Laser-induced fluorescence and infrared spectroscopic studies on the specific solvation of tris(1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedionato)europium(III) in an ionic liquid

The extraction constant and the two-phase stability constant (KD,Mβ3) of tris(2-thenoyltrifluoroacetonato)europium(III) between 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][Tf2N]) as an ionic liquid and an aqueous phase were determined by considering the extraction equilibria including anionic tetrakis(2-thenoyltrifluoroacetonato)europate(III). Specific solute–solvent interactions between the neutral Eu(III) chelate and [C4mim][Tf2N] molecules were revealed from the relationships between the distribution constant of the enol form of 2-thenoyltrifluoroacetone (Htta) as a proton chelate and the distribution constant (KD,M) of the neutral Eu(III) chelate because the [C4mim][Tf2N] system gave the high KD,Mβ3 value compared with those in conventional molecular solvents such as benzene and 1,2-dichloroethane. The coordination environment of Eu3+ in the neutral Eu(III) chelate in [C4mim][Tf2N] was investigated by time-resolved laser-induced fluorescence spectroscopy and infrared absorption spectroscopy. Both methods consistently indicated that not only the Eu(III) chelate extracted but also Eu(tta)3(H2O)3 synthesized as a solid crystal were almost completely dehydrated in [C4mim][Tf2N] saturated with water. Consequently, the higher KD,M or extractability of the neutral Eu(III) chelate in the [C4mim][Tf2N] system can be ascribed to the dehydration of the Eu(III) chelate, which is caused by the specific solvation with [C4mim][Tf2N] molecules.

The distribution equilibrium of Eu(III) between an ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][Tf2N]), and an aqueous phase with 2-thenoyltrifluoroacetone (Htta) was studied to determine the two-phase stability constant. Furthermore, the coordination environment of Eu3+ in the neutral Eu(III) chelate in the [C4mim][Tf2N] system was investigated by time-resolved laser-induced fluorescence spectroscopy and infrared absorption spectroscopy. Not only the neutral Eu(tta)3 chelate extracted but also Eu(tta)3(H2O)3 synthesized as a solid crystal were almost completely dehydrated in [C4mim][Tf2N] saturated with water.Figure optionsDownload as PowerPoint slideHighlights
► Two-phase stability constant of the Eu(III) chelate in ionic liquid was determined.
► Solute–solvent interactions between the Eu(III) chelate and ionic liquid were revealed.
► The Eu(III) chelate was completely dehydrated in ionic liquid saturated with water.
► The Eu(III) chelate can be solvated or coordinated with ionic liquid molecules.
► Specific solvation by ionic liquid molecules caused higher extractability of Eu(III).