Crystal structure and Hirshfeld surface analysis of (E)-1-[2,2-dibromo-1-(2-nitrophenyl)ethenyl]-2-(4-fluorophenyl)diazene

The packing of the title compound features C—H⋯O hydrogen bonds, C—F⋯π interactions, aromatic π–π stacking and short Br⋯O contacts.


Chemical context
Azo dyes are chemical compounds with the general formula R-N N-R 0 , where R and R 0 can be either aryl, hetrocycle or alkyl functional groups. They find many applications such as molecular switches, optical data storage, antimicrobial agent, colour-changing materials, non-linear optics, molecular recognition, dye-sensitized solar cells, liquid crystals, catalysis, etc. (see, for example, Kopylovich et al., 2012;MacLeod et al., 2012;Viswanathan et al., 2019). Both E/Z isomerization and azo-to-hydrazo tautomerization of azo dyes is an important feature in the synthesis and design of new functional materials (Mahmudov et al., , 2020Mizar et al., 2012). On the other hand, the attachment of non-covalent bond-donor or acceptor centres to the azo dyes can be used as a synthetic strategy for the improvement of the functional properties of this class of organic compounds (Gurbanov et al., 2020a,b).
As part of our ongoing work in this area we have attached -F, -Br and -NO 2 functional groups and aryl rings to the -N N-moiety, leading to the title compound, C 14 H 8 Br 2 FN 3 O 2 , and determined its crystal structure.

Structural commentary
As shown in Fig. 1, the molecular conformation of the title compound is not planar, the nitro-substituted benzene ring and the 4-fluorophenyl ring forming a dihedral angle of 65.73 (7) . There is a slight twist about the C1 C2 double bond with the dihedral angle between C1/Br1/Br2 and C2/C3/ N2 being 3.35 (15) , perhaps to minimize steric repulsion between Br2 and H8. Considered together, the N3/N2/C2/C1/ Br1/Br2 moiety subtends dihedral angles of 70.40 (7) and 14.14 (7) with the C3-C8 and C9-C14 rings, respectively. In the molecule, the aromatic ring and olefin synthon adopt a trans-configuration with respect to the N N double bond and are almost coplanar with a C2-N2 N3-C9 torsion angle of À178.50 (11) . All of the other bond lengths and angles in the title compound are similar to those in the related azo compounds reported in the Database survey.

Hirshfeld surface analysis
CrystalExplorer17 (Turner et al., 2017) was used to calculate the Hirshfeld surfaces for the title compound and generate the two-dimensional fingerprint plots. On the d norm surface, red, white, and blue regions indicate contacts with distances shorter, longer, and roughly equal to the van der Waals radii for the title compound (Fig. 3, Tables 1 and 2).

Figure 3
The three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.24 to 1.44 a.u.
The overall two-dimensional fingerprint plot (Fig. 4a) and those delineated into HÁ Á ÁH, OÁ Á ÁH/HÁ Á ÁO, BrÁ Á ÁH/HÁ Á ÁBr, BrÁ Á ÁC/CÁ Á ÁBr and FÁ Á ÁH/HÁ Á ÁF contacts (McKinnon et al., 2007) are illustrated in Fig. 4b-f, respectively. The most important interaction is HÁ Á ÁH, contributing 17.4% to the overall surface, which is reflected in Fig. 4b as widely scattered points of high density due to the large hydrogen content of the molecule, with the tip at d e = d i = 1.15 Å . The reciprocal OÁ Á ÁH/HÁ Á ÁO interactions appear as two symmetrical broad wings with d e + d i ' 2.40 Å and contribute 16.3% to the Hirshfeld surface (Fig. 4c). In the BrÁ Á ÁH/HÁ Á ÁBr fingerprint plot, there are two symmetrical wings with d e + d i ' 2.85 Å and they contribute 15.5% to the Hirshfeld surface (Fig. 4d). The pair of characteristic wings in the fingerprint plot delineated into BrÁ Á ÁC/CÁ Á ÁBr contacts ( Fig. 8e; 10.1% contribution to the Hirshfeld surface), have the tips at d e + d i ' 3.80 Å , while for FÁ Á ÁH/HÁ Á ÁF contacts ( Fig. 4f; 8.1% contribution to the Hirshfeld surface), they have the tips at d e + d i ' 2.60 Å . The remaining contributions from the other different interatomic contacts to the Hirshfeld surfaces are listed in Table 3. The dominance of H-atom contacts suggest that van der Waals interactions play the major role in establishing the crystal packing for the title compound (Hathwar et al., 2015).  (Shikhaliyev et al., 2018) and LEQXIR (VII) (Shikhaliyev et al., 2018).

Database survey
In the crystal of (I), molecules are linked into inversion dimers via short halogen-halogen contacts [Cl1Á Á ÁCl1 = 3.3763 (9) Å C16-Cl1Á Á ÁCl1 = 141.47 (7) The full two-dimensional fingerprint plot (a) for the title compound and those delineated into ( other directional contacts could be identified and the shortest aromatic-ring-centroid separation is greater than 5.25 Å . In the crystals of (II) and (III), the aromatic rings form dihedral angles of 64.1 (2) and 60.9 (2) , respectively. Molecules are linked through weak XÁ Á ÁCl contacts [X = Cl for (II) and Br for (III)], C-HÁ Á ÁCl and C-ClÁ Á Á interactions into sheets lying parallel to the ab plane. In the crystal of (IV), the planes of the benzene rings make a dihedral angle of 56.13 (13) . Molecules are stacked in columns along the a-axis direction via weak C-HÁ Á ÁCl hydrogen bonds and face-to-facestacking interactions. The crystal packing is further consolidated by short ClÁ Á ÁCl contacts. In (V), the benzene rings form a dihedral angle of 63.29 (8) . Molecules are linked by C-HÁ Á ÁO hydrogen bonds into zigzag chains running along the caxis direction. The crystal packing also features C-ClÁ Á Á, C-FÁ Á Á and N-OÁ Á Á interactions. In the crystals of (VI) and (VII), the dihedral angles between the aromatic rings are 60.31 (14) and 56.18 (12) , respectively. In (VI) C-HÁ Á ÁN and short ClÁ Á ÁCl contacts are observed and in (VII), C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds and short ClÁ Á ÁO contacts occur.

(E)-1-[2,2-Dibromo-1-(2-nitrophenyl)ethenyl]-2-(4-fluorophenyl)diazene
Crystal data where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.005 Δρ max = 0.83 e Å −3 Δρ min = −0.46 e Å −3 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 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 > 2sigma(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.