| Abstract
| - The coordination ability of the hexaphosphinoylated p-tert-butylcalix[6]arene B6bL6 toward actinides is established, as well as its good separation ability of the actinide ions UO22+ and Th(IV) over trivalent rare earths such as La(III), Eu(III), and Y(III). Spectrophotometric titration of uranyl with B6bL6 in CH3CN yields log β11 = 7.1 and log β12= 12.5 for the 1:1 and 1:2 (UO22+/B6bL6) species, respectively. Actinide complexes with 1:1 and 1:2 (M/L) stoichiometries are isolated and characterized by elemental analysis, IR, and UV−vis. Compounds 1 and 3 fulfill their CN = 8 just with B6bL6, while compounds 2 and 4 require coordinated nitrates and/or water molecules. The luminescence spectra of the uranyl complexes and the parameters such as FWMH, vibronic spacing (υsp), and the U−O bond length, as well as the luminescence lifetimes, permit the understanding of the coordination chemistry of these actinide calixarene complexes. Energy transfer from the B6bL6 ligand to the uranyl ion is demonstrated to be relevant in compound 1 with Qabs = 2.0%. The uranyl complex emission reveals a biexponential decay with τs from 210 to 220 μs and τL from 490 to 650 μs for compounds 1 and 3, respectively. The liquid−liquid extraction results demonstrate the good extraction capability of B6bL6 toward actinides but not for rare earths at room temperature. The extracted species keeps the 1(cation)/1(calixarene) ratio for the UO22+, Th4+, and Eu3+ ions. A good capacity of B6bL6 toward Th4+ ions using aqueous phase 2 containing even up to 0.3 M thorium nitrate and an organic phase of 2.47 × 10−4 M B6bL6 in chloroform is found. The spectroscopic properties of the isolated uranyl complexes and the extraction studies reveal a uranophilic nature of B6bL6. The molecular modeling results are in good agreement with the experimental findings.
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