From 1D Chain to 3D Framework Uranyl Diphosphonates: Syntheses, Crystal Structures, and Selective Ion Exchange

In this work, we demonstrate a family of new inorganic–organic
hybrid uranyl diphosphonates based on 1-hydroxyethylidenediphosphonic
acid (H4L) linker by using hydrothermal method. These compounds,
(Hbpi)­[(UO2)­(H2O)­(HL)]·H2O (UP-1), represents 1D structure, (Hbpi)­[(UO2)­(H2O)­(HL)] (UP-2), (H2dib)0.5[(UO2)­(H2O)­(HL)] (UP-3), and [(UO2)­(H2O)­(H2L)]·2H2O (UP-4) feature 2D architectures, (H2bipy)­{[(UO2)­(H2O)]2[(UO2)­(H2O)2]­(L)2}·2H2O (UP-5), and (H3O)2{[(UO2)­(H2O)]3(L)2}·2H2O (UP-6) adopt 3D networks (bpi: 1-(biphenyl-4-yl)-1H-imidazole, dib: 1,4-di­(1H-imidazol-1-yl)­benzene,
bipy: 2,2′-bipyridine). Among them, UP-1, UP-2, UP-3, and UP-4 possess the
same structural building unit but with different structures. UP-5 and UP-6 feature the same UO2/L ratio of 3:2 but a different structural building unit. Photoluminescence
studies reveal that UP-5 displays characteristic emissions
of uranyl cations. Ion-exchange experiments demonstrate that the H3O+ in UP-6 can be easily and selectively
exchanged by monovalent cations including Na+, K+, Cs+, and Ag+ cations, whereas the framework
retains identical as confirmed by single-crystal X-ray diffractions.