Abstract
The crystal structures of 2,3-bis-(thio-phen-2-yl)pyrido[2,3-b]pyrazine, C15H9N3S2 (1), and 7-bromo-2,3-bis-(thio-phen-2-yl)pyrido[2,3-b]pyrazine, C15H8BrN3S2 (2), are discussed. Both mol-ecules crystallize in space group P21/c. In 1, the thienyl rings are inclined to the mean plane of the pyrido-pyrazine moiety by 6.16 (7) and 86.66 (8)°, where as in 2 the corresponding dihedral angles are 33.29 (11) and 19.84 (9)°. The pyrido-pyrazine moiety is relatively planar in 1 with the two rings being inclined to each other by 1.33 (7)°. In 2, however, the pyrido-pyrazine moiety is buckled with the corresponding dihedral angle being larger at 8.78 (10)°. In the crystal of 1, the packing creates inter-secting bilayers; the layering results from the pyrido-pyrazine moieties being engaged in offset π-stacking, where the inter-planar distance is 3.431 (9) Å with an offset 1.14 Å. In the crystal of 2, the mol-ecules pack head-to-head and are linked by a series of C-H⋯Br and C-H⋯N inter-molecular inter-actions, forming layers parallel to the ab plane.