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

摘要

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.