using a riding model, with U iso (H) = 1.2U eq (C) and 1.5U eq (O). The ratio of observed to unique reflections is low (44%); this is caused by the fact that the crystal diffracted weakly.

Figures
Fig . 1. The molecular structure of the title compound, showing the atom-numbering scheme and displacement ellipsoids drawn at the 30% probability level. The intramolecular N2-H2B···O2 hydrogen bond is shown as a dashed line.  Table 1 for details (H-atoms not involved in hydrogen bonding have been omitted for clarity).

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.