Solvent extraction of europium(III) trifluoromethanesulfonate into nitrobenzene by using [2.2.2]paracyclophane – Experimental and theoretical study

Abstract

The extraction constant corresponding to the equilibrium Eu3+(aq) + 3A-(aq) + 1(nb) ⇌ 1 Eu3+(nb) + 3A–(nb) occurring in the two-phase water–nitrobenzene system (A-=CF3SO3-; 1 = [2.2.2]paracyclophane; aq = aqueous phase, nb = nitrobenzene phase) was determined as logKex(Eu3+,3A–) = -5.7 ± 0.1. Further, the stability constant of the 1 Eu3+ complex in nitrobenzene saturated with water was calculated as log Knb(1 Eu3+) = 7.4 ± 0.1. Finally, by using quantum chemical calculations, the most probable conformation of the cationic complex species 1 Eu3+ was derived. In the resulting complex, the “central” cation Eu3+, fully located in the cavity of the parent [2.2.2]paracyclophane ligand, is bound to all three benzene rings of [2.2.2]paracyclophane via cation-π interaction.