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.

本工作通过水热合成法，以1-羟基亚乙基二膦酸（1-hydroxyethylidenediphosphonic acid，H4L）为桥联配体，构筑了一系列新型无机-有机杂化二膦酸铀酰化合物。其中，(Hbpi)[(UO2)(H2O)(HL)]·H2O（标记为UP-1）呈现一维结构；(Hbpi)[(UO2)(H2O)(HL)]（UP-2）、(H2dib)0.5[(UO2)(H2O)(HL)]（UP-3）以及[(UO2)(H2O)(H2L)]·2H2O（UP-4）均具有二维骨架结构；(H2bipy){[(UO2)(H2O)]2[(UO2)(H2O)2](L)2}·2H2O（UP-5）与(H3O)2{[(UO2)(H2O)]3(L)2}·2H2O（UP-6）则构筑为三维网络结构。（注：bpi为1-(联苯-4-基)-1H-咪唑，dib为1,4-二(1H-咪唑-1-基)苯，bipy为2,2'-联吡啶）
上述UP-1、UP-2、UP-3与UP-4具有相同的结构构筑基元，但呈现不同的空间拓扑结构。UP-5与UP-6拥有相同的UO2/L摩尔比（3:2），但结构构筑基元存在差异。
光致发光性能测试表明，UP-5可展现出铀酰阳离子的特征发射峰。离子交换实验结果显示，UP-6中的H3O+可被Na+、K+、Cs+及Ag+等一价阳离子高效且选择性地交换，且经单晶X射线衍射表征证实，交换后的框架结构保持不变。