A Nanosized Uranyl Camphorate Cage and its Use as a Building Unit in a Metal−Organic Framework

The reaction of uranyl nitrate with (1R,3S)-(+)-camphoric acid (H2L) in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) gives the chiral octanuclear cage [(UO2)8(L12H8)]·12H2O (1), which displays an approximately cubic shape with the metal ions as apexes and an internal cavity of ca. 7 Å in length. Complex 1, which is the first example of a homoleptic nanosized cage including uranyl ions, can further be used as a supramolecular building block to generate coordination polymers, as exemplified by the compound [Ba(H2O)8]2[(UO2)8Ba2(L12)(H2O)4]·8H2O (2), obtained in the presence of Ba(CH3COO)2. In 2, which retains the overall packing mode of cages present in 1, a two-dimensional assembly is formed through bridging by the carboxylate-bound alkaline-earth metal cations. However, whereas 1 displays extended channels, these are obstructed by counterions in 2.