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-