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

将三氟型稀土盐Ln(TfO)_3或Ln(Tf_2N)_3 （Ln = Nd, Eu）与相应阴离子1-乙基-3-甲基咪唑三氟甲磺酸盐（EMITfO）和1-乙基-3-甲基咪唑双（（三氟甲基）磺酰）酰胺（EMILTf_2N）溶解在咪唑型室温熔盐中，研究稀土离子在非水离子液体中的氧化还原行为。以1-乙基咪唑和三氟甲烷磺酸甲酯为原料，在干燥的1,1,1-三氯乙烷中反应制备了EMITfO。用1-乙基-3-甲基咪唑溴化剂（EMIBr）与二（三氟甲基）磺酰酰胺锂（LiTf_2N）在去离子水中反应，再用二氯甲烷萃取制备EMITf_2N；EMIBr是由1-甲基咪唑与溴乙烷在1,1,1-三氯乙烷中反应而得。得到的熔盐在120-150℃下真空干燥。3天以上。稀土盐在相应熔盐中的溶解度超过0.1 mol dm^<-3>。Ln(TfO)_3不溶于EMITf_2N，而Ln(Tf_2N)_3可溶于EMIITfO和EMITf_2N。循环伏安图表明，Eu^<2+>/Eu^<3+>的氧化还原电位在EMITfO中约为-0.9 V，在EMITf_2N中约为+0.3 V，在EMITf_2N中约为。在EMJTfO和EMITf_2N的1/1混合物（体积）中，-0.9 V vs. I_3^-/I^-。与TfO相比，Tf_2N^-阴离子的刘易斯碱度较低，这说明Tf_2N^-型室温熔盐是稀土离子阴极电解的理想溶剂。以三甲基己基溴化铵（TMHABr）与LiTf_2N反应制备了一种新型常温熔盐——三甲基己基铵双（（三氟甲基）磺酰）酰胺（TMHATf_2N）。Nd(Tf_2N)_3在TMHATf_2N中的溶解度大于0.1 mol dm^<-3>。由于TMHATf_2N的电化学窗口超过5.5 V，该熔盐也是一种很有前途的常温下稀土电沉积溶剂。

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.