Ionic liquids based on FeCl3 and FeCl2.: Raman scattering and ab initio calculations

We have prepared ionic liquids by mixing either iron(IT) chloride or iron(III) chloride with 1-butyl-3-methylimidazolium chloride (BMIC). Iron(II) chloride forms ionic liquids from a mole ratio, of I FeCl2/3 BMIC to almost 1 FeCl2/1 BMIC. Both Raman scattering and ah initio calculations indicate: that FeCl42- is the predominant iron-containing species in these liquids. Iron(III) chloride forms ionic liquids from a mole ratio of 1 FeCl3/1.9 BMIC to 1.7 FeCl3/1 BMIC. When BMIC is in excess, Raman scattering indicates the presence of FeCl4-. When FeCl3 is in excess, Fe2Cl7- begins to appear and the amount of Fe2Cl7- increases with increasing amounts of FeCl3. Ionic liquids were also prepared from a mixture of FeCl2 and FeCl3 and are discussed. Finally, we have used both Hartree-Fock and density functional theory methods to compute the optimized structures and vibrational spectra for these species. An analysis of the results using an all-electron basis set, 6-31C*, as well as two different effective core potential basis sets, LANL2DZ and CEP-31G is presented.