Crystal structure and Hirshfeld surface analysis of (E)-4-{2,2-dichloro-1-[(3,5-dimethylphenyl)diazenyl]ethenyl}-N,N-dimethylaniline

In the crystal of the title compound, the molecules are associated into inversion dimers via short Cl⋯Cl halogen bonds.


Chemical context
Aromatic azo compounds provide ubiquitous motifs in organic chemistry and are widely used as organic dyes, indicators, pigments, food additives, ligands, radical reaction initiators, therapeutic agents, etc. Mahmudov et al., 2013). On the other hand, the study of both inter-and intramolecular non-covalent interactions in azo compounds is important for our understanding of the factors governing the assembly of the molecules into supramolecular systems (see, for example, Mahmudov et al., 2015;Shixaliyev et al., 2014). When compared to well-explored hydrogenbonding and -interactions (see, for example, Akbari et al., 2017;Mahmoudi et al., 2018), the exploration of new intermolecular interactions such as halogen, chalcogen, pnictogen, tetrel and triel bonds is in progress. Thus, decorating the structure of azo compounds with tailored functionalities (halogen, chalcogen and tetrel bond-donor centres) can be an important strategy to control and tune their functional properties such as their analytical and solvatochromic behaviour Mahmudov & Pombeiro, 2016).
In order to continue our work in this direction, we now describe the synthesis and structure of the title compound, C 18 H 19 Cl 2 N 3 (I) and its Hirshfeld surface analysis. ISSN 2056-9890

Structural commentary
The title compound has a non-planar molecular conformation (Fig. 1); the dihedral angle between the planes of the C1-C6 and C8-C13 aromatic rings is 77.07 (10) . The amine N atom as well as the directly adjacent arene C atom are displaced out of the plane of the other five aromatic C atoms: the deviations are À0.009 (2) for C11 and À0.065 (2) Å for N3. Some key torsion angles describing the molecular conformation are -178.40 (15)

Hirshfeld surface analysis
The Hirshfeld surface (McKinnon et al., 2007) for (I) and its associated two-dimensional fingerprint plots (Spackman & McKinnon, 2002) were calculated using CrystalExplorer17 (Turner et al., 2017). Red, white and blue regions visible on the d norm surface indicate contacts with distances shorter, longer and approximately equal to the van der Waals radii: the surface for (I) (Fig. 3) is almost featureless, indicating a lack of directional interactions.
The overall two-dimensional fingerprint plot (Fig. 4a) and those delineated into HÁ Á ÁH, ClÁ Á ÁH/HÁ Á ÁCl and CÁ Á ÁH/HÁ Á ÁC contacts (McKinnon et al., 2007) are illustrated in Fig. 4b-d, respectively and percentage contributions to the Hirshfeld surface are given in Table 1. The most important interaction is HÁ Á ÁH, contributing 43.9% 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 ClÁ Á ÁH/HÁ Á ÁCl interactions appear as two symmetrical broad wings with d e + d i ' 3.05 Å and contribute 22.9% to the Hirshfeld surface ( The molecular structure of (I) with displacement ellipsoids drawn at the 30% probability level.

Figure 2
Crystal packing for (I) viewed along the a-axis direction.

Database survey
In the crystals of HONBOE and HONBUK, the aromatic rings form dihedral angles of 60.9 (2) and 64.1 (2) , respectively. Molecules are linked through weak XÁ Á ÁCl contacts (X = Br for HONBOE and Cl for HONBUK), C-HÁ Á ÁCl and C-ClÁ Á Á interactions into sheets parallel to the ab plane. Additional van der Waals interactions consolidate the threedimensional packing. In the crystal of HODQAV, 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 XIZREG, 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 c-axis direction. The crystal packing also features C-ClÁ Á Á, C-FÁ Á Á and N-OÁ Á Á interactions. In the crystals of LEQXIR and LEQXOX, the dihedral angles between the aromatic rings are 56.18 (12) and 60.31 (14) , respectively. In LEQXIR, C-HÁ Á ÁN and C-HÁ Á ÁO hydrogen bonds and short ClÁ Á ÁO contacts occur and in LEQXOX C-HÁ Á ÁN and short ClÁ Á ÁCl contacts are observed.

Computing details
Data collection: APEX3 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS (Sheldrick, 2008); program(s) used to refine structure: SHELXL2016/6 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: PLATON (Spek, 2020).  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.