5-Bromobenzene-1,3-dicarbonitrile

The asymmetric unit of the title compound, C8H3BrN2, consists of two molecules. The crystal structure features undulating molecular sheets with the molecules linked by C—H⋯N hydrogen bonds with one N atom acting as a bifurcated acceptor. N⋯Br interactions also occur [N⋯Br = 2.991 (3) and 3.099 (3) Å]. Interlayer association is accomplished by offset face-to-face arene interactions [centroid–centroid distance = 3.768 (4) Å].

This work was performed within the Cluster of Excellence "Structure Design of Novel High-Performance Materials via Atomic Design and Defect Engineering (ADDE)" which is supported financially by the European Union (European Regional Development Fund) and by the Ministry of Science and Art of Saxony (SMWK).

Comment
Aromatic nitriles are important intermediate compounds in organic synthesis (Ishii et al., 2011). They can smoothly be converted into a great many of other functional groups, such as carboxylic acids, amidines, amines, esters and ketones (Sandier et al., 1983). Futhermore, they are used as functional materials, pharmaceuticals, dyes and liquid crystals (Fabiani et al., 1999). Recently, aromatic nitriles have also arisen interest for their capability of forming supramolecular interactions that turned out to good account in organic crystal engineering (Desiraju & Harlow, 1989;Reddy et al., 1993;Tiekink et al., 2010) or the construction of metal-organic framework structures (Leonard & MacGillivray, 2010). Relating to this latter topics, the title compound has been synthesized as a precursor and was identified by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2 1 /c with two molecules in the asymmetric part of the unit cell ( Fig. 1). The bond distances and angles within the aromatic rings agree well with those found in the crystal structure of 1,3,5-tricyanobenzene (Reddy et al., 1995). According to a tilt angle of 12.3 (1) ° between the independent molecules, the crystal structure is composed of undulated molecular layers with the molecules linked by C-H···N hydrogen bonds (Desiraju & Steiner, 1999) [d(H)···N) 2.61 -2.72 Å; C-H···N 114 -168 °]. In this coordination structure (Figs. 2 and 3), the nitrogen N1 acts as a bifurcated acceptor (Steiner, 2002). Moreover, the interatomic distances between N2 and the bromo substituents of neighbouring molecules [2.991 (2) and 3.099 (2) Å], being considerably shorter than the sum of van der Waals radii of the respective atoms (3.40 Å), indicate the presence of N···Br interactions (Rowland & Taylor, 1996). In direction of the stacking axis of the molecular sheets, the crystal is stabilized by offset face-to-face arene interactions [Cg A ···Cg A = 3.768 (4) Å] (Dance, 2004).

Experimental
The title compound was synthesized from 5-bromo-1,3-benzenedicarboxylic acid following the literature procedure (Doyle & Haseltine, 1994). Single crystals of X-ray diffraction quality were obtained as colourless plates via crystallization from acetone.

Refinement
H atoms were positioned geometrically and allowed to ride on their respective parent atoms, with C-H = 0.95 Å and U iso (H) = 1.2 U eq (C) for aryl.

Figure 3
A view along the b-axis showing the intermolecular contacts as broken lines. 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 > σ(F 2 ) is used only for calculating R-factors(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.