The synthesis and binding properties towards different cations of a series of tripodal ligands functionalized with N-acyl-(thio)urea and picolin(thio)amide moieties are described. For the extraction of Am 3+ and Eu 3+ the compounds are not efficient. However, N-acylurea derivative 10 exhibit a significant selectivity for Am 3+ over Eu 3+ . Upon addition of the synergistic hexabrominated bis(dicarbollide)cobalt anion (Br 6 -COSAN) the distribution coefficients for Am 3+ and Eu 3+ in-
The synthesis and binding properties towards different cations of a series of tripodal ligands functionalized with N-acyl-(thio)urea and picolin(thio)amide moieties are described. For the extraction of Am 3+ and Eu 3+ the compounds are not efficient. However, N-acylurea derivative 10 exhibit a significant selectivity for Am 3+ over Eu 3+ . Upon addition of the synergistic hexabrominated bis(dicarbollide)cobalt anion (Br 6 -COSAN) the distribution coefficients for Am 3+ and Eu 3+ in-
“…The chlorinated cobalt bis(dicarbollide)s [(B 9 C 2 H 8 Cl 3 ) 2 Co] À (hereafter noted CCD À ) belong to a class of bulky ''peanutshaped'' anions 1 that are used in conjunction with extractant molecules for efficient liquid-liquid extraction of cations. 2 The anions can be used as such (generally introduced as their Cs + CCD À or H 3 O + CCD À salts in the organic phase), [3][4][5][6][7][8][9] or grafted onto complexing moieties (phosphoryl containing ligands, glycols), sometimes anchored on organized platforms like calixarenes or cavitands. 10,11 Due to their very high hydrophobicity, high chemical and radiochemical stability, and the extreme acidity of the conjugated acid, dicarbollides display great potentials in the field of nuclear waste partitioning from highly acidic aqueous solutions.…”
We report a molecular dynamics study of chlorinated cobalt bis(dicarbollide) anions [(B(9)C(2)H(8)Cl(3))(2)Co](-)"CCD(-)" in octanol and at the octanol-water interface, with the main aim to understand why these hydrophobic species act as strong synergists in assisted liquid-liquid cation extraction. Neat octanol is quite heterogeneous and is found to display dual solvation properties, allowing to well solubilize CCD(-), Cs(+) salts in the form of diluted pairs or oligomers, without displaying aggregation. At the aqueous interface, octanol behaves as an amphiphile, forming either monolayers or bilayers, depending on the initial state and confinement conditions. In biphasic octanol-water systems, CCD(-) anions are found to mainly partition to the organic phase, thus attracting Cs(+) or even more hydrophilic counterions like Eu(3+) into that phase. The remaining CCD(-) anions adsorb at the interface, but are less surface active than at the chloroform interface. Finally, we compare the interfacial behavior of the Eu(BTP)(3)(3+) complex in the absence and in the presence of CCD(-) anions and extractant molecules. It is found that when the CCD(-)'s are concentrated enough, the complex is extracted to the octanol phase. Otherwise, it is trapped at the interface, attracted by water. These results are compared to those obtained with chloroform as organic phase and discussed in the context of synergistic effect of CCD(-) in liquid-liquid extraction, pointing to the importance of dual solvation properties of octanol and of the hydrophobic character of CCD(-) for synergistic extraction of cations.
“…Since its first synthesis in 1965, the cobalt bis(dicarbollide) anion [(B 9 C 2 H 11 ) 2 Co] - and its derivatives (Figure ) found important applications in various domains such as in the medical field as tumor imaging agents, , in organic synthesis as superacid, and in the partitioning of radioactive ions by liquid−liquid extraction. − In this context, these hydrophobic anions have first been used in combination with complexing agents such as PEG and CMPO molecules for the simultaneous extraction of Cs + , Sr 2+ , and actinides (Russian UNiversal EXtraction “UNEX” process , ). When added as synergistic agents to extractant molecules such as crown ethers, calixarenes, phosphoryl derivatives, − or grafted onto such chelating platforms, , they markedly improve the ion extraction efficiency. So far, little is known, however, on the solution properties of these anions in pure liquids or heterogeneous liquid mixtures and on the mechanism of synergistic extraction. , 1 Dicarbollide XCD - anions (hydrogens not shown for clarity).…”
We report a molecular dynamics study of cobalt bis(dicarbollide) anions [(B(9)C(2)H(8)X(3))(2)Co](-) (XCD(-)) commonly used in liquid-liquid extraction (X = H, Me, Cl, or Br), showing that these anions, although lacking the amphiphilic topology, behave as anionic surfactants. In pure water, they display "hydrophobic attractions", leading to the formation of aggregates of different sizes and shapes depending on the counterions. When simulated at a water/"oil" interface, the different anions (HCD(-), MeCD(-), CCD(-), and BrCD(-)) are found to be surface active. As a result, the simulated M(n+) counterions (M(n+) = Na(+), K(+), Cs(+), H(3)O(+), UO(2)(2+), Eu(3+)) concentrate on the aqueous side of the interface, forming a "double layer" whose characteristics are modulated by the hydrophobic character of the anion and by M(n+). The highly hydrophilic Eu(3+) or UO(2)(2+) cations that are generally "repelled" by aqueous interfaces are attracted by dicarbollides near the interface, which is crucial as far as the mechanism of assisted cation extraction to the oil phase is concerned. These cations interact with interfacial XCD(-) in their fully hydrated Eu(H(2)O)(9)(3+) and UO(2)(H(2)O)(5)(2+) forms, whereas the less hydrophilic monocharged cations display intimate contacts via their X substituents. The results obtained with the TIP3P and OPLS models for the solvents are confirmed with other water models (TIP5P or a polarizable 4P-Pol water) and with more polar "oil" models. The importance of interfacial phenomena is further demonstrated by simulations with a high oil-water ratio, leading to the formation of a micelle covered with CCD's. We suggest that the interfacial activity of dicarbollides and related hydrophobic anions is an important feature of synergism in liquid-liquid extraction of hard cations (e.g., for nuclear waste partitioning).
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