Reactivity of 1,3,5-Trithiacyclohexane and 1,3,5-Triselenacyclohexane towards molecular diiodine. Crystal structures of the diiodine adducts

The reactions between I-2 and the donors (D) 1,3,5-trithiacyclohexane (1) and 1,3,5-trithiacyclohexane (2), in methylene chloride and hot benzene respectively (1:1 I-2:D molar ratio) give the solid adducts 1 . I-2 (I) and 2 . I-2 (II) whose structures have been solved by X-ray diffraction. The use of an excess of diiodine up to the molar ratio 2:1 always gives II from 2, and 1 . 2I(2) (III) from 1. Compound I consists of polymeric chains in which each diiodine bridges between different 1 molecules, while II consists of discrete molecular units. The Raman nu(I-I) frequency and I-I bond distance in I fits well with the previously found linear correlation. This correlation suggests two different I-I bond distances for III. The comparison of the FT-IR and FT-Raman spectra for II is consistent with the three-body model for Se-I-I. The association constant between 1 and I-2 in methylene chloride has been also studied both by UV-visible and C-13 NMR spectroscopy, giving K values at 21 degrees C in good agreement.