Crystal structure and Hirshfeld surface analysis of a new polymorph of (E)-2-(4-bromophenyl)-1-[2,2-dibromo-1-(3-nitrophenyl)ethenyl]diazene

The a new polymorph of the title compound is reported in which the C—H⋯O hydrogen bonds and π-π stacking interactions link molecules into the layers in the crystal.

A new polymorph of the title compound, C 14 H 8 Br 3 N 3 O 2 , (form-2) was obtained in the same manner as the previously reported form-1 . Acta Cryst. E78,[732][733][734][735][736]. The structure of the new polymorph is stabilized by a C-HÁ Á ÁO hydrogen bond that links molecules into chains. These chains are linked by face-to-facestacking interactions, resulting in a layered structure. Short inter-molecular BrÁ Á ÁO contacts and van der Waals interactions between the layers aid in the cohesion of the crystal packing. In the previously reported form-1, C-HÁ Á ÁBr interactions connect molecules into zigzag chains, which are linked by C-BrÁ Á Á interactions into layers, whereas the van der Waals interactions between the layers stabilize the crystal packing of form-2. Hirshfeld molecular surface analysis was used to compare the intermolecular interactions of the polymorphs.

Chemical context
Aromatic azo compounds provide ubiquitous motifs in organic chemistry and are widely used as indicators, organic dyes, pigments, radical reaction initiators, food additives, therapeutic agents, etc. (Zollinger 1994(Zollinger , 1995Gurbanov et al., 2020a,b). Moreover, in azo dyes the ligands play a crucial role in coordination chemistry and in the construction of functional materials, such as ionophores, self-assembled layers, catalysts, antimicrobial agents, liquid crystals and semiconductors (Ma et al., 2020(Ma et al., , 2021Mahmudov et al., 2010Mahmudov et al., , 2013. Depending on the attached functional groups, the chemical and physical properties of azo dyes and their transition-metal complexes can be improved. The azo-to-hydrazo tautomerization as well as E/Z isomerization of azo dyes are key phenomena in the synthesis and design of new functional materials (Shixaliyev et al., 2013(Shixaliyev et al., , 2014. Moreover, an attachment of donor or acceptor centres of non-covalent bonds to the azo compounds can be applied as a synthetic strategy in the improvement of functional properties of their metal complexes (Mahmudov et al., , 2022. Thus, we have attached bromine and nitro substituents to the aryl rings leading to a new azo dye, (E)-1-(2,2-dibromo-1-(3-nitrophenyl)vinyl)-2-(4-bromophenyl)diazene, which can participate in intermolecular halogen and hydrogen bonds as well as in -interactions.

Structural commentary
A view of the molecule of the new polymorph (henceforth referred to as form-2) is shown in Fig. 1. The central fragment of the molecule, C1/C2/N2/N3/C3/C9/Br1/Br2, is almost planar with the largest deviation from mean plane being 0.101 (1) Å for Br1. This plane forms dihedral angles of 13.51 (7) and 61.26 (7) with the planes of the bromine-and nitro-substituted aromatic rings, respectively. In the previously reported polymorph (form-1), the corresponding angles were 26.35 (15) and 72.57 (14) . All bond lengths and angles in the title compound are in agreement with those reported for the related azo compounds discussed in the Database survey section.

Figure 2
View down the a-axis of the C-HÁ Á ÁO andinteractions (dashed lines) in the title compound.

Figure 3
View down the b-axis of the C-HÁ Á ÁO andinteractions (dashed lines) in the title compound.
form-1 of the title compound , C-HÁ Á ÁBr interactions connect molecules, generating zigzag C(8) chains along the [100] direction, which are linked by C-BrÁ Á Á interactions into layers parallel to (001), and van der Waals interactions between layers contribute to the crystal cohesion. Crystal Explorer 17.5 (Turner et al., 2017) was used to perform a Hirshfeld surface analysis of form-2 and to generate the related two-dimensional fingerprint plots, with a standard resolution of the three-dimensional d norm surfaces plotted over a fixed colour scale of À0.1471 (red) to +1.1715 (blue) a.u. (Fig. 5). The red areas on the surface present short contacts and negative d norm values, which correspond to the C-HÁ Á ÁO hydrogen bonds mentioned above ( Table 1). The red patch that appears around O1 is due to the C8-H8Á Á ÁO1 interaction, which is critical for the molecular packing of the title compound. In form-1, the C-HÁ Á ÁBr interactions are also prominent .    View down the c-axis of the C-HÁ Á ÁO andinteractions (dashed lines) in the title compound. Table 2 Summary of short interatomic contacts (Å ) in the title compound.

Database survey
C-HÁ Á ÁBr interactions connect the molecules in the crystal of the form-1 polymorph of the title compound, (I), resulting in zigzag C(8) chains along the [100] direction. These chains are connected by C-BrÁ Á Á interactions into layers parallel to (001). van der Waals interactions between the layers contribute to the crystal cohesion.
The molecules in (II) are joined into layers parallel to (011) by C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds. C-BrÁ Á Á and C-FÁ Á Á contacts, as well asstacking interactions, strengthen the crystal packing The molecules in the crystal of (III) are connected into chains running parallel to [001] by C-HÁ Á ÁO hydrogen bonds. C-FÁ Á Á contacts andstacking interactions help to consolidate the crystal packing, and short BrÁ Á ÁO [2.9828 (13) Å ] distances are also observed.
In the crystal of (IV), 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 radii 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 (V) and (VI), the molecules are linked through weak XÁ Á ÁCl contacts [X = Cl for (V) and Br for (VI)], C-HÁ Á ÁCl and C-ClÁ Á Á interactions into sheets lying parallel to (001).
In the crystal of (VII), the molecules are stacked in columns along [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.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were positioned geometrically and allowed to ride on their parent atoms (C-H = 0.95 Å ) with U iso (H) = 1.2U eq (C).

Data collection
Bruker AXS D8 QUEST, Photon III detector diffractometer Radiation source: fine-focus sealed X-Ray tube Graphite monochromator Detector resolution: 7.31 pixels mm -1 φ and ω shutterless scans Absorption correction: multi-scan (SADABS; Krause et al., 2015). where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max = 0.002 Δρ max = 0.68 e Å −3 Δρ min = −0.52 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.