A second orthorhombic polymorph of 4-{[(1 E ,2 E )-3-(4-methoxyphenyl)prop-2-en-1-ylidene]amino}-1,5-dimethyl-2-phenyl-1 H -pyrazol-3(2 H )-one

The second orthorhombic polymorph of the title compound, C 21 H 21 N 3 O 2 , ( I ), crystallizes in space group Pna 2 1 , compared to Pbca for the first orthorhombic polymorph ( I i ) [Obasi et al. (2016). J. Mol. Struct . 1120 , 180–186]. The difference in the structure of the two polymorphs resides in the orientation of the 4-methoxy moiety of the (4-methoxyphenyl)allylidene unit with respect to the phenyl ring to which it is attached. Compound ( I ) also exhibits rotational disorder of the phenyl ring of the 4-aminoantipyrine moiety. In the crystal of ( I ), the molecules are linked by C—H...O and C—H...N hydrogen bonds, forming a three-dimensional network. The conformations, Hirshfeld surfaces, and two-dimensional fingerprint plots of the two polymorphs and closely related structures are compared.