N-(4-Bromophenyl)pyrazine-2-carboxamide

The molecule of the title compound, C11H8BrN3O, is close to planar (r.m.s. deviation of all 16 non-H atoms = 0.103 Å), a conformation stabilized by an intramolecular N—H⋯N hydrogen bond, which generates an S(5) ring. In the crystal structure, supramolecular chains mediated by C—H⋯O contacts (along a) are linked into a double layer via N⋯Br halogen bonds [3.207 (5) Å] and C—Br⋯π interactions [Br⋯ring centroid(pyrazine) = 3.446 (3) Å]. The layers stack along the b axis via weak π–π interactions [ring centroid(pyrazine)⋯ring centroid(benzene) distance = 3.803 (4) Å].

The use of the EPSRC X-ray Crystallographic Service at the University of Southampton, England, and the valuable assistance of the staff there are gratefully acknowledged. JLW acknowledges support from CAPES (Brazil).

Comment
Pyrazinamide has well known anti-mycobacterial activity and is the one of the most important drugs used in tuberculosis treatment (Chaisson et al., 2002;Gordin et al., 2000;de Souza, 2006). In continuation of our studies on pyrazinamide derivatives (Wardell et al., 2008;Baddeley et al., 2009;Howie et al., 2010a,b,c,d), we report the structure of N-(4bromophenyl)pyrazine-2-carboxamide, the title compound, (I).
The molecular structure of (I), Fig. 1, is essentially planar with the dihedral angle formed between the pyrazine and benzene rings being 10.2 (3)°; the r.m.s. deviation of all 16 non-H atoms = 0.103 Å (Spek, 2009). The observed conformation is stabilized by an intramolecular N-H···N hydrogen bond, Table 1.

Refinement
The C-bound H atoms were geometrically placed (C-H = 0.95 Å) and refined as riding with U iso (H) = 1.2U eq (C). The N-bound H atom was located from a difference map and refined with the distance restraint N-H = 0.88 (1) Å, and with U iso (H) = 1.2U eq (N). Fig. 1. The molecular structure of (I) showing displacement ellipsoids at the 50% probability level.

Figures
supplementary materials sup-2 Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.