Raman spectroscopy of ionic liquids derived from 1-n-butyl-3-methylimidazolium chloride and niobium chloride or zinc chloride mixtures

Anionic species formed in mixtures of 1-n-butyl-3-methylimidazolium chloride (BMICl) with different amounts of niobium pentachloride (NbCl5) or zinc dichloride (ZnCl2) were investigated by Raman spectroscopy. In the BMICl and NbCl5 ionic mixtures the presence of the anion NbCl6- was detected for all compositions (molar fraction, X-NbCl5) and a mixture of this anion and the neutral Nb2Cl10 in acid ones. Two different anions were observed for basic mixtures of BMICl and ZnCl2: ZnCl42- (0 < X-ZnCl2 < 0.35) and Zn2Cl(6)(2-) (X-ZnCl2 > 0.3), whereas for acidic ones three species were detected: Zn2Cl62- (XZnC2, < 0.7), Zn3Cl82- (X-ZnCl2 > 0.7) and Zn4Cl102- (X-ZnCl2 > 0.7). It has also been observed that in both cases, the formation of larger anions causes a shift of the C-H stretching modes to higher wavenumbers as the result of a decrease in the hydrogen bond between Cl and the hydrogens from the cation. Copyright (C) 2008 John Wiley & Sons, Ltd.