Raman spectra of AlCl3-AlkCl and trends in species formation

The Raman spectra of LiCl-AlCl3, KCl-AlCl3 and CsCl-AlCl3 melts in the concentration range 50–100 mol.% AlCl3 are presented. The melt structure of these systems are discussed in terms of the species AlCl4−, Al2Cl7−, Al2Cl6 and higher polymers. The relative stabilities of the different species are studied as a function of the cation environment. Perturbation of the AlCl4− and Al2Cl7− vibrations due to the alkali counterion is found and interpreted in terms of change of symmetry, force constants and masses. The bridge structure of Al2Cl7− is discussed.