Structural and Electrochemical Properties of YbIII in Various Ionic Liquids

Solvation and ligand exchange reactions of ytterbium(III) as a model for the late trivalent f-elements have been studied in triflate and bistriflylamide ionic liquids (ILs) with the purpose of contributing to a wider understanding of f-element organometallic catalysis, as well as separation and nuclear fuel reprocessing, in ILs. Using the compounds [C(4)mpyr](3)[Yb(OTf)(6)] and [C(4)mpyr][Yb(Tf2N)(4)] [C(4)mpyr = N-methyl-N-propylpyrrolidinium; OTf = triflate, trifluoromethanesul.fonate; Tf2N = bistriflylamide, bis(trifluoromethanesulfonyl)amide] we were able to structurally characterize the local surroundings of Yb3+ in the ILs [C(4)mpyr][OTf] and [C(4)mpyr][Tf2N] unequivocally. The formation of [C(4)mpyr](3)[Yb(OTf6]-[C(4)mpyr][Tf2N] from a solution of Yb(Tf2N)(3) in [C(4)mpyr][OTf] shows that the stronger coordinating OTf- anion completely replaces the less Lewis basic Tf2N- anion in the first coordination sphere of the lanthanide ion. As expected, such a ligand exchange could not be observed for Yb(OTf)(3) in [C(4)mpyr][Tf2N]. The ion exchange in the lanthanide coordination sphere can be efficiently monitored by means of cyclic voltammetry (CV). CV measurements also indicate that Yb3+ adopts a mixed OTf-/Tf2N- coordination environment when Yb(OTf)(3) is dissolved in [C(4)mpyr][Tf2N]. The measured half-wave potentials of the studied systems can be linked to the electron-donor properties of the metal cation.