Uranyl Ion Complexation by Aliphatic Dicarboxylic Acids in the Presence of Cucurbiturils as Additional Ligands or Structure-Directing Agents

Abstract

A series of nine complexes has been obtained from the hydrothermal reaction of uranyl nitrate with long-chain alkyldicarboxylic acids (HOOC-(CH2)n–2-COOH, denoted H2Cn) in the presence of cucurbit[6]uril (CB6), dimethylformamide (DMF), which generates dimethylammonium cations in situ, and additional alkaline-earth metal ions in some cases. The crystal structures of the three complexes [H2NMe2]2[(UO2)4O2(OH)2(C8)2(CB6)]·8H2O (1), [H2NMe2]2[(UO2)4O2(OH)2(C9)2(CB6)]·5H2O (2), and [H2NMe2]2[(UO2)4O2(OH)2(C9)2(CB6)]·8H2O (3) are closely related, since all contain the same tetranuclear motif held by two μ3-oxo and two μ2-hydroxo ions, and attached to CB6 by uranyl-O-carbonyl bonds. Two-dimensional assemblies are formed in 1 and 2 and a three-dimensional framework in 3. The cucurbituril molecule is not coordinated in compounds 4–9 but is present as a structure-directing agent. The complex [H2NMe2]2[(UO2)4O2(C6)3]·CB8·8H2O (4), in which cucurbit[8]uril (CB8) comes from the initial CB6, displays a stacking of plan...