Reaction of Selenium with Bromine in the Presence of Methyltriphenylphosphonium Bromide: Syntheses and Crystal Structures of [PMePh 3 ] 2 [Se 2 Br 6 ] and [PMePh 3 ] 2 [SeBr 6 (SeBr 2 ) 2 ]

The brown crystals of [PMePh 3 ] 2 [Se 2 Br 6 ] ( 1 ) and red crystals of [PMePh 3 ] 2 [SeBr 6 (SeBr 2 ) 2 ] ( 2 ) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of methyltriphenylphosphonium bromide. The crystal structures of 1 and 2 has been determined by the X‐ray methods and refined to R = 0.0373 for 2397 reflections and 0.0397 for 3417 reflections, respectively. The salt 1 crystallizes in the monoclinic space group P 2 1 / n with the cell dimensions a = 13.202(5) Å, b = 11.954(4) Å, c = 13.418(6) Å, β = 93.08(4)° (193(2)). The crystals of 2 are triclinic, space group $P{\bar 1}$ with the cell dimensions a = 10.266(3) Å, b = 11.311(3) Å, c = 11.619(2) Å, α = 108.87(2)°, β = 105.72(2)°, γ = 99.40(2)° (193(2) K). In the solid state structure of 1 the dinuclear hexabromo‐diselenate(II) anion is centrosymmetric and consists of two distorted almost square planar SeBr 4 units sharing a common edge through two μ ‐bridging Br atoms. The terminal Se II –Br bonds are 2.3984(11) and 2.4273(11) Å, whereas the bridging μ Br–Se II bonds are 2.7817(11) and 2.9081(12) Å. In the solid state the trinuclear [SeBr 6 (SeBr 2 ) 2 ] 2− anion of 2 is centrosymmetric too and contains a nearly regular [SeBr 6 ] octahedron where the four equatorial bromo ligands each have developed bonds to the Se II atoms of the SeBr 2 molecules. The contacts between the bridging bromo and the Se II atoms of the SeBr 2 molecules are 3.0603(15) and 3.1043(12) Å, and can be interpreted as bonds of the donor‐acceptor type with the bridging bromo ligands as donors and the SeBr 2 molecules as acceptors. The Se IV –Br distances are in the range 2.5570(9)–2.5773(11) Å and the Se II –Br bond lengths in coordinated SeBr 2 molecules – 2.3411(12) and 2.3421(10) Å.