Layered and three-dimensional uranyl–organic assemblies with 4,4′-oxidiphthalic acid

Hydrothermal reactions of uranyl nitrate and 4,4′-oxidiphthalic acid (H4L) resulted in the formation of three new uranyl–organic framework materials, namely (NH4)2[(UO2)3(L)2]·5H2O (1), (NEt4)[(UO2)3(H2O)(L)(HL)] (2) and (UO2)7(H2O)2(phen)4(L)2(HL)2 (3) (NEt4 = tetraethylammonium, phen = 1,10-phenanthroline). These three structures all comprise common uranyl pentagonal bipyramids. In 1, UO7 polyhedra are linked by hexadentate ligands to form a 3D framework with 1D channels, in which are located NH4+ ions and water molecules. While in 2, the organic ligands adopt pentadentate and hexadentate coordination modes, ligating UO7 units to create a layered structure with channels filled by NEt4+ ions. For 3, uranyl square bipyramids are also accommodated together with pentagonal bipyramids, which are linked by tetradentate carboxylate ligands to produce the layered assembly. Phen molecules also coordinate to the uranyl centers to build up the structure. Luminescent studies indicate that 2 and 3 exhibit the characteristic uranyl emission.

Graphical abstractThree uranyl carboxylates with layered and framework structures have been prepared by hydrothermal reaction of uranyl nitrate and flexible 4,4′-oxidiphthalic acid. Typical vibronically coupled charge-transfer based emissions of uranyl cation were demonstrated by these compounds.Figure optionsDownload full-size imageDownload as PowerPoint slide