Reaction of Selenium with Bromine in the Presence of Methyltriphenylphosphonium Bromide: Syntheses and Crystal Structures of [PMePh3](2)[Se2Br6] and [PMePh3](2)[SeBr6(SeBr2)(2)]

摘要

The brown crystals of [PMePh3](2)[Se2Br6] (1) and red crystals of [PMePh3](2)[SeBr6(SeBr2)(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 I crystallizes in the monoclinic space group P2(1) with the cell dimensions a = 13.202(5) angstrom, b = 11.954(4) angstrom, c = 13.418(6) angstrom, beta = 93.08(4)degrees (193(2)). The crystals of 2 are tri-clinic, space group P (I) over bar with the cell dimensions a 10.266(3) angstrom, b = 11.31](3) angstrom, c = 11.619(2) angstrom, alpha = 108.87(2)degrees, beta= 105.72(2)degrees, gamma = 99.40(2)degrees (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 SeBr4 units sharing a common edge through two mu-bridging Br atoms. The terminal Se-II-Br bonds are 21.3984(11) and 2.4273(11) angstrom, whereas the bridging mu Br-Se-II bonds are 2.7817(11) and 2.9081(12) angstrom. In the solid state the trinuclear [SeBr6(SeBr2)(2)](2-) anion of 2 is centrosymmetric too and contains a nearly regular [SeBr6] octahedron where the four equatorial bromo ligands each have developed bonds to the Se-II atoms of the SeBr2 molecules. The contacts between the bridging bromo and the Se-II atoms of the SeBr2 molecules are 3.0603(15) and 3.1043(12) angstrom, and can be interpreted as bonds of the donor-acceptor type with the bridging bromo ligands as donors and the SeBr2 molecules as acceptors. The Se-IV-Br distances are in the range 2.5570(9)-2.5773(11) angstrom and the Se-II-Br bond lengths in coordinated SeBr2 molecules - 2.3411(12) and 2.3421 (10) angstrom.