Structure of molten iron chloride: Neutron scattering and modeling

Neutron-diffraction measurements of molten FeCl₃, combined with model calculations and computer simulations, show that on melting the local structure of Fe changes from an octahedral to a tetrahedral environment. A similar change is observed in AlCl₃, in contrast to YCl₃, for example, where the octahedral coordination of Y is preserved on melting. The local structure of the liquid can be described in terms of Fe₂Cl₆ molecular units, similar to those observed in the vapor phase but with strong intermolecular interactions. Detailed information about the orientational correlations between molecules is derived from the simulations and compared with recent results on another molecular liquid, propylene glycol.