Physicochemical Properties and Theoretical Modeling of Actinide Complexes with a para-tert-Butylcalix[6]arene Bearing Phosphinoyl Pendants. Extraction Capability of the Calixarene toward f Elements

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 UO2 2+ and Th(IV) over trivalent rare earths such as La(III), Eu(III), and Y(III). Spectrophotometric titration of uranyl with B6bL6 in CH 3CN yields log beta 11 = 7.1 and log beta 12 = 12.5 for the 1:1 and 1:2 (UO2 2+/B 6bL6) 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 B 6bL (6), 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 (upsilon sp), 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 Q abs = 2.0%. The uranyl complex emission reveals a biexponential decay with tau s from 210 to 220 micros and tau L from 490 to 650 micros for compounds 1 and 3, respectively. The liquid-liquid extraction results demonstrate the good extraction capability of B 6bL (6) toward actinides but not for rare earths at room temperature. The extracted species keeps the 1(cation)/1(calixarene) ratio for the UO2 2+, Th 4+, and Eu 3+ ions. A good capacity of B6bL 6 toward Th4+ ions using aqueous phase 2 containing even up to 0.3 M thorium nitrate and an organic phase of 2.47 x 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.

5f-Element complexes with a p-tert-butylcalix[4]arene bearing phosphinoyl pendant arms: Separation from rare earths and structural studies

“…The hygroscopic 1:1 and 1:2 complexes were prepared according to the procedure reported recently for B 6 bL 6 [11]. Yield: 65%.…”

“…Therefore, complexes with weakly a-emitting, long half-life radio-elements such as uranium [2][3][4][5][6] and tetravalent thorium [7] have been the most studied while lanthanide ions (Ln), in an indirect way, have afforded knowledge on the chemical behavior of trivalent actinides [8,9]. Thorium coordination chemistry is also well documented, both with respect to hydration and hydrolysis [10], complexes with oxygen-and nitrogen-donor ligands [7], macrocyclic complexes [11][12][13], and even quadruple-stranded helicates [14].…”

“…Effectiveness of these macrocycles in the treatment of radioactive wastes containing lanthanides, actinides, alkaline, and alkaline earths has been practically demonstrated [27]. Few calixarene complexes with thorium have been reported [11,21] while phosphorylated calixarenes have been successfully used for thorium extraction [11,13,17,18,25,26].…”

“…Taking into account these considerations, we have been involved during the past years in the synthesis of two series of calix[n]arenes (n = 4, 6, 8, Scheme 1) fitted with ether amide [28,29] and phosphinoyl pendant arms on the narrow rim [11,[30][31][32]. We have reported the structural and photophysical properties of their lanthanide complexes [28][29][30][31][32].…”

“…We have reported the structural and photophysical properties of their lanthanide complexes [28][29][30][31][32]. Recently, our work has been expanded to the study of actinide complexes formed with the phosphinoyl-derivatized calix [6]arene B 6 bL 6 , as well as to its extraction capability toward uranyl, thorium(IV), and representative trivalent rare earths (Y, La, Eu) [11]. The synergistic effect of the phosphinoyl-derivatized calix [4]arene B 4 bL 4 in the extraction of lanthanides with a pyrazolone derivative has also been shortly reported by one of us [33].…”