Two polymorphic forms of the title compound, C24H20Cl2N4, were obtained and characterized using X-ray crystal structure analysis. Colourless crystals of polymorph (Ia) were obtained from the oily mother residue. Recrystallization of polymorph (Ia) from an acetone-methanol mixture resulted in pale-yellow crystals of polymorph (Ib). The major feature distinguishing the two polymorphic forms is their interaction modes, and hence their packing arrangements. In the crystal structure of polymorph (Ia), there are N-H...N hydrogen bonds and also aromatic pi-pi stacking interactions between molecules. The molecules of polymorph (Ib) are linked by N-H...Cl hydrogen bonds only.