Anhydrous Praseodymium Salts in the Ionic Liquid [bmpyr][Tf₂N]: Structural and Optical Properties of [bmpyr]₄[PrI₆][Tf₂N] and [bmyr]₂[Pr(Tf₂N)₅]

Purposely designed ionic liquids can be excellent solvents for spectroscopic studies of rare earth compounds. Absorption and emission spectra of anhydrous PrI 3 and Pr(Tf 2 N) 3 in the ionic liquid 1,1- n -butyl-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide, [bmpyr][Tf 2 N], at room temperature are presented together with the emission spectra of solid [bmpyr] 2 [Pr(Tf 2 N) 5 ] and [bmpyr] 4 [PrI 6 ][Tf 2 N]. After excitation into the 3 P 1 level, remarkable luminescence not only from the 1 D 2 level but also from the 3 P 0 and even from the 3 P 1 level is observed. Amazingly in the case of the solid compounds and even more astonishing for a solution of Pr(Tf 2 N) 3 in [bmpyr][Tf 2 N] the strongest luminescence transitions start from the 3 P 0 level. From a solution of PrI 3 in [bmpyr][Tf 2 N] single crystals of [bmpyr] 4 [PrI 6 ][Tf 2 N] were grown. The compound crystallizes in the space group P 4 3 2 1 2 with a = b = 1464.8(2) pm and c = 2846.9(5) pm at 298(2) K and a = b = 1454.52(7) pm and c = 2852.4(2) pm at 170(2) K, respectively. The structure is characterized by [PrI 6 ] octahedra winding along the 4 3 screw parallel to the crystallographic c axis. Above each octahedral face one 1-butyl-1-methyl-pyrrolidinium cation is tangentially located. The bis(trifluoromethylsulfonyl)amide anions fill the remaining space. From a solution of Pr(Tf 2 N) 3 in [bmpyr][Tf 2 N] the compound [bmpyr] 2 [Pr(Tf 2 N) 5 ] is obtained which crystallizes triclinic, space group P 1̄, with a = 12.3217(13) pm, b = 12.4275(14) pm, c = 22.6422(24) pm, α = 94.440(9)°, β = 102.630(8)°, and γ = 105.791(9)°. Here the main structural feature is the separation of the hydrophobic [Pr(Tf 2 N) 5 ] 2 - and hydrophilic bmypr + parts in the structure.