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Kravchuk DV, Augustine LJ, Rajapaksha H, Benthin GC, Batista ER, Yang P, Forbes TZ. Insights into the Mechanism of Neptunium Oxidation to the Heptavalent State. Chemistry 2024; 30:e202304049. [PMID: 38183632 DOI: 10.1002/chem.202304049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Revised: 12/29/2023] [Accepted: 01/02/2024] [Indexed: 01/08/2024]
Abstract
Neptunium can exist in multiple oxidation states, including the rare and poorly understood heptavalent form. In this work, we monitored the formation of heptavalent neptunium [Np(VII)O4(OH)2]3- during ozonolysis of aqueous MOH (M=Li, Na, K) solutions using a combined experimental and theoretical approach. All experimental reactions were closely monitored via absorption and vibrational spectroscopy to follow both the oxidation state and the speciation of neptunium guided by the calculated vibrational frequencies for various neptunium species. The mechanism of the reaction partly involves oxidative dissolution of transient Np(VI) oxide/hydroxide solid phases, the identity of which are dependent on the co-precipitating counter-cation Li+/Na+/K+. Additional calculations suggest that the most favorable energetic pathway occurs through the reaction of a [Np(V)O2(OH)4]3- with the hydroxide radical to form [Np(VI)O2(OH)4]2-, followed by an additional oxidation with HO⋅ to create [Np(VII)O4(OH)2]3-.
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Affiliation(s)
- Dmytro V Kravchuk
- Department of Chemistry, University of Iowa, Iowa City, Iowa, 52242, United States
| | - Logan J Augustine
- Department of Chemistry, University of Iowa, Iowa City, Iowa, 52242, United States
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, United States
| | - Harindu Rajapaksha
- Department of Chemistry, University of Iowa, Iowa City, Iowa, 52242, United States
| | - Grant C Benthin
- Department of Chemistry, University of Iowa, Iowa City, Iowa, 52242, United States
| | - Enrique R Batista
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, United States
| | - Ping Yang
- Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545, United States
| | - Tori Z Forbes
- Department of Chemistry, University of Iowa, Iowa City, Iowa, 52242, United States
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2
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Raghavan A, Cahill CL. Orbital Engineering Mediated by Cation Conjugation in Luminescent Uranyl-Organic Hybrid Materials. Angew Chem Int Ed Engl 2024; 63:e202318161. [PMID: 38141052 DOI: 10.1002/anie.202318161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 12/20/2023] [Accepted: 12/22/2023] [Indexed: 12/24/2023]
Abstract
A series of compounds of the form [HAr]2 [UO2 X4 ] is reported here, wherein Ar is systematically varied between pyridine (1-X), quinoline (2-X), acridine (3-X), 2,5-dimethylpyrazine (4-X), quinoxaline (5-X), and phenazine (6-X), and X=Cl or Br. With greater conjugation in the organic cation, a larger quenching in uranyl luminescence is observed in the solid state. Supporting our luminescence experiments with computation, we map out the potential energy diagrams for the singlet and triplet states of both the [HAr]+ cations and [UO2 Cl4 ]2- anion in the crystalline state, and of the assembly. The distinct energy transfer pathways in each compound are discussed.
