The crystal and molecular structure of syn-2,11-dithia[3,3]metacyclophane

The crystal structure of syn-2,11-dithia[3,3]metacyclophane, C 16 H 16 S 2 , has been determined by single crystal X-ray diffraction and refined to an R-value of 0.049. The crystal is monoclinic with cell dimensions a = 1898.2(5), b = 795.7(3), c = 924.1(4) pm, β = 100.03°(4). The space group is P2 1 /n with 4 molecules per cell, D m = 1.34 g cm −3 , D c = 1.317 g cm −3 . Of several possible syn conformations, the molecule is found in that with the largest SS distance of 697.4 pm. The benzenoid rings form a dihedral angle of 20.6°. The distance between the pair of aromatic H atoms which are ortho to two methylene groups is 273.0 pm, with 305.2 pm between the carbon atoms to which they are attached. Small angular distortions are observed at these carbon atoms. Mean bond lengths are: CS 181.0(12), CC (aromatic) 138.5(8), CC (bridge) 151.0(11) pm. Mean bond angles are: CSC 104°(1), SCC 115.4°(9). The CCC angles are in the range 117.9-122.7°. The molecule possesses an approximate (non-crystallographic) 2-fold axis of symmetry passing through the midpoints of C(8)C(18) and C(4)C(14). The aromatic rings are planar, with the methylene carbons 5-11 pm out of plane on the sulphur side. The S(1) is 171.8(2) pm from plane 1 and 136.8(2) pm from plane 2, while for S(2) the corresponding values are 136.0(2) and 175.3(2) respectively. 1 Hmr data have been re-examined and compared with those obtained for other cyclophanes, together with 13 Cmr data and are consistent with the fact that in solution 2,11-dithia[3,3]metacyclophane, 1 , exists as the syn-conformer with no appreciable participation of the anti-conformer. All related dithia[3,3]metacyclophanes which have internal aryl hydrogens (i.e., no internal substituents) likewise appear to be syn from 1 Hmr data.