A New Motif in Halogen Bonding: Cooperative Intermolecular S−Br⋅⋅⋅O, O⋅⋅⋅F, and F⋅⋅⋅F Associations in the Crystal Packing of α,ω-Di(sulfonyl bromide) Perfluoroalkanes

We recently reported the first examples of S−Cl⋅⋅⋅O halogen bonding complemented by short F⋅⋅⋅F contacts between neighboring chains that resulted in stabilized crystals of ClSO₂(CF₂)₄SO₂Cl and ClSO₂(CF₂)₆SO₂Cl. More recently, other researchers studied our crystallographic data further using an Independent Gradient Model (IGM), and they suggested if one goes beyond IUPAC's proposed ‘less than the sum of the van der Waals radii’ criterion that even more noncovalent interactions between fluorine atoms on neighboring chains as well as Cl⋅⋅⋅Cl, Cl⋅⋅⋅S, O⋅⋅⋅F, and O⋅⋅⋅S attractive interactions can be found. With that said, we have prepared samples of the related BrSO₂(CF₂)_nSO₂Br derivatives (where n=4, 6, 8, and others), which give rise to even stronger S−Br⋅⋅⋅O halogen bonding interactions complemented minimally by O⋅⋅⋅F and F⋅⋅⋅F intermolecular interactions as shown by X-ray crystallography and computational chemistry using IGM isosurface plots. Additional spectroscopic characterization (multinuclear NMR, FT-IR, and MS) of the disulfonyl bromide derivatives BrSO₂(CF₂)₄SO₂Br, BrSO₂(CF₂)₆SO₂Br, and BrSO₂(CF₂)₈SO₂Br has also been obtained as well as some preliminary spectroscopic evidence for BrSO₂(CF₂)₂SO₂Br and BrSO₂CF₂O(CF₂)₂OCF₂SO₂Br. The implication of these results toward the preparation of the corresponding disulfonyl iodides is discussed.