Ga-71 NMR spectroscopy of solutions of gallium tribromide in aromatic solvents

The Ga-71 NMR spectra of solutions of gallium tribromide in different aromatic solvents have been recorded, and dependences of chemical shift on concentration, temperature and solvent observed. Such effects are absent in the corresponding solutions of Me3Ga. The Ga-71 chemical shift changes are consistent with the dissociation of the dimeric form of gallium tribromide to the monomer, as observed in the gas phase, but a study of effect of added H2O or Et2O indicates that solutions of gallium tribromide contain no monomeric species and the changes are best accounted for in terms of rapid chemical exchange between two different dimeric forms of gallium tribromide, one closed and the other half-open. With increasing solvating power of the aromatic solvent, the equilibrium between these dimeric structures favours the half-open solvated species.