(E)-1-(2,4-Dichlorophenyl)-3-[3-(4-methoxyphenyl)-1-phenyl-1H-pyrazol-4-yl]prop-2-en-1-one

In the title molecule, C25H18Cl2N2O2, the dihedral angles between the pyrazole ring and its N- and C-bonded benzene rings are 8.28 (11) and 40.89 (10)°, respectively. The dihedral angle between the benzene rings is 39.03 (11)°. The title molecule exists in a trans conformation with respect to the acyclic C=C bond. In the crystal, molecules are linked into inversion dimers by pairs of intermolecular C—H⋯O hydrogen bonds, generating R 2 2(14) loops.

In the title molecule, C 25 H 18 Cl 2 N 2 O 2 , the dihedral angles between the pyrazole ring and its N-and C-bonded benzene rings are 8.28 (11) and 40.89 (10) , respectively. The dihedral angle between the benzene rings is 39.03 (11) . The title molecule exists in a trans conformation with respect to the acyclic C C bond. In the crystal, molecules are linked into inversion dimers by pairs of intermolecular C-HÁ Á ÁO hydrogen bonds, generating R 2 2 (14) loops.

Comment
As part of our ongoing studies of pyrazole derivatives (Fun et al., 2011a,b), we have synthesized the title compound to study its crystal structure.

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. 3-(4-Methoxyphenyl)-1-phenyl-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 293 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 out was filtered, washed with water, dried and crystallized from ethanol to yield colourless blocks. Yield: 1.45 g, 80.55 %. M.p. : 447-449 K.

Refinement
All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 or 0.96 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl group.

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq