Counterion-Controlled Formation of Layered Honeycomb and Polythreading Uranyl Networks and the Highly Sensitive and Selective Detection of Fe3+ in Aqueous Media.

Under hydrothermal conditions, six uranium coordination polymers were obtained by employing the ligand of tris(2-carboxyethyl) isocyanurate (H3tci) and different combinations of d-block metal ions (Mn2+, Co2+, Zn2+, Ni2+) or N-donors (triethylamine (Et3N), 2,2'-bipyridine (2,2'-bipy)). Three uranium polymers [(UO2)2(tci)2]1/2-·[Mn2(µ2-O)(H2O)8]1/2+·2H2O (1), [(UO2)2(tci)2]1/2-·[Co2(µ2-O)(H2O)8]1/2+ (2), and [(UO2)2(tci)2]1/2-·[Zn2(µ2-O)(H2O)8]1/2+·2H2O (3) containing transition metal hydrated ions, crystallized as two-dimensional coordination polymers with the common (6, 3) net topology. X-ray crystal structures of 1-3 display that they have similar honeycomb-like frameworks with all ligands bis-chelating. [UO2(tci)]-3·[Ni(H2O)6]2+(H3O)+·2H2O (4) and [UO2(tci)]-·[NH(CH2CH3)3]1/3+·(2H3O+)1/3 (5) are made up of four interlocked sets and exhibit the 4-fold-interpenetrated frameworks. [UO2(tci)]-·(C10H9N2)+·H2O (6) comprises the 2,2'-bipy cation as counterion and represents a 2D grid layered structure. Additional metals and the N-donors are all free in the complexes, acting as the templates and compensation of the charge equilibrium. The solid-state emission spectra indicate that all of the synthesized compounds own fluorescence emissions. Furthermore, the results of the quenching ability of Fe3+ for complexes 5 and 6 exhibit their highly sensitive and selective detection for Fe3+ ions. Moreover, the uranium complexes can be used as a potential probe for Fe3+ in aqueous solutions.