Crystal structures and Hirshfeld surface analyses of the two isotypic compounds (E)-1-(4-bromophenyl)-2-[2,2-dichloro-1-(4-nitrophenyl)ethenyl]diazene and (E)-1-(4-chlorophenyl)-2-[2,2-dichloro-1-(4-nitrophenyl)ethenyl]diazene

In the crystals of the two isotypic compounds, molecules are linked by weak halogen–halogen (Br⋯Cl or Cl⋯Cl) contacts and C—Cl⋯π interactions into sheets lying parallel to the ab plane.


Supramolecular features and Hirshfeld surface analysis
As a result of the isotypism of (I) and (II), the packing features are generally very similar in the two structures. Molecules are linked by weak BrÁ Á ÁCl contacts [for (I)] or ClÁ Á ÁCl contacts [for (II)] and C-HÁ Á ÁCl interactions into chains extending along the a-axis direction (Tables 1-3; Figs. 3  and 4). Additional C-ClÁ Á Á interactions lead to the formation of sheets parallel to the ab plane (Fig. 5). van der Waals interactions (Table 3) consolidate the three-dimensional packing.
Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was used to investigate the intermolecular interactions in the crystal structures of both compounds (CrystalExplorer3.1; Wolff et al., 2012). The surface plots (Spackman et al., 2008) mapped over d norm were generated to quantify and visualize the intermolecular interactions and to explain the observed crystal packing. Dark-red spots on the d norm surface arise as a result of short interatomic contacts (Tables 1-3) The molecular structure of (I) with displacement ellipsoids drawn at the 30% probability level.

Figure 2
The molecular structure of (II) with displacement ellipsoids drawn at the 30% probability level. Table 1 Hydrogen-bond geometry (Å , ) for (I).

Figure 3
Packing in the crystal structure of (I) showing chains running parallel to the a-axis.
For (I), the red points, which represent closer contacts and negative d norm values on the surface, correspond to the C-HÁ Á ÁO interactions. The reciprocal OÁ Á ÁH/HÁ Á ÁO interactions appear as two symmetrical broad wings in the two-dimensional fingerprint plots with d e + d i ' 2.5 Å and contribute 13.1% to the Hirshfeld surface (Fig. 6b). The reciprocal ClÁ Á ÁH/HÁ Á ÁCl interaction with a contribution of 13.8% is present as sharp symmetrical spikes at d e + d i ' 2.8 Å (Fig. 6c).
For (II), the percentage contributions of various contacts to the total Hirshfeld surface are shown in the two-dimensional fingerprint plots in Fig. 7. The reciprocal ClÁ Á ÁH/HÁ Á ÁCl interactions appear as two symmetrical broad wings with d e + d i ' 2.9 Å and contribute 21.9% to the Hirshfeld surface (Fig. 7b) Table 3 Summary of short interatomic contacts (Å ) in the crystal structures of compounds (I) and (II).

Figure 5
Formation of sheets in (II) parallel to ab through C-ClÁ Á Á contacts.
butions of both compounds to the Hirshfeld surfaces from the various other interatomic contacts are comparatively listed in Table 4. Although there is almost agreement on the values given for the molecules of (I) and (II), some differences are due to the different halogen atoms substituting the phenyl ring and the different molecular environment in the crystal structures. In the crystal of HODQAV, molecules are stacked in columns along the a axis via weak C-HÁ Á ÁCl hydrogen bonds and face-to-facestacking interactions. The crystal packing is further stabilized by short ClÁ Á ÁCl contacts. In XIZREG, molecules are linked by C-HÁ Á ÁO hydrogen bonds into zigzag chains running along the c-axis direction. The crystal packing is further stabilized by C-ClÁ Á Á, C-FÁ Á Á and N-OÁ Á Á interactions. In the crystal of LEQXIR, C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds and ClÁ Á ÁO contacts were found, and in LEQXOX, C-HÁ Á ÁN and ClÁ Á ÁCl contacts are observed.

Computing details
For both structures, data collection: APEX3 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXT2016/6 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016/6 (Sheldrick, 2015b); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: PLATON (Spek, 2009).  Absolute structure: Refined as an inversion twin Absolute structure parameter: 0.008 (13) 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. Refined as a 2-component inversion twin.   (Parsons et al., 2013). Absolute structure parameter: 0.14 (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.