5,6-Dihydro-1,4-dithiine-2,3-dicarboxylic anhydride

The heterocyclic fused ring geometry of the title compound coincides with the geometries of related molecules but without directed intermolecular contacts determining the crystal packing.


Structure description
The unit-cell parameters for the title compound have been reported previously [Grabowski, 1968;Cambridge Structural Database (CSD;Groom et al., 2016) refcode QQQDIA], but atomic coordinates are not available.Related compounds with reported three-dimensional atomic coordinates are the phthalamide (DTHPIM; Kirfel et al., 1975), the thieno (ZUHQUQ; Skabara et al., 2003) and the monohydroxy (USUMOL; Kurbangalieva et al., 2010) analogs, all of which are reported to crystallize in the monoclinic space groups P2 1 /c or P2 1 /n.We report here the three-dimensional structure of 5,6-dihydro-1,4-dithiine-2,3-dicarboxylic anhydride, which crystallizes in the triclinic space group P1 with unit-cell parameters in agreement with those reported by Grabowski.The molecule (Fig. 1) consists of furandione and dihydro-1,4-dithiine rings fused by a common carbon-carbon double bond (atoms C3 and C4) and is largely planar (r.m.s.deviation of 0.044 A ˚from the mean plane for all atoms except the CH 2 groups).The CH 2 groups are twisted about the molecular plane in order to reduce angle strain, with C1 data reports 0.323 (3) A ˚above and C2 0.528 (3) A ˚below, and an S1-C1-C2-S2 torsion angle of À70.39 (17) .The S-C bond lengths are 0.096 (7) A ˚shorter for bonds to sp 2 -hybridized C atoms than to those with sp 3 -hybridization (Table 1).The interior bond angles within the furandione ring are close to idealized values for a uniform pentagon, ranging from 107.44 (17) to 108.36 (18) .The O C-O angles have expected values of 121-122 for an sp 2 -hybridized center, while the external O C-C angles average 130.2 (7) in order to accommodate the geometry of the planar ring.These details agree well with the geometrical parameters for maleic anhydride [MLEICA (Marsh et al., 1962) and MLEICA01 (Lutz, 2001)].
The geometrical details for the related compounds listed above agree closely with those of the title compound.In particular, the S-C-C-S torsion-angle magnitudes range from 68.10 to 70.75 and the S-C bond lengths to sp 2 -hybridized C atoms average 0.087 (14) A ˚shorter than those to sp 3hybridized C atoms, with the phthalamide analog providing the closest agreement [average sp 3 -sp 2 bond length difference = 0.0995 (7) A ˚].A DFT geometry optimization in vacuo [B3LYP functional, cc-pTVZ basis set; GAMESS (Schmidt et al., 1993)] yields similar results, with an S-C-C-S torsion angle of À69.6 and S-C bond lengths of 1.730 and 1.829A ˚to sp 2 -and sp 3 -hybridized C atoms, respectively.An electrostatic potential plot with the optimized molecule visible is presented in Fig. 2.
The unit-cell packing of the title compound consists of sheets of molecules lying parallel to (112), with neighboring sheets related by inversion.The molecular planes are approximately coplanar with the sheet, with molecules forming head-to-tail rows parallel to [110] within the sheet.Neighboring rows within the sheet have opposite orientations, while rows on neighboring sheets straddle each other.This packing differs from that of similar molecules, where directed hydrogen bonding or short SÁ Á ÁO contacts feature prominently, with the head-to-tail rows of molecules in the title compound rationalized in terms of optimized dipole-dipole interactions.A ball-and-stick diagram of a sheet is presented in Fig. 3 and a unit-cell packing diagram viewed edge on to the sheets is presented in Fig. 4.
Electrostatic potential plot of the title molecule with the optimized geometry visible.Red represents the most negatively charged regions, while blue represents the most positively charged.

Figure 1
Displacement ellipsoid plot at the 50% probability level of the formula unit of the title compound, showing labels for non-H atoms.

Figure 3
Figure 3Ball-and stick diagram of the sheet structure viewed perpendiciular to (112).

Figure 4
Figure 4Ball-and-stick packing diagram of a unit cell, with axis labels viewed along[110], showing the stacking of four sheets to generate the three-dimensional structure.

Table 2
Experimental details.