Crystal structure, Hirshfeld surface and crystal void analysis, intermolecular interaction energies, DFT calculations and energy frameworks of 2H-benzo[b][1,4]thiazin-3(4H)-one 1,1-dioxide

In the title compound, the thiazine ring exhibits a screw-boat conformation. In the crystal, corrugated layers of molecules parallel to the ab plane are formed by N—H⋯O and C—H⋯O hydrogen bonds together with C—H⋯π(ring) and S=O⋯π(ring) interactions. The layers are connected by additional C—H⋯O hydrogen bonds and π-stacking interactions.


Figure 1
The title molecule with atom labelling and displacement ellipsoids drawn at the 50% probability level.
Cg2 is the centroid of the C1-C6 benzene ring.

Figure 2
The crystal structure of (I) viewed along the c axis with N-H� � �O and C-H� � �O hydrogen bonds depicted, respectively, by violet and black dashed lines.C-H� � ��(ring) and C O� � ��(ring) interactions are depicted, respectively, by green and dark-pink dashed lines and noninteracting hydrogen atoms are omitted for clarity.

Figure 3
The crystal structure of (I) viewed along the b axis with N-H� � �O and C-H� � �O hydrogen bonds depicted, respectively, by violet and black dashed lines.C-H� � ��(ring), C O� � ��(ring) and slipped �-stacking interactions are depicted, respectively, by green, dark-pink and orange dashed lines.Non-interacting hydrogen atoms are omitted for clarity.

Hirshfeld surface analysis
To visualize the intermolecular interactions in the crystal of (I), a Hirshfeld surface (HS) analysis (Hirshfeld, 1977) was carried out with Crystal Explorer (Spackman et al., 2021).In the HS plotted over d norm in the range À 0.4976 to 1.2253 a.u.(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 (distant contact) than the van der Waals radii, respectively (Venkatesan et al., 2016).The bright-red spots 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)  View of the three-dimensional Hirshfeld surface of (I) plotted over d norm .

Figure 5
View of the three-dimensional Hirshfeld surface of (I) plotted over electrostatic potential energy using the STO-3 G basis set at the Hartree-Fock level of theory.

Figure 6
Hirshfeld surface of (I) plotted over shape-index.

Figure 7
The The large number of H� � �O/O� � �H, H� � �H and H� � �C/C� � �H interactions suggest that van der Waals interactions play the major role in the crystal packing (Hathwar et al., 2015).
The strength of the crystal packing is important for determining the response to an applied mechanical force.If the crystal packing results in significant voids, then the molecules are not tightly packed and a small amount of applied external mechanical force may easily break the crystal.To check the mechanical stability of the crystal, a void analysis was performed by adding up the electron densities of the spherically symmetric atoms contained in the asymmetric unit (Turner et al., 2011).The void surface is defined as an isosurface of the procrystal electron density and is calculated for the whole unit cell where the void surface meets the boundary of the unit cell and capping faces are generated to create an enclosed volume.The volume of the crystal voids (Fig. 9a,b) and the percentage of free space in the unit cell are calculated as 75.4A ˚3 and 9.3%, respectively.Thus, the crystal packing appears compact and the mechanical stability should be substantial.
Energy frameworks combine the calculation of intermolecular interaction energies with a graphical representation of their magnitude (Turner et al., 2015).Energies between molecular pairs are represented as cylinders joining the centroids of pairs of molecules with the cylinder radius proportional to the relative strength of the corresponding interaction energy.Energy frameworks were constructed for E ele (shown in Fig. 10), E dis and E tot .The evaluation of the electrostatic, dispersion and total energy frameworks indicate that the stabilization is dominated via the electrostatic energy contribution in the crystal structure of (I).

