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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 of two carbamoylmethylphosphate (CMP)-and -phosphine oxide (CMPO)-tetrafunctionalized cavitands with a propyl spacer between the cavitand platform and the chelating sites is described. Liquid-liquid extractions with CMP(O)-and N-acyl(thio)urea-tetrafunctionalized cavitands were performed from aqueous nitric acid into dichloromethane or o-nitrophenyl hexyl ether (NPHE). The extraction of americium (III) and europium (III) from aqueous nitric acid into NPHE was studied in both the absence and presence of Br 6 -COSAN as a synergist. CMP(O) cavitands are more efficient extractants than the corresponding Nacyl(thio)urea derivatives, whereas the latter ones show an interesting selectivity for americium (III) over europium (III) in the presence of Br 6 -COSAN. The introduction of a propyl chain between the cavitand platform and the chelating groups increases the

shows that CMPO tripodand 3 is very selective for Eu 3+ and forms a very stable complex (log b ML = 28.3). Liquid-liquid extractions performed with Eu 3+ and Am 3+ show reasonable extraction properties of the CMP(O) tripodands 3, 11 and 13 in 1,1,2,2-tetrachloroethane, while in 1-octanol for all tripodands studied the distribution coefficients are low. Upon addition of the synergistic agent hexabrominated cobalt bis(dicarbollide) anion (bromo-COSAN) the distribution coefficients for Am 3+ and Eu 3+ extraction increase considerably for CMP(O) tripodands 3 and 4. Covalently linked COSAN only enhances the extraction of Am 3+ and Eu 3+ at 0.001-0.01 M HNO 3 . The functionalization of dendrimer coated magnetic silica particles with CMP(O) tripodands led to very effective particles (31 and 32) for Am 3+ and Eu 3+ removal from 0.01 M HNO 3 solutions.