Uranyl Ion Complexes with all-cis-1,3,5-Cyclohexanetricarboxylate: Unexpected Framework and Nanotubular Assemblies

all-cis-1,3,5-Cyclohexanetricarboxylic acid (LH₃) was reacted with uranyl nitrate under solvo-hydrothermal conditions, either alone or in the presence of additional metal cations (Na⁺, K⁺, Ni²⁺, Cu²⁺, or Tb³⁺), resulting in the crystallization of a series of eight complexes which were characterized by their crystal structures and luminescence properties. The six complexes [UO₂(H₂O)₅]­[UO₂(L)]₂­·2H₂O­·3THF (1), [Ni­(bipy)₂­(H₂O)₂]­[UO₂(L)]₂­·4H₂O (2), [Ni­(bipy)₃]­[Ni­(bipy)₂­(H₂O)₂]­[UO₂(L)]₄­·5H₂O (3), [Ni­(H₂O)₆]­[UO₂(L)]₂­·2H₂O (4), [Cu­(H₂O)₆]­[UO₂(L)]₂­·2H₂O (5), and [Tb­(H₂O)₈]­[UO₂(L)]₃­·8H₂O (6) all contain the same {UO₂(L)⁻}_∞ anionic motif, in which the uranyl ion is tris-chelated by three L^3– anions to give a two-dimensional assembly with hexagonal {6³} topology. The reaction of uranyl nitrate alone with LH₃ in water/N-methyl-2-pyrrolidone (NMP) yields the complex [(UO₂)₃(L)₂­(NMP)₂] (7), which crystallizes as a three-dimensional framework. Finally, in the presence of Na⁺, K⁺, or even Kemp’s triacid (cis,cis-1,3,5-trimethylcyclohexane-1,3,5-tricarboxylic acid), the complex [UO₂(LH)] (8) is generated, the structure of which displays a well-resolved nanotubular species possibly associated with extremely disordered molecules or counterions of uncertain nature. These nanotubules have {6³} topology and can be seen as resulting from the folding of the two-dimensional assembly present in the former complexes. Emission spectra measured in the solid state show the usual vibronic fine structure, with various degrees of resolution and quenching.