Uranyl and mixed uranyl-lanthanide complexes with p-sulfonatocalix[4]arene

The reaction of uranyl nitrate with p-sulfonatocalix[4]arene (H(4)C4S), carried out in water at room temperature in the presence of either NMe4OH or lanthanide nitrates, yielded the three complexes [NMe4](2)[UO2(C4S)]center dot 0.5H(2)O (1), [Ce-2(C4S) (H2O)(15)][UO2(C4S)]center dot 15H(2)O (2) and [Eu(H2O)(8.5)][UO2Eu(C4S)(2) (H2O)(7)]center dot 13H(2)O (3), which were crystallographically characterized. Complexes 1 and 2 display a two-dimensional {[UO2 (C4S)](2-)}(n) anionic assembly in which the uranyl ion is bound to one chelating bidentate and three monodentate sulfonate groups from four C4S(4-) anions. The packing in 1 is of the bi-layer type, with counter-ions in the interlayer space, while the uranyl-C4S sheets in 2 are associated with layers comprising one-dimensional {[Ce-2(C4S)(H2O)(15)](2+)}(n) ribbons, thus giving a heterogeneous bi-layer arrangement. The uranyl environment in complex 3 is the same as in 1 and 2, but coordination of europium to one sulfonate group pertaining to a uranyl-bound anion results in the formation of a one-dimensional, ribbon-like heterometallic coordination polymer. These structures are the first to be reported for uranyl complexes with a p-sulfonated calixarene and also for uranyl-organic coordination polymers involving calixarenes.