N-Saccharinylmethyl ether

In the title molecule [systematic name: 1,1,1′,1′-tetraoxo-2,2′-(oxydimethylene)bi(1,2-benzothiazol-3-one)], C16H12N2O7S2, the benzisothiazole ring systems are individually planar [maximum deviations of 0.0497 (13) and 0.0195 (19) Å] and their mean planes are inclined at a dihedral angle of 62.76 (4)°. The crystal structure is stabilized by weak intermolecular C—H⋯O interactions. Two O atoms bonded to two S atoms and four aryl H atoms belonging to two symmetry-related molecules lying about an inversion center form a hydrogen-bonded 10-membered ring with graph-set notation R 4 2(10).


Comment
The derivatives of saccharin have found applications as bioactive substances (Plath et al., 1998;Salzburg et al., 1987). They are considered to be the most potent orally active human leucocyte elastase (HLE) inhibitors for the treatment of asthma and other inflammatory diseases (Kapui et al., 2003). Continuing our investigations in the synthesis and development of new saccharin derivatives (Ahmad et al., 2010;Siddiqui et al., 2010) with medicinal potentials, we now report the crystal structure of a novel compound in this paper.
The title compound is presented in Fig. 1. The benzisothiazole ring systems are individually planar with maximum deviations being 0.0497 (13) and 0.0195 (19) Å for S1 and C15 atoms from the mean-planes S1/N1/C1-C7 and S2/N2/ C9-C15, respectively; the mean-planes are inclined at 62.76 (4)° with respect to each other. The structure is devoid of classical hydrogen bonds. However, intramolecular and intermolecular interactions of the type C-H···O are present in the structure. Two oxygen atoms bonded to two S atoms and four aryl hydrogen atoms belonging to two symmetry related molecules lying about inversion center form a hydrogen bonded ten membered ring which may be described in the graph set notation as R 4 2 (10) (Bernstein et al., 1995); details have been given in Tab. 1 and Fig. 2.
The bond distances and angles in the title molecule agree well with the cortresponding bond distances and angles reported in closely related compounds (Ahmad et al., 2009;Gul et al., 2010;Khalid et al., 2010;Siddiqui et al., 2007;2008).

Experimental
The synthesis of the title compound will be reported in a future paper. Suitable crystals of the title compound were grown from a solution of CHCl 3 by slow evaporation at room temperature.

Refinement
Though all the H atoms could be distinguished in the difference Fourier map the H-atoms were included at geometrically idealized positions and refined in riding-model approximation with the following constraints: C-H distances were set to 0.95 and 0.99 Å, for aryl and methylene H-atoms, respectively, and U iso (H) were allowed at 1.2U eq (C). The final difference map was essentially featurless. Fig. 1. The title molecule with the displacement ellipsoids plotted at 50% probability level (Farrugia, 1997

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 > σ(F 2 ) is used only for calculating Rfactors(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.