6-Bromo-4-oxo-4H-chromene-3-carbaldehyde

In the title compound, C10H5BrO3, a brominated 3-formylchromone derivative, the non-H atoms are essentially coplanar (r.m.s. deviation = 0.0420 Å), with the largest deviation from its mean plane [0.109 (2) Å] being found for the ring-bound carbonyl O atom. In the crystal, molecules are linked through halogen bonds [Br⋯O = 3.191 (2) Å, C—Br⋯O = 167.32 (10)° and C=O⋯Br = 168.4 (2)°] along [101]. Molecules are assembled into layers parallel to (101) via π–π stacking interactions along the b axis [shortest centroid–centroid distance between the pyran and benzene rings = 3.495 (2) Å].


Structural commentary
Halogen bonds have been found to occur in organic, inorganic, and biological systems, and have recently attracted much attention in medicinal chemistry, chemical biology and supramolecular chemistry (Auffinger et al., 2004, Metrangolo et al., 2005, Wilcken et al., 2013, Sirimulla et al., 2013. We have recently reported the crystal structures of dihalogenated As part of our interest in this type of chemical bonding, we herein report the crystal structure of a monobrominated 3formylchromone derivative 6-bromo-4-oxo-4H-chromene-3-carbaldehyde. The objective of this study is to reveal whether halogen bond(s) can be formed in the crystal structure of the title compound with the bromine atom at 6-position and without a halogen atom at 8-position.
The mean deviation of the least-square planes for the non-hydrogen atoms is 0.0420 Å, and the largest deviation is 0.109 (2) Å for O2. These mean that these atoms are essentially coplanar (Fig.1).
Halogen bond was observed between the bromine atom at 6-position and the formyl oxygen atom of the translationsymmetry equivalent ii [Br1···O3 ii = 3.191 (2) Å, ii: x -1, y, z + 1] along [101], as shown in Fig.2. The angles of C-Br···O and Br···O=C are 167.32 (10) and 168.4 (2)°, respectively. Thus, it is found that halogen bonds are formed for the bromine atoms not only at 8-position but also at 6-position, as shown in the top right and bottom right of Fig.3.
The space group and crystal packing mode of the title compound are the same with those of 6-chloro-4-oxo-4Hchromene-3-carbaldehyde. On the other hand, halogen bond is observed in the former and not in the latter, as shown in the bottom of Fig.3. These should be accounted for by the larger size of the σ hole of the bromine atom at 6-position (Wilcken et al., 2013). These results might be applicable for rational drug design.

Synthesis and crystallization
Single crystals suitable for X-ray diffraction were obtained by slow evaporation of an N,N-dimethylformamide solution of the commercially available title compound at room temperature.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. The C(sp 2 )-bound hydrogen atoms were placed in geometrical positions [C-H 0.95 Å, U iso (H) = 1.2U eq (C)], and refined using a riding model.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq