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A second polymorph of the title compound, C21H16N4, is reported. The original polymorph was solved by our group [Matsumoto et al. (2003). Tetrahedron Lett. 44, 2861-2864] in the monoclinic space group C2/c and refined to R = 0.050. Now the crystal structure of a tetragonal polymorph (space group P-421c) has been solved and refined to R = 0.036. In the crystal, there are no strong intermolecular interactions. Reflecting the high symmetry of the molecular structure, the asymmetric unit is a quarter of the molecule, and the molecule exhibits S4 symmetry along the c axis in the crystal.