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

Abstract

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.