The X-ray crystal structures of SeBr3SbF6 and TeBr3AsF6

• Published in: Canadian journal of chemistry 1980-04, Vol.58 (8), p.851-857
• Main Authors: Passmore, Jack, Richardson, E. Keith, Whidden, Tom K, White, Peter S
• Format: Article
• Language: English
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v80-132

The crystal structures of SeBr 3 SbF 6 and TeBr 3 AsF 6 were determined by X-ray diffraction methods. Single crystals of SeBr 3 SbF 6 are orthorhombic, space group P2 1 2 1 2, with a = 9.454(5) Å, b = 12.623(6) Å, c = 8.272(4) Å, and Z = 4. Single crystals of TeBr 3 AsF 6 are monoclinic, space group P2 1 /c, with a = 7.994(3) Å, b = 10.118(3) Å, c = 12.306(3) Å, β = 99.66(2)°, and Z = 4. The cations in each salt have essentially C 3v symmetry and the average SeBr distance in SeBr 3 SbF 6 is 2.269(8) Å and the average BrSeBr angle is 100.9(3)°. Analogous data for TeBr 3 AsF 6 are: TeBr = 2.432(3) Å; BrTeBr = 97.92(9)°. Anions in each salt are essentially octahedral. The bond angles in isoelectronic Group V and Group VI trihalide molecules and cations are compared and found to be very similar. However, those found for Group VI trihalide cations are greater than (5 pairs) those observed in isoelectronic Group V molecules determined in the solid state, and angles estimated for Group VI cations in gas phase are greater (8 pairs) than those found for the related gas phase Group V trihalide partners. This result implies that geometries, at least in part, are determined by the relative sizes of the constituent atoms. The crystallography of the related salts SeBr 3 AsF 6 and SBr 3 MF 6 (M = As, Sb) was studied by single crystal and powder diffraction methods. Salts containing the same anion were found to be isostructural.