N′-[(1E)-1-(2-Fluorophenyl)ethylidene]pyridine-3-carbohydrazide

The title compound, C14H12FN3O, adopts an E conformation with respect to the azomethine double bond whereas the N and methyl C atoms are in a Z conformation with respect to the same bond. The ketonic O and azomethine N atoms are cis to each other. The non-planar molecule [the dihedral angle between the benzene rings is 7.44 (11)°] exists in an amido form with a C=O bond length of 1.221 (2) Å. In the crystal, a bifurcated N—H⋯(O,N) hydrogen bond is formed between the amide H atom and the keto O and imine N atoms of an adjacent molecule, leading to the formation of chains propagating along the b-axis direction. Through a 180° rotation of the fluorophenyl ring, the F atom is disordered over two sites with an occupancy ratio of 0.632 (4):0.368 (4).

The molecule crystallizes in orthorhombic space group Pbcn. The title compound adopts an E configuration with respect to the azomethine olefinic bond whilst the C8 and N2 atoms are in Z configuration with respect to the same bond with torsion angles for C1-C7-N1-N2 and N2-N1-C7-C8 of 177.76 (16) and -0.9 (3)°, respectively (Fig. 1). The ketonic O and the azomethine N are cis to each other with a torsion angle of -0.3 (3)°. The molecule exists in the amido form with a C9=O1 bond length of 1.221 (2) Å which is very close to the reported C=O bond length in a similar structure (Nair et al., 2012). The pyridyl and fluorophenyl rings make dihedral angles of 45.44 (7) and 42.48 (6)° with the C(=O)N 2 CC central unit making the molecule non-planar.
A bifurcated hydrogen bond is formed between the amide H atom and the keto oxygen, O1 and imine nitrogen atom, N1 of an adjacent molecule which leads to formation of a hydrogen bonded chains of molecules that propagate along the baxis direction of the structure (Fig. 2) with donor-acceptor distances of 3.163 (2) Å and 3.148 (2) Å respectively. In addition to the above intermolecular H bonding interactions, a non-classical H bond between H8A of methyl carbon C8 and the fluorine (F1) atom also stabilizes the packing. The non-classical H bonding features a C8···F1 distance of 3.169 (3) Å and links the molecules in a zigzag fashion (Fig. 2). No significant π···π interactions with centroid-centroid distances of less than 4 Å are observed in the structure.
Through a 180° rotation of the fluorophenyl ring, the fluorine atom F1 is disordered over two sites in a ratio of 63.3 (4):36.7 (4). Similar instances of positional disorder had been previously reported (Nayak et al., 2012).

Experimental
The title compound was prepared by adapting a reported procedure (Mangalam & Kurup, 2011). Methanolic solutions of nicotinic acid hydrazide (0.137 g, 1 mmol) and 2-fluoroacetophenone (0.138 g, 1 mmol) were combined, a few drops of glacial acetic acid were added, and the mixture was heated to reflux for 6 h. On cooling the mixture, crystals of the hydrazone separated out. The crystals were filtered off, washed with a minimum quantity of methanol and dried over P 4 O 10 in vacuo. Crystals suitable for X-ray analysis were obtained in 80% yield (0.2048 g) from methanolic solution by slow evaporation. The melting point of the prepared compound was found to be 186 °C.

Refinement
The disordered fluorine atoms F1 and F1B were refined freely, with the sum of their occupancy factors constrained to 1.0. Disordered hydrogen atoms H2 and H6 were placed in geometrically idealized positions and were constrained to ride on their parent C atoms with C-H distances of 0.93 Å. The N2-H2′ distance was restrained to 0.88 (1) Å. The remaining H atoms were placed in calculated positions, guided by difference maps, with C-H bond distances 0.93-0.96 Å. H atoms were assigned as U iso (H) = 1.2U eq (carrier) or 1.5U eq (methyl C). Omitted owing to bad disagreement were the reflections (2 2 3), (5 2 1) and (2 0 0).

N′-[(1E)-1-(2-Fluorophenyl)ethylidene]pyridine-3-carbohydrazide
Crystal data 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 Occ. (