Crystal structure, Hirshfeld surface analysis, interaction energy and DFT studies of (2Z)-2-(2,4-dichlorobenzylidene)-4-nonyl-3,4-dihydro-2H-1,4-benzothiazin-3-one

The title compound contains 1,4-benzothiazine and 2,4-dichlorophenylmethylidene units in which the dihydrothiazine ring adopts a screw-boat conformation. In the crystal, intermolecular C—HBnz⋯OThz (Bnz = benzene and Thz = thiazine) hydrogen bonds form chains of molecules extending along the a-axis direction which are connected to their inversion-related counterparts by C—HBnz⋯ClDchlphy (Dchlphy = 2,4-dichlorophenyl) hydrogen bonds and C—HDchlphy⋯π (ring) interactions. These double chains are further linked by C—HDchlphy⋯OThz hydrogen bonds to form stepped layers approximately parallel to (012).


Figure 1
The molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.

Figure 3
Perspective view of one double chain and half of a second showing the C-H Dchlphy Á Á ÁO Thz (Dchlphy = 2,4-dichlorophenyl and Thz = thiazine) hydrogen bond connecting them. Intermolecular interactions depicted as in Fig. 2.

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 by using Crystal Explorer 17.5 (Turner et al., 2017). 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, and the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the van der Waals radii (Venkatesan et al., 2016). The bright-red spots appearing near O1 and hydrogen atom H15 indicate their roles as the respective donors and/or acceptors; 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. 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 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 suggests that there are nointeractions in (I). The overall two-dimensional fingerprint plot, Fig. 7a, and those delineated into HÁ Á ÁH, CÁ Á ÁH/HÁ Á ÁC, ClÁ Á ÁH/H Á Á Á Cl, OÁ Á ÁH/HÁ Á ÁO and SÁ Á ÁH/ HÁ Á ÁS contacts (McKinnon et al., 2007) are illustrated in Fig. 7b-f, respectively, together with their relative contributions to the Hirshfeld surface. The most important interaction is HÁ Á ÁH (Table 2), contributing 44.7% to the overall crystal packing, which is reflected in Fig. 7b as widely scattered points of high density due to the large hydrogen content of the molecule with the tip at d e = d i = 1.09 Å . The presence of C-HÁ Á Á interactions is indicated by the fringed pairs of characteristic wings in the fingerprint plot delineated into CÁ Á ÁH/ HÁ Á ÁC contacts (Fig. 7c View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.6343 to 1.4076 a.u.

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 7
The full two-dimensional fingerprint plots for the title compound

DFT calculations
The optimized structure of the title compound, (I), in the gas phase was generated theoretically via density functional theory (DFT) using the standard B3LYP functional and 6-311G(d,p) basis-set calculations as implemented in GAUS-SIAN 09 (Frisch et al., 2009). The theoretical and experimental results are in good agreement (Table 3). The highest-occupied molecular orbital (HOMO), acting as an electron donor, and the lowest-unoccupied molecular orbital (LUMO), acting as an electron acceptor, are very important parameters for quantum chemistry. When the energy gap is small, the molecule is highly polarizable and has high chemical reactivity. The DFT calculations provide some important information on the reactivity and site selectivity of the molecular framework. E HOMO and E LUMO clarify the inevitable charge-exchange collaboration inside the studied material, and together with the electronegativity (), hardness (), potential (), electrophilicity (!) and softness () are recorded in Table 4. The significance of and is to evaluate both the reactivity and stability. The electron transition from the HOMO to the LUMO energy level is shown in Fig. 9. The HOMO and LUMO are localized in the plane extending from the whole (2Z)-2-[(2,4-dichlorophenyl)methylidene]-4-nonyl-3,4-dihydro-2H-1,4-benzothiazin-3-one ring.

Figure 9
The energy band gap of the title compound.

Table 3
Comparison of the selected (X-ray and DFT) geometric data (Å , ).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 5. The two carbon atoms at the end of the nonyl chain, C23 and C24, are disordered in a 0.562 (4)/ 0.438 (4) ratio. These were refined with restraints that the two components have comparable geometries. The H atoms on these carbons as well as those on C22 were included as riding contributions in idealized positions (C-H = 0.99 Å with U iso (H) = 1.5U eq (C).

Funding information
The support of NSF-MRI grant No. 1228232 for the purchase of the diffractometer and Tulane University for support of the   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 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. The two carbons at the end of the nonyl chain, C23 and C24, are disordered in a 0.562 (4)/0.438 (4) ratio. These were refined with restraints that the two components have comparable geometries. The H-atoms on these carbons as well as those on C22 were included as riding contributions in idealized positions.