In the title compound, C21H16ClN3O2, the pyrazolone ring and the O=C-C=C-N mean plane [maximum deviation = 0.022 (2) Å] are nearly coplanar, making a dihedral angle 4.56 (8)°, while the phenyl and pyrazole rings subtend a dihedral angle of 19.75 (8)°. The compound is in the enamine-keto form and its structure is stabilized by an intra-molecular N-H⋯O hydrogen bond. In the crystal, mol-ecules are linked via C-H⋯N hydrogen bonds, forming chains along [010]. Between the chains there are π-π inter-actions [inter-centroid distances = 3.3902 (9) and 3.5956 (11) Å], linking the chains to form sheets parallel to (10-1).
Keywords: 4-acylpyrazolone; crystal structure; hydrogen bonding; o-chloroaniline; pyrazolone.