Uranyl Ion Complexes with Cucurbit[n]urils (n = 6, 7, and 8): A New Family of Uranyl-Organic Frameworks

Uranyl ion complexation by cucurbit[n]urils (CBn, n = 6, 7, 8) was investigated, mostly under hydrothermal conditions, and the crystal structure of six novel complexes was determined. In compounds [UO2(H2O)5](NO3)2·CB6·4H2O (1) and [UO2(NO3)2(H2O)2]·CB6·7H2O (2), CB6 acts as a second-sphere ligand through hydrogen bonding to uranyl aquo ligands, while in all other complexes, [(UO2)4(CB6)O2(OH)2(H2O)6](NO3)2·CB6·8H2O (3), [(UO2)2(CB6)3(H2O)6][(UO2)2(NO3)4(C10H16O4)]2·CB6·8H2O (4), [(UO2)2(CB7)(SO4)2(H2O)2]·4H2O (5), and [(UO2)6(CB8)(SO4)6(H2O)10]·18H2O (6), uranyl coordination to one or two CB carbonyl groups is present. A one-dimensional polymer with tetranuclear, μ3-oxo-bridged subunits and a three-decker dinuclear complex are formed in 3 and 4, respectively, with in both cases numerous CH···O interactions between CB6 molecules, either within the complex or involving other CB6 molecules present as guests. The CB7 and CB8 complexes 5 and 6, both obtained in the presence of sulfuric acid, involve either di...