Dissertation
Actinyl interactions: structural characteristics and vibrational properties
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Spring 2022
DOI: 10.17077/etd.006445
Abstract
The actinyl cation, An(V/VI)O2n+ (n=1,2) is the prevalent species in aqueous systems for uranium and neptunium, yet the full extent in which the oxygen atoms(oxo) within the cation influence chemical speciation and properties is not yet fully understood. When tightly bound to the actinide center, the oxo groups are thought of as terminal and unable to engage with external species. Beyond the inherent properties associated with the metal center, equatorially coordinated ligands can influence the covalently bound oxo groups, in turn impacting the availability of the axially bound oxygens to participate in additional interactions, such as hydrogen bonding and/or coordination to additional actinyl centers (actinyl-actinyl interactions). Interactions with the oxo atoms can result in a deviation from traditional vibrational signals associated with the linear triatomic [O=An=O] moiety as well as influence stability and overall speciation, all of which can directly impact identification of radioactive materials in environmental systems and the radiochemical separations of nuclear waste and related materials. To understand the role and extent to which the oxo atom can be engaged in solution and solid-state materials a step-by-step approach was taken to delineate the specific chemical environments which promote these oxo-interactions and evaluation of the spectral signals of the An(V/VI)O2n+ (n=1,2) when it participates in interactions of varied strength.
The objective of my thesis work was to determine how the spectroscopic properties and physical properties of actinyl species change upon varying the coordination through differing degrees of interactions (hydrogen bonds, direct covalent interactions, polymerization) in solution and solid state. Within the scope of actinyl studies, projects were developed looking at three specific actinyl cations: the uranyl (VI) cation [UO2]2+, the neptunyl(V) cation [NpO2]+ and the neptunyl (VI) cation [NpO2]2+. Throughout the studies the fundamental differences of [U(VI)O2]2+, [Np(V)O2]1+ and [Np(VI)O2]2+ to participate with neighboring donor molecules capable of hydrogen bonding or coordinate to alkali cations is explored. The conditions that led to the formation of actinyl-actinyl interactions for [Np(V)O2]+ in solution phase and crystalline materials is also focused on. The changes in vibrational bands of the actinyl cation was found to occur via shifts of the symmetric ν1 or the activation of traditionally Raman inactive bands. Species that display strong bonds to the oxo, particularly interactions to secondary actinyl moieties, show multiple unique Raman vibrational bands separate than that of an uncoordinated O=An=O moiety. This dissertation significantly enhances our understanding of the coordination chemistry and corresponding vibrational features of the actinyl cation in aqueous environments.
Details
- Title: Subtitle
- Actinyl interactions: structural characteristics and vibrational properties
- Creators
- Mikaela Mary F. Pyrch
- Contributors
- Tori Z. Forbes (Advisor)Scott R. Daly (Committee Member)Edward G. Gillan (Committee Member)F. Christopher Pigge (Committee Member)Leonard R. MacGillivray (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Chemistry
- Date degree season
- Spring 2022
- DOI
- 10.17077/etd.006445
- Publisher
- University of Iowa
- Number of pages
- xxvi, 329 pages
- Copyright
- Copyright 2022 Mikaela Mary F. Pyrch
- Language
- English
- Description illustrations
- Charts, graphs, tables
- Description bibliographic
- Includes bibliographical references (pages 305-324).
- Public Abstract (ETD)
Uranium (U) and Neptunium (Np) are long-lived radionuclides that are present in waste generated from nuclear energy and will be major contributors to the total radioactivity of the waste for the foreseeable future (10,000-1,000,000 years from now). Particularly, neptunium is problematic within nuclear waste separations due to challenges in predicting its chemistry.
The actinyl cation AnO2n+ (where An=U, Np, and n=1, 2) cation is the main form of uranium and neptunium in acidic aqueous solutions. The chemical behavior and stability of actinyl species are driven by the chemical components present in the system. Interactions with the oxygen atom of the neptunyl cation may impact the chemistry of these species, but little is understood about how specific interactions (hydrogen bonds, interactions with alkali cation or other neptunyl cations) influence the properties of both solution and solid-state species. In this work, we evaluate how interactions between neptunyl species in coordination complexes results in changes of characteristic properties associated with the actinyl through vibrational studies. Crystalline materials were synthesized through slow evaporation techniques and characterized via single crystal X-ray diffraction and solid-state Raman spectroscopy, and then compared to related aqueous solutions. These results provide knowledge on the behavior of uranium and neptunium in the presence of other constituents, which may have implications in future separations processes and the storage of actinide containing materials.
- Academic Unit
- Chemistry
- Record Identifier
- 9984271053902771
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