Speciation of Rare‐Earth Metal Complexes in Ionic Liquids: A Multiple‐Technique Approach

Abstract

The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl)imide ([Hbet][Tf(2)N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu(2)(bet)(8)(H(2)O)(4)][Tf(2)N](6), [Eu(2)(bet)(8)(H(2)O)(2)][Tf(2)N](6) x 2 H(2)O, and [Y(2)(bet)(6)(H(2)O)(4)][Tf(2)N](6) were found to consist of dimers. These rare-earth complexes are well soluble in the ionic liquids [Hbet][Tf(2)N] and [C(4)mim][Tf(2)N] (C(4)mim = 1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, (1)H, (13)C, and (89)Y NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry.

The Soft Material Obtained from an Europium (III)-Containing Ionic Liquid

“…Only limited papers about the higher concentration of the lanthanide ions in ionic liquid have been reported. 12,15,[17][18][19] Incorporating lanthanide ions as an anion into ionic liquids is an effective way to increase the concentration of lanthanides. 13,14,16 An alternative approach to increase the solubility of metal salts is to use task-specific ionic liquids (TSIL) bearing a complexing moiety.…”

Interactions between trivalent rare earth oxides and mixed [Hbet][Tf2N]:H2O systems in the development of a one-step process for the separation of light from heavy rare earth elements

“…that can be adjusted by varying either the anion or the cation to achieve applications that are credible alternatives to conventional solvents for the extraction, separation and purification of metals and metal oxides [5][6][7][8][9][10]. A series of publications from Binneman's and Nockemann's research groups [6,[11][12][13][14][15][16] using betaine as an extractant [12,13], and in the recovery of europium (Eu) and yttrium (Y) from lamp phosphor waste powders [14]. The solubility of the rare earth oxides in…”

“…water mixtures is high due to the formation of complexes between the RE and oxygen atoms of the betaine carboxylate groups [11,18].…”

Formation of Complexes in RTIL and Ion Separations

“…Room temperature ionic liquids (RTILs) are gaining an increasing interest as a unique medium for a complex formation and development of new inorganic materials (Cocalia et al, 2006;Billard et al, 2003;Yan et al, 2010;Vendilo et al, 2010;Nockemann et al, 2009;Nockemann et al, 2008;Murding & Tang, 2010;Billard & Gaillard, 2009;Taubert, 2004;Tang et al, 2008). Among the most promising fields the RTIL-based lithium batteries (Lewandowski & SwiderskaMocek, 2009;Rosol et al, 2009) and recent applications of ionic liquids in the separation technology (Dundan & Kyung, 2010;Dietz, 2006) can be considered as a "hot" research topic.…”