(E)-N′-(2,3,4-Trihydroxybenzylidene)isonicotinohydrazide dihydrate

In the title isoniazid derivative, C13H11N3O4·2H2O, the Schiff base molecule exists in an E configuration with respect to the acyclic C=N bond. An intramolecular O—H⋯N hydrogen bond forms a six-membered ring, producing an S(6) ring motif. The essentially planar pyridine ring [maximum deviation = 0.0119 (8) Å] is inclined at a dihedral angle of 7.30 (4)° with respect to the benzene ring. In the crystal, intermolecular O—H⋯N, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds link the molecules into two-dimensional arrays lying parallel to the (10) plane. These arrays are further interconnected into a three-dimensional extended network via O—H⋯O and C—H⋯O hydrogen bonds. A weak intermolecular π–π interaction [centroid-to-centroid distance = 3.5627 (5) Å] is also observed.

In the title isoniazid derivative, C 13 H 11 N 3 O 4 Á2H 2 O, the Schiff base molecule exists in an E configuration with respect to the acyclic C N bond. An intramolecular O-HÁ Á ÁN hydrogen bond forms a six-membered ring, producing an S(6) ring motif. The essentially planar pyridine ring [maximum deviation = 0.0119 (8) Å ] is inclined at a dihedral angle of 7.30 (4) with respect to the benzene ring. In the crystal, intermolecular O-HÁ Á ÁN, O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds link the molecules into two-dimensional arrays lying parallel to the (101) plane. These arrays are further interconnected into a three-dimensional extended network via O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds. A weak intermolecularinteraction [centroid-to-centroid distance = 3.5627 (5) Å ] is also observed.

Comment
In the search of new compounds, isoniazid derivatives have been found to possess potential tuberculostatic activity (Janin, 2007;Maccari et al., 2005;Slayden & Barry, 2000). Schiff bases have attracted much attention because of their biological activity (Kahwa et al., 1986). As a part of our current work on synthesis of (E)-N'-substituted isonicotinohydrazide derivatives, in this paper we present the crystal structure of the title compound.
There is a slight inclination between the pyridine and benzene rings, as indicated by the dihedral angle formed of 7.30 (4)°.

Experimental
The isoniazid derivative was prepared following the procedure by Lourenço et al., 2008. The title compound was prepared by the reaction between 2,3,4-trihydroxybenzaldehyde (1.0 eq) with isoniazid (1.0 eq) in ethanol/water. After stirring for 1-3 h at room temperature, the resulting mixture was concentrated under reduced pressure. The residue, purified by washing with cold ethanol and ethyl ether, afforded the pure derivative. The brown-coloured single crystals suitable for X-ray analysis were obtained by recrystallization with ethanol.

Refinement
All H atoms were located from difference Fourier map and allowed to refine freely with N-H = 0.890 (16) Fig. 1. The asymmetric unit of the title isoniazid derivative, showing 50% probability displacement ellipsoids for non-H atoms and the atom-numbering scheme. An intramolecular hydrogen bond is shown as dashed line.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1)K.
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.