Synergistic extraction of some divalent cations into nitrobenzene by using dicarbollylcobaltate and substituted calix[5]arenes

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibriums Sr${}^{2+}$ (aq) + 2 picrate (aq) + L (nb) ⇔ SrL${}^{2+}$ (nb) + 2 picrate (nb) and M${}^{2+}$ (aq) + SrL${}^{2+}$ (nb) ⇔ ML${}^{2+}$ (nb) + Sr${}^{2+}$ (aq) taking place in the two-phase water-nitrobenzene system (M${}^{2+}$ = Ca${}^{2+}$, Ba${}^{2+}$, Pb${}^{2+}$, Cu${}^{2+}$, Zn${}^{2+}$, Cd${}^{2+}$, Mn${}^{2+}$, Co${}^{2+}$, Ni${}^{2+}$, UO${}_2^{2+}$ ; L = substituted calix[5]arenes; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Moreover, the stability constants of the ML${}^{2+}$ complexes in nitrobenzene saturated with water were calculated. Very high stability constants of pentaethyl p-tert-butylcalix[5]arene pentaacetate ligand with Ba${}^{2+}$ cation has been found.