1,3-Diphenyl-4,5-dihydro-1H-pyrazol-5-one

In the title pyrazolone derivative, C15H12N2O, the five-membered ring is approximately planar (r.m.s. deviation = 0.018 Å), and the N- and C-bound benzene rings are inclined to this plane [dihedral angles = 21.45 (10) and 6.96 (10)°, respectively] and form a dihedral angle of 20.42 (10)° with each other. Supramolecular layers are formed in the crystal structure via C—H⋯O and C—H⋯N interactions, and these are assembled into double layers by C—H⋯π and π–π interactions between the pyrazole and C-bound benzene rings [ring centroid–centroid distance = 3.6476 (12) Å]. The double layers stack along the a axis being connected by π–π interactions between the N- and C-bound benzene rings [ring centroid–centroid distance = 3.7718 (12) Å].

In the title pyrazolone derivative, C 15 H 12 N 2 O, the fivemembered ring is approximately planar (r.m.s. deviation = 0.018 Å ), and the N-and C-bound benzene rings are inclined to this plane [dihedral angles = 21.45 (10) and 6.96 (10) , respectively] and form a dihedral angle of 20.42 (10) with each other. Supramolecular layers are formed in the crystal structure via C-HÁ Á ÁO and C-HÁ Á ÁN interactions, and these are assembled into double layers by C-HÁ Á Á andinteractions between the pyrazole and C-bound benzene rings [ring centroid-centroid distance = 3.6476 (12) Å ]. The double layers stack along the a axis being connected byinteractions between the N-and C-bound benzene rings [ring centroid-centroid distance = 3.7718 (12) Å ].

Comment
Pyrazoles are key structures in numerous compounds of therapeutic importance (Sil et al., 2005, Haddad et al., 2004. Compounds containing this ring system are known to display diverse pharmacological activities, for example as antimalarial agents (Bekhit et al., 2012), anti-tuberculosis agents (Castagnolo et al., 2008), and as SARS-coronavirus protease inhibitors (Ramajayam et al., 2010).
In the title compound, Fig. 2, crystallography proves the IIc tautomer in the solid-state. The pyrazole ring is planar with a r.m.s. deviation for the fitted atoms of 0.018 Å; the maximum deviations from this plane are 0.015 (1) Å (for the N1 atom) and -0.015 (1) Å (C8). The N-and C-bound benzene rings are inclined to this plane forming dihedral angles of 21.45 (10) and 6.96 (10)°, respectively; the dihedral angle between the benzene rings is 20.42 (10)° consistent with a nonplanar molecule.

Experimental
A solution of PhNHNH 2 (1 mmol) and PhCOCH 2 CO 2 Et (1 mmol) in EtOH (15 ml) was refluxed for 1 h. The reaction mixture was maintained at room temperature and crystals of the titled compound were collected after 2 days, M.pt: 408-410 K: lit. value 409-411 K (Kimata et al., 2007). IR and NMR spectra are in agreement with published data (Castagnolo

Refinement
The C-bound H atoms were geometrically placed (C-H = 0.95-0.99 Å) and refined as riding with U iso (H) = 1.2U eq (C).
Owing to poor agreement one reflection, i.e. (3 1 1), was removed from the final cycles of refinement. The maximum and minimum residual electron density peaks of 0.74 and 0.20 e Å -3 , respectively, were located 1.02 Å and 0.58 Å from the H8a and O1 atoms, respectively.

Computing details
Data collection: COLLECT (Hooft, 1998); cell refinement: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); data reduction: DENZO (Otwinowski & Minor, 1997) and COLLECT (Hooft, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: publCIF (Westrip, 2010).  The molecular structure of (I) showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.  A view in projection down the c axis of the crystal packing in (I). The C-H···O, C-H···N, C-H···π and π-π interactions shown as orange, blue, brown and purple dashed lines, respectively. where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.74 e Å −3 Δρ min = −0.20 e Å −3 Special details Geometry. All s.u.'s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.'s are taken into account individually in the estimation of s.u.'s in distances, angles and torsion angles; correlations between s.u.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.'s is used for estimating s.u.'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 > 2σ(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.