TRLFS and EXAFS investigations of lanthanide and actinide complexation by triflate and perchlorate in an ionic liquid

Abstract

The solvation of the Eu-perchlorate (ClO4–) and triflate (CF3SO3–, OTf–) salts as well as of Cm(ClO4)3 and Am(ClO4)3 in the ionic liquid C4mimTf2N (1-butyl-3-methylimidazolium-bis(trifluoromethylsulfonyl)imide) has been comparatively investigated by application of laser fluorescence spectroscopy and X-ray absorption spectroscopy. Moreover, the ClO4–/OTf– ligand exchange reaction for the two actinide cations has been analyzed by the same spectroscopic techniques. A structural model for the different complexes was determined by the interpretation of the spectroscopic data. The lanthanide and the two actinide cations show the same coordination in C4mimTf2N. Moreover, a sequence for the strength of complexing ligands could be deduced from the spectroscopic data for the lanthanide and the two actinides: ClO4–>OTf–≥Tf2N–>H2O

Time-Resolved Laser Fluorescence Spectroscopy and Extended X-Ray Absorption Spectroscopy Investigations of the N3− Complexation of Eu(III), Cm(III), and Am(III) in an Ionic Liquid: Differences and Similarities

“…That is, the determined luminescence lifetime represents an average lifetime of the different solution species. 12 With increasing azide concentration up to 1.1 × 10 -3 M, the emission intensity decreases. Again, this effect is not due to the dilution of Eu(III).…”

“…The emission spectrum of 1 × 10 -2 M Eu(OTf) 3 at different N 3 -concentrations (Figure 1) exhibits two peak maxima at 588 and 611 nm that can be attributed to the 5 D 0 f 7 F 1 and 5 D 0 f 7 F 2 transitions. 11,12 The luminescence decay of the sample before addition of N 3 -shows biexponential behavior (Figure 2). According to the literature, the fit results in a longer emission lifetime of 2.5 ( 0.2 ms which can be attributed to a Eu(III)-species without water in the first coordination sphere.…”

“…The ratio of the two luminescence transitions gives a value of R F2/F1 ) 2.5 ( 0.1 and is in good accordance with the published data. 11,12 With increasing N 3 -concentration, the Eu luminescence is affected in two respects. In the range from 1 × 10 -5 M to 1.1 × 10 -3 M azide, the luminescence intensity decreases by nearly 1 order of magnitude (Figure 1).…”

“…It is well-known that beside XAFS, 16 the luminescence spectroscopy of Eu(III) and Cm(III) is a useful tool in studying the structure and chemical reactivity of the two f-element cations in solution, 11,12 as well as at the solid-solution interface 17 and in solid matrixes. 18,19 The emission bands of Eu(III) originate from electronic transitions from the lowest excited state 5 D 0 to the ground-state manifold 7 F J (J ) 0, 1, ..., 6).…”

“…It was shown by our group that, switching to ILs as solvent phase, lanthanides and actinides exhibit different chemical reactivity toward their interaction with cations 11 and complexing anions. 12 In the cited studies, the differences in chemical behavior of the lanthanide and actinide was assumed to be related to the higher covalent contribution of the metal-ligand bonding in the actinide complexes as compared to the lanthanide complexes. As a continuation to the cited investigations and because N-based extractants are used in Ln-An separation schemes, the presented study intends to compare the complexation of the lanthanide cation Eu 3+ and the actinide cations Cm 3+ and Am 3+ with the most simple donor N 3 -as a model system for organic N-based extractants.…”