4-(4-Acetyl-5-methyl-1H-1,2,3-triazol-1-yl)benzonitrile: crystal structure and Hirshfeld surface analysis

The title molecule is twisted with the dihedral angle between the N-bound 4-cyanophenyl and C-bound acetyl groups of the 1,2,3-triazoyl ring being 60.82 (13)°. The molecular packing is sustained by carbonyl-C=O⋯π(triazoyl), cyano-C≡N⋯π(triazoyl) and π–π stacking interactions.


Chemical context
The 1,2,3-triazoles comprise an interesting class of heterocyclic compounds, with diverse applications in biological and material chemistry (Struthers et al., 2010;Bonandi et al., 2017;Dheer et al., 2017). In particular, 1,2,3-triazoles containing a carbonyl or carboxyl group in their structures have received considerable attention as they are found in a great number of biologically and pharmaceutically active molecules that exhibit a broad spectrum of properties (Shu et al., 2009;Morzherin et al., 2011;Cheng et al., 2012;Gilchrist et al., 2014). In this context, the organocatalytic cycloaddition reaction of organic azides with -ketoesters, -ketoamides, enones and allyl ketones has proven to be a powerful strategy for the synthesis of such class of compounds (John et al., 2015;Lima et al., 2015). Although much progress has been achieved, most of the available methodologies usually employ a homogenous catalyst, which can be difficult to recover. In view of environmental concerns, very recently, we reported for the first time, a heterogeneous strategy for the synthesis of 1,4,5-trissubstituted-1,2,3-triazoles through the 1,3-dipolar cycloaddition between aryl azides and active methylene compounds using CuO nanoparticles as catalyst in DMSO under microwave irradiation (Dias et al., 2018). The title compound, (I), was prepared in this study and despite having been prepared by another route in a different study (Kamalraj et al., 2008), no crystal structure is available. The availability of crystals in the latter study prompted the present structural analysis.

Structural commentary
The molecular structure of (I), Fig. 1, comprises an essentially planar 1,2,3-triazolyl ring with a r.m.s. deviation of the fitted atoms of 0.0030 Å ; the maximum deviation of 0.0037 (9) Å is found for the N2 atom. A 4-cyanophenyl residue is connected to the 1,2,3-triazolyl ring at the N1-position and forms a dihedral angle of 54.64 (5) with it, indicating a significant twist between the rings. By contrast, the acetyl group connected at the C2-position is approximately co-planar with the central ring, forming a dihedral angle of 6.8 (3) . The dihedral angle between the phenyl and acetyl groups is 60.82 (13) , indicating a dis-rotatory relationship. The acetylcarbonyl group occupies a position approximately syn to the ring-bound methyl substituent with the C1-C2-C3-O1 and C4-C1-C2-C3 torsion angles being 6.2 (3) and À1.5 (3) , respectively.

Supramolecular features
The molecular packing of (I) features interactions involving both the five-and six-membered rings. Centrosymmetrically related molecules are connected via carbonyl-C OÁ Á Á(triazoyl) interactions, Table 1. Further connections between molecules are of the type cyano-C NÁ Á Á(triazoyl) to the opposite face of the five-membered ring (Fig. 2, Table 1), which together lead to a supramolecular layer parallel to (101). The OÁ Á Á or NÁ Á Á separations for these interactions are significantly longer that the van der Waals' separations for these species (3.32 and 3.35 Å , respectively) but the noncovalent interactions plots (see below) indicate that they are weakly attractive in nature. Connections between the layers giving rise to a three-dimensional architecture are weakstacking interactions between centrosymmetrically related phenyl rings, with the inter-centroid separation being 3.9242 (9) Å ; symmetry operation (i): 2 À x, 2 À y, 1 À z. A view of the unit cell contents is shown in Fig. 2. The specified and other weak intermolecular interactions are discussed in more detail below in Hirshfeld surface analysis.

Hirshfeld surface analysis
The Hirshfeld surface calculations for (I) were performed in accord with related studies (Caracelli et al., 2018) and provide information on the influence of other weak intermolecular interactions instrumental in the molecular packing. In addition to the presence of carbonyl-C OÁ Á Á(triazolyl) and cyano-C NÁ Á Á(triazolyl) interactions (Table 1) in the formation of three-dimensional architecture as discussed above, the molecular packing also features weak C-HÁ Á ÁN interactions. On the Hirshfeld surface mapped over d norm in Fig. 3 Symmetry codes: (i) Àx þ 1; Ày þ 2; Àz þ 1; (ii) x À 1 2 ; Ày þ 1 2 ; z À 1 2 .

