1-[3,5-Bis(4-fluorophenyl)-4,5-dihydro-1H-pyrazol-1-yl]ethanone

In the asymmetric unit of the title compound, C17H14F2N2O, there are three independent molecules (A, B and C) which differ slightly in the relative orientations of the two fluorophenyl rings. In molecules A and C one of the fluorophenyl rings is disordered over two positions, with occupancy ratios of 0.72 (2):0.28 (2) for molecule A and 0.67 (2):0.33 (2) for molecule C. The dihedral angle between the two fluorophenyl rings in the independent molecules lie in the range 70.3 (3)–84.0 (3)°. In the crystal structure, the molecules are linked via intermolecular C—H⋯O and C—H⋯F hydrogen bonds and π⋯π stacking interactions [centroid–centroid distance = 3.7508 (13) Å], forming a three-dimensional network.

In the asymmetric unit of the title compound, C 17 H 14 F 2 N 2 O, there are three independent molecules (A, B and C) which differ slightly in the relative orientations of the two fluorophenyl rings. In molecules A and C one of the fluorophenyl rings is disordered over two positions, with occupancy ratios of 0.72 (2):0.28 (2) for molecule A and 0.67 (2):0.33 (2) for molecule C. The dihedral angle between the two fluorophenyl rings in the independent molecules lie in the range 70.3 (3)-84.0 (3) . In the crystal structure, the molecules are linked via intermolecular C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds and Á Á Á stacking interactions [centroid-centroid distance = 3.7508 (13) Å ], forming a three-dimensional network.

Comment
Considerable attention has been focused on substituted pyrazoline compounds, due to their biological activity. In particular, they are used as antitumor, antibacterial, antifungal, antiviral, antiparasitic, anti-tubercular and insecticidal agents (Hes et al., 1978;Manna et al., 2005;Amir et al., 2008). Some of these compounds have also exhibit anti-inflammatory, anti-diabetic, anaesthetic and analgesic properties (Garge et al., 1971;Regaila et al., 1979). Among the pyrazoline derivatives, 1-acetyl-pyrazolines have been identified as one of the most promising scaffold. In the field of medicinal chemistry, 1-acetyl-pyrazoline derivatives have been found to display anticancer and anti-inflammatory activities. In addition, pyrazolines have played a crucial part in the development of the theory of heterocyclic chemistry and are also used extensively in organic synthesis (Klimova et al., 1999;Bhaskarreddy et al., 1997).
In view of the biological importance of pyrazolines, we report here the crystal structure of a new pyrazoline derivative.
The asymmetric unit of the title compound consists of three crystallographically independent molecules, A, B and C ( Fig.   1). In each independent molecule, the pyrazole ring adopts a flattened envelope conformation; the flap atoms C9A, C9B and C9C are displaced by 0.078 (3) and 0.099 (3) and 0.205 (3) Å from the planes of the other four atoms. The dihedral angle between the two fluorophenyl rings are: 70.3 (3) and 72.7 (9)° in the major and minor components of molecule A, 74.73 (10)° in molecule B and 84.0 (3) and 76.1 (9)° in the major and minor components of molecule C.
In the crystal structure (Fig. 2), the molecules are linked through intermolecular C-H···O and C-H···F hydrogen bonds (see Table 1) to form three-dimensional network. The crystal structure is further stabilized by weak π···π stacking interactions between C10A-C15A and C10B-C15B phenyl rings at (x, y, z), with a ring centroid-to-centroid distance of 3.7509 (13)Å.

Experimental
A mixture of (2E)-1,3-bis(4-fluorophenyl)prop-2-en-1-one (2.44 g, 0.01 mol) and hydrazine hydrate (0.5ml, 0.01 mol) in ethanol (25 ml) in presence of glacial acetic acid (2 ml) was refluxed for 5 h. The reaction mixture was cooled and poured into 50 ml ice-cold water. The precipitate was collected by filtration and purified by recrystallization from ethanol. One of the 4-fluorophenyl rings (F1/C1-C6) in molecules A and C are each disordered over two positions with occupancies of 0.72 (2) and 0.28 (2) for molecule A, and 0.67 (2) and 0.33 (2) for molecule C. In all disorder components atoms closer than 1.7 Å were restrained to have the same U ij components and all bonds were subjected to a rigid bond restraint. The 1,2-and 1,3-distances in the major and minor disorder components were restrained to be the same. H atoms were positioned geometrically [C-H = 0.93-0.98 Å] and were refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). A rotating group model was used for the methyl groups.  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 > 2σ(F 2 ) is used only for calculating Rfactors(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.