The solvent extraction of Eu(III) from aqueous chloride phase into hydrophobic ionic liquids (ILs), 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides ([C(1)C(n)im(+)][Tf2N-], n = 4 and 10) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide by the beta-diketone benzoylacetone (HBA) alone and in combination with N,N-diisobutyl-2-(octylphenylphosphoryl)acetamide (CMPO) or 5,11,17,23-ter t-butyl-25,26,27,28-tetrakis(dimethylphosphinoylmethoxy) calix[4]arene, (C4) was investigated. The interaction between the two extractants (HBA-CMPO, acidic/neutral) in deuterochloroform has been studied by H-1, C-13 and P-31 NMR spectra and NOESY experiment. The Q NMR analytical technique based on H-1 and F-19 spectra was also applied for determination of [C(1)C(4)im(+)] and [Tf2N-] entities transferred into the aqueous phase. The interaction between ([C(1)C(4)pyr(+)][Tf2N-] and the chelating component of the extracting phase was checked as well. Eu(III) was not so efficiently extracted by the two synergistic systems HBA/CMPO(C4)/[C(1)C(n)im(+)][Tf2N-], although an enhancement was established. The effect of the IL cation alkyl chain length and nature on the extraction process was analyzed. For the first time in synergistic solvent extraction an IL was estimated as a modifier in order to evaluate its influence on the supramolecular aggregation in acidicineutral/CHCl3 systems. (C) 2017 Elsevier B.V. All rights reserved.