Synthesis and crystal structure of 3-phenyl-1,4,2-dithiazole-5-thione

The first crystal structure is reported of a molecule containing the 1,4,2-dithiazole-5-thione heterocycle. The packing features aromatic π–π stacking, weak C—H⋯S interactions and short S⋯S interactions.

The 1,4,2-dithiazole-5-thione heterocycle is a member of a rich family of isomeric ring systems. Derivatives of 1,2,4-dithiazole-5-thione include xanthane hydride, which has been the subject of structural analysis (Stanford, 1963) and is used industrially as a sulfur-transfer agent in the vulcanization of rubber and the sulfuration of oligonucleotides. The crystal structure of the isomeric ring system 1,3,2-dithiazole-4-thione has also been reported (Oakley et al., 1987).
The incorporation of the preparation, isolation and structural characterization of heterocyclic compounds to demonstrate the chemistry of carboxylic acid derivatives in the undergraduate organic chemistry laboratory has been previously described (Nason et al., 2017). To date, our attention has been focused on the synthesis of derivatives of the 1,3,4-oxathiazol-2-one heterocycle because of the relative ease of preparation and, until recently, the limited research studying the chemistry of the heterocycle family. In our search for a new focus heterocycle, the small library of existing publications on the 1,4,2-dithiazole-5-thione derivatives coupled to the relative ease of synthesis made this ring system a target for investigation and we now describe the synthesis and crystal structure of the title compound, C 8 H 5 NS 3 .

Structural commentary
The structure of the title compound ( Fig. 1) reveals that the heterocycle and the aromatic ring are essentially co-planar [C8-C3-C2-S2 = À2.91 (13) ]. The C2-C3 [1.4721 (14) Å ] bond is not significantly shorter than the accepted value for a Csp 2 -Csp 2 single bond (1.48 Å ) but it is longer than the average (1.45 AE 0.03 Å ) of similar Csp 2 -Csp 2 inter-ring bonds found in the related oxathiazolone derivatives (Nason et al., 2017). The extension of delocalization between the rings is sufficient to direct the observed co-planarity. The sum of the internal angles of the heterocyclic ring (539.9 ) is almost ideal for five membered rings (540 ).
Within the heterocycle moiety, the molecule shows significant (p < 0.01) structural differences (Kooijman, 2005) to similar regions in the related oxathiazolone derivatives, and for reference, the comparison will be made to 5-phenyl-1,3,4oxathiazol-2-one (Schriver et al., 1995). In the title compound, the C2 N1 double bond [1.2961 (13) Å ] is significantly longer (and weaker) than in the oxathiazolone [1.268 (6) Å ] while the C1-S1 bond [1.7248 (11) Å ] is shorter [1.754 (5) Å ]. These differences are consistent with a higher degree of delocalization in the title heterocycle as compared to the oxathiazolone. The current -island structural model for oxathiazolone heterocycles has been suggested to explain the decarboxylation to form the nitrile sulfides (Krayushkin et al., 2010) with longer, weaker endocyclic C-S bonds consistent with lower extrusion temperatures (Zhu et al., 2017).
Conversely, in the title molecule the C1-S1 bond is shorter and stronger, which is consistent with the observed resistance of 1,4,2-dithiazole-5-thiones to thermally extrude CS 2 to form nitrile sulfides (Greig et al., 1985). The endocyclic C-S bonds are significantly (p < 0.01) asymmetric with the C1-S1 bond the shortest of the three bonds, consistent with a higher bond order and character while the C1-S2 bond [1.7363 (11) Å ] is longer but not as long as the C2-S2 bond [1.7587 (10) Å ]. This pattern of bond lengths is in agreement with a more extensive, and less localized, delocalization in this heterocycle than in the comparable oxathiazolone derivatives.

Supramolecular features
The extended structure of the title compound featurescentroid stacking (Fig. 2) The molecular structure of the title compound, showing anisotropic displacement ellipsoids projected at 50% probability.

Figure 2
Packing diagram illustrating centroid-stacking interactions down the baxis direction (a) between parallel-aligned ring systems with co-planar molecules flipped across an inversion centre [centroid-to-centroid distance = 3.712 (6) Å ] and packed back to back [centroid-to-centroid distance = 3.717 (6) Å ]. The three molecules are staggered with an angle of 166.698 (17) and two molecules fit within the the P1 unit cell. (Table 1; Fig. 3) and one chain of sulfur-sulfur interactions (Fig. 4). The packing of two molecules across an inversion centre results in one of two centroid-stacking interactions. The molecules exists as co-planar and parallel chains of heterocycles, with supramolecular contacts confirmed by the statistically constant centroid-to-centroid distances between rings in different adjacent chains [3.717 (6) and 3.712 (6) Å ] with the latter centroid-to-centroid distance across the inversion centre. The plane of the molecule is roughly perpendicular to the b axis and the molecular centroids form a chain-to-chain, stepwise angle [166.698 (17) ] on the a axis. Head-to-toe hydrogen-bonding interactions between C5 and C6 donors to the exocyclic thione S3 with HÁ Á ÁS distances of 2.96 and 3.11 Å , respectively (Fig. 3) form the primary cohesion along the a-and c-axis directions. In addition, the rest of the phenyl ring hydrogen atoms are involved with side-on, out-of-plane step-wise hydrogen bonds between H4 and N1 (2.89 Å ), H5Á Á ÁS1 (3.04 Å ), H7Á Á ÁS3 (3.06 Å ) and H8Á Á ÁS2 (3.10 Å ). The sulfur-sulfur interactions occur as a chain out of plane between the thione S3 and S1 atoms within the ring (Fig. 4). While the observed HÁ Á ÁS hydrogen bonding between the molecules is weak (AE van der Waals radii SÁ Á ÁH = 3.0 Å ), they aid the orientation of the molecules within the out-of-plane chains. In contrast, the SÁ Á ÁS contact distance [3.575 (11) Å ] may appear to be close to the accepted sum of the van der Waals radii (3.6 Å ) but when the known anisotropy of sulfur contacts [in plane SÁ Á ÁS contact 3.20 Å and perpendicular SÁ Á ÁS contact 4.06 Å (Constantinides et al., 2021)] are factored, it is revealed that the contact is a significant contributor to the supramolecular packing of the compound.

Database survey
A search of the Cambridge Structural Database (Version 5.41, September 2021; Groom et al., 2016) revealed that there are six crystal structures reported for molecules containing the neutral 1,4,2-dithiazole heterocyclic ring (Chu et al., 1993;Oakley et al., 1993Oakley et al., , 1994Feng et al., 2016). The thione moiety in the structure of 3-phenyl-1,4,2-dithiazole-5-thione, however, makes this the first crystal structure reported for this heterocyclic system with a thione substituent at the C1 position.

Synthesis and crystallization
A solution of trichloromethanesulfenyl chloride (10.17 g, 22.81 mmol) in chloroform (10.17 g) was added dropwise to a warmed solution of thiobenzamide (6.161 g, 44.91 mmol) in chloroform (240 ml) according to a literature procedure (Greig et al., 1985). The reaction mixture was refluxed for 4 h followed by evaporation in a crystallizing dish to a yelloworange residue (7.002 g). The crude product was recrystallized twice in 95% ethanol to give the product as bright-yellow crystalline needles (Fig. 5)  A packing diagram of the title compound showing interchain SÁ Á ÁS contacts of 3.575 (11) Å and the stepwise progression of the chains going down the b-axis, stepping towards the a-axis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All H atoms were geometrically placed (C-H = 0.95 Å ) and refined as riding atoms with U iso (H) = 1.2U eq (C). 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.