Vibrational modes and structure of liquid and gaseous zirconium tetrachloride and of molten ZrCl4–CsCl mixtures ‡

Raman spectra of liquid and gaseous zirconium tetrachloride and of molten ZrCl4–CsCl mixtures have been measured. Changes of the relative Raman intensities in the vapor phase, near and above the critical point, have established the dimerization reaction 2ZrCl4(g) ⇄ Zr2Cl8(g), ΔHR = –56.6 ± 1.1 kJ mol–1. Spectra of solid and molten zirconium chloride show that in the liquid phase ZrCl4 monomers are present in equilibrium with polymer-like (ZrCl4)n species. A systematic investigation of the Raman spectra of the solid mixtures formed upon cooling the ZrCl4–CsCl melts at different compositions has shown that apart from the known Cs2ZrCl6 a new compound with stoichiometry CsZr2Cl9 is also formed. The spectra of solid and molten Cs2ZrCl6 and CsZr2Cl9 show that ZrCl62– and the Zr2Cl9– are present in both phases. In molten ZrCl4–CsCl mixtures and at compositions xZrCl4 0.66) the spectra indicate an equilibrium between the ionic Zr2Cl9–, the ZrCl4 monomer and the (ZrCl4)n polymer-like species. All data suggest that the value of n is small and most probably hexamers and/or dimers are the predominant ‘polymer’ species in these melts.