2-Phenyl-5-(trifluoromethyl)pyrazol-3(2H)-one

The title compound, C10H7F3N2O, is an analogue of pyrazolone derivatives with potential analgesic and anti-inflammatory properties. Its molecular structure consists of phenyl and pyrazol-3(2H)-one units with a dihedral angle between the mean planes of the rings of 33.0 (1)°. The crystal structure is stabilized by an intermolecular hydrogen bond between the N—H group and the carbonyl O atom of the pyrazol-3(2H)-one ring which links the molecules into supramolecular C(5) chains along [001] and by weak π–π stacking interactions between the phenyl rings [centroid-centroid distance = 3.881 (2) Å]. The F atoms are disordered over two positions with refined site occupancies of 0.768(11) and 0.232(11).

The title compound, C 10 H 7 F 3 N 2 O, is an analogue of pyrazolone derivatives with potential analgesic and anti-inflammatory properties. Its molecular structure consists of phenyl and pyrazol-3(2H)-one units with a dihedral angle between the mean planes of the rings of 33.0 (1) . The crystal structure is stabilized by an intermolecular hydrogen bond between the N-H group and the carbonyl O atom of the pyrazol-3(2H)one ring which links the molecules into supramolecular C(5) chains along [001] and by weakstacking interactions between the phenyl rings [centroid-centroid distance = 3.881 (2) Å ]. The F atoms are disordered over two positions with refined site occupancies of 0.768(11) and 0.232(11).

Comment
The pyrazolone analgesics (such as phenylbutazone) have effects similar to those of aspirin. They were commonly used to treat rheumatoid arthritis and has been the focus of medicinal chemists for over last 100 years because of the outstanding pharmacological properties shown by several of its derivatives (Kees et al., 1996). The interest in such compounds, pyrazolone derivative, arises from the fact that the incorporation of heteroatoms can result an ancillary ligand to study their photoactive lanthanide complexes. These compounds possess several sites for substitution, allowing for a systematic analysis of their effects on the photo optical properties. Particulary the luminescence properties of the Eu and Tb complexes.
The molecular structure of (I) consists of a phenyl group bonded to 2-N of the dihydropyrazole heterocyclic ring (Fig. 1).
These rings are twisted with respect to each other and the dihedral angle between the mean plane is 33.0 (1)°.The molecules are linked into chains by one intermolecular N-H···O hydrogen bond. Atoms N2 in the molecules at (x,y,z) acts as hydrogen bonds donor vía atom H2 to atoms O1 at (-x, 3/2+y, -1-z) so generating by translation one C(5) chains running parallel to [001] direction (Bernstein et al., 1995), (Fig. 2, Table 1) and the crystal structure is reinforced by a weak face-to-face π-π stacking interactions between phenyl rings with the centroid-centroid distance of 3.881 (2) Å.

Refinement
All non-H atoms were refined with anisotropic displacement parameters. H Ar atoms were placed at their idealized positions with distances of 0.93 Å and U eq fixed at 1.2 U iso of the preceding atom. H atom attached to N atom was located from Fourier difference map and treated with riding model. Fluorine atoms are disordered over two alternative positions with refined site occupancies of 0.768 (11) and 0.232 (11). Fig. 1. The molecular structure of (I) with labeling scheme. Displacement ellipsoids are shown at the 40% probability level.