N′-[(E)-(3-Fluoropyridin-2-yl)methylidene]pyridine-3-carbohydrazide dihydrate

The organic molecule in the title dihydrate, C12H9FN4O·2H2O, exists in the E conformation with respect to the azomethane C=N double bond. The molecule is approximately planar, with a maximum deviation of 0.117 (1) Å for the carbonyl O atom from the mean plane of the molecule. Both pyridine rings are essentially coplanar with the central C(=O)N2C unit [dihedral angles = 1.99 (7) and 5.71 (8)°], exhibiting a significant difference in dihedral angles from its benzohydrazide analogue. The crystal packing features N—H⋯O, O—H⋯N and O—H⋯O hydrogen-bond interactions, which lead to the formation of a chain along the c-axis direction through one of the water molecules present, and these chains are stacked one over the other by means of π–π interactions [with centroid–centroid distances of 3.7099 (10) and 3.6322 (10) Å] between the aromatic rings in neighbouring antiparallel molecules, building a three-dimensional supramolecular network.

The organic molecule in the title dihydrate, C 12 H 9 FN 4 OÁ2H 2 O, exists in the E conformation with respect to the azomethane C N double bond. The molecule is approximately planar, with a maximum deviation of 0.117 (1) Å for the carbonyl O atom from the mean plane of the molecule. Both pyridine rings are essentially coplanar with the central C( O)N 2 C unit [dihedral angles = 1.99 (7) and 5.71 (8) ], exhibiting a significant difference in dihedral angles from its benzohydrazide analogue. The crystal packing features N-HÁ Á ÁO, O-HÁ Á ÁN and O-HÁ Á ÁO hydrogen-bond interactions, which lead to the formation of a chain along the c-axis direction through one of the water molecules present, and these chains are stacked one over the other by means ofinteractions [with centroid-centroid distances of 3.7099 (10) and 3.6322 (10) Å ] between the aromatic rings in neighbouring antiparallel molecules, building a three-dimensional supramolecular network.

Comment
Carbohydrazides have attracted much attention for their excellent biological properties. Moreover, carbohydrazides derived from 2-acetylpyridine are known to inhibit the proliferation of tumour cells to a greater extent compared to standard anticancer agents (Havanur et al., 2010;Sreeja et al., 2004). In addition, metal complexes with carbohydrazides exhibit antimicrobial, DNA-binding and cytotoxic activities. It has also been shown that these metal complexes can be potent inhibitors of cell growth and DNA synthesis (Despaigne et al., 2010). We report herein the crystal structure of the title compound, a new carbohydrazide.
This molecule adopts an E configuration ( Fig. 1) with respect to the C6=N2 bond and it exists in the amido form with a C7=O1 bond length of 1.2211 (18) Å which is very close to the reported C=O bond length of similar structure of benzene analogue (Nair et al., 2012). The O1 and N2 atoms are in a Z configuration with respect to C7-N3 having a tortional angle of -0.6 (3)°. The molecule is almost planar with maximum deviation of 0.117 (1) Å for the atom O1 from the mean plane of the molecule (r.m.s. deviation, 0.0513). The pyridyl ring having F atom is essentially coplanar with the central C(=O)N 2 C unit (dihedral angle 5.71 (8)°), the other pyridyl ring exhibits a torsion angle of 1.99 (7) Table 1). One of the water molecules acts as both a hydrogen bond acceptor as well as a donor towards another carbohydrazide molecule while the other acts only as hydrogen bond donor. By means of these interactions the molecules are chained through one of the water molecules to form infinite chains parallel to the c axis of the unit cell (Fig. 3). These parallel chains are stacked one over the other by means of two π-π interactions between the two aromatic rings of the neighbouring anti parallel molecules ( Fig. 4) with centeroid-centeroid distances of 3.7099 (10) and 3.6322 (10) Å. Fig. 5 shows the stacked packing of the molecules along a axis in the unit cell.

Experimental
The title compound was prepared by adapting a reported procedure (Kuriakose et al., 2007). A solution of 3-fluoropyridine-2-carbaldehyde (1.25 g,1 mmol) in ethanol (10 ml) was mixed with an ethanolic solution (10 ml) of pyridine-3carbohydrazide (1.37 g,1 mmol). The mixture was boiled under reflux for 12 h after adding few drops of glacial acetic acid and then cooled to room temperature. Colorless needle shaped crystals, suitable for single-crystal analysis, were obtained after slow evaporation of the solution in air for a few days.

Refinement
The atoms H3′, H1A, H1B, H2A and H2B were located from a difference Fourier map and refined isotropically.    Hydrogen-bonding interactions showing the chain progressing along c axis.

Figure 4
Hydrogen-bonding and π-π interactions in the lattice.

Figure 5
Packing diagram showing the stacked packing arrangement of the molecules along a axis.

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

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq O2S 0.5863 (