Figure 2
A view of the unit-cell contents shown in projection down the b axis. The C OÁ Á Á(triazoyl), C NÁ Á Á(triazoyl) and (tolyl)-(tolyl) contacts are shown as orange, blue and purple dashed lines, respectively.

Figure 1
The molecular structure of (I), showing the atom-labelling scheme and displacement ellipsoids at the 50% probability level.
triazolyl-N3, cyano-N4 (Fig. 3a), phenyl-H8 and H10 atoms (Fig. 3b), and the diminutive-red spots near cyano-N4 (Fig. 3b) and phenyl-H7 ( Fig. 3a) atoms. The influence of short interatomic CÁ Á ÁO/OÁ Á ÁC contacts involving methyl-C4 and carbonyl-O1 atoms ( Table 2) is also observed as the faint-red spots near these atoms in Fig. 3b. The donors and acceptors of intermolecular C-HÁ Á ÁN interactions are also evident as the blue and red regions corresponding to positive and negative electrostatic potentials, respectively, on the Hirshfeld surface mapped over electrostatic potential shown in Fig. 4. Views of the immediate environment about a reference molecule within the Hirshfeld surface mapped over the shape-index property, highlighting intermolecular C OÁ Á Á, C NÁ Á Á andstacking interactions, are illustrated in Fig Table 3. The short interatomic HÁ Á ÁH contact involving symmetry-related methyl-H4C atoms (Table 2) is viewed as the cone-shaped tip at d e + d i $ 2.3 Å in the fingerprint plot delineated into HÁ Á ÁH contacts (Fig. 6b). The second largest contribution to the Hirshfeld surface, i.e. 26.2%, is from NÁ Á ÁH/HÁ Á ÁN contacts (Fig. 6c) and arise from the intermolecular C-HÁ Á ÁN contacts involving cyano-N4 and tria-  Table 2 Summary of short interatomic contacts (Å ) in (I).

Figure 3
Two views of the Hirshfeld surface for (I) mapped over d norm in the range À0.065 to +1.215 a.u.

Figure 4
Two views of the Hirshfeld surface mapped over the electrostatic potential in the range À0.092 to +0.055 a.u. The red and blue regions represent negative and positive electrostatic potentials, respectively. zolyl-N3 atoms (Table 2) and are viewed as the pair of overlapping green and blue spikes with their tips at d e + d i $2.5 Å .

Non-covalent interaction plots
Non-covalent interaction (NCI) plots are a convenient means by which the nature of an interaction between residues may be assessed in terms of being attractive or otherwise (Johnson et al., 2010;Contreras-García et al., 2011). In NCI plots, a weakly attractive interaction will appear green on the isosurface, whereas attractive and repulsive interactions will result in blue and red isosurfaces, respectively. The NCI plots for the interacting entities of the carbonyl-C OÁ Á Á(triazolyl) and cyano-C NÁ Á Á(triazolyl) interactions are shown in Fig. 7a,b, indicating the weakly attractive nature of these interactions. The arrows in Fig. 7b, highlight a weak phenyl-C-HÁ Á ÁN(cyano) interaction (Table 2).

Database survey
There are four closely related compounds in the literature whereby the cyano group of (I) is replaced by chloride and bromide, which are isostructural (Zeghada et al., 2011), methyl (El-Hiti et al., 2017) and nitro (Vinutha et al. (2013); two independent molecules comprise the asymmetric unit of the nitro compound. Key dihedral angle data are included in Table 4. This shows that the greatest variations in dihedral angles between the phenyl and acetyl residues is found for the two independent molecules of the nitro compound. The

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 5. The carbon-bound H atoms were placed in calculated positions (C-H = 0.93-0.96 Å ) and were included in the refinement in the riding model approximation, with U iso (H) set to 1.2-1.5U eq (C).   Note: (a) Two independent molecules comprise the asymmetric unit.

4-(4-Acetyl-5-methyl-1H-1,2,3-triazol-1-yl)benzonitrile
Crystal data 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.