Abstract
We confirm that synthetic uranyl hydroxide hydrate metaschoepite [(UO)24O(OH)6]·5H2O 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.
| Original language | English |
|---|---|
| Pages (from-to) | 7310-7323 |
| Number of pages | 14 |
| Journal | Inorganic Chemistry |
| Volume | 58 |
| Issue number | 11 |
| DOIs | |
| State | Published - Jun 3 2019 |
Funding
We thank Michael Lance in the Materials Science and Technology Division at Oak Ridge National Laboratory (ORNL) for the use of his FTIR, as well as Doug Abernathy, Ashfia Huq, and Melanie Kirkham at the Spallation Neutron Source at ORNL for their assistance collecting neutron diffraction and scattering data. Tyler L. Spano and Michael W. Ambrogio in the Nuclear Nonproliferation Division at ORNL provided helpful comments on this manuscript. Neutron diffraction and inelastic neutron scattering data were collected at the Spallation Neutron Source, which is a U.S. Department of Energy Office of Science user facility. Images of crystal structures were produced using VESTA.66 This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy (DOE). The U.S. government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/ doe-public-access-plan). This material is based upon work supported by the U.S. Department of Homeland Security under grant award number 2012-DN-130-NF0001. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the U.S. Department of Homeland Security.
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| U.S. Department of Homeland Security | 2012-DN-130-NF0001 |