Structure of monomeric and dimeric molecules of erbium tribromide from gas-phase electron diffraction data

The structural investigation of molecules in the vapour over erbium tribromide has been performed by synchronous gas-phase electron diffraction and mass spectrometry at T = 1095(10) K. The presence of a small amount (2.5%) of dimeric molecules was detected. For ErBr3 the thermal average bond length rg(Er–Br) = 258.2(6) pm and the valence angle ∠g(Br–Er–Br) = 116.0(14)° have been determined. This value of the average bond angle corresponds to the planar or near planar equilibrium structure of the monomeric molecule taking into account the shrinkage effect. The structural parameters of Er2Br6 have also been obtained.