N′-[(1E)-4-Diethylamino-2-hydroxybenzidene]benzohydrazide

In the title compound, C18H21N3O2, the dihedral angle between the phenyl and benzene rings is 36.85 (10)°. The methyl C atom of one of the ethyl groups is disordered over two positions with site occupancies of 0.810 (8) and 0.190 (8). The molecular structure is stabilized by a classical intramolecular O—H⋯N hydrogen bond. The crystal structure exhibits weak intermolecular N—H⋯O, C—H⋯O and C—H⋯π interactions.

In the title compound, C 18 H 21 N 3 O 2 , the dihedral angle between the phenyl and benzene rings is 36.85 (10) . The methyl C atom of one of the ethyl groups is disordered over two positions with site occupancies of 0.810 (8) and 0.190 (8). The molecular structure is stabilized by a classical intramolecular O-HÁ Á ÁN hydrogen bond. The crystal structure exhibits weak intermolecular N-HÁ Á ÁO, C-HÁ Á ÁO and C-HÁ Á Á interactions.   Table 1 Hydrogen-bond geometry (Å , ).

Comment
In view of the biological actitivities of Schiff base ligands which are known to exhibit anti-viral, anti-cancer, anti-bacterial, anti-fungal, anti-inflammatory, anti-convulsant and anti-HIV activities (Pandeya et al., 1999;Singh & Dash, 1988;Kelley et al., 1995;Tarafder et al., 2002), we report herein the molecular and crystal structures of the title compound.

Experimental
The benzoic acid hydrazide (5 mmol) in methanol (10 ml) was stirred in a round bottom flask followed by drop wise addition of methanolic solution of 4-(diethylamino)salicylaldehyde (5 mmol). The reaction mixture was then refluxed for three hours and upon cooling to 273 K. A pale yellow crystalline solid precipitates from the mixture was separated out. Crystalline product was washed with ice cold ethanol and dried in vacuo over anhydrous CaCl 2 . Single crystals suitable for the X-ray diffraction were obtained by slow evaporation of a solution of the title compound in DMF at room temperature. Melting point 500 K.

Refinement
The site occupancy factors for disordered C atom were refined as C18/C18A = 0.810 (8) 5U eq (C) for methyl droups and U iso (H) = 1.2U eq (C) for other. Fig. 1. The molecular structure of title compound with the atom numbering scheme. Displacement ellipsoids are drawn at 30% probability level. For disordered ethyl group only major moiety is presented. H atoms are shown as a small spheres of arbitrary radius.

Special details
Geometry. All s.u.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix.
The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.