5-Methyl-4-(5-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)-2-phenyl-1H-pyrazol-3(2H)-one

The crystal structure of bispyrazolone, recrystallized from DMSO, indicates that the enamine tautomer is favored.

data reports phenyl rings is 39.44 (6) . The ring systems in the halves of the molecules have significantly different degrees of rotation with respect to one another. The dihedral angle between the C9-C14 phenyl ring and the N1/N2/C1-C3 pyrazolone ring is 34.29 (6) while that between the C15-C20 phenyl ring and the N3/N4/C5-C7 pyrazolone ring is 13.75 (7) . The latter is a consequence of intramolecular C-HÁ Á ÁO hydrogen bonding between the C20-H20 group on the phenyl ring and the O2 atom of the pyrazolone ring (Table 1, Fig. 2).
In the crystal, the molecules pack in a manner that maximizes intermolecular hydrogen bonding. Both oxygen atoms and both N-H groups of each bispyrazolone molecule are involved in forming four hydrogen bonds with three neighboring molecules (Table 1, Fig. 2). The intermolecular hydrogen bond axes lie approximately in the bc plane of the unit cell. Thus hydrogen-bonded sheets of the molecules stack perpendicular to the a axis (Fig. 3).

Synthesis and crystallization
A sample of the title compound was used as received from Sigma-Aldrich, and dissolved in hot dimethylsulfoxide. Colorless crystals were obtained by slow cooling of this solution to 298 K.

Figure 3
Packing of the molecules viewed approximately along the a axis with hydrogen bonds shown as dotted lines.

Figure 1
The title molecule with the labeling scheme and displacement ellipsoids drawn at the 50% probability level.

5-Methyl-4-(5-methyl-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-4-yl)-2-phenyl-1H-pyrazol-3(2H)-one
Crystal data T min = 0.874, T max = 1.000 16964 measured reflections 3336 independent reflections 3020 reflections with I > 2σ(I) 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. The H atoms bound to N2 and N4 were located in a difference map and refined. All hydrogen atoms were located in a difference map and were refined isotropically without constraints.