Anomalous concentration dependence of the coordination behavior of Cl − ion to Ln 3+ ion (Ln 3+ = rare‐earth ion) in anhydrous LnCl 3 alcohol solutions

Raman spectroscopic measurements were carried out for the anhydrous LnCl 3 ·20ROH· X LiCl solutions (Ln 3+ = La 3+ − Lu 3+ , 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 Ln 3+ ions in anhydrous LnCl 3 alcohol solutions. Copyright © 2007 John Wiley & Sons, Ltd.