Syntheses of THF Solutions of SeX₂ (X = Cl, Br) and a New Route to Selenium Sulfides Se_nS_8-n (n = 1−5):  X-ray Crystal Structures of SeCl₂(tht)₂ and SeCl₂·tmtu

A simple and efficient synthesis of solutions of pure SeCl2 in THF or dioxane (ca. 0.4 M) at 23 °C was achieved by treatment of elemental selenium with an equimolar amount of SO2Cl2. SeCl2 was characterized by 77Se NMR and Raman spectra. SeCl2 forms 1:1 or 1:2 adducts with tetramethylthiourea (tmtu) or tetrahydrothiophene (tht), respectively. The crystal structure of SeCl2·tmtu (1) reveals a T-shaped geometry [d(Se−Cl) = 2.443(4) Å] with weak intramolecular Se···Cl interactions [d(Se−Cl) = 3.276(4) Å]. Crystals of 1 are triclinic, space group P1̄, with a = 8.473(3) Å, b = 9.236(3) Å, c = 7.709(4) Å, α = 109.90(3)°, β = 92.26(4)°, γ = 107.89(3)°, V = 532.9(4) Å3, and Z = 2. The complex SeCl2(tht)2 (2) adopts a square planar geometry with d(Se−Cl) = 2.4149(8) Å. Crystals of 2 are monoclinic, space group C2/c, with a = 15.6784(8) Å, b = 9.1678(4) Å, c = 9.1246(4) Å, β = 110.892(2)°, V = 1225.3(1) Å,3 and Z = 4. The reaction of Ph3PS with SeCl2 gives Ph3PCl2 and a complex mixture of selenium sulfides SenS8-n (n = 1−5), which were identified by 77Se NMR. Halogen exchange between SeCl2 and Me3SiBr in THF yields thermally unstable SeBr2 (ca. 0.4 M) characterized by 77Se NMR and Raman spectra.