4-(4-Fluorophenyl)-1-(4-nitrophenyl)-3-(pyridin-4-yl)-1H-pyrazol-5-amine

In the crystal structure of the title compound, C20H14FN5O2, the pyrazole ring forms dihedral angles of 59.3 (2), 25.6 (2) and 46.0 (2)° with the directly attached 4-fluorophenyl, pyridine and nitrophenyl rings, respectively. The crystal packing is characterized by intermolecular N—H⋯N and N—H⋯O hydrogen bonds.

The crystal packing (Fig. 2) shows that the amino function acts as a hydrogen bond donor of two intermolecular hydrogen bonds -one to the nitrogen atom (N26) of the pyridine ring and another one to one oxygen atom (O14) of the nitro group of two different molecules. The length of the hydrogen bonds is 2.19 Å and 2.29 Å, respectively ( Table 1).
The two hydrogen bonds result in a two dimensional network parallel to the b-c-plan.
Experimental 20 mmol of LDA was added to 30 ml of dry THF in a three neck flask and cooled to 195 K. 14 mmol of 4-fluorophenylacetonitril in 10 ml THF was added dropwise and the reaction mixture was stirred for 45 min. 5 mmol of N-(4-nitrophenyl)-4-pyridinecarbohydrazonoyl chloride was added slowly to the reaction and stirring was continued for 1 h. After warming to 293 K, 50 ml of water was added to the reaction mixture and extracted with ethyl acetate (2x 50 ml). The organic layer was dried over Na 2 SO 4 . The solvent was removed under redued pressure to about 5 ml and the pure product precipitated. Yield: 36%. Recrystallization from THF/diethylether resulted in crystals suitable for X-ray.

Refinement
Hydrogen atoms attached to carbons were placed at calculated positions with C-H = 0.95 Å (aromatic) or 0.98-0.99 Å (sp 3 C-atom). H atoms bonded to N were located in a difference map and constrained to this position. All H atoms were refined in the riding-model approximation with isotropic displacement parameters (set at 1.2-1.5 times of the U eq of the parent atom).

Computing details
Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software (Enraf-Nonius, 1989  View of the title compound. Displacement ellipsoids are drawn at the 50% probability level. H atoms are depicted as circles of arbitrary size.

Figure 2
Crystal structure of the title compound with view along the a-axis (hydrogen bonding is shown with dashed lines). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.49 e Å −3 Δρ min = −0.73 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.056 (6) 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.