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 (CB n, n = 6, 7, 8) was investigated, mostly under hydrothermal conditions, and the crystal structure of six novel complexes was determined. In compounds [UO 2 (H 2 O) 5 ](NO 3 ) 2 ·CB6·4H 2 O ( 1 ) and [UO 2 (NO 3 ) 2 (H 2 O) 2 ]·CB6·7H 2 O ( 2 ), CB6 acts as a second-sphere ligand through hydrogen bonding to uranyl aquo ligands, while in all other complexes, [(UO 2 ) 4 (CB6)O 2 (OH) 2 (H 2 O) 6 ](NO 3 ) 2 ·CB6·8H 2 O ( 3 ), [(UO 2 ) 2 (CB6) 3 (H 2 O) 6 ][(UO 2 ) 2 (NO 3 ) 4 (C 10 H 16 O 4 )] 2 ·CB6·8H 2 O ( 4 ), [(UO 2 ) 2 (CB7)(SO 4 ) 2 (H 2 O) 2 ]·4H 2 O ( 5 ), and [(UO 2 ) 6 (CB8)(SO 4 ) 6 (H 2 O) 10 ]·18H 2 O ( 6 ), uranyl coordination to one or two CB carbonyl groups is present. A one-dimensional polymer with tetranuclear, μ 3 -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 dimeric ( 5 ) or polymeric ( 6 ) uranyl sulfate subunits, which are further connected through tetradentate CB molecules to give two-dimensional frameworks. Cylindrical channels result from the stacking of CB7 molecules in complex 5 .