DFT calculations
The optimized structure of (I) was computed in the gas phase using density functional theory (DFT) with the standard B3LYP functional and 6-311 G(d,p) basis-set calculations (Becke, 1993), employing the GAUSSIAN 09 software (Frisch et al., 2009).The theoretical and experimental results exhibit a good agreement, as summarized in Table 2.
The highest-occupied molecular orbital (HOMO), functioning as an electron donor, and the lowest-unoccupied molecular orbital (LUMO), acting as an electron acceptor, serve as vital parameters in quantum chemistry.A small energy gap signifies high molecular polarizability and enhanced chemical reactivity.The DFT calculations provided crucial insights into the reactivity and site selectivity of the molecular framework.Parameters such as E HOMO and E LUMO , electronegativity (�), hardness (�), dipole moment (�), electrophilicity (!) and softness (�) are compiled in Table 3.Both � and � are essential for assessing reactivity and stability.The electron transition from HOMO to LUMO energy levels is depicted in Fig. 11

Figure 10
The energy framework for the electrostatic energy, viewed down the b axis for a cluster of molecules, where the a axis is vertical and the c axis is horizontal.The cylindrical radius is proportional to the relative strength of the corresponding energy and adjusted to the scale factor of 80 with a cut-off value of 5 kJ mol À 1 within 2 � 2 � 2 unit cells.

Figure 11
The energy band gap of (I).

Synthesis and crystallization
3,4-Dihydro-2H-1,4-benzothiazin-3-one (1.2 mmol) was dissolved in 3 ml of acetic acid and added dropwise into a solution of potassium permanganate (1.81 mmol) in 6 ml of water.After stirring for one h at room temperature, a solution of sodium thiosulfate pentahydrate (20% wt ) was added to react with excessive potassium permanganate.The precipitate obtained was filtered and recrystallized from ethanol to yield single-crystals suitable for X-ray structure analysis..

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. H-atoms attached to carbon were placed in calculated positions (C-H = 0.95-0.99A ˚) and were included as riding contributions with isotropic displacement parameters 1.2 or 1.5 times those of the attached atoms.That attached to nitrogen was placed in a location derived from a difference map and refined with a DFIX 0.91 0.01 instruction.
Two reflections affected by the beamstop were omitted from the final refinement.

Special details
Experimental.The diffraction data were obtained from 9 sets of frames, each of width 0.5° in ω or φ, collected with scan parameters determined by the "strategy" routine in APEX4.The scan time was 15 sec/frame.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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å
Figure 4 full two-dimensional fingerprint plots for the title compound, showing (a) all interactions, (b) H� � �O/O� � �H, (c) H� � �H, (d) H� � �C/ C� � �H, (e) O� � �C/C� � �O, (f) C� � �C, (g) H� � �N/N� � �H, (h) O� � �O and (i) C� � �N/N� � �C interactions.The d i and d e values are the closest internal and external distances (in A ˚) from given points on the Hirshfeld surface contacts.N� � �H, O� � �O and C� � �N/N� � �C contacts(McKinnon et al., 2007) are illustrated in Fig.7b-i, respectively, together with their relative contributions to the Hirshfeld surface.The most important interaction is H� � �O/O� � �H, contributing 49.4% to the overall crystal packing, which is reflected in Fig.7b, where the symmetric pair of spikes is observed with the tips at d e + d i = 1.98A ˚.The H� � �H contacts contribute 23.0% to the overall crystal packing, which is reflected in Fig.7cas widely scattered points of high density due to the large hydrogen content of the molecule with the tip at d e = d i = 1.13A ˚.In the presence of C-H� � �� interactions, the pair of characteristic wings in the fingerprint plot delineated into H� � �C/C� � �H contacts, Fig.7d, make a 14.1% contribution to the HS and viewed with the tips at d e + d i = 2.59 A ˚.The wing pair of C� � �O/O� � �C contacts (Fig.7e) with 4.9% contribution to the HS is viewed at d e + d i = 3.30A ˚.The C� � �C contacts (Fig.7f) appearing as a bulletshaped distribution of points make a contribution of 3.7% to the HS with the tip at d e = d i = 1.70A ˚.The spikes of H� � �N/ N� � �H contacts (Fig.7g) with 3.2% contribution to the HS are viewed at d e + d i = 2.75 A ˚. Finally, the O� � �O (Fig.7h) and C� � �N/N� � �C (Fig.7i) contacts contribute 1.3% and 0.4%, respectively, to the HS.The Hirshfeld surface representations with the function d norm plotted onto the surface are shown for the H� � �O/O� � �H, H� � �H and H� � �C/C� � �H interactions in Fig.8a-c, respectively.The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the packing.

Figure 9
Figure 9 Graphical views of voids in the crystal packing of (I), (a) along the a axis and (b) along the b axis.

Table 2
Comparison of the selected (X-ray and DFT) geometric data (A ˚, � ).

Table 4
Experimental details.
Computer programs: APEX4 and SAINT