Crystal structure, Hirshfeld surface analysis and computational study of 2-chloro-N-[4-(methylsulfanyl)phenyl]acetamide

In the title compound, the amide functional group –C(=O)NH– adopts a trans conformation with the four atoms nearly coplanar. This conformation promotes the formation of a C(4) hydrogen-bonded chain propagating along the [010] direction.


Chemical context
Methylthioanilines are a class of S-and N-heterocyclic compounds that are widely used in antimicrobial applications (Chatterjee et al., 2012;Martin et al., 2016;Das et al., 2017;Cross et al., 2018). Metal-methylthioaniline complexes have also been utilized in many applications including as homogeneous catalysts, organic semiconductors, antibacterial and antifungal drugs (Chen et al., 2019;Kumar et al., 2017;Mandal et al., 2018;Wang et al., 2009). In this research, we report the synthesis and the solid state structure of 2-chloro-N- [4-(methylsulfanyl)phenyl]acetamide, a methylthioaniline derivative. Hirshfeld surface analysis was used to investigate the interactions within the crystal structure and DFT calculations were performed to study the frontier molecular orbitals of the title compound and also its electronic properties. ISSN 2056-9890

Structural commentary
The asymmetric unit of the title compound contains one molecule (Fig. 1). The central part of the molecule, including the six-membered ring, the S and N atoms, is fairly planar (r.m.s. deviation of 0.0142 for the eight fitted non-hydrogen atoms). The terminal methyl group deviates from this plane, atom C9 being displaced by À0.498 (4) Å to the mean plane. On the other side of the benzene ring, the C( O)CH 2 group also deviates slightly from the central plane in the opposite direction [deviations of 0.246 (3), 0.324 (3) and 0.489 (4) Å for atoms C2, O1 and C1, respectively] while the terminal Cl atom is almost in-plane [À0.007 (3) Å ] as a result of the N1-C2-C1-Cl1 torsion angle of À150.97 (18) . The amide functional group adopts a trans conformation with the four atoms nearly coplanar as shown by the O1-C2-N1-H1 torsion angle of À176.5 (19) . An intramolecular C-HÁ Á ÁO contact is observed (Table 1).

Supramolecular features
The main feature of the crystal packing is the presence of an N-HÁ Á ÁO hydrogen-bonded chain along the a-axis direction (Table 1) with graph set C(4). A view along the a axis showing the unit-cell packing is shown in Fig. 2a while the hydrogenbonded chain is illustrated in Fig. 2b. Apart from the hydrogen-bonding interactions,stacking is observed between inversion-related molecules. The distance between the ring centroids is 3.8890 (14) Å while the distance between the mean planes is 3.3922 (10) Å (slippage 1.904 Å ).

Figure 2
The molecular packing in the title compound: (a) view of the unit-cell contents shown in projection down the a axis; (b) view of the supramolecular chain perpendicular to the b axis originated by the N-HÁ Á ÁO hydrogen bonding (shown as red dashed lines). Displacement ellipsoids are drawn at the 50% probability level.

Figure 1
The molecular structure of the title compound, showing the atomlabelling scheme and displacement ellipsoids at the 50% probability level.

Computational Methods
DFT calculations were carried out to optimize the structure of the title compound using the CAM-B3LYP method and the 6-311G(d,p) basis set in an ethanol solvent within the Gaus-sian09 program package . DFT was chosen because it is a good compromise between the computational time and the description of the electronic correlation and has been found to be the best method to obtain accuracy for molecular geometry and electronic transition energies for organic molecules (Perdew et al., 2005;Niskanen et al., 2014;Arı et al., 2017;Miengmern et al., 2019). Time-dependent density functional theory (TD-DFT) (Jacquemin et al., 2009) was also used for the calculation of the electronic transitions of the title compound in conjunction with the polarized continuum model (PCM) for computation of the solvent effect . The theoretical absorption spectrum of the optimized structure of the titled compound in ethanol solvent was obtained using the TD-DFT method. The electronic properties such as E HOMO , E LUMO , and the energy gap between HOMO and LUMO of the optimized structure were also determined and the electronic structure of the title compound was visualized in order to understand the hyperconjugative interactions and charge delocalization.

Computational study
The DFT structure optimization of the compound was performed starting from the X-ray geometry at the CAM-B3LYP/6-311G(d,p) level of theory in an ethanol solvent. The experimental and calculated geometrical parameters such as bond lengths and angles show good agreement although most of the calculated bond lengths are slightly longer than X-ray values (about 0.01 Å ) because experimental values are for interacting molecules in the crystal lattice, whereas the computational method deals with an isolated molecule in the solvent phase. We used the TD-CAM-B3LYP/6-311G(d,p) method to predict the absorption spectrum of the title compound in ethanol, also considering the excited states in the calculation. The maximum absorption wavelength ( max ) of the title compound was obtained using this method. As seen in Table 2 The shape-index Hirshfeld surface of the title compound plotted in the range from À1.0000 to 1.0000 a.u.  View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.5588 to 1.0138 a.u.
the strong absorption at max = 250 nm and the oscillator strength f = 0.7144 are due to the S 0 !S 2 electronic transition with a wave function of two configurations [(HOMO-!LUMO) and (HOMO!L+4)]. The transition from HOMO to LUMO is mainly responsible for the formation of the maximum wavelength at 250 nm (Table 3). Fig. 6 shows the shape of molecular orbitals participating in the absorption at max = 250 nm. The electron density of the HOMO is mainly focused on the -C C-group in the phenyl ring, the sulfur atom, S-CH 3 , -NH C and -C O groups, whereas the LUMO is mainly focused on the C-C group in the phenyl ring. Therefore, the electronic transition from HOMO to LUMO mainly corresponds to the -* electron. The other excited states of the title compound have a very small intensity that is nearly forbidden by orbital symmetry considerations.

Synthesis and crystallization
The title compound was prepared by combining 4-(methylthio)aniline (5.0 g), chloroacetylchloride (4.30 mL) and triethylamine (7.50 mL) in dichloromethane (10 mL) at a controlled temperature using an ice bath. After stirring under an N 2 atmosphere for 24 h, the reaction mixture was poured into water and extracted with 30 mL CH 2 Cl 2 (3 times). The organic layer was dried with anhydrous Na 2 SO 4 . The mixture product was purified by column chromatography using 9:1 CH 2 Cl 2 /EtOAc as an eluent, affording a light-brown solid, yield 42%. Light-brown crystals were grown by evaporating a solution of the title compound in a mixture of dichloromethane and hexane (1:1) at room temperature. 1 Table 2 The electronic absorption spectrum of the title compound calculated by the TD-CAM-B3LYP/6-311G(d,p) method.

Figure 6
The molecular orbitals (MO) regarding information of the absorption spectrum of the title compound at the S 0 !S 1 and S 0 !S 2 states calculated by the CAM-B3LYP/6-311 G(d,p) method.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All C-bound H atoms were positioned geometrically and refined using a riding model with d(C-H) = 0.95 Å and U iso (H) = 1.2U eq (C) for aromatic and d(C-H) = 0.98 Å , U iso (H) = 1.5U eq (C) for methyl H atoms. The N-bound H atom (H1) was located in a difference-Fourier map and freely refined.

2-Chloro-N-[4-(methylsulfanyl)phenyl]acetamide
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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )