Crystal structure of a tetrakis-substituted pyrazine compound: 2,3,5,6-tetrakis(bromomethyl)pyrazine1

The title molecule crystallizes with two half-molecules in the asymmetric unit, the whole molecules being generated by twofold rotation symmetry. In the crystal, there are two interpenetrating three-dimensional networks involving the individual molecules that are linked by C—H⋯Br and Br⋯Br interactions.


Structural commentary
The title compound, Fig. 1, crystallizes with two half-molecules per asymmetric unit. The whole molecules (A and B) are generated by twofold rotation symmetry. In molecule A, the twofold axis is normal to the pyrazine ring passing through the centre of the ring. In molecule B, the twofold rotation axis lies in the plane of the pyrazine ring bisecting the C6-6 ii and C7-C7 ii bonds [symmetry code: (ii) y, x, Àz]. Placed side by side, it can be seen that the two molecules are almost perfect mirror images of each other (Fig. 1). The best fit of the two molecules, ISSN 1600-5368 calculated using the Molecular Overlay routine in Mercury (Macrae et al., 2008), was obtained for inverted molecule B on molecule A with an r.m.s. deviation of 0.1048 Å and a maximum deviation of any two equivalent atoms of 0.2246 Å .

Figure 2
A view along the b axis of the crystal packing of the A molecules of the title compound. The weak C-HÁ Á ÁBr hydrogen bonds and BrÁ Á ÁBr interactions are shown as dashed lines (see Table 2 for details).

Figure 3
A view along the b axis of the crystal packing of the title compound. The C-HÁ Á ÁBr hydrogen bonds and BrÁ Á ÁBr interactions are shown as dashed lines (see Table 2 for details; A molecules blue, B molecules red).

Synthesis and crystallization
The title compound was prepared by a modification of the procedure described by Ferigo et al. (1994). To 2,3,5,6-tetramethylpyrazine (28 g, 0.28 mol) in CCl 4 (1 l) was added wellground N-bromosuccinimide (150 g, 0.84 mol). The mixture was stirred vigorously and heated to reflux. As soon as the reflux set in, the mixture was irradiated for 5 h with two 200 W lamps fitted at least 10 cm at opposite sides of the flask. After the mixture was then cooled firstly to room temperature and the floating succinimide filtered off.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The C-bound H atoms were included in calculated positions and treated as riding atoms: C-H = 0.97 Å with U iso (H) = 1.2U eq (C).  (Spek, 2009) and publCIF (Westrip, 2010).