(E)-1-(2,4-Dichlorophenyl)-3-(1,3-diphenyl-1H-pyrazol-4-yl)prop-2-en-1-one

In the title molecule, C24H16Cl2N2O, the dihedral angles between the pyrazole ring and its N- and C-bonded phenyl rings are 7.06 (10) and 53.15 (10)°, respectively. The dihedral angle between the two pendant rings is 52.32 (10)°. The molecule exists in a trans conformation with respect to the acyclic C=C bond. In the crystal, inversion dimers occur in which each molecule is linked to the other by two C—H⋯O hydrogen bonds to the same acceptor O atom. There are also short Cl⋯Cl contacts [3.3492 (9) Å] and C—H⋯π interactions.

In the title molecule, C 24 H 16 Cl 2 N 2 O, the dihedral angles between the pyrazole ring and its N-and C-bonded phenyl rings are 7.06 (10) and 53.15 (10) , respectively. The dihedral angle between the two pendant rings is 52.32 (10) . The molecule exists in a trans conformation with respect to the acyclic C C bond. In the crystal, inversion dimers occur in which each molecule is linked to the other by two C-HÁ Á ÁO hydrogen bonds to the same acceptor O atom. There are also short ClÁ Á ÁCl contacts [3.3492 (9) Å ] and C-HÁ Á Á interactions.   Table 1 Hydrogen-bond geometry (Å , ).
The benzene rings form a dihedral angle of 52.32 (10)°. The title molecule exists in trans conformation with respect to the acyclic C8═C9 bond [bond length = 1.330 (2) Å]. Bond lengths (Allen et al., 1987) and angles are within normal ranges.
There is a short Cl2···Cl2 contact (symmetry code : -x, 1-y, 1-z) with distance = 3.3492 (9) Å which is shorter than the sum of van der Waals radii of the Cl atoms.

Experimental
To a cold, stirred mixture of methanol (20 ml) and sodium hydroxide (12.09 mmol), 2,4-dichloroacetophenone (4.03 mmol) was added. The reaction mixture was stirred for 10 min. 1,3-Diphenyl-1H-pyrazole-4-carbaldehyde (4.03 mmol) was added to this solution followed by tetrahydrofuran (30 ml). The solution was further stirred for 2 h at 273 K and then at room temperature for 5 h. It was then poured into ice cold water. The resulting solution was neutralized with Dil. HCl. The solid that separated was filtered, washed with water, dried and crystallized from ethanol to yield colourless blocks of (I). Yield: 1.28 g, 76.19 %. M.p.: 406-408 K.

Refinement
All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 Å and U iso (H) = 1.2 U eq (C). Fig. 1. The molecular structure of the title compound showing 30% probability displacement ellipsoids for non-H atoms.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.