A triclinic polymorph with Z=3 of N,N′-bis(2-pyridyl)oxamide

The asymmetric unit of the title compound, C12H10N4O2, contains three half-molecules. Each half-molecule is completed by crystallographic inversion symmetry. The title compound, (I), is a polymorph of the structure, (II), reported by Hsu & Chen [Eur. J. Inorg. Chem. (2004), 1488-1493]. In the original report, the compound crystallized in the tetragonal space group P <file type="gif" name="AYE_ez2234_mu1.gif"/> 2(1)c (Z = 8), whereas the structure reported here is triclinic (P <file type="gif" name="AYE_ez2234_mu2.gif"/> , Z = 3). In both forms, each oxamide molecule is almost planar (with maximum deviations are 0.266 and 0.166 angstrom) and the O atoms are trans oriented. The principal difference between the two forms lies in the different hydrogen-bonding patterns. In (I), two N-H center dot center dot center dot O and one N-H center dot center dot center dot N hydrogen bonds link the molecules, forming a two-dimensional network, whereas in (II) there are no classical hydrogen bonds to O atoms and only weak C-H center dot center dot center dot O interactions are found along with rings of N-H center dot center dot center dot N bonds.