(E)-N′-(2,4,5-Trimethoxybenzylidene)isonicotinohydrazide dihydrate

The asymmetric unit of the title compound, C16H17N3O4·2H2O, contains one Schiff base molecule and two water molecules. The Schiff base molecule exists in an E configuration with respect to the C=N double bond and is essentially planar, the dihedral angle between the benzene and pyridine rings being 5.48 (8)°. The three methoxy groups are also coplanar with the benzene ring [C—O—C—C torsion angles = 3.9 (2), 178.51 (15) and 0.8 (2) Å]. In the crystal structure, the water molecules link the molecules into a three-dimensional network via intermolecular N—H⋯O, O—H⋯O, O—H⋯N and C—H⋯O hydrogen bonds.


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). As a part of a current work of synthesis of such derivatives, in this paper we present the crystal structure of the title compound which was synthesized in our lab.
The asymmetric unit consists of one Schiff base molecule and two water molecules (Fig. 1). The geometry parameters are comparable to those related structures (Naveenkumar et al., 2009(Naveenkumar et al., , 2010aShi, 2005). The molecule exists in an E configuration with respect to the C7═N3 double bond. The molecule is essentially coplanar with dihedral angle between the benzene ring and the pyridine ring being 5.48 (8) Table 1).

Experimental
The isoniazid derivative was prepared following the procedure by Lourenco et al., (2008). The title compound was prepared by reaction between 2, 4, 5-trimethoxybenzaldehyde (1.0 eq) and isoniazid (1.0 eq) in ethanol/water. After stirring for 1-3 hours 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 yellow single crystal suitable for X-ray analysis was obtained by recrystalization with methanol.

Refinement
N-bound and O-bound hydrogen atoms were located from the difference Fourier map. The N-bound hydrogen atom was refined freely and the O-bound hydrogen atoms were constrained to ride on the parent atom with U iso (H) = 1.5 U eq (O).
The rest of hydrogen atoms were positioned geometrically [C-H = 0.93 or 0.96 Å] and refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). Rotating-group models were applied for the methyl groups. As there is not enough anomalous dispersion to determine the absolute configuration, 4136 Friedel pairs were merged before final refinement. Fig. 1. The molecular structure of the title compound with atom labels and 50% probability ellipsoids for non-H atoms.  (Cosier & Glazer, 1986) operating at 100.0 (1) K.

Figures
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.