“…Of particular interest has been the inclusion of the uranyl ion in macrocycles; however, the majority of structural studies concern complexes in which the crown ligand is linked to the uranyl ion via hydrogen bonds (Rogers, Bond, Hippie, Rollins & Henry, 1991;Gutberlet, Dreissig, Luger, Bechthold, Maung & Knochel, 1989) and few structural studies show a direct uranyl-crown coordination (Navaza, Villain & Charpin, 1984;Dejean, Charpin, Folcher, Rigny, Navaza & Tsoucaris, 1987;Deshayes, Keller, Lance, Navaza, Nierlich & Vigner, 1993). The probability of the uranyl complexing in the crown cavity is increased by a judicious choice of the solvent-anion pair, which has to be poorly coordinating with respect to the uranyl.…”