Uranyl–Alkali Metal Ion Heterometallic Complexes with Cucurbit[6]uril and a Sulfonated Catechol

2011-07-06T00:00:00Z (GMT) by Pierre Thuéry
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 cosolvent. 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+ heterotetranuclear 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.