Concentration dependence of the coordination of Cl− ions to Ln3+ ions (Ln3+=rare earth ion) in anhydrous methanol LnCl3 solutions

Raman spectroscopic measurements were carried out for the anhydrous LnCl3·20MeOH·XLiCl solutions (Ln3+=Pr3+, Gd3+ and Ho3+, X=0-4) in both liquid and glassy states. Salt concentration dependence of the frequency for the Ln-Cl stretching Raman band (νLn-Cl) is examined in conjunction with the formation of chloro-rare earth complexes. We have obtained the very interesting results that the chloro-complexations of gadolinium and holmium ions in these solutions show very peculiar behavior as to the salt concentration dependence at room temperature: the νLn-Cl frequency increases with increasing concentration. On the other hand, the νLn-Cl frequency of the PrCl3·20MeOH·XLiCl solution shows normal behavior as to the salt concentration dependence: νLn-Cl decreases with increasing chloride concentration. We present a possible mechanism for this anomalous concentration dependence of coordination of Cl− ions to Ln3+ ions in anhydrous methanol LnCl3 solutions.