Crystal structure, DFT calculations and Hirshfeld surface analysis of 3-(4-methylphenyl)-6-nitro-1H-indazole

The asymmetric unit of the title compound consist of two independent molecules. In the crystal, N–H⋯O and C—H⋯O hydrogen bonds form zigzag chains along the b-axis direction. Additional C—H⋯O hydrogen bonds link the chains into layers parallel to (10). These are connected by slipped π-stacking and C—H⋯π(ring) interactions.

The asymmetric unit of the title compound, C 14 H 11 N 3 O 3 , consists of two independent molecules having very similar conformations in which the indazole moieties are planar. The independent molecules are distinguished by small differences in the rotational orientations of the nitro groups. In the crystal, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds form zigzag chains along the b-axis direction. Additional C-HÁ Á ÁO hydrogen bonds link the chains into layers parallel to (101). These are connected by slipped -stacking and C-HÁ Á Á(ring) interactions.

Chemical context
Indazoles are an important class of heterocyclic compounds having a wide range of biological and pharmaceutical applications. There is enormous potential in the synthesis of novel heterocyclic systems to be used as building blocks for the next generation of pharmaceuticals as anti-bacterial, anti-depressant and anti-inflammatory agents. Fused aromatic 1H and 2H-indazoles are well recognized for their anti-hypertensive and anti-cancer properties while other indazole derivatives are a versatile class of compounds that have found use in biology, catalysis and medicinal chemistry (Schmidt et al., 2008). Although rare in nature (Liu et al., 2004;Ali et al., 2008), indazoles exhibit a variety of biological activities such as HIV protease inhibition (Patel et al., 1999), antiarrhythmic and analgesic activities (Mosti et al., 2000) and antitumor activity and antihypertensive properties (Bouissane et al., 2006;Abbassi et al., 2012). As a continuation of our studies of indazole derivatives (Mohamed Abdelahi et al., 2017a,b,c), we report the synthesis and structure of the title compound, (I). ISSN 2056-9890

Figure 2
Detail of one zigzag chain in (I) viewed along the a-axis direction. N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds are shown, respectively, by blue and black dashed lines.

Figure 3
Plan view of the layer structure of (I) seen along the c-axis direction.
Portions of one chain extend horizontally with the intrachain hydrogen bonds depicted as in Fig. 2. The C-HÁ Á ÁO hydrogen bonds connecting the chains into layers are depicted by purple dashed lines.

Figure 1
The asymmetric unit of (I) with the labelling scheme and 50% probability ellipsoids.

Figure 4
Elevation view of the layer structure of (I) projected on (401).
-stacking and C-HÁ Á Á(ring) interactions are shown, respectively, by orange and green dashed lines. Hydrogen bonds are depicted as in Fig. 2.
ino)-1H-indazole (Gzella & Wrzeciono, 2001). The structures of the nitro derivatives are fairly similar to that in the present work in that the indazole moieties are essentially planar with the nitro groups twisted out the plane by 3-6 . In the 4-methylphenyl derivative, the phenyl ring is inclined to the plane of the indazole moiety by 12.94 (8) .

DFT calculations
The structure of the title compound in the gas phase was optimized by means of density functional theory. The DFT calculation was performed by the hybrid B3LYP method, which is based on the idea of Becke and considers a mixture of the exact (HF) and DFT exchange utilizing the B3 functional together with the LYP correlation functional (Becke, 1993;Lee et al., 1988;Miehlich et al., 1989). The B3LYP calculation was performed in conjunction with a triple-x basis set which was designed for the DFT optimization [designated as TZVP (DFT orbital); Godbout et al., 1992]. After obtaining the converged geometry, the harmonic vibrational frequencies were calculated at the same theoretical level to confirm that the number of the imaginary frequency is zero for the stationary point. Both the geometry optimization and harmonic vibrational frequency analysis of the title compound were carried out with the Gaussian16 program (Frisch et al., 2016).

Hirshfeld surface calculations
Both the definition of a molecule in a condensed phase and the recognition of distinct entities in molecular liquids and crystals are fundamental concepts in chemistry. Based on Hirshfeld's partitioning scheme, a method to divide the electron distribution in a crystalline phase into molecular fragments was proposed (Spackman & Byrom, 1997;McKinnon et al., 2004;Spackman & Jayatilaka, 2009). This partitioned the crystal into regions where the electron distribution of a sum of spherical atoms for the molecule dominates over the corresponding sum of the crystal. Because it derived from Hirshfeld's stockholder partitioning, the molecular surface is named the Hirshfeld surface. In this study, the Hirshfeld surface analysis of the title compound was performed using the CrystalExplorer program (Turner et al., 2017).

theoretical comparison of the title compound
The results of the B3LYP geometry optimization of (I) are depicted in Fig. 5 and a comparative study of the gas-phase structure and the solid-phase one for (I) was performed, with the results summarized in Table 2 together with a previous geometrical study on 1H-indazole itself (Hathaway et al., 1998). The discrepancy between our B3LYP result and the previous MP2(fc) calculations may be due to the substitutent effects of both the NO 2 and methoxyphenyl groups (Hathaway et al., 1998).

Hirshfeld analysis of the title compound
The standard resolution molecular Hirshfeld surface (d norm ) of the title compound is shown in Fig. 6 and is transparent so the molecular moiety can be visualized in a similar orientation for all of the structures around which they were calculated. The 3D d norm surface can be used to identify very close intermolecular interactions with d norm being negative (positive) when intermolecular contacts are shorter (longer) than the sum of the van der Waals radii. The d norm value is mapped onto the Hirshfeld surface by red, white or blue colours. The red regions represent closer contacts with a negative d norm while the blue regions represent longer contacts with a positive d norm and the white regions represent contacts equal to the van der Waals separation with d norm equal to zero. As depicted in Fig. 6, the major interactions in the title compound are the intermolecular HÁ Á ÁO and HÁ Á ÁN hydrogen bonds.
The 2D fingerprint plots highlight particular atom-pair contacts and enable the separation of contributions from The B3LYP-optimized geometries (Å , ) of (I). Table 2 The B3LYP-optimized and the X-ray structural parameters (Å , ) for (I). B3LYP X-ray 1H-indazole a different interaction types that overlap in the full fingerprint.
Using the standard 0.6-2.6 Å view with the d e and d i distance scales displayed on the graph axes, the 2D fingerprint plot for the title compound is shown in Fig. 7(a). Including the reciprocal contacts, the contribution of the OÁ Á ÁH contacts (15.7%) for the title compound is larger than that of the NÁ Á ÁH contacts (4.6%) [ Fig. 7(b) and 7(c)].

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 Two-dimensional fingerprint plots of (I): (a) full, (b) resolved into HÁ Á ÁO contacts; (c) resolved into HÁ Á ÁN contacts.
those attached to nitrogen were placed in locations derived from a difference map and their parameters adjusted to give N-H = 0.91 Å . All were included as riding contributions with U iso (H) = 1.2-1.5U eq (C,N).

Funding information
JTM thanks Tulane University for support of the Tulane Crystallography Laboratory. This publication was prepared with the support of the RUDN University Program 5-100.

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. H-atoms attached to carbon were placed in calculated positions (C-H = 0.95 -0.98 Å) while those attached to nitrogen were placed in locations derived from a difference map and their parameters adjusted to give N-H = 0.91 Å. All were included as riding contributions with isotropic displacement parameters 1.2 -1.5 times those of the attached atoms.