Microwave Spectrum and Structure of Pentafluorosulfur Bromide

Abstract

Rotational spectra of pentafluorosulfur bromide observed with a video microwave spectrometer in the region 51–54 kMc/sec were fitted to the following molecular constants and structural parameters: S32F5Br79–B0 = 1172.153±0.002 Mc/sec, DJ = 0.0672±0.0400 kc/sec, DJK = 0, eQq(Br79) = 800±5 Mc/sec; S32F5Br81–B0 = 1159.875±0.002 Mc/sec, DJ = 0.1612±0.0400 kc/sec, DJK = 0, eQq(Br81) = 705±5 Mc/sec; θF–S–F(axial) = 88° (assumed), dS–Br = 2.1902±0.0065 Å, dS–F = 1.5970±0.0025 Å. The long S–Br bond distance is attributed to the steric interaction between the bromine atom and the F4 group. The value of the quadrupole coupling constant for the bromine nucleus suggests that the S–Br bond is predominantly covalent with some ionic character from resonance forms involving a positive charge on the bromine atom.