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

Abstract

In this work, we demonstrate a family of new inorganic-organic hybrid uranyl diphosphonates based on 1-hydroxyethylidenediphosphonic acid (H(4)L) linker by using hydrothermal method. These compounds, (Hbpi)[(UO(2))(H(2)O)(HL)]·H(2)O (UP-1), represents 1D structure, (Hbpi)[(UO(2))(H(2)O)(HL)] (UP-2), (H(2)dib)(0.5)[(UO(2))(H(2)O)(HL)] (UP-3), and [(UO(2))(H(2)O)(H(2)L)]·2H(2)O (UP-4) feature 2D architectures, (H(2)bipy){[(UO(2))(H(2)O)](2)[(UO(2))(H(2)O)(2)](L)(2)}·2H(2)O (UP-5), and (H(3)O)(2){[(UO(2))(H(2)O)](3)(L)(2)}·2H(2)O (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 UO(2)/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 H(3)O(+) 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.