Kirkegaard Marie C, Niedziela J L, Miskowiec Andrew, Shields Ashley E, Anderson Brian B
Nuclear Nonproliferation Division , Oak Ridge National Laboratory , Oak Ridge , Tennessee 37831 , United States.
Bredesen Center for Interdisciplinary Research and Graduate Education , University of Tennessee , Knoxville , Tennessee 37996 , United States.
Inorg Chem. 2019 Jun 3;58(11):7310-7323. doi: 10.1021/acs.inorgchem.9b00460. Epub 2019 May 17.
We confirm that synthetic uranyl hydroxide hydrate metaschoepite [(UO)2O(OH)]·5HO is unstable against dehydration under dry conditions, and we present a structural and vibrational spectroscopic study of synthetic metaschoepite and its ambient temperature dehydration product. Complementary structural (X-ray diffraction and neutron diffraction) and vibrational spectroscopic techniques (Raman spectroscopy, infrared spectroscopy, and inelastic neutron scattering) are used to probe different components of these species. Analysis of the dehydration product suggests that it contains both pentagonally coordinated and hexagonally coordinated uranyl ions, necessitating that some uranyl ions undergo a coordination change during the dehydration of pentagonally coordinated metaschoepite. Vibrational spectra of metaschoepite and its dehydration product are interpreted with power spectra generated from ab initio molecular dynamics trajectories, allowing assignment of all major features. We identify the uranyl symmetric stretching modes of the four distinct uranyl ions in synthetic metaschoepite and clarify the assignment of lower energy Raman modes in both structures. The coanalysis of experimental and computational data reveals a strong coupling between the uranyl stretching modes and hydroxide bending modes in the anhydrous structure, leading to the presence of several high-energy combination bands in the inelastic neutron scattering data.
我们证实，合成的水合氢氧化铀酰变水铀矿[(UO)₂O(OH)]·5H₂O在干燥条件下对脱水不稳定，并且我们展示了对合成变水铀矿及其室温脱水产物的结构和振动光谱研究。使用互补的结构（X射线衍射和中子衍射）和振动光谱技术（拉曼光谱、红外光谱和非弹性中子散射）来探测这些物质的不同成分。对脱水产物的分析表明，它包含五配位和六配位的铀酰离子，这使得一些铀酰离子在五配位变水铀矿脱水过程中发生配位变化。变水铀矿及其脱水产物的振动光谱通过从头算分子动力学轨迹生成的功率谱进行解释，从而对所有主要特征进行了归属。我们确定了合成变水铀矿中四种不同铀酰离子的铀酰对称拉伸模式，并阐明了两种结构中低能量拉曼模式的归属。实验数据和计算数据的共同分析揭示了无水结构中铀酰拉伸模式和氢氧化物弯曲模式之间的强耦合，导致非弹性中子散射数据中出现几个高能量组合带。
