Crystal structure and Hirshfeld surface analysis of ethyl 2-{4-[(3-methyl-2-oxo-1,2-dihydroquinoxalin-1-yl)methyl]-1H-1,2,3-triazol-1-yl}acetate

The dihydroqinoxalinone portion of the molecule is planar to within 0.0512 (12) Å. In the crystal, a combination of C—H⋯O and C—H⋯N hydrogen bonds together with slipped π-stacking and C—H⋯π(ring) interactions lead to the formation of chains extending along the c-axis direction. The chains are linked into layers parallel to the bc plane by sets of four C—H⋯O hydrogen bonds and the layers are tied together by complementary π-stacking interactions.


Figure 2
Detail of the intermolecular interactions viewed along the b-axis direction. C-HÁ Á ÁO and N-HÁ Á ÁO hydrogen bonds are shown, respectively, by black and purple dashed lines. Slipped -stacking and C-HÁ Á Á (ring) interactions are shown, respectively, by orange and green dashed lines.

Figure 1
The title molecule with the labelling scheme and 50% probability ellipsoids.

Figure 3
Plane view of one layer along the a-axis direction with intermolecular interactions depicted as in Fig. 2.

Hirshfeld surface analysis
Visualization and exploration of intermolecular close contacts in the crystal structure of the title compound is invaluable. Thus, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) was carried out by using CrystalExplorer17.5 (Turner et al., 2017) to investigate the locations of atom-atom short contacts with the potential to form hydrogen bonds and the quantitative ratios of these interactions as well as those of the -stacking interactions. In the HS plotted over d norm (Fig. 4), the white surface indicates contacts with distances equal to the sum of van der Waals radii, while the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the van der Waals radii, respectively (Venkatesan et al., 2016). The brightred spots appearing near O1, O2, N1, N3 and hydrogen atoms H5, H4, H9B and H12 indicate their roles as the respective donors and acceptors in the dominant C-HÁ Á ÁO and C-HÁ Á ÁN hydrogen bonds; they also appear as blue and red regions corresponding to positive and negative potentials on the HS mapped over electrostatic potential (Spackman et al., 2008;Jayatilaka et al., 2005) shown in Fig. 5. The blue regions indicate positive electrostatic potential (hydrogen-bond donors), while the red regions indicate negative electrostatic potential (hydrogen-bond acceptors).
The shape-index of the HS is a tool to visualizestacking interactions by the presence of adjacent red and blue triangles; if there are no adjacent red and/or blue triangles, then there are nointeractions. Fig. 6 clearly suggest that there are interactions present in the title compound.

Figure 5
View of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range À0.0500 to 0.0500 a.u. using the STO-3 G basis set at the Hartree-Fock level of theory. Hydrogen-bond donors and acceptors are shown as blue and red regions around the atoms, corresponding to positive and negative potentials, respectively.

Figure 6
Hirshfeld surface of the title compound plotted over shape-index. besides the HÁ Á ÁO/OÁ Á ÁH contacts (Table 2) and is viewed as pair of spikes with the tips at d e + d i $ 2.27 Å . The HÁ Á ÁN/ NÁ Á ÁH contacts in the structure with 17.0% contribution to the HS have a symmetrical distribution of points, Fig. 7d, with the tips at d e + d i $ 2.30 Å arising from the short interatomic C-HÁ Á ÁN hydrogen bonding (Table 1) as well as from the HÁ Á ÁN/ NÁ Á ÁH contacts (Table 3). The presence of a weak C-HÁ Á Á interaction (Table 1) results in two pairs of characteristic wings in the fingerprint plot delineated into HÁ Á ÁC/CÁ Á ÁH contacts with a 10.4% contribution to the HS, Fig. 7e, while the two pairs of thin and thick edges at d e + d i $ 2.77 and 2.67 Å , respectively, result from the interatomic HÁ Á ÁC/CÁ Á ÁH contacts ( Table 2). The interatomic CÁ Á ÁC contacts (Table 2) with a 3.6% contribution to the HS appear as an arrow-shaped distribution of points in Fig. 7f, with the vertex at d e = d i = 1.71 Å . Finally, the CÁ Á ÁN/NÁ Á ÁC (Fig. 7g) contacts (Table 3) Table 2 Selected interatomic distances (Å ).

Synthesis and crystallization
To a solution of 3-methyl-1-(prop-2-ynyl)-3,4-dihydroquinoxalin-2(1H)-one (0.65 mmol) in ethanol (20 mL) was added ethyl azidoacetate (1.04 mmol). The mixture was stirred under reflux for 24 h. After completion of the reaction (monitored by TLC), the solution was concentrated and the residue was purified by column chromatography on silica gel by using as eluent a hexane/ethyl acetate (9/1) mixture. Crystals were obtained when the solvent was allowed to evaporate. The solid product isolated was recrystallized from ethanol to afford yellow crystals in 75% yield.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms were located in a difference-Fourier map and were refined freely. Eleven reflections appearing near the top of the frames on which they were recorded were omitted from the final refinement as they appeared to have been partially obscured by the nozzle of the low-temperature attachment.   program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018/1 (Sheldrick, 2015b); molecular graphics: DIAMOND (Brandenburg & Putz, 2012); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Special details
Experimental. The diffraction data were collected in three sets of 363 frames (0.5° width in ω) at φ = 0, 120 and 240°. A scan time of 40 sec/frame was used. Analysis of 226 reflections having I/σ(I) > 12 and chosen from the full data set with CELL_NOW (Sheldrick, 2008) showed the crystal to belong to the triclinic system and to be twinned by a 176° rotation about the real axis 1,-0.8,-0.11. The raw data were processed using the multi-component version of SAINT under control of the two-component orientation file generated by CELL_NOW. 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.
Refined as a 2-component twin.