N′-[(E)-1-(2-Fluorophenyl)ethylidene]pyridine-4-carbohydrazide

The title compound, C14H12FN3O, adopts an E conformation with respect to the azomethine bond. The pyridyl and fluorobenzene rings make dihedral angles of 38.58 (6) and 41.61 (5)° respectively with the central C(=O)N2CC unit, resulting in a non-planar molecule. The intermolecular interactions comprise two classical N—H⋯O and N—H⋯N hydrogen bonds and four non-classical C—H⋯O and C—H⋯F hydrogen bonds. These interactions are augmented by a weak π–π interaction between the benzene and pyridyl rings of neighbouring molecules, with a centroid–centroid distance of 3.9226 (10) Å. This leads to a three-dimensional supramolecular assembly in the crystal system. The F atom is disordered over two sites in a 0.559 (3): 0.441 (3) ratio, through a 180° rotation of the fluorobenzene ring.

The title compound, C 14 H 12 FN 3 O, adopts an E conformation with respect to the azomethine bond. The pyridyl and fluorobenzene rings make dihedral angles of 38.58 (6) and 41.61 (5) respectively with the central C(=O)N 2 CC unit, resulting in a non-planar molecule. The intermolecular interactions comprise two classical N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds and four non-classical C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds. These interactions are augmented by a weakinteraction between the benzene and pyridyl rings of neighbouring molecules, with a centroidcentroid distance of 3.9226 (10) Å . This leads to a threedimensional supramolecular assembly in the crystal system. The F atom is disordered over two sites in a 0.559 (3): 0.441 (3) ratio, through a 180 rotation of the fluorobenzene ring.
Data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 and SAINT (Bruker, 2004); data reduction: SAINT and XPREP (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2010); software used to prepare material for publication: SHELXL97 and publCIF (Westrip, 2010  The chemistry of Schiff bases has attracted a great deal of interest in recent years. These compounds play an important role in the development of various proteins and enzymes (Kahwa et al., 1986;Santos et al., 2001). A number of hydrazones derived from isoniazid were reported to be active antitubercular agents and were found to be less toxic than isoniazid (Rollas & Kucukguzel, 2007). In this paper we report the synthesis and crystal structure of the title compound.
The molecule crystallizes in monoclinic space group P2 1 /c. The 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 of -177.77 (8) (Table 1). In addition to this, there are four non-classical C-H···O and C-H···F H bonding interactions present with D···A distances of 3.1603 (19), 3.0680 (13), 3.238 (2) and 3.1849 (19) Å connecting various adjacent molecules together with the main molecule (Fig. 2). The hydrogen atoms at N2 and C8 form bifurcated hydrogen bonds with O1 & N1 and F1 and O1 respectively (Fig. 2). A weak π···π interaction between the phenyl and the pyridyl ring of the neighbouring molecules also supports to form a three-dimensional supramolecular assembly together with the dominant H bonding interactions with a centroid-centroid distance of 3.9226 (10) Å (Fig. 2). Fig. 3 shows the packing of the molecules by means of hydrogen bonding and π-π interactions along a axis.
Through a 180° rotation of the fluorophenyl ring, the fluorine atom F1 is disordered over two sites in a ratio of 56.0 (1):44.0 (1). Similar instances of positional disorder had been previously reported (Sreeja et al., 2014).

Experimental
The title compound was prepared by adapting a reported procedure (Mangalam & Kurup, 2011). Methanolic solutions of pyridine-4-carbohydrazide (0.137 g, 1 mmol) and 1-(2-fluorophenyl)ethanone (0.138 g, 1 mmol) was refluxed, in presence of a few drops of glacial acetic acid for 6 h. On cooling the reactant media, colourless crystals of hydrazones were separated out. The crystals were filtered and washed with minimum quantity of methanol and dried over P 4 O 10 in vacuo. Good quality block shaped crystals suitable for X-ray analysis, were obtained from methanolic solution by slow evaporation.

Refinement
The fluorine atoms F1 and F1B of this molecule were refined freely, with the sum of their occupancy factors constrained to 1.0. The H5 at C5 atom is placed in geometrically idealized position with occupancy factor equal to that F1, and its coordinates were fixed. The H1 atom was refined with restrained distance of 0.93 Å with occupancy factor equal to that of F1B. The N2-H2′ distance was restrained to 0.88±0.01 Å. The H atoms on the rest of C 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)=1.2Ueq(carrier) or 1.5Ueq (methyl C).  Hydrogen-bonding and π···π interactions in the title compound. The minor components of fluorine and hydrogen atoms of the disorder are omitted.

Figure 3
Packing diagram of the title compound 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 Occ. (