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

The reaction of uranyl nitrate with p-sulfonatocalix[4]arene (H4C4S), carried out in water at room temperature in the presence of either NMe4OH or lanthanide nitrates, yielded the three complexes [NMe4]2[UO2(C4S)]·0.5H2O (1), [Ce2(C4S)(H2O)15][UO2(C4S)]·15H2O (2) and [Eu(H2O)8.5][UO2Eu(C4S)2(H2O)7]·13H2O (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 C4S4− 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 {[Ce2(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.