Syntheses of THF Solutions of SeX₂ (X = Cl, Br) and a New Route to Selenium Sulfides SenS₈₋n (n = 1−5):  X-ray Crystal Structures of SeCl₂(tht)₂ and SeCl₂·tmtu

A simple and efficient synthesis of solutions of pure SeCl 2 in THF or dioxane (ca. 0.4 M) at 23 °C was achieved by treatment of elemental selenium with an equimolar amount of SO 2 Cl 2 . SeCl 2 was characterized by 77 Se NMR and Raman spectra. SeCl 2 forms 1:1 or 1:2 adducts with tetramethylthiourea (tmtu) or tetrahydrothiophene (tht), respectively. The crystal structure of SeCl 2 ·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 P 1̄, 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) Å 3, and Z = 2. The complex SeCl 2 (tht) 2 ( 2 ) adopts a square planar geometry with d (Se−Cl) = 2.4149(8) Å. Crystals of 2 are monoclinic, space group C 2/ 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 Ph 3 PS with SeCl 2 gives Ph 3 PCl 2 and a complex mixture of selenium sulfides Se n S 8 - n ( n = 1−5), which were identified by 77 Se NMR. Halogen exchange between SeCl 2 and Me 3 SiBr in THF yields thermally unstable SeBr 2 (ca. 0.4 M) characterized by 77 Se NMR and Raman spectra.