Vibrational Spectra and Molecular Symmetry of Diboron Tetrabromide in the Crystalline and Fluid States

Abstract

The infrared spectra of B2Br4 have been studied from 4000 to 33 cm−1 in the gaseous and crystalline states. The Raman spectra of the liquid at low temperatures and of the crystalline solid have been studied to 30 and 40 cm−1, respectively. Eleven of the twelve vibrational modes have been assigned whereas the low-lying torsional mode is calculated to be between 15 and 20 cm−1. Based on the vibrational analysis, it is concluded that the staggered D2d conformation is maintained in both the fluid and crystalline states. This behavior is contrary to what has been observed for both the B2F4 and B2Cl4 molecules. It is concluded that the increased steric interactions which would occur in the planar form preclude this conformation for the bromide.