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

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posted on 13.12.2005, 00:00 authored by Arash Babai, Anja-Verena Mudring
Purposely designed ionic liquids can be excellent solvents for spectroscopic studies of rare earth compounds. Absorption and emission spectra of anhydrous PrI3 and Pr(Tf2N)3 in the ionic liquid 1,1-n-butyl-methylpyrrolidinium bis(trifluoromethanesulfonyl)amide, [bmpyr][Tf2N], at room temperature are presented together with the emission spectra of solid [bmpyr]2[Pr(Tf2N)5] and [bmpyr]4[PrI6][Tf2N]. After excitation into the 3P1 level, remarkable luminescence not only from the 1D2 level but also from the 3P0 and even from the 3P1 level is observed. Amazingly in the case of the solid compounds and even more astonishing for a solution of Pr(Tf2N)3 in [bmpyr][Tf2N] the strongest luminescence transitions start from the 3P0 level. From a solution of PrI3 in [bmpyr][Tf2N] single crystals of [bmpyr]4[PrI6][Tf2N] were grown. The compound crystallizes in the space group P43212 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 [PrI6] octahedra winding along the 43 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(Tf2N)3 in [bmpyr][Tf2N] the compound [bmpyr]2[Pr(Tf2N)5] is obtained which crystallizes triclinic, space group P1̄, 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(Tf2N)5]2- and hydrophilic bmypr+ parts in the structure.