Uranyl-Based Metallamacrocycles: Tri- and Tetranuclear Complexes with (2<i>R</i>,3<i>R</i>,4<i>S</i>,5<i>S</i>)-Tetrahydrofurantetracarboxylic Acid

The trinuclear [UO2L]36- and tetranuclear [UO2L]48- metallamacrocycles, obtained by reaction of uranyl nitrate with the rigidly angular ligand (2R,3R,4S,5S)-tetrahydrofurantetracarboxylic acid (H4L) in a basic medium, are in equilibrium in methanol solution. Depending on the counterion, one or the other can be selectively isolated in crystal form. These rare examples of supramolecules incorporating actinide ions confirm the high potential and unique features of uranyl as a building block. Uranyl complexation through both the tri- and bidentate sites of the ligand is at variance with previous assumptions resulting from molecular modeling in nuclear waste reprocessing studies.