2-Bromopyridine-3-carboxylic acid

The carboxylic acid residue in the title compound, C6H4BrNO2, is twisted out of the plane of the other atoms, as indicated by the (Br)C—C—C—Ocarbonyl torsion angle of −20.1 (9)°. In the crystal, supramolecular chains mediated by O—H⋯N hydrogen bonds are formed with base vector [201] and C—H⋯O interactions reinforce the packing.

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

Comment
The structure of the title compound, (I), was determined in connection with on-going studies of biological activitiess, e.g.
anti-mycobacterial activity, of N-heterocyclic compounds (Cunico et al. 2006;, as we have embarked on complementary systematic structural investigations in order to ascertain supramolecular aggregation patterns (Kaiser et al., 2009).
In the molecular structure of (I), Fig. 1, the carbonyl-O2 atom is approximately syn to the bromide. The carboxylic acid residue is twisted out of the plane of the pyridine ring as seen in the value of the C2/C3/C7/O1 torsion angle of 161.1 (5)°.

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 atoms were located from a difference map and refined with U iso (H) = 1.5U eq (N). Fig. 1. The molecular structure of (I) showing displacement ellipsoids at the 50% probability level. 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.