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Lontchi EM, Vasiliu M, Dixon DA. Hydrolysis Reactions of the High Oxidation State Dimers Th 2O 4, Pa 2O 5, U 2O 6, and Np 2O 6. A Computational Study. J Phys Chem A 2023; 127:6732-6748. [PMID: 37549315 DOI: 10.1021/acs.jpca.3c03455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/09/2023]
Abstract
The energetics of the hydrolysis reactions for high oxidation states of the dimeric actinide species Th2IVO4, Pa2VO5, and U2VIO6 were calculated at the CCSD(T) level and those for triplet Np2VIO6 at the B3LYP level. Hydrolysis is initiated by the formation of a Lewis acid/base adduct with H2O (physisorbed product), followed by a proton transfer to form a dihydroxide molecule (chemisorbed product); this process was repeated until the initial actinide oxide is fully hydrolyzed. For Th2O4, hydrolysis (chemisorption) by the initial and subsequent H2O molecules prefers proton transfer to terminal oxo groups before the bridge oxo groups. The overall Th2O4 hydration pathway is exothermic with chemisorbed products preferred over the physisorption products, and the fully hydrolyzed Th2(OH)8 can form exothermically. Hydrolysis of Pa2O5 forms isomers of similar energies with no initial preference for bridge or terminal hydroxy groups. The most exothermic hydrolysis product for Pa is Pa2O(OH)8 and the most stable species is Pa2O(OH)8(H2O). Hydrolysis of U2O6 and Np2O6 with strong [O═An═O]2+ actinyl groups occurs first at the bridging oxygens rather than at the terminal oxo groups. The U2O6 and Np2O6 pathways predict hydrated products to be more favored than hydrolyzed products, as more H2O molecules are added. The stability of the U and Np clusters is predicted to decrease with increasing number of hydroxyl groups. The most stable species on the hydration reaction coordinate for U and Np is An2O3(OH)6(H2O).
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Affiliation(s)
- Eddy M Lontchi
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
| | - Monica Vasiliu
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
| | - David A Dixon
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
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Theoretical investigation of the structure and spectroscopy of uranium oxide species. Theor Chem Acc 2023. [DOI: 10.1007/s00214-022-02947-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Marks JH, Batchelor AG, Blais JRC, Duncan MA. Cation Complexes of Uranium and Thorium with Cyclooctatetraene: Photochemistry and Decomposition Products. J Phys Chem A 2022; 126:4230-4240. [PMID: 35749286 DOI: 10.1021/acs.jpca.2c03035] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Ion-molecule complexes of uranium or thorium singly-charged positive ions bound to cyclooctatetraene (COT), i.e., M+(COT)1,2, are produced by laser ablation and studied with UV laser photodissociation. The ions are selected by mass and excited at 355 or 532 nm, and the ionized dissociation products are detected using a reflectron time-of-flight mass spectrometer. The abundant fragments M+(C6H6), M+(C4H4), and M+(C2H2) occur for complexes of both metals, whereas the M+(C4H2), M+(C3H3), and M+(C5H5) fragments are prominent for uranium complexes but not for thorium. Additional experiments investigate the dissociation of M+(benzene)1,2 ions which may be intermediates in the fragmentation of the COT ions. The experiments are complemented by computational quantum chemistry to investigate the structures and energetics of fragment ions. Various cation-π and metallacycle structures are indicated for different fragment ions. The metal ion-ligand bond energies for corresponding complex ions are systematically greater for the thorium species. The computed thermochemistry makes it possible to explain the mechanistic details of the photochemical fragmentation processes and to reveal new actinide organometallic structures.
