Lithium ionophore VIII as an extraordinarily strong receptor for the trivalent europium cation

On the basis of extraction experiments and γ-activity measurements, the extraction constant corresponding to the equilibrium Eu 3+ (aq) + 3A − (aq) + 1 (nb) ⇆ 1 · Eu 3+ (nb) + 3A ‑ (nb) occurring in the two-phase water–nitrobenzene system (A − = CF 3 SO − 3 ; 1 = lithium ionophore VIII; aq = aqueous phase, nb = nitrobenzene phase) was determined as log K ex ( 1 · Eu 3+ , 3A ‑ ) = 2.5 ± 0.1. Furthermore, the extremely high stability constant of the 1 · Eu 3+ complex in nitrobenzene saturated with water was calculated: log β nb ( 1 · Eu 3+ ) = 15.6 ± 0.1.

Finally, by using DFT calculations, the most probable structure of the cationic complex species 1 · Eu 3+ was derived. In the resulting complex, the ‘central’ cation Eu 3+ is bound by six very strong bond interactions to the corresponding six oxygen atoms of the parent ligand 1 . It is evident that this exceptionally effective receptor 1 for the Eu 3+ cation could be considered as a potential extraction agent for nuclear waste treatment.