Uranyl-alkali metal ion hetero metallic complexes with cucurbit[6]uril and a sulfonated catechol

The reaction of uranyl nitrate with cucurbit[6]uril (CB6) under hydrothermal conditions and in the presence of alkali metal ion nitrates has been investigated. Two complexes with Na+ have been obtained, [Na3(CB6)(H2O)8][(UO2)2(OH)2(NO3)4].NO3.2H2O (1) and [Na1.5(CB6)(H2O)4][(UO2)6O2(OH)6(HCOO)3.5(H2O)].8H2O (2), which differ by the presence in the latter of formate ions due to the hydrolysis of the dimethylformamide co-solvent. Both 1 and 2 display columnar, cationic Na+-CB6 complexes, with independent, anionic dinuclear (1) or one-dimensional polymeric (2) uranyl complexes. The molecular species [(UO2)3K3O1.5(OH)3(HCOO)3(CB6)3(H2O)6(DMF)3].3H2O(3) is an original arrangement in which three K+ ions assemble three CB6 molecules around a trigonal axis and are themselves bound to the terminal oxo groups of a μ3-oxo-centered uranyl trinuclear unit. Only in the case of the cesium-containing complex [(UO2)2Cs2(OH)3(CB6)(H2O)4][(UO2)2Cs2(OH)3(NO3)2 (CB6)(H2O)2][(UO2)2(OH)2(NO3)4].2NO3.10H2O (4) is uranyl coordination to CB6 observed, resulting in the formation of columns with alternate CB6 molecules and [(UO2)2Cs2(OH)2]4+ hetero-tetra-nuclear units held by two μ3-hydroxo ions. 4,5-Dihydroxy-1,3-benzenedisulfonic acid (Tiron, H4tir) was used as an additional ligand so as to create bridges between the uranyl and alkali metal ions. Its disodium salt yielded the complexes [UO2Na3(Htir)(CB6)(H2O)11][UO2(Htir)(H2O)3].NO3.11H2O (5) and [(UO2)2Na2(Htir)2(CB6)(H2O)8].4H2O (6), obtained at room temperature and under hydrothermal conditions, respectively. Uranyl is chelated in both cases by one phenoxide and one sulfonate oxygen atoms. Whereas 5 is once more a columnar arrangement, with the uranyl complex units bound on either side, 6 is a two-dimensional assembly in which the uranyl ions are located on the outside of the sheets. Replacement of sodium by potassium ions gave the complex [(UO2)2K2(Htir)2(CB6)(H2O)8].4H2O (7), in which, notwithstanding its closeness to 6, the different connectivity due to the larger size of potassium ions brings about the formation of a three-dimensional framework. These results show the considerable variety of architectures which can be generated in the uranyl-cucurbituril system, depending on the presence of additional cations and ligands, and also the potential of sulfonates in uranyl coordination chemistry. (author)