Lu Kimbal T, Zhang Yingjie, Aughterson Robert D, Zheng Rongkun
Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.
School of Physics, The University of Sydney, Camperdown, New South Wales 2006, Australia.
Dalton Trans. 2020 Nov 17;49(44):15854-15863. doi: 10.1039/d0dt02944k.
Two uranyl oxide hydrate frameworks (UOFs) incorporating either Eu(iii) or Gd(iii) ions were synthesized hydrothermally and structurally studied. The uranyl oxide hydroxide layers similar to those in β-U3O8 with both tetragonal and pentagonal bipyramidal uranium polyhedra are connected with pairs of pentagonal bipyramidal uranium polyhedra through uranyl cation-cation interactions to form three-dimensional frameworks with Eu(iii) or Gd(iii) ions inside the channels. Both SEM and TEM examinations revealed needle crystal morphologies and a U:Eu/Gd ratio of 5.5, with the TEM-SAED pattern indexed to the orthorhombic crystal structure C2221, as also determined using synchrotron single-crystal X-ray diffraction. Raman spectroscopy revealed the band splitting of uranyl symmetric stretching vibrations, reflecting the presence of a unique pentavalent uranium centre in octahedral coordination geometry. The presence of pentavalent uranium in both UOFs was confirmed with diffuse reflectance spectroscopy. Given that layer-structured uranyl oxide hydroxy hydrate phases are dominant for both light and heavy lanthanide ions under similar reaction conditions, the ionic radius plays an important role in controlling the structure types, with UOFs formed only for Eu(iii) and Gd(iii) ions in the lanthanide series. These new UOFs with lanthanide ions may have various implications especially in nuclear materials.
通过水热法合成了两种分别掺入铕（Ⅲ）或钆（Ⅲ）离子的氢氧化铀酰水合物框架（UOFs）并对其进行了结构研究。与β-U3O8中类似的氢氧化铀酰层，含有四方和五角双锥铀多面体，通过铀酰阳离子-阳离子相互作用与成对的五角双锥铀多面体相连，形成三维框架，通道内含有铕（Ⅲ）或钆（Ⅲ）离子。扫描电子显微镜（SEM）和透射电子显微镜（TEM）检查均显示出针状晶体形态，铀与铕/钆的比例为5.5，透射电子显微镜选区电子衍射（TEM-SAED）图谱与正交晶体结构C2221相匹配，这也通过同步辐射单晶X射线衍射确定。拉曼光谱显示了铀酰对称伸缩振动的谱带分裂，反映出在八面体配位几何结构中存在独特的五价铀中心。通过漫反射光谱证实了两种UOFs中均存在五价铀。鉴于在相似反应条件下，层状结构的氢氧化铀酰水合物相对于轻、重镧系离子均占主导地位，离子半径在控制结构类型方面起着重要作用，在镧系元素中仅铕（Ⅲ）和钆（Ⅲ）离子形成了UOFs。这些含有镧系离子的新型UOFs可能具有多种意义，特别是在核材料方面。