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Affiliation(s)
- Joshua H Marks
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Anna G Batchelor
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - John R C Blais
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - Michael A Duncan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
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Marks JH, Rittgers BM, Van Stipdonk MJ, Duncan MA. Photodissociation and Infrared Spectroscopy of Uranium-Nitrogen Cation Complexes. J Phys Chem A 2021; 125:7278-7288. [PMID: 34387501 DOI: 10.1021/acs.jpca.1c05823] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Laser vaporization of uranium in a pulsed supersonic expansion of nitrogen is used to produce complexes of the form U+(N2)n (n = 1-8). These ions are mass selected in a reflectron time-of-flight spectrometer and studied with visible and UV laser fixed-frequency photodissociation and with tunable infrared laser photodissociation spectroscopy. The dissociation patterns and spectroscopy of U+(N2)n indicate that N2 ligands are intact molecules and that there is no insertion chemistry resulting in UN+ or NUN+. Fixed frequency photodissociation at 532 and 355 nm indicate that the U+-N2 bond dissociation energy varies little with changing coordination. The photon energy and the number of ligands eliminated allow an estimate of the average U+-N2 dissociation energy of 12 kcal/mol. Infrared bands are observed for these complexes near the N-N stretch vibration via elimination of N2 molecules. These resonances are observed to be shifted about 130 cm-1 to the red from the free-N2 frequency for complexes with n = 3-8. Density functional theory indicates that U+ is most stable in the sextet state in these complexes and that N2 molecules bind in end-on configurations. The fully coordinated complex is predicted to be U+(N2)8, which has a cubic structure. The vibrational frequencies predicted by theory are consistently lower than those in the experiment, independent of the isomeric structure or spin state of the complexes. Despite its failure to reproduce the infrared spectra, theory provides an average U+-N2 dissociation energy of 11.8 ± 0.5 kcal/mol, in good agreement with the value from the experiments.
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Affiliation(s)
- J H Marks
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - B M Rittgers
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
| | - M J Van Stipdonk
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, United States
| | - M A Duncan
- Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States
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Lontchi EM, Vasiliu M, Tatina LM, Caccamo AC, Gomez AN, Gibson JK, Dixon DA. Hydrolysis of Small Oxo/Hydroxo Molecules Containing High Oxidation State Actinides (Th, Pa, U, Np, Pu): A Computational Study. J Phys Chem A 2021; 125:6158-6170. [PMID: 34240864 DOI: 10.1021/acs.jpca.1c04048] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The energetics of hydrolysis reactions for high oxidation states of oxo/hydroxo monomeric actinide species (ThIVO2, PaIVO2, UIVO2, PaVO2(OH), UVO2(OH), UVIO3, NpVIO3, NpVIIO3(OH), and PuVIIO3(OH)) were calculated at the CCSD(T) level. The first step is the formation of a Lewis acid/base adduct with H2O (hydration), followed by a proton transfer to form a dihydroxide molecule (hydrolysis); this process is repeated until all oxo groups are hydrolyzed. The physisorption (hydration) for each H2O addition was predicted to be exothermic, ca. -20 kcal/mol. The hydrolysis products are preferred energetically over the hydration products for the +IV and +V oxidation states. The compounds with AnVI are a turning point in terms of favoring hydration over hydrolysis. For AnVIIO3(OH), hydration products are preferred, and only two waters can bind; the complete hydrolysis process is now endothermic, and the oxidation state for the An in An(OH)7 is +VI with two OH groups each having one-half an electron. The natural bond order charges and the reaction energies provide insights into the nature of the hydrolysis/hydration processes. The actinide charges and bond ionicity generally decrease across the period. The ionic character decreases as the oxidation state and coordination number increase so that covalency increases moving to the right in the actinide period.
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Affiliation(s)
- Eddy M Lontchi
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
| | - Monica Vasiliu
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
| | - Lauren M Tatina
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
| | - Alyssa C Caccamo
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
| | - Amber N Gomez
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
| | - John K Gibson
- Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
| | - David A Dixon
- Department of Chemistry and Biochemistry, The University of Alabama, Shelby Hall, Tuscaloosa, Alabama 35487-0336, United States
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Vasiliu M, Peterson KA, Dixon DA. Calculated Ionization Potentials of MO3 and MO2 for M = U, Mo, W, and Nd. J Phys Chem A 2020; 124:6913-6919. [DOI: 10.1021/acs.jpca.0c05925] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Monica Vasiliu
- Department of Chemistry and Biochemistry, University of Alabama, Tuscaloosa, Alabama 35401, United States
| | - Kirk A. Peterson
- Department of Chemistry, Washington State University, Pullman, Washington 99164, United States
| | - David A. Dixon
- Department of Chemistry and Biochemistry, University of Alabama, Tuscaloosa, Alabama 35401, United States
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