Coordination Polymers and Frameworks in Uranyl Ion Complexes with Sulfonates and Cucurbit[6]uril

The complexes formed by uranyl nitrate with the three positional isomers of sulfobenzoate and with ethanedisulfonate anions in the presence of cucurbit[6]uril (CB6) under hydrothermal conditions were investigated by single-crystal X-ray diffraction. 2-Sulfobenzoate (2-SB2–) chelates the uranyl ion through one carboxylate and one sulfonate oxygen atoms in the three complexes [UO2(2-SB)(H2O)3]2·CB6·12H2O (1), [Na(CB6)(H2O)4][UO2(2-SB)(H2O)2]2·NO3·3H2O (2), and {[UO2(2-SB)(H2O)2]2Cs(CB6)(OH)(H2O)5}·2H2O (3). While 1 is a monomer, 2 and 3 display neutral dimeric [UO2(2-SB)(H2O)2]2 units. In 2, these units are bound to the sodium ion complex of CB6 through hydrogen bonds, while, in 3, bonding of one of the uranyl water ligands to cesium gives a one-dimensional coordination polymer. 3-Sulfobenzoate (3-SB2–) gives the three-dimensional framework [(UO2)2Cs2(3-SB)3(CB6)(H2O)4.5]·7.5H2O (4), in which carboxylate groups are chelating or bridging uranyl ions, and sulfonate groups are coordinated to uranyl and cesium ions, the latter being also bound to CB6 carbonyl groups. In contrast, the para isomer 4-SB2– gives the molecular species [UO2K2(4-SB)2(CB6)(H2O)9]·11H2O (5), in which uranyl is bound to one monodentate carboxylate group from each ligand, and one sulfonate oxygen atom is bound to one of the potassium ions complexed by CB6. Ethanedisulfonate (EDS2–) was chosen as a potentially bridging, homo-difunctional ligand devoid of the strongly uranyl-binding carboxylate groups. The complex [(UO2)4(EDS)(OH)6(CB6)(H2O)2]·8H2O (6) is a three-dimensional framework with a remarkable architecture: uranyl-bridging hydroxides give rise to undulated chains which are linked to one another by bridging, tetradentate disulfonate ligands to give planar two-dimensional subunits displaying large [(UO2)8(EDS)2(OH)10] rings, and these sheets are assembled into a unique network by uranyl-bound CB6 molecules. Both frameworks 4 and 6 are novel examples of the association of uranyl–organic sheets with CB6 columns or layers, a quite frequent feature in this family of compounds.