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Affiliation(s)
- Adharsh Raghavan
- Department of Chemistry, The George Washington University, 800 22nd St NW, Washington, DC 20052, USA
| | - Christopher L Cahill
- Department of Chemistry, The George Washington University, 800 22nd St NW, Washington, DC 20052, USA
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Rajapaksha H, Benthin GC, Markun EL, Mason SE, Forbes TZ. Synthesis, characterization, and density functional theory investigation of (CH 6N 3) 2[NpO 2Cl 3] and Rb[NpO 2Cl 2(H 2O)] chain structures. Dalton Trans 2024. [PMID: 38265201 DOI: 10.1039/d3dt03630h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2024]
Abstract
The actinyl tetrachloro complex [An(V/VI)O2Cl4]2-/3- tends to form discrete molecular units in both solution and solid state materials, but related aquachloro complexes have been observed as both discrete coordination compounds and 1-D chain topologies. Subtle differences in the inner sphere coordination significantly influence the formation of structural topologies in the actinyl chloride system, but the exact reasoning for these variations has not been delineated. In the current study, we present the synthesis, structural characterization, and vibrational analysis of two 1-D neptunyl(V) chain compounds: (CH6N3)2[NpO2Cl3] (Np-Gua) and Rb[NpO2Cl2(H2O)] (Np-Rb). Bonding and non-covalent interactions (NCIs) in the systems were evaluated using periodic Density Functional Theory (DFT) to link these properties to related phases. We observed ∼6.5% and ∼3.9% weakening of NpO bonds in Np-Gua and Np-Rb compared to the reference Cs3[NpO2Cl4]. NCI analysis distinguished specific assembly modes, where Np-Gua was connected via hydrogen bonding (N-H⋯Cleq and N-H⋯Oyl) and Np-Rb contained both cation interactions (Rb+⋯Oyl and Rb+⋯Cleq) and hydrogen bonding (Oeq-H⋯Oyl) networks. Thermodynamically viable formation pathways for both compounds were explored using DFT methodology. The [NpO2Cl4](aq)3- and [NpO2Cl3(H2O)](aq)2- substructures were identified as precursors to Np-Gua and [NpO2Cl3(H2O)](aq)2- and [NpO2Cl2(H2O)2](aq)- were isolated as the primary building units of Np-Rb. Finally, we utilized DFT to analyze the vibrational modes for Np-Gua and Np-Rb, where we found evidence of the NpO bond weakening within the Np(V) chain structures compared to [NpO2Cl4]3-.
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Affiliation(s)
| | - Grant C Benthin
- Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA.
| | - Emma L Markun
- Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA.
| | - Sara E Mason
- Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA.
- Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA.
| | - Tori Z Forbes
- Department of Chemistry, University of Iowa, Iowa City, IA 52242, USA.
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Rajapaksha H, Benthin GC, Kravchuk DV, Lightfoot H, Mason SE, Forbes TZ. Three-Dimensional Noncovalent Interaction Network within [NpO 2Cl 4] 2- Coordination Compounds: Influence on Thermochemical and Vibrational Properties. Inorg Chem 2023; 62:17265-17275. [PMID: 37816161 PMCID: PMC10598792 DOI: 10.1021/acs.inorgchem.3c02502] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2023] [Indexed: 10/12/2023]
Abstract
Noncovalent interactions (NCIs) can influence the stability and chemical properties of pentavalent and hexavalent actinyl (AnO2+/2+) compounds. In this work, the impact of NCIs (actinyl-hydrogen and actinyl-cation interactions) on the enthalpy of formation (ΔHf) and vibrational features was evaluated using Np(VI) tetrachloro compounds as the model system. We calculated the ΔHf values of these solid-state compounds through density functional theory+ thermodynamics (DFT+ T) and validated the results against experimental ΔHf values obtained through isothermal acid calorimetry. Three structural descriptors were evaluated to develop predictors for ΔHf, finding a strong link between ΔHf and hydrogen bond energy (EHtotal) for neptunyl-hydrogen interactions and total electrostatic attraction energy (Eelectrostatictotal) for neptunyl-cation interactions. Finally, we used Raman spectroscopy together with bond order analysis to probe Np=O bond perturbation due to NCIs. Our results showed a strong correlation between the degree of NCIs by axial oxygen and red-shifting of Np=O symmetrical stretch (ν1) wavenumbers and quantitatively demonstrated that NCIs can weaken the Np=O bond. These properties were then compared to those of related U(VI) and Np(V) phases to evaluate the effects of subtle differences in the NCIs and overall properties. In general, the outcomes of our study demonstrated the role of NCIs in stabilizing actinyl solid materials, which consequently governs their thermochemical behaviors and vibrational signatures.
