(E)-N′-(2,4,6-Trihydroxybenzylidene)isonicotinohydrazide sesquihydrate

In the title compound, C13H11N3O4·1.5H2O, the pyridine ring forms a dihedral angle of 1.50 (6)° with the benzene ring. An intramolecular O—H⋯N hydrogen bond forms a six-membered ring with an S(6) ring motif. In the crystal structure, one water molecule is disordered over two positions around an inversion centre with site-occupancy factors of 0.5. Intermolecular O—H⋯N, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds consolidate the structure into a three dimensional network. A π–π stacking interaction with a centroid–centroid distance of 3.5949 (7) Å is also present.

In the title compound, C 13 H 11 N 3 O 4 Á1.5H 2 O, the pyridine ring forms a dihedral angle of 1.50 (6) with the benzene ring. An intramolecular O-HÁ Á ÁN hydrogen bond forms a sixmembered ring with an S(6) ring motif. In the crystal structure, one water molecule is disordered over two positions around an inversion centre with site-occupancy factors of 0.5. Intermolecular O-HÁ Á ÁN, O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds consolidate the structure into a three dimensional network. Astacking interaction with a centroid-centroid distance of 3.5949 (7) Å is also present.

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 a current work of synthesis of (E)-N'-(substitutedbenzylidene)isonicotinohydrazide derivatives, in this paper we present the crystal structure of the title compound.

Experimental
The isoniazid derivative was prepared following the procedure by Lourenco et al. (2008). (E)-N'-(2,4,6trihydroxybenzylidene)isonicotinohydrazide hydrate was prepared by reaction between the 2,4,6-trihydroxy benzaldehyde (1.0 eq) with isoniazid (1.0 eq) in ethanol/water. After stirring for 1 to 3 h at room temperature, the resulting mixture was concentrated under reduced pressure. The residue after being purified by washing with cold ethanol and ethyl ether, afforded the pure derivative. Colourless single crystals suitable for X-ray analysis were obtained by recrystallization with methanol.

Refinement
All the H atoms were located from a difference Fourier map. H1W1, H2W1, H1W2 and H2W2 were allowed to ride on their parent atoms to which they were attached, with U iso (H) = 1.5U eq (parent atom). The remaining H were refined freely.  Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme. Dashed line indicates the intramolecular hydrogen bond. Atom O2WA was generated by symmetry code -x+1, -y+1, -z.

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 > 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.