On the structure of liquid antimony pentafluoride

The liquid structure of antimony pentafluoride at room temperature has been investigated using neutron and high-energy X-ray diffraction and subsequently modelled using Empirical Potential structure refinement. The neutron diffraction measurements show that each antimony centre is surrounded by 6 fluorine atoms; four at a non-bridging distance of 1.86 ± 0.03 Å and two bridging fluorines at a distance of 2.03 ± 0.06 Å. The X-ray data show an additional peak at 3.93 ± 0.03 Å attributed to antimony-antimony contacts. The diffraction data were fit to three models; cis-monomer, isolated tetramer and cis-linked chains. The X-ray data rule out the cis-monomer model but good fits are obtained for the isolated tetramer and cis-linked chain models. It is argued that the liquid is comprised of chains of cis-linked tetrameric building blocks when these data and modelling results are considered in light of NMR measurements.