| Summary: | In the title compound, C13H8BrN3S2, one propynyl substituent lies approximately in the plane of the pyridopyrazine ring system, while the other is twisted away from this plane. In the crystal, offset π–π stacking interactions between the pyridine and pyrazine rings with a centroid–centroid distance of 3.740 (1) Å stack the molecules along the a-axis direction. At the conclusion of the initial refinement, a significant residual peak remained in the difference map. This suggested an alternate location for the Br atom but at a very low occupancy. Further refinement with Br disordered over two sites yielded a population ratio for the two Br sites of 97:3. As the refined location of the minor Br site leads to unequal C—C—Br angles, we feel that the results indicate a `whole molecule' disorder rather than the presence of a minor amount of an isomer. Unfortunately, the very low amount of the second component of the disorder prevented the location of any of its other atoms.
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