EUROPIUM(III) EXTRACTION WITH NEW RESORCINARENE CAVITAND CMP(O) LIGANDS - SOLVENT-EXTRACTION AND MECHANISTIC STUDY

The new neutral resorcinarene cavitand CMP(O) Ligands A, B, and C [Ph- CMPO-N(Pr), Ph-CMPO-N(H), and Et-CMP-N(Pr), respectively] extract Eu(I II) from medium acidic lithium nitrate solutions. The proposed model f or the 1:1 stoichiometric extraction of Eu(NO3)(3) is valid for [LiNO3 ] > 1-2 M, and with excess ligand relative to the metal ion concentrat ion (extraction constants K-ex = 1.7 x 10(3), 3.5 x 10(1), and 8.0 x 1 0(1) M-4 for A, B and C, respectively). At increasing nitric acid conc entration [log a(H+) > -2] protonation of the ligands A-C (protonation constants K-1(H) = 1.1 - 3.1 M-2) results in a decrease of the distri bution coefficients. At higher nitrate concentrations (>2.5 M) an addi tional LiNO3 molecule associates with the complexes, resulting in incr eased distribution ratios (mainly for ligand A; association constant K -ex = 0.05 M-2). Variation of the anion largely influences the extrac tions resulting from the different anion lipophilicities.