Synthesis , Characterization and Crystal Structures of 3 , 5-Bis ( 4-fluorophenyl )-4 , 5-dihydro-1 H-pyrazole-1-carboxamide and 3 , 5-Bis ( 4-fluorophenyl )-4 , 5-dihydro-1 H-pyrazole-1-carbothioamide

Two new pyrazoline derivatives, 3,5-bis(4-fluorophenyl)-4,5-dihydropyrazole1-carboxamide (1) and 3,5-bis(4-fluorophenyl)-4,5-dihydropyrazole-1-carbothioamide (2), were synthesized by reacting 4,4'-difluoro chalcone with semicarbazide hydrochloride and thiosemicarbazide in ethanolic sodium hydroxide solution. Both the compounds were confirmed by single crystal X-ray diffraction data and supported by IR, NMR, and mass spectral data. In 1, crystal packing is stabilized by N–H...O hydrogen bonds and weak N–H...N, N–H...F and C–H...F intermolecular interactions. In 2, only weak N–H...F and N–H...S intermolecular interactions are observed. Crystal data: C16H13F2N3O, (1), Mr = 301.29, monoclinic, C2/c, a = 17.6219(6) Å, b = 10.8735(3) Å, c = 15.3216(5) Å, β = 102.864(3)°, V = 2862.11(16) Å, Z = 8, T = 173 K, R(F) = 0.0511, wR(F) = 0.1333; C16H13F2N3S, (2), Mr = 317.35, monoclinic, P21/c, a = 14.339(2) Å, b = 11.1478(17) Å, c = 9.541(2)(5) Å, β = 107.007(18)°, V = 1458.5(5) Å, Z = 4, T = 173 K, R(F) = 0.0413, wR(F) = 0.0959. OPEN ACCESS Crystals 2012, 2 1109


Introduction
Pyrazolines are well known, and important nitrogen-containing five-membered heterocyclic compounds and various methods have been reported for their synthesis [1,2].Substituted pyrazolines are useful in pharmaceutical and agrochemical research.They display various biological activities such as antitumor, antibacterial, antifungal, antiviral, antiparasitic, anti-tubercular and insecticidal [3][4][5].Some of these compounds have also antioxidant, anti-inflammatory and analgesic properties [6,7].Due to these interesting activities of diversely substituted pyrazolines as biological agents, considerable attention has been focused on this class.In addition, pyrazolines have played a crucial part in the development of the theory in heterocyclic chemistry and also used extensively in organic synthesis [8].

Results and Discussion
The IR spectrum of compound 1 (Figure S1) showed a forked band at 3452 cm −1 corresponding to NH 2 group and a band at 1681 cm −1 assigned to the carbonyl group.While, the IR spectrum of compound 2 (Figure S2) demonstrated a forked band at 3475 cm −1 corresponding to a NH 2 -group and a band at 1365 cm −1 corresponding to a C=S group.The IR spectra of both the compounds showed a -C=N-stretch at 1577 & 1599 cm −1 , which confirmed the formation of the pyrazoline moiety.In the 1 H NMR spectra of pyrazolines (Figures S3 and S4), protons H A and H B are geminal protons at the C4 carbon.They appeared in the region 3.03-3.12ppm and 3.75-3.84ppm as a doublet of doublets for both the compounds.The CH proton at C5 also appeared as a doublet of doublets in the region of 5.38-5.89ppm, due to vicinal coupling with two non-equivalent geminal protons of the C4 carbon.Beside these signals, the amino protons appeared as broad singlet signal at δ 6.5 in compound 1 and as two singlet signals at δ 7.95 & 8.02 in compound 2. LCMS (Figures S5 and S6) and elemental analysis also gave satisfactory results for both of the compounds.

General
The synthesis of the target compounds is outlined in Scheme 1.
Melting points were taken in open capillary tubes and were uncorrected.The purity of the compounds was confirmed by thin layer chromatography using Merck silica gel 60 F254 coated aluminum plates.IR spectra were recorded on Shimadzu-FTIR Infrared spectrometer in KBr (mmax in cm −1 ). 1 H (400 MHz) NMR spectra were recorded on a Bruker AMX 400 spectrometer, with 5 mm BB −1H TUBES with TMS as internal standard.LCMS was obtained using Agilent 1200 series LC and Micromass zQ spectrometer.Elemental analyses were carried out by using VARIO EL-III (Elementar Analysensysteme GmBH).

Data Collection and Refinement
Crystallographic data for both 1 and 2 were collected on an Agilent Gemini CCD-Diffractometer with monochromatic Mo-Kα radiation (λ = 0.71073 Å) and an EOS detector [20].The structures were solved by direct methods [21], full-matrix least-squares refinement [21] on F 2 with 313 1 or 219 2 parameters.In both 1 and 2, H1NA, and H1NB, were located in a difference map and refined isotropically.All of the remaining H atoms were placed in their calculated positions and then refined using the riding model with C-H lengths of 0.93 or 0.98 Å (CH) or 0.97 Å (CH 2 ).The isotropic displacement parameters for these atoms were set to 1.19 to 1.20 (CH, CH 2 ), times U eq of the parent atom.

Figure 2 .
Figure 2. Molecular structure of 1 showing the atom labeling scheme and 50% probability displacement ellipsoids.

Figure 3 .
Figure 3. Molecular structure of 2 showing the atom labeling scheme and 50% probability displacement ellipsoids.

Figure 4 .
Figure 4. Packing diagram of 1 viewed along the b axis.Dashed lines indicate N-H...O hydrogen bonds forming an inversion dimer.Additional weak N-H…F and C-H…F intermolecular interactions further link the molecules into a sheet-like structure in the ac-plane.Remaining H atoms have been removed for clarity.

Figure 5 .
Figure 5. Packing diagram of 2 viewed along the b axis.Dashed lines indicate N-H...F and N-H...S hydrogen bonds forming chains along (001).Remaining H atoms have been removed for clarity.