4-Benzyl-1-(4-nitrophenyl)-1H-1,2,3-triazole: crystal structure and Hirshfeld analysis

In the title compound, the 1,2,3-triazoyl ring is flanked by nitrobenzene and benzyl substituents with the dihedral angle of 70.60 (9)° between rings indicating a twisted l-shape for the molecular conformation.


Chemical context
The 1,2,3-triazoles comprise an important class of molecules, having a number of applications in biology and materials science. As reviewed recently, 1,2,3-triazoles display various potential pharmaceutical properties including anti-cancer, anti-viral, anti-tuberculosis and anti-microbial activities (Tron et al., 2008;Thirumurugan et al., 2013). The 1,2,3-triazole chromophore can function as a most useful scaffold in bioconjugation owing to its rigid framework, stability, and, crucially, water-solubility (Jewett & Bertozzi, 2010;Holub & Kirshenbaum, 2010). Further applications are known in the fields of dyes, photostabilizers and as agrochemicals (Golas & Matyjaszewski, 2010;Qin et al., 2010). Very recently, a new and efficient synthesis for a metal-free and regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles was described (Ali et al., 2014). Among the compounds synthesized in that study was the title compound, (I). Herein, the crystal and molecular structures of (I) are described along with an analysis of the Hirshfeld surface.

Structural commentary
The molecular structure of (I), Fig. 1, comprises a central, strictly planar 1,2,3-triazolyl ring (r.m.s. deviation of the five fitted atoms = 0.001 Å ) flanked by C-and N-bound benzyl and 4-nitrobenzene substituents, respectively. The dihedral angle between the five-membered ring and phenyl ring is 83.23 (10) , indicating a near perpendicular relationship. By contrast, the benzene ring is closer to co-planar to the triazolyl ring, forming a dihedral angle of 13.95 (9) . The dihedral angle between the outer rings is 70.60 (9) , indicating that the molecule has a skewed-shape based on the letter L. The nitro group is co-planar with the benzene ring to which it is bound as seen in the value of the C12-C13-N4-O1 torsion angle of 0.4 (3) .

Hirshfeld surface analysis
The study of the Hirshfeld surface and intermolecular interactions of (I) has been carried out using standard parameters of the CrystalExplorer package (Wolff et al., 2012) and using similar protocols as in earlier studies (Zukerman-Schpector et al., 2017). In (I), the Hirshfeld surface is controlled by attractive interactions such as non-conventional C-HÁ Á Á, C-HÁ Á ÁO, C-HÁ Á ÁN hydrogen bonds andinteractions. The aforementioned contacts contribute around 70% to the overall surface area, Fig. 3 and Table 2. The repulsive HÁ Á ÁH interactions account for the remaining 30%, Fig. 3b. These observations may be rationalized in terms of the structure having electron-rich groups, i.e. the three aromatic rings and the nitro substituent, for which the electron densities are highly delocalized allowing them to have significant overlap in the molecular packing.  Table 1 Hydrogen-bond geometry (Å , ).

Figure 2
A view of the unit-cell contents in projection down the a axis. The C-HÁ Á ÁO, C-HÁ Á Á and nitro-OÁ Á Á contacts are shown as orange, purple and blue dashed lines, respectively.

Figure 1
The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 35% probability level.  Table 3 Summary of short interatomic contacts (Å ) in (I).

research communications
Contact Distance Symmetry operation 3.00 2 À x, Ày, 2 À z  As attractive interactions, the CÁ Á ÁH/HÁ Á ÁC contacts contribute a significant role (26.1%) to the overall surface area. These contacts arise mainly from C-HÁ Á Á contacts spread over the entire molecule in which all rings, i.e. the triazole, nitrobenzene and benzyl rings, function as H-atom acceptors, Tables 1 and 3, and Fig. 3c. The OÁ Á ÁH/HÁ Á ÁO contacts contribute 21.0% to the Hirshfeld surface area. In essence, this arises owing to non-conventional C-HÁ Á ÁO hydrogen bonds, Fig. 3d. There are two different H-donor carbon atoms participating in the weak C-HÁ Á ÁO interactions, one of which is the methylene-C3 atom, Table 1, and the other being the nitrobenzene-C12 atom, Table 3. The NÁ Á ÁH/HÁ Á ÁN contacts contribute approximately 16% to the overall surface area, Fig. 3e. Non conventional C-HÁ Á ÁN hydrogen bonds are formed with nitrobenzene-C atoms as Hatom donors, Table 3 and Fig. 3f. The CÁ Á ÁN/NÁ Á ÁC and CÁ Á ÁO/ OÁ Á ÁC contacts contribute around 6% to the Hirshfeld surface, Table 2 and Fig. 3f and g. Other surface contacts do not contribute significantly to the molecular packing.

Database survey
There are only relatively few 1,2,3-triazole structures in the literature having N-bound aryl groups and C-bound alkyl substituents. The two molecules closest to (I) have N-bound 4-chlorobenzene and C-bound n-butyl groups, i.e. (II) (Sarode et al., 2016), and N-bound 4-nitrobenzene and C-bound n-hexyl groups, i.e. (III) (Muhammad et al., 2015). In (II), the dihedral angle between the two planes is 22.59 (7) and the n-butyl group is co-planar with the the five-membered ring as seen in the sp 2 -C-C quaternary -C-C methylene = 0.06 (4) and C methylene -C-C-C methyl = À177.39 (19) torsion angles. In (III), the aromatic rings are considerably more co-planar, cf. (I) and (II), with the dihedral angle between them being 2.65 (8) . With respect to the n-hexyl substituent, the structure of (III) resembles that of (I) in that the sp 2 -C-C quaternary -C-C methylene torsion angle is À118.4 (3) .

Synthesis and crystallization
The title compound was prepared as described in the literature (Ali et al., 2014). Crystals of (I) for the X-ray study were obtained by slow evaporation from an ethyl acetate/n-hexane solution (5:1 v/v

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 4. The carbon-bound H atoms were placed in calculated positions (C-H = 0.93-0.97 Å ) and were included in the refinement in the riding-model approximation, with U iso (H) set to 1.2U eq (C).  program(s) used to solve structure: SIR2014 (Burla et al., 2015); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012) and DIAMOND (Brandenburg, 2006); software used to prepare material for publication: MarvinSketch (ChemAxon, 2010) and publCIF (Westrip, 2010). 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.