Crystal structure of 3-bromo-2-hydroxybenzonitrile

The crystal structure of the title compound, C7H4BrNO, has been determined, revealing a partial molecular packing disorder such that a 180° rotation of the molecule about the phenol C—O bond results in disorder of the bromine and nitrile groups. The disorder has been parameterized as a disorder of only the bromine and nitrile substituents on a unique phenol ring. An intramolecular O—H⋯Br contact occurs. In the crystal, O—H⋯Br/O—H⋯Nnitrile hydrogen bonding is present between the disordered bromine and nitrile substituents and the phenol group, forming a spiral chain about a twofold screw axis extending parallel to the b-axis direction. Within this spiral chain, the molecules also interact, forming offset face-to-face π-stacking interactions with plane-to-centroid distance of 3.487 (1) Å.

3-Bromo-2-hydroxybenzonitrile, (Fig. 1), crystallizes with a partial molecular packing disorder, where the bromine and nitrile substituents ortho to the phenol group are disordered with one another via a 180° rotation of the molecule about the carbon-oxygen bond of the phenol moiety. The disorder has been modeled as a disorder of only the bromine and nitrile substituents on a unique phenol ring, where the phenolic hydroxyl itself is not disordered, and the model has been refined with the help of similarity and advanced rigid bond restraints (Thorn et al., 2012). Although the accuracy of the observed metrical parameters for the disordered groups is impacted by the refinement of the disorder, the bond lengths are nevertheless comparable to those found in related structures. The nitrile bond lengths C7-N1 and C7A-N1A of 1.161 (4) and 1.14 (2) Å, respectively, are similar to those seen in the related structures 5-bromo-2-hydroxybenzonitrile, with nitrile C≡N distance 1.142 (4) Å (Oh & Tanski, 2012), and the unbrominated analog, o-cyanophenol, with C≡N distance 1.136 (2) Å (Beswick et al., 1996). The aromatic bromine bond lengths C1-Br1A and C3-Br1 of 1.988 (5) Å and 1.907 (2) Å, respectively, are also similar to those seen in the related structure 5-bromo-2-hydroxybenzonitrile, with C-Br length 1.897 (3) Å (Oh & Tanski, 2012).
The molecules of the title compound pack together in the solid state with intermolecular O-H···Br/O-H···N nitrile hydrogen bonding (Fig. 2, Table 2). The hydrogen bonding is disordered with respect to the disordered bromine and nitrile substituents, not with respect to the phenol hydroxyl, which is found to have only one orientation. This hydrogen bonding forms a one-dimensional spiral chain extending parallel to the crystallographic b-axis, about the two-fold screw axis in P2 1 /c with direction [0,1,0] at 1/2, y, 1/4. Within the chains, the molecules also interact via an offset face-to-face πstacking interaction. This π-stacking is characterized by a centroid-to-centroid distance of 3.8488 (2) Å, a plane-tocentroid distance of 3.487 (1) Å, and a ring offset or ring-slippage distance of 1.630 (2) Å (Hunter & Saunders, 1990;Lueckheide et al., 2013).

S3. Refinement
The structure was refined against F 2 using all data with SHELXL2014 (Sheldrick, 2015), employing established refinement strategies (Müller, 2009). All non-hydrogen atoms were refined anisotropically. Hydrogen atoms on carbon were included in calculated positions and refined using a riding model at C-H = 0.95 Å and U iso (H) = 1.2 × U eq (C) of the aryl C-atoms. Coordinates for the hydrogen atom on oxygen were taken from the difference Fourier synthesis and the hydrogen atom was subsequently refined semi-freely with the help of an O-H distance restraint (target value 0.84 (2) Å) while constraining its U iso to 1.5 times the U eq of the oxygen atom. The extinction parameter refined to zero and was removed from the refinement. The structure exhibits a partial molecular disorder. The disorder was successfully modeled and refined with the help of similarity restraints on 1,2-and 1,3-distances and displacement parameters as well as advanced rigid-bond restraints (Thorn et al., 2012) for anisotropic displacement parameters, and interatomic distance restraints.

Figure 1
A view of the title compound showing the disordered nitrile and bromine substituents, with displacement ellipsoids shown at the 50% probability level.

Figure 2
A view of the intermolecular O-H···Br/O-H···N nitrile hydrogen bonding interactions (dashed lines) forming a helical one-dimensional chain, with displacement ellipsoids shown at the 50% probability level. See Table 1 for symmetry code

(i). A thin solid line indicates an intramolecular O-H···Br hydrogen bond, and a thick solid line indicates a π-stacking
centroid-to-centroid interaction.