Anomalous concentration dependence of the coordination behavior of Cl− ion to Ln3+ ion (Ln3+ = rare‐earth ion) in anhydrous LnCl3 alcohol solutions

Raman spectroscopic measurements were carried out for the anhydrous LnCl₃·20ROH·XLiCl solutions (Ln³⁺ = La³⁺− Lu³⁺, X = 0–3; ROH = MeOH, EtOH, n‐PrOH) in the liquid state. The salt concentration (X) dependence of the wavenumber for the Ln–Cl stretching Raman band (ν_Ln–Cl) is examined in conjunction with the formation of chloro‐rare‐earth complexes. We have obtained very intriguing results including the fact that the chloro complexations of the middle rare‐earth ions (e.g. gadolinium, holmium ions, etc.) in the MeOH and EtOH solutions show peculiar behavior with regard to the salt concentration dependence: the ν_Ln–Cl wavenumber increases with the increasing chloride concentration. However, the ν_Ln–Cl wavenumbers of the light and heavy rare‐earth (e.g. lanthanum, lutetium, etc.) salt solutions show normal behavior; i.e. ν_Ln–Cl decreases with the increasing chloride concentration. On the other hand, in the n‐PrOH solutions, the ν_Ln–Cl frequency in the solutions of all the rare‐earth elements exhibits a normal behavior. We now present a possible mechanism for this anomalous concentration dependence of coordination of Cl⁻ ions to Ln³⁺ ions in anhydrous LnCl₃ alcohol solutions. Copyright © 2007 John Wiley & Sons, Ltd.