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

The title compound, C20H18N4O2, known as bis-pyrazolone, was crystallized from dimethyl sulfoxide. The structure has ortho-rhom-bic (Pbca) symmetry at 150 K, and displays both intra- and inter-molecular hydrogen bonding through C-H⋯O and N-H⋯O contacts, respectively. None of the phenyl and pyrazolone rings in the mol-ecule are coplanar. The dihedral angle between the pyrazolone rings is 66.18 (5)°.