Crystal structure and Hirshfeld analysis of 2-(5-bromothiophen-2-yl)acetonitrile

The crystal structure of 2-(5-bromothiophen-2-yl)acetonitrile, previously reported as a liquid, has short centrosymmetric Type I Br⋯Br halogen interactions.


Chemical context
Cyano-substituted molecules have found widespread use as functional materials for a variety of applications in organic electronics (Kim & Lim, 2014). For example, the title compound, 2-(5-bromothiophen-2-yl)acetonitrile, has been incorporated into materials for use in organic semiconductors (Park et al., 2016), sensors (Ding et al., 2015), dye-sensitized solar cells (Li et al., 2016), and organic solar cells (Kwon et al., 2015). Although the chemical literature has previously identified the title compound, 1, as a liquid (Cho et al., 2004;Chung et al., 2009;Lu et al., 2014;Wan et al., 2009;Zou et al., 2009), we have found that with proper purification, this molecule crystallizes under ambient conditions.

Structural commentary
The molecular structure of 1 is illustrated in Fig. 1. The asymmetric unit is composed of one complete molecule of 1. The C1-C2, C2-C3, and C3-C4 bond lengths are consistent with some conjugation in the thienyl -system (Table 1). While both the C4-C5 and C5-C6 bond lengths are consistent with single C-C bonds, the C5-C6 bond length is shorter, likely as a result of the sp hybridization at C6. Although conjugation across the molecule is not evident from the pattern of bond lengths, the structure is remarkably planar with an r.m.s. deviation from planarity of 0.071 Å for all non-hydrogen atoms. ISSN 2056-9890

Supramolecular Features
The structure packs with centrosymmetricdimers, though the distance between least-squares planes formed by non-H atoms of the molecules is beyond the sum of the van der Waals radii at 3.637 Å . Molecules pack in a herringbone pattern with a dihedral angle of 65.2 between the least-squares planes formed by molecules related by the 2 1 screw axis (Fig. 2). The structure has several unique types of intermolecular features. Each molecule participates in centrosymmetric halogenbonding dimers of Type I (Desiraju & Parthasarathy, 1989) with BrÁ Á ÁBr contacts at 3.582 (1) Å and a C1-Br1Á Á ÁBr1 angle of 140.7 (1) (Fig. 3). Each molecule also engages in two weaker C-HÁ Á ÁN interactions, one as an sp 3 -hybridized C5-H5B donor and the other as an acceptor (N1) of this type of interaction (Table 2, Fig. 4). It is noteworthy that the two methylene hydrogen atoms are acidic on account of the electron-withdrawing nature of the cyano group and hence their participation in the formation of C-HÁ Á ÁN hydrogen bonds is significant. Additionally, atom S1 contributes to two unique intermolecular interactions. S1 acts as acceptor for an interaction with C3-H3 as the donor. These SÁ Á ÁH interactions are organized in a C 1 1 (4) graph-set motif parallel to [101]. An edge-to-face S1Á Á Á(C1-C2 midpoint) interaction is also present at a distance of 3.391 Å (sum of van der Waals radii = 3.50 Å ). These SÁ Á Á close contacts are organized in chains parallel to [010].

Hirshfeld surface analysis
Intermolecular interactions were studied further through analysis of the Hirshfeld surface, generated using Crystal-Explorer   Intermolecular halogen interaction of 1. Symmetry code: (i) 2 À x, Ày, 1 À z.
described for 1 to the total Hirshfeld surfaces are summarized in Table 3. While NÁ Á ÁH contacts comprise the largest percentage of contacts to the Hirshfeld surface described, the angular and distance components involved in the C-HÁ Á ÁN hydrogen-bonding interactions do not suggest that these interactions dominate the packing. The BrÁ Á ÁBr contacts comprise the smallest percentage of interatomic contacts described, however these BrÁ Á ÁBr atom contacts [3.582 (1) Å ] are the shortest of all the contacts described, relative to the van der Waals radii sums (À0.118 Å ). The observation that CÁ Á ÁC contacts comprise only a small percentage of the interatomic contacts is consistent with minorstacking contributions and the observed stacking distance beyond the sum of the van der Waals radii.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. H atoms were placed in calculated positions and refined in the riding-model approximation with distances of C-H = 0.95 and 0.99 Å for the thiophene and methylene groups, respectively, and with U iso (H) = 1.2U eq (C).
A single low-angle reflection was rejected from these highquality data sets due to the arrangement of the instrument with a conservatively sized beam stop and a fixed-position detector. The large number of reflections in the data sets (and the Fourier-transform relationship of intensities to atoms) ensures that no particular bias was thereby introduced.

Figure 5
Hirshfeld surface of 1 mapped over d norm , shown in two orientations in the range À0.0639 to 0.93667 a.u. Red areas highlight intermolecular contacts shorter than the sum of the van der Waals radii.   program(s) used to refine structure: SHELXL2013 (Sheldrick, 2015); molecular graphics: Mercury (Macrae et al., 2008) and publCIF (Westrip, 2010); software used to prepare material for publication: CrystalStructure (Rigaku, 2014).

2-(5-Bromothiophen-2-yl)acetonitrile
Crystal data Special details Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes. Refinement. Refinement was performed using all reflections. The weighted R-factor (wR) and goodness of fit (S) are based on F 2 . R-factor (gt) are based on F. The threshold expression of F 2 > 2.0 sigma(F 2 ) is used only for calculating Rfactor (gt).