Mechanisms of Metal Ion Transfer into Room-Temperature Ionic Liquids:  The Role of Anion Exchange

Abstract

The structure and stoichiometry of the lanthanide(III) (Ln) complexes with the ligand 2-thenoyltrifluoroacetone (Htta) formed in a biphasic aqueous room-temperature ionic liquid system have been studied by complementary physicochemical methods. Equilibrium thermodynamics, optical absorption and luminescence spectroscopies, high-energy X-ray scattering, EXAFS, and molecular dynamics simulations all support the formation of anionic Nd(tta)4(-) or Eu(tta)4(-) complexes with no water coordinated to the metal center in 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide (C4mim+Tf2N(-)), rather than the hydrated, neutral complexes, M(tta)(3)(H2O)n)(n = 2 or 3), that form in nonpolar molecular solvents, such as xylene or chloroform. The presence of anionic lanthanide complexes in C4mim+Tf2N(-) is made possible by the exchange of the ionic liquid anions into the aqueous phase for the lanthanide complex. The resulting complexes in the ionic liquid phase should be thought of as weak C4mim+Ln(tta)4(-) ion pairs which exert little influence on the structure of the ionic liquid phase.

Highly Selective Synergism for the Extraction of Lanthanoid(III) Ions with β-Diketones and Trioctylphosphine Oxide in an Ionic Liquid

“…[7][8][9] Because ILs can also act as liquid ion exchangers, not only neutral but also charged complexes are extractable into the IL phase by ion exchange with the cationic or anionic constituent of the ILs. [10][11][12][13] Thus, the extractability and separability of metal ions in the IL extraction system are expected to differ from those of the usual organic solvent systems. 14,15 Recently, the present authors have reported on the synergistic ionic-liquid extraction of lanthanoids(III) (Ln(III)) with 2-thenoyltrifluoroacetone (Htta) as an acidic chelating extractant and several neutral ligands in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][Tf2N]).…”

Ionic liquids in sample preparation

“…with 1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedione (HTTA) as chelating agent, the mechanism was anion exchange rather than cation exchange [35]:…”

Extraction Behavior of Divalent Metal Cations in Ionic Liquid Chelate Extraction Systems Using 1-Alkyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imides and Thenoyltrifluoroacetone

“…Many researchers have reported on the IL solvent extraction of metal cations, [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] and several reviews concerning the method have been published. [35][36][37][38] In the use of an IL as an extraction solvent, however, the recovery of the extracted metals is a serious problem because the IL phase cannot be evaporated.…”