Synthesis and Crystal Structure of Bis(tetraphenylphosphonium) Hexabromo‐diselenate(II)‐bis{dibromodiselenate(I)}, [PPh4]2[Se2Br6(Se2Br2)2], the Salt of a Mixed‐valence Bromoselenate(II,I) Anion

Abstract

AbstractThe Red crystals of [PPh4]2[Se2Br6(Se2Br2)2] (1) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of tetraphenylphosphonium bromide. The crystal structure of 1 has been determined by X‐ray diffraction and refined to R = 0.0201 for 4024 reflections. The crystals are triclinic, space group $\rm P{\bar 1}$ with Z = 2 and a = 11.2757(4) Å, b = 12.3347(5) Å, c = 12.4948(5) Å, α = 113.152(4)°, β = 114.745(4)°, γ = 91.208(3)° (120(2) K). In the solid state the anion of 1 is built up of the Se2Br6 core and two Se2Br2 molecules each of which is linked to one of the trans‐positioned terminal Brt atoms of the Se2Br6 core. The central Se2Br6 part consists of a nearly planar arrangement of two planar SeBr4 units sharing a common edge through two μ2‐bridging Br atoms. The contact between the Brt and the SeI atom of the Se2Br2 molecule is 3.0872(5) Å and can be interpreted as a bond of the donor‐acceptor type with the Brt as donor and the Se2Br2 molecule as acceptor. The terminal SeII–Br and μ2Br–SeII bond lengths are 2.3654(4), 2.6699(5) Å and 2.5482(5), 3.0265(5) Å, respectively. The bond lengths in the coordinated Se2Br2 molecule are: SeI–SeI = 2.2686(5) Å, SeI–Br = 2.3779(5) and 2.3810(5) Å.