Crystal structures and Hirshfeld surfaces of two 1,3-benzoxathiol-2-one derivatives

The packing motifs in the title compounds both feature C—H⋯O interactions but they show distinctly different Hirshfeld surface fingerprints.

A recent study reported the syntheses and antifungal activities of some derivatives of tioxolone (Terra et al., 2018). In the present article we report the crystal structures and Hirshfeld surface analyses of two compounds with different substituents at the 6-position of the ring system obtained in that study, viz. 6-methoxy-1,3-benzoxathiol-2-one, C 9 H 8 O 3 S, (I), and 2-oxo-1,3-benzoxathiol-6-yl acetate, C 9 H 8 O 3 S, (II).

Figure 3
Fragment of a [111] hydrogen-bonded chain in (I); all hydrogen atoms except H5 and H7 have been omitted for clarity. Symmetry codes as in Table 1.

Figure 5
Hirshfeld fingerprint plot for (I) correspond to the short, classical O-HÁ Á ÁO hydrogen bond found in this structure (compare: McKinnon et al., 2007). In (I) and (II), the wingtips associated with the longer and presumably weaker C-HÁ Á ÁO bonds are far less pronounced.
When the fingerprint plots are decomposed into the separate types of contacts (McKinnon et al., 2007), some interesting differences arise (Table 3): as a percentage of surface interactions, HÁ Á ÁH contacts (i.e. van der Waals interactions) are far more prominent in (I) than in (II), which is comparable with EVOQEL, whereas CÁ Á ÁH/HÁ Á ÁC contacts are similar for the three structures. The OÁ Á ÁH/HÁ Á ÁO contacts are the most important contributors in all three structures, and in (II) they actually contribute a higher percentage to the surface than in EVOQEL, despite the fact that EVOQEL features both O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds and only one of its hydrogen atoms is not involved in such bonds (Byres & Cox, 2004). The CÁ Á ÁC contacts (associated with aromaticstacking) contribute a small percentage in (I) and (II) and about twice the amount in EVOQEL where the shortest centroid-centroid separation is 3.508 (2) Å . Despite the small percentage for (II), the Hirshfeld surface ( Fig. 8) clearly shows red spots associated with these contacts. The SÁ Á ÁH/HÁ Á ÁS contacts are similar in the three structures, and not insignificant at $10% of the surfaces, but they can hardly represent directional C-HÁ Á ÁS hydrogen bonds, as the shortest HÁ Á ÁS separations (3.21, 3.11 and 3.28 Å in (I), (II) and EVOQEL, respectively) are much longer than the van der Waals contact distance (Bondi, 1964) Table 3 Hirshfeld contact interactions (%).

Figure 8
Hirshfeld surface plot mapped over d norm for (II) showing red spots associated with short CÁ Á ÁC and CÁ Á ÁO contacts: the slightly smaller spots refer to the former. OÁ Á ÁS contacts have very different contributions in the three structures: negligible in (I), but clearly present in (II) and EVOQEL. This seems to correlate with the shortest SÁ Á ÁO contact distances of 3.623 (2), 3.2742 (10) and 3.341 (2) Å for (I), (II) and EVOQEL, respectively: the distance in (II) is actually slightly shorter than the van der Waals contact distance of 3.32Å for sulfur and oxygen,

Synthesis and crystallization
Compounds (I) and (II) were prepared as described previously (Terra et al., 2018) and recrystallized from methanol solution as colourless plates of (I) and colourless blocks of (II).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 4. The hydrogen atoms were geometrically placed (C-H = 0.95-0.99 Å ) and refined as riding atoms. The constraint U iso (H) = 1.2U eq (carrier) or 1.5U eq (methyl carrier) was applied in all cases. The methyl groups were allowed to rotate, but not to tip, to best fit the electron density.

6-Methoxy-1,3-benzoxathiol-2-one (I)
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.