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The title compound, C16H6N6, is a polymorph of the previously reported structure [Kozlov & Goldberg (2008). Acta Cryst. C64, o498–o501]. Unlike the previously reported monoclinic polymorph (space group P21/c, Z = 8), the title compound reveals orthorhombic symmetry (space group Pnma, Z = 4). The molecule shows crystallographic mirror symmetry, while the previously reported structure exhibits two independent molecules per asymmetric unit. In the title compound, adjacent molecules are essentially parallel along the c axis and tend to be vertical along the b axis with dihedral angles of 72.02 (6)°. However, in the reported polymorph, the entire crystal structure shows an antiparallel arrangement of adjacent columns related by inversion centers and the two independent molecules are nearly parallel with a dihedral angle of 2.48 (6)°.