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

Abstract

The extraction constant and the two-phase stability constant ( K D,M β 3) of tris(2-thenoyltrifluoroacetonato)europium(III) between 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C 4mim][Tf 2N]) 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 [C 4mim][Tf 2N] 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 ( K D,M) of the neutral Eu(III) chelate because the [C 4mim][Tf 2N] system gave the high K D,M β 3 value compared with those in conventional molecular solvents such as benzene and 1,2-dichloroethane. The coordination environment of Eu 3+ in the neutral Eu(III) chelate in [C 4mim][Tf 2N] 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(H 2O) 3 synthesized as a solid crystal were almost completely dehydrated in [C 4mim][Tf 2N] saturated with water. Consequently, the higher K D,M or extractability of the neutral Eu(III) chelate in the [C 4mim][Tf 2N] system can be ascribed to the dehydration of the Eu(III) chelate, which is caused by the specific solvation with [C 4mim][Tf 2N] molecules.