The X-ray crystal structures of SeBr3SbF6 and TeBr3AsF6

Abstract

The crystal structures of SeBr3SbF6 and TeBr3AsF6 were determined by X-ray diffraction methods. Single crystals of SeBr3SbF6 are orthorhombic, space group P21212, with a = 9.454(5) Å, b = 12.623(6) Å, c = 8.272(4) Å, and Z = 4. Single crystals of TeBr3AsF6 are monoclinic, space group P21/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 C3v symmetry and the average Se—Br distance in SeBr3SbF6 is 2.269(8) Å and the average Br—Se—Br angle is 100.9(3)°. Analogous data for TeBr3AsF6 are: Te—Br = 2.432(3) Å; Br—Te—Br = 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 SeBr3AsF6 and SBr3MF6 (M = As, Sb) was studied by single crystal and powder diffraction methods. Salts containing the same anion were found to be isostructural.