Vibrational modes and structure of molten iron(III) chloride

Raman spectra of dark brown-black iron(III) chloride melts have been obtained at 600 K using resonance and micro-Raman techniques. The main polarized bands seen in the spectra are at 310, 414 and 452 cm−1 and their relative intensities depend on the frequency of the laser excitation line. The data are interpreted to indicate that the predominant species in the melt are Fe2Cl6 bitetrahedral molecules plus charged molecular species which are formed according to the dissociation scheme: 2Fe2Cl6 ⇌ Fe2Cl5++Fe2Cl7−. The proposed liquid structure accounts for both the near ionic conductivity of the melt and the average coordination number of iron(III) in the melt, found to be ∼3.8 by neutron diffraction.