An electrochemical and spectroscopic study of Nd(III) and Pr(III) coordination in the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ionic liquid containing chloride ion.
The coordination and accessible oxidation states of Nd and Pr were investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BuMePyroTf2N) by using electronic absorption spectroscopy, cyclic staircase voltammetry, and controlled potential coulometry. These experiments were carried out in the neat ionic liquid (IL) and in the IL containing free Cl(-) from the dissolution of BuMePyroCl. The electrolytic dissolution of Ln = Nd and Pr metal in this IL produces only the respective Ln(3+) ions. These trivalent species can be reduced to Ln(2+), but the resulting divalent species exhibit only transient stability, undergoing rapid disproportionation to Ln(3+) and Ln(0). The intensity of the hypersensitive (4)G5/2 ← (4)I9/2 electronic transition for Nd(3+) dissolved in the IL was substantially larger than it was in noncoordinating solvents such as aqueous HClO4, indicating moderate interactions between Nd(3+) and Tf2N(-) ions, probably resulting in anionic species such as [Nd(Tf2N)x]((x-3)-). The addition of Cl(-) to [Ln(Tf2N)x]((x-3)-) solutions results in the precipitation of LnCl3(s) (s = solid). The LnCl3(s) redissolves to give the octahedral complex [LnCl6](3-) as the Cl(-) concentration is raised further. In the IL containing excess chloride, the (3)P0 ← (3)H4 transition for [PrCl6](3-) exhibits ligand-mediated pseudohypersensitive behavior.
Department of Chemistry and Biochemistry, University of Mississippi , University, Mississippi 38677, United States.
Li-Hsien
LH
Chou
Charles L
CL
Hussey