Structural and Electrochemical Properties of Yb^III in Various Ionic Liquids

Abstract

Abstract 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(Tf 2 N) 4 ] [C 4 mpyr = N ‐methyl‐ N ‐propylpyrrolidinium; OTf = triflate, trifluoromethanesulfonate; Tf 2 N = bistriflylamide, bis(trifluoromethanesulfonyl)amide] we were able to structurally characterize the local surroundings of Yb 3+ in the ILs [C 4 mpyr][OTf] and [C 4 mpyr][Tf 2 N]unequivocally. The formation of [C 4 mpyr] 3 [Yb(OTf) 6 ][C 4 mpyr][Tf 2 N] from a solution of Yb(Tf 2 N) 3 in [C 4 mpyr][OTf] shows that the stronger coordinating OTf – anion completely replaces the less Lewis basic Tf 2 N – 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][Tf 2 N]. The ion exchange in the lanthanide coordination sphere can be efficiently monitored by means of cyclic voltammetry (CV). CV measurements also indicate that Yb 3+ adopts a mixed OTf – /Tf 2 N – coordination environment when Yb(OTf) 3 is dissolved in [C 4 mpyr][Tf 2 N]. The measured half‐wave potentials of the studied systems can be linked to the electron‐donor properties of the metal cation.