Crystal structure and Hirshfeld surface analysis of 2-methyl-3-nitro-N-[(E)-(5-nitrothiophen-2-yl)methylidene]aniline

The title compound is a Schiff base formed from 5-nitrothiophene-2-carbaldehyde and 2-methyl-3-nitroaniline. In the crystal, the molecules are linked by weak C—H⋯O hydrogen bonds.

The title compound, C 12 H 9 N 3 O 4 S, synthesized by condensation of 5-nitrothiophene-2-carbaldehyde and 2-methyl-3-nitroaniline, crystallizes in the orthorhombic space group P2 1 2 1 2 1 . In the molecule, the aromatic benzene and thiophene rings are twisted with respect to each other, making a dihedral angle of 23.16 (7) . In the crystal, molecules are linked by intermolecular C-HÁ Á ÁO hydrogen bonds into chains extending along the c-axis direction. Weakstacking interactions along the a-axis direction provide additional stabilization of the crystal structure. The roles of the various intermolecular interactions were clarified by Hirshfeld surface analysis, which reveals that the crystal packing is dominated by OÁ Á ÁH (39%) and HÁ Á ÁH (21.3%) contacts. The crystal studied was refined as a two-component inversion twin.

Chemical context
Bioactivity is an important topic, which includes many areas such as the synthesis of new drugs, creams, agricultural products and so on. In this respect, Schiff bases are organic molecules suitable for bioactivity applications because of the imine bond that increases the lipophilic character of the molecule. The imine bond provides a synthetic route to structural chirality, changes the electronic properties and leads to solubility in different media (Tarafder et al., 2008). Schiff bases can include heterocycles or amino acid residues and can be easily obtained by the condensation of primary amines with aldehydes or ketones without by-products, thus giving the pure product for biological treatments (Yu et al., 2009;Lobana et al., 2009). Many natural products contain thiophene groups, which lead to pharmacological properties. Thiophenecontaining molecules are used in medicinal chemistry for therapeutic applications (Mishra et al., 2011). 5-Nitrothiophene-2-carboxaldehyde derivatives exhibit antibacterial properties (Foroumadi et al., 2003). This highly reactive molecule has been used in chemosensor applications (Ye et al., 2019). In the present study, a new Schiff base, 2-methyl-3nitro-N-[(E)-(5-nitrothiophen-2-yl)methylidene]aniline (I), was obtained in crystalline form from the reaction of 5-nitrothiophene-2-carbaldehyde with 2-methyl-3-nitroaniline.

Structural commentary
The molecular structure of the title compound is shown in Fig. 1. The molecule adopts the E configuration with respect to the C N bond and the benzene and thiophene rings form a dihedral angle of 23.16 (7) . The deviation from planarity can be attributed to packing forces. The nitro group attached to the thiophene ring is strongly conjugated with the -system of this ring, as evident from the short N2-C7 distance (see Table 1). As a result, this nitro group is almost coplanar with the thiophene ring. The nitro group attached to the benzene ring is twisted by 48.4 (2) with respect to this ring, and thus the -conjugation is much weaker in this case. The length of the C8 N2 bond is 1.277 (4) Å , which is consistent with those in the related structures 4-(naphthalen-2-yl)-N-[(Z)-4-propoxybenzylidene]-1,3-thiazol-2-amine [1.284 (3) Å ; Sheakh Mohamad et al., 2020] and (E)-2,4-di-tert-butyl-6-[(3-chloro-4-methylphenylimino)methyl]phenol [1.278 (4) Å ; Kansiz et al., 2018]. The C9-S1 and C12-S1 bonds in the thiophene ring are slightly shorter than a standard Csp 2 -S single bond (1.76 Å ; Allen et al., 1987) as a result of the -conjugation with the double bonds. At the same time, these S-C bonds are longer than those in the structure of 6-[(E)-2-(thiophen-2-yl)ethenyl]-4,5-dihydropyridazin-3(2H)one [1.691 (3) Å ; Daoui et al., 2019].

Figure 2
A view of the crystal packing of the title compound parallel to the bc plane. C-HÁ Á ÁO interactions are indicated by dotted lines.

Figure 1
The molecular structure of the title compound with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level.
bond lengths in all of the reference structures. The C-S bond lengths in EXIWIS, FIBKUZ and TONBAB range from 1.694 (3) to 1.730 (2) Å . The corresponding bond lengths in the title compound fall within these limits.

Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was carried out using the CrystalExplorer17.5 (Turner et al., 2017). The Hirshfeld surface and the associated two-dimensional fingerprint plots were used to quantify the various intermolecular interactions in the title compound. The Hirshfeld surfaces mapped over d norm and electrostatic potential are illustrated in Fig. 3. In Fig. 3a, the red spots correspond to the OÁ Á ÁH contacts. The electrostatic potential (Fig. 3b) shows donor (red) and acceptor (blue) regions. The percentage contribution of various interactions is shown in the fingerprint plot (Fig. 4). The most important interactions for determining the morphology of the crystal are HÁ Á ÁH, OÁ Á ÁH and SÁ Á ÁH contacts, their individual contributions being 39%, 21.3% and 5.9%, respectively. CÁ Á ÁN/NÁ Á ÁC (5.8%) and CÁ Á ÁH/HÁ Á ÁC (5.4%) contacts are also observed. The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the crystal packing.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The C-bound H atoms were placed in idealized positions and refined using a riding model with C-H = 0.93-0.96 Å and U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other C-bound H atoms. The structure was refined as a two-component inversion twin. Two-dimensional fingerprint plots for the title compound, with the relative contributions of the atom pairs to the Hirshfeld surface.   ; program(s) used to solve structure: SHELXT2017/1 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2017/1 (Sheldrick, 2015b); molecular graphics: PLATON (Spek, 2020); software used to prepare material for publication: WinGX (Farrugia, 2012).
Absolute structure parameter: 0.59 (15) 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.