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

C—H⋯Br interactions connect molecules in the crystal, resulting in zigzag C(8) chains along the [100] direction. C—Br⋯π interactions connect these chains into parallel layers to (002). van der Waals interactions between the layers aid in the cohesion of the crystal packing.


Chemical context
Azo dyes constitute the largest production volume (ca 70%) of the dye industry today, and their relative importance may increase further in the future (Lipskikh et al., 2018). They play a crucial role in the printing market, the design of functional materials attributed to smart hydrogen bonding, photo-triggered structural switching, self-assembled layers, ionophores, liquid crystals, semiconductors, indicators, spectrophotometric reagents for determination of metal ions, photoluminescent materials, catalysts, antimicrobial agents, optical recording media, spin-coating films, etc (Zollinger, 1994(Zollinger, , 1995Gurbanov et al., 2020a,b;Mahmudov et al., 2010Mahmudov et al., , 2013. Depending on the attached substituents, the functional properties of azo compounds and their metal complexes can be improved/ controlled (Ma et al., 2020(Ma et al., , 2021. Both E/Z isomerism and azo-hydrazo tautomerism properties of azo dyes are key phenomena in the synthesis and development of new functional materials (Shixaliyev et al., 2018(Shixaliyev et al., , 2019. The attachment of non-covalent bond acceptor or donor centres to the azo dyes can be used as a synthetic strategy for the improvement of the functional properties of their metal complexes (Mahmudov et al., , 2022. Thus, we have attached bromine atoms and a nitro group together with aryl rings to the -N N-linkage leading to a new azo compound, (E)-2-(4bromophenyl)-1-[2,2-dibromo-1-(4-nitrophenyl)ethenyl]di-azene, which can provide intermolecular halogen and hydrogen bonds as well as -interactions.

Structural commentary
The molecule of the title compound ( Fig. 1) consists of three almost planar groups: the central dibromoethenyldiazene fragment [largest deviation from the l.s. plane is 0.039 (3) Å for N2] and two attached aromatic rings. The mean planes of these rings form dihedral angles with the plane of the central fragment of 26.35 (15) and 72.57 (14) for the bromine-and nitro-substituted rings, respectively. The nitro group is twisted by 8.1 (2) with respect to the C3-C8 aromatic ring. The C2-N2 bond distance of 1.406 (4) Å indicates -conjugation between ethene and diazo groups. All other bond lengths and angles in the title compound are similar to those reported for the related azo compounds discussed in the Database survey section.

Figure 2
View down the a-axis of the title compound showing the C-HÁ Á ÁBr interactions.

Figure 3
View down the b-axis of the title compound, showing the C-BrÁ Á Á interactions.

Figure 1
The molecular structure of the title compound. Displacement ellipsoids are drawn at the 50% probability level.
layers parallel to (001) (Fig. 4). van der Waals interactions between the layers help to keep the crystal packing together. Crystal Explorer 17.5 (Turner et al., 2017) was used to perform a Hirshfeld surface analysis and to generate the corresponding two-dimensional fingerprint plots, with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed color scale of À0.1401 (red) to 1.1158 (blue) a.u. (Fig. 5). The red patches represent short contacts and negative d norm values on the surface, which correspond to the C-HÁ Á ÁBr hydrogen bonds discussed above (Table 1). The C10-H10Á Á ÁBr1 interactions, which are important for molecular packing of the title compound, are responsible for the red patch that appears around Br1.

Figure 6
The full two-dimensional fingerprint plots for the title compound, showing all interactions (a) and delineated into (b) BrÁ Á ÁH/HÁ Á ÁBr, (c) CÁ Á ÁH/HÁ Á ÁC, (d) OÁ Á ÁH/HÁ Á ÁO, and (e) HÁ Á ÁH interactions. The d i and d e values are the closest internal and external distances (in Å ) from given points on the Hirshfeld surface. Table 2 Summary of short interatomic contacts (Å ) in the title compound.
View down the c axis of the title compound, showing the C-BrÁ Á Á interactions. In (I), the molecules are connected by C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds into layers parallel to (011). The crystal packing is consolidated by C-BrÁ Á Á and C-FÁ Á Á contacts, as well as bystacking interactions. In the crystal of (II), the molecules are linked into chains running parallel to [001] by C-HÁ Á ÁO hydrogen bonds. The crystal packing is consolidated by C-FÁ Á Á contacts andstacking interactions, and short BrÁ Á ÁO [2.9828 (13) Å ] distances are also observed. In the crystal of (III), the 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) ] compared to the van der Waals radius sum of 3.50 Å for two chlorine atoms. No other directional contacts could be identified, and the shortest aromatic ring centroid separation is greater than 5.25 Å . In the crystals of (IV) and (V), the molecules are linked through weak XÁ Á ÁCl contacts [X = Cl for (IV) and Br for (V)], C-HÁ Á ÁCl and C-ClÁ Á Á interactions into sheets lying parallel to (001). In the crystal of (VI), the molecules are stacked in columns parallel to [100] 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 (VII), molecules are linked by C-HÁ Á ÁO hydrogen bonds into zigzag chains running parallel to [001]. The crystal packing also features C-ClÁ Á Á, C-FÁ Á Á and N-OÁ Á Á interactions. In (VIII), C-HÁ Á ÁN and short ClÁ Á ÁCl contacts are observed, and in (IX), C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds and short ClÁ Á ÁO contacts occur.

(E)-2-(4-Bromophenyl)-1-[2,2-dibromo-1-(4-nitrophenyl)ethenyl]diazene
Crystal data  (Parsons et al., 2013). Absolute structure parameter: 0.003 (5) 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.

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