A Raman spectroscopic study of liquid boron(III) bromide

The Raman spectrum of liquid boron(III) bromide was found to contain evidence of the dimeric species (BBr3)2. Quantitative Raman spectroscopic measurements of the intensity of the ν(BBr) symmetric stretching band at 280 cm−1 in the spectrum of liquid boron(III) bromide over the temperature range 233–293 K have been made. Dimerisation to the extent of about 2% was observed over this temperature range, significantly less than was previously observed for boron(III) chloride. An average enthalpy of boron—bromine bond formation for the dimeric species, ΔHO = −0.9 ± 0.8 kJ mol−1, has been evaluated. The results are discussed in relation to the Lewis acid strengths of boron(III) chloride and bromide.