Synthesis and crystal structure of bis(tetraphenylphosphonium) hexabromodiselenate(II)-bis{dibromodiselenate(I)}, [PPh4](2)[Se2Br6(Se2Br2)(2)], the salt of a mixed-valence Bromoselenate(II,I) anion

摘要

The 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 P (1) over bar with Z = 2 and a = 11.2757(4) angstrom, b = 12.3347(5) angstrom, c = 12.4948(5) angstrom, alpha = 113.152(4)degrees, beta = 114.745(4)degrees, gamma = 91.208(3)degrees (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 Bi-, 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 mu(2)-bridging Br atoms. The contact between the Br, and the Se-I atom of the Se2Br2 molecule is 3.0872(5) angstrom and can be interpreted as a bond of the donor-acceptor type with the Br-t as donor and the Se2Br2 molecule as acceptor. The terminal Se-II - Br and mu Br-2 - Se-II bond lengths are 2.3654(4), 2.6699(5) A and 2.5482(5), 3.0265(5) angstrom, respectively The bond lengths in the coordinated Se2Br2 molecule are: Se-I - Se-I = 2.2686(5) angstrom, Se-I - Br = 2.3779(5) and 2.3810(5) angstrom.