2′-(3-Hydroxybenzylidene)pyrazine-2-carbohydrazide monohydrate

The title compound, C12H10N4O2·H2O, was synthesized by the reaction of pyrazine-2-carboxylic acid hydrazide and 3-hydroxybenzaldehyde in ethanol. In the crystal structure, the organic molecules are linked into extended chains by intermolecular N(amide)—H⋯O(hydroxy) hydrogen bonds. Additional hydrogen bonds between the water molecule and three adjacent organic molecules, as well as face-to-face π–π stacking interactions between the benzene and pyrazine rings [centroid-to-centroid separation = 3.669 (2) Å and offset = 1.362 Å], link the molecules into a three-dimensional framework.

The title compound, C 12 H 10 N 4 O 2 ÁH 2 O, was synthesized by the reaction of pyrazine-2-carboxylic acid hydrazide and 3hydroxybenzaldehyde in ethanol. In the crystal structure, the organic molecules are linked into extended chains by intermolecular N(amide)-HÁ Á ÁO(hydroxy) hydrogen bonds. Additional hydrogen bonds between the water molecule and three adjacent organic molecules, as well as face-to-facestacking interactions between the benzene and pyrazine rings [centroid-to-centroid separation = 3.669 (2) Å and offset = 1.362 Å ], link the molecules into a three-dimensional framework.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LN2011).

Comment
Hydrazonecarbonyl compounds have received considerable attention due to their pharmacological activities (Parashar et al., 1988) and photochromic properties (Hadjoudis et al., 1987). A series of similar pyrazinylcarboxylic acid hydrazones has been reported previously (Gardner et al., 1956). As a continuation of the work of our group, we report here the crystal structure of 2'-(3-hydroxybenzylidene)pyrazine-2-carbohydrazide monohydrate, (I).
The asymmetric unit contains one organic molecule and one molecule of H 2 O. The carbohydrazide molecule deviates only slightly from planarity with a dihedral angle of 11.60 (3)° between the planes of the pyrazinyl and phenyl rings ( Fig. 1).
In the crystal, the organic molecules of (I) are arranged in slightly tilted rows. Within the rows, amide atom N3 acts as a hydrogen bond donor to the atom O2 of the hydroxy group in a neighbouring molecule, thereby forming extended chains, which run parallel to the a axis (Table 1, Fig. 2).
The water O atom acts as a hydrogen bond acceptor from the hydroxy group of an organic molecule. One water H atom forms a hydrogen bond with the N atom in the pyrazinyl ring of another adjacent molecule, while the other H atom forms bifurcated hydrogen bonds with the carbonyl O atom, O1, and the N4 atom from another molecule of I, thereby forming a five-membered hydrogen bond ring (Fig. 3).
The crystal packing is characterized by π···π stacking interactions. The molecules are stacked in an antiparalled fashion, with a pyrazinyl to phenyl ring centroid-centroid separation of 3.669 (2) Å and an offset of 1.362 Å. Together with the hydrogen bonds, these interactions lead to a three-dimensional supramolecular network pattern (Fig. 3).

Experimental
Compound (I) was synthesized by the reaction of pyrazine-2-carboxylic acid hydrazide (0.01 mol, 1.38 g) and 3-hydroxybenzaldehyde (0.01 mol, 1.52 g) in ethanol. The solution was refluxed for 3 h. After cooling down, the solid product was filtered and recrystallized from ethanol with a yield of 75%, m.p. 540-541 K. Crystals suitable for single-crystal X-ray diffraction were grown by slow evaporation of a mixture of methanol and water (5: 1).

Refinement
All H atoms were initially located in a difference Fourier map. The carbon bound H atoms were then constrained to an ideal geometry, with C(phenyl)-H distances of 0.93 Å and U iso (H) = 1.2U eq (C). The H atoms attached to the hydroxy and water O atoms and to the N atom were refined freely with U iso (H) = 1.5U eq (O) and 1.2U eq (N), respectively.
supplementary materials sup-2 Figures   Fig. 1. The structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.