Preparetion of Rare-earth Metal Films by Electrochemical Deposition from Non-aqueous Madia with High-purity

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Triflate-type rare earth salts, Ln(TfO)_3 or Ln(Tf_2N)_3 (Ln = Nd, Eu), were dissolved in imidazolium-type room temperature molten salts with corresponding anion, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITfO) and 1-ethyl-3-methylimidazoium bis((trifluoromethyl)sulfonyl)amide (EMILTf_2N), in order to investigate redox behavior of rare earth ions in the nonaqueous ionic liquids. EMITfO was prepared by the reaction of 1-ethylimidazol with Methyl trifluoromethanesulfonate in dried 1,1,1-trichloroethane. EMITf_2N was prepared by the reaction of 1-ethyl-3-methylimidazolium bromide (EMIBr) with lithium bis((trifluoromethyl)sulfonyl)amide (LiTf_2N) in deionized water followed by extraction with dichloromethane ; the EMIBr was obtained by the reaction of 1-methylimidazol with bromoethane in 1,1,1-trichioroethane. The resulting molten salts were dried in vacuo at 120-150 。C for more than 3 days.Solubility of the rare earth salts into the corresponding molten salts exceeds 0.1 mol dm^<-3>. Ln(TfO)_3 is not soluble in EMITf_2N, whereas Ln(Tf_2N)_3 soluble in both EMIITfO and EMITf_2N.Cyclic voltammograms show that the redox potentials of Eu^<2+>/Eu^<3+> were ca. -0.9 V in EMITfO, +0.3 V in EMITf_2N, and ca.. -0.9 V vs. I_3^-/I^- in 1/1 mixture (in volume) of EMJTfO and EMITf_2N.These phenomena are explained by a lower Lewis basicity of Tf_2N^- anion compared to TfO, suggesting Tf_2N^--type room temperature molten salts are promising solvents for cathode electrolysis of rare earth ions.A new ammonium-type room temperature molten salt, trimethylhexylammonium bis((trifluoromethyl)sulfonyl)amide (TMHATf_2N), was also prepared by the reaction of trimethylhexylammonium bromide (TMHABr) with LiTf_2N.Solubility of Nd(Tf_2N)_3 into the TMHATf_2N was more than 0.1 mol dm^<-3>. Since the electrochemical window of TMHATf_2N exceeds 5.5 V, the molten salt is also a promising solvent for electrodeposition of rare earths at ambient temperature.