A Highly Adjustable Coordination System: Nanotubular and Molecular Cage Species in Uranyl Ion Complexes with Kemp’s Triacid

A unique example
of topology tailoring in a uranyl–organic
system is provided by the three-pronged Kemp’s tricarboxylate
ligand. While unexceptional one-dimensional polymers are formed with
uranyl alone under solvo-hydrothermal conditions, addition of Ni2+ ions yields the nanotubular species [(UO2)2Ni­(L)2(H2O)4]∞, with a hydrophilic inner cavity lined by hydrated Ni2+ ions, and a hydrophobic outer surface. The further presence of 2,2′-bipyridine
brings about the trapping of Ni2+ ions into counterions
and formation of the octanuclear pseudocubic cage [(UO2)8(L)6(H2O)6]2–.