title: An ortho-rhom-bic polymorph of pyrazino-[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile.
abstract: The title compound, C(16)H(6)N(6), is a polymorph of the previously reported structure [Kozlov & Goldberg (2008 ▶). Acta Cryst. C64, o498-o501]. Unlike the previously reported monoclinic polymorph (space group P2(1)/c, Z = 8), the title compound reveals ortho-rhom-bic symmetry (space group Pnma, Z = 4). The mol-ecule shows crystallographic mirror symmetry, while the previously reported structure exhibits two independent mol-ecules per asymmetric unit. In the title compound, adjacent mol-ecules 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 anti-parallel arrangement of adjacent columns related by inversion centers and the two independent mol-ecules are nearly parallel with a dihedral angle of 2.48 (6)°.
authors.forename: Wei
authors.initials: W
authors.lastname: Yang
authors.forename: Qi-Ming
authors.initials: QM
authors.lastname: Qiu
authors.forename: Li-Li
authors.initials: LL
authors.lastname: Zhou
authors.forename: Qiong-Hua
authors.initials: QH
authors.lastname: Jin
authors.forename: Cun-Lin
authors.initials: CL
authors.lastname: Zhang