Crystal structure and Hirshfeld surface analysis of 1-[(1-butyl-1H-1,2,3-triazol-4-yl)methyl]-3-methylquinoxalin-2(1H)-one

The title compound is built up from a planar quinoxalinone ring system linked through a methylene bridge to a 1,2,3-triazole ring, which is inclined by 67.09 (4)° to the quinoxalinone ring plane.


Structural commentary
The title compound, (I), is built up from the two fused sixmembered rings of a quinoxalinone moiety linked through a ISSN 2056-9890 methylene bridge to a 1,2,3-triazole ring, which in turn carries an n-butyl substituent on N3 (Fig. 1). The dihydroquinoxaline unit is planar within 0.029 (1) Å (r.m.s. deviation of the fitted atoms = 0.0123 Å ) and the triazole ring is inclined by 67.09 (4) to the above-mentioned plane. The molecule adopts a Z-shaped conformation with the (1H-1,2,3-triazol-5-yl)methyl substituent projecting well out of the mean plane of the dihydroquinxalone unit, as indicated by the C1-N2-C10-C11 torsion angle of 90.85 (16) . The n-butyl group is oriented in the opposite direction as seen from the N4-N3-C13-C14 torsion angle of À95.26 (16) (Fig. 2).

Database Survey
A search of the CSD (Version 5.39, updated May 2018;Groom et al., 2016) using the fragment shown in Scheme 2 (R = C, R1 = nothing) generated 37 hits. Of these, the ones most comparable to the title molecule have R1 = CH 3 and R = CH 2 C CH (Benzeid et al., 2009), CH 2 Ph (Ramli et al., 2010a(Ramli et al., , 2018, C 2 H 5 (Benzeid et al., 2008), (1,3-oxazolidin-3-yl)ethyl (Caleb et al., 2009), CH 2 CH CH 2 (Ramli et al., 2010b) and the isomer with R = (1-butyl-1H-1,2,3-triazol-5-yl)methyl (Abad et al., 2018a). Those with R = CH 2 C CH and C 2 H 5 have Z 0 = 1. A common feature of the above subset as well as the majority of the other compounds with different R1 substituents is the geometry of the bicyclic unit, which is either planar or has a slight end-to-end twist. Another feature is the orientation of the R group, which generally has a C-N-C-C torsion angle >65 and in quite a few cases, this is close to 90 . A comparison of the conformation of the title molecule with that of its (1-butyl-1H-1,2,3-triazol-5-yl)methyl isomer shows that the latter has a U shape with the R group extending back over the bicyclic unit as the result of an intramolecular C-HÁ Á ÁO hydrogen bond from the hydrogen of the butyl group while in the former, the more remote position of the butyl group on the triazole ring disfavours such an interaction and the molecule adopts a Z shape. This conformation is favoured by the opportunity for -stacking and C-HÁ Á Á(ring) interactions in the crystal. Packing viewed along the a-axis direction. C-HÁ Á ÁN hydrogen bonds are shown by black dashed lines while -stacking and C-HÁ Á Á(ring) interactions are shown, respectively, by orange and green dashed lines.

Hirshfeld surface analysis
In order to visualize the intermolecular interactions in the crystal of the title compound, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) was carried out using CrystalExplorer17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 3), the white surface indicates contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distant contact) than the sum of the van der Waals radii, respectively (Venkatesan et al., 2016). The bright-red spots appearing near the hydrogen atom H12 indicates their role as the respective donors and/or acceptors in the dominant 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) as shown in  Fig. 6(b)-(i), respectively, together with their relative contributions to the Hirshfeld surface. The most important interaction is HÁ Á ÁH contributing 52.7% to the overall crystal packing, which is reflected in Fig. 6(b) as widely scattered points of high density due to the large hydrogen content of the molecule. The split spike with the tip at d e = d i = 1.13 Å in Fig. 6(b) is due to the short interatomic HÁ Á ÁH contacts ( View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.2380 to 1.1723 a.u.

Figure 4
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.

Synthesis and crystallization
To a solution of 3-methyl-1-(prop-2-ynyl)-3,4-dihydroquinoxalin-2(1H)-one (0.68 mmol) in ethanol (15 mL) was added 1-azidobutane (1.03 mmol). The reaction mixture was stirred under reflux for 72 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 the mixture (hexane/ethyl acetate 8:2). The solid product obtained was crystallized from ethanol to afford colourless crystals in 78% 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 freely refined.

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. 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.