Crystal structures and Hirshfeld surface analyses of two new tetrakis-substituted pyrazines and a degredation product

Abstract

The two new tetrakis-substituted pyrazines, 1,1′,1′′,1′′′-(pyrazine-2,3,5,6-tetrayl) tetrakis(N,N-dimethylmethanamine), C16H32N6, (I) and N,N′,N′′,N′′′-[pyrazine-2,3,5,6-tetrayltetrakis(methylene)]tetrakis(N-methylaniline), C36H40N6, (II), both crystallize with half a molecule in the asymmetric unit; the whole molecules are generated by inversion symmetry. There are weak intramolecular C—H...N hydrogen bonds present in both molecules and in (II) the pendant N-methylaniline rings are linked by a C—H...π interaction. The degredation product, N,N′-[(6-phenyl-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazine-2,3-diyl)bis(methylene)]bis(N-methylaniline), C28H29N5, (III), was obtained several times by reacting (II) with different metal salts. Here, the 6-phenyl ring is almost coplanar with the planar pyrrolo[3,4-b]pyrazine unit (r.m.s. deviation = 0.029 Å), with a dihedral angle of 4.41 (10)° between them. The two N-methylaniline rings are inclined to the planar pyrrolo[3,4-b]pyrazine unit by 88.26 (10) and 89.71 (10)°, and to each other by 72.56 (13)°. There are also weak intramolecular C—H...N hydrogen bonds present involving the pyrazine ring and the two N-methylaniline groups. In the crystal of (I), there are no significant intermolecular contacts present, while in (II) molecules are linked by a pair of C—H...π interactions, forming chains along the c-axis direction. In the crystal of (III), molecules are linked by two pairs of C—H...π interactions, forming inversion dimers, which in turn are linked by offset π–π interactions [intercentroid distance = 3.8492 (19) Å], forming ribbons along the b-axis direction.