Solvation of Uranyl(II), Europium(III) and Europium(II) Cations in “Basic” Room-Temperature Ionic Liquids: A Theoretical Study
✍ Scribed by Alain Chaumont; Georges Wipff
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 412 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
We report a molecular dynamics study of the solvation of UO~2~^2+^, Eu^3+^ and Eu^2+^ ions in two “basic” (Lewis acidity) room‐temperature ionic liquids (IL) composed of the 1‐ethyl‐3‐methylimidazolium cation (EMI^+^) and a mixture of AlCl~4~^−^ and Cl^−^ anions, in which the Cl^−^/AlCl~4~^−^ ratio is about 1 and 3, respectively. The study reveals the importance of the [UO~2~Cl~4~]^2−^ species, which spontaneously form during most simulations, and that the first solvation shell of europium is filled with Cl^−^ and AlCl~4~^−^ ions embedded in a cationic EMI^+^ shell. The stability of the [UO~2~Cl~4~]^2−^ and [Eu^III^Cl~6~]^3−^ complexes is supported by quantum mechanical calculations, according to which the uranyl and europium cations intrinsically prefer Cl^−^ to the AlCl~4~^−^ ion. In the gas phase, however, [Eu^III^Cl~6~]^3−^ and [Eu^II^Cl~6~]^4−^ complexes are predicted to be metastable and to lose two to three Cl^−^ ions. This contrasts with the results of simulations of complexes in ILs, in which the “solvation” of the europium complexes increases with the number of coordinated chlorides, leading to an equilibrium between different chloro species. The behavior of the hydrated [Eu(OH~2~)~8~]^3+^ complex is considered in the basic liquids; the complex exchanges H~2~O molecules with Cl^−^ ions to form mixed [EuCl~3~(OH~2~)~4~] and [EuCl~4~(OH~2~)~3~]^−^ complexes. The results of the simulations allow us to better understand the microscopic nature and solvation of lanthanide and actinide complexes in “basic” ionic liquids.