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Affiliation(s)
- Harindu Rajapaksha
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Grant C. Benthin
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Dmytro V. Kravchuk
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Haley Lightfoot
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Sara E. Mason
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
- Center
for Functional Nanomaterials, Brookhaven
National Laboratory, Upton, New York 11973, United States
| | - Tori Z. Forbes
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
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Hutchison DC, Kravchuk DV, Rajapaksha H, Stegman S, Forbes TZ, Wilson RE. Synthesis of Single Crystal Li 2NpO 4 and Li 4NpO 5 from Aqueous Lithium Hydroxide Solutions under Mild Hydrothermal Conditions. Inorg Chem 2023; 62:16564-16573. [PMID: 37768147 DOI: 10.1021/acs.inorgchem.3c02460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/29/2023]
Abstract
The ternary oxides, Li2NpO4 and Li4NpO5, were synthesized under mild hydrothermal conditions using concentrated LiOH solutions containing NpO2(NO3)2. The reactions resulted in the formation of single crystals of both compounds, enabling the determination of their single crystal structures for the first time. Exploration of the synthetic phase space demonstrates that the resulting neptunate phases are dependent on the concentration of LiOH, transitioning from Li2NpO4, containing a typical octahedral neptunyl geometry with two shorter Np≡O bonds, at lower LiOH concentrations to Li4NpO5 with two long and four short Np-O bonds under saturated solution conditions. Reactions exploring the same synthetic conditions are also reported for uranyl(VI) for comparison. Raman spectra of the compounds were collected and analyzed to evaluate the Np-O bonding in these compounds.
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Affiliation(s)
- Danielle C Hutchison
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Dmytro V Kravchuk
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Harindu Rajapaksha
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Samantha Stegman
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Tori Z Forbes
- Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Richard E Wilson
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Lemont, Illinois 60439, United States
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Rajapaksha H, Mason SE, Forbes TZ. Synthesis, Characterization, and Density Functional Theory Investigation of the Solid-State [UO 2Cl 4(H 2O)] 2- Complex. Inorg Chem 2023; 62:14318-14325. [PMID: 37610833 PMCID: PMC10481372 DOI: 10.1021/acs.inorgchem.3c01725] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Indexed: 08/25/2023]
Abstract
A significant number of solid-state [UO2Cl4]2- coordination compounds have been synthesized and structurally characterized. Yet, despite their purposive relative abundance in aqueous solutions, characterization of aquachlorouranium(VI) complexes remain rare. In the current study, a solid-state uranyl aqua chloro complex ((C4H12N2)2[UO2Cl4(H2O)]Cl2) was synthesized using piperazinium as a charge-balancing ligand, and the structure was determined using single-crystal X-ray diffraction. Using periodic density functional theory, the electronic structure of the [UO2Cl4(H2O)]2- complex was compared to [UO2Cl4]2- to uncover the strengthening of the U═O bond in [UO2Cl4(H2O)]2-. Changes in the strength of the U═O bond were validated further with Raman and IR spectroscopy, where uranyl symmetrical (ν1) and asymmetrical (ν3) stretches were blue-shifted compared to the reference [UO2Cl4]2- complex. Furthermore, the formation energy of the solid-state (C4H12N2)2[UO2Cl4(H2O)]Cl2 complex was calculated to be -287.60 ± 1.75 kJ mol-1 using isothermal acid calorimetry. The demonstrated higher stability relative to the related [UO2Cl4]2- complex was related to the relative stoichiometry of the counterions.
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Affiliation(s)
- Harindu Rajapaksha
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
| | - Sara E. Mason
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
- Center
for Functional Nanomaterials, Brookhaven
National Laboratory, Upton, New York 11973, United States
| | - Tori Z. Forbes
- Department
of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States
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Rajapaksha H, Augustine LJ, Mason SE, Forbes TZ. Guiding Principles for the Rational Design of Hybrid Materials: Use of DFT Methodology for Evaluating Non-Covalent Interactions in a Uranyl Tetrahalide Model System. Angew Chem Int Ed Engl 2023; 62:e202305073. [PMID: 37177866 DOI: 10.1002/anie.202305073] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Revised: 05/11/2023] [Accepted: 05/12/2023] [Indexed: 05/15/2023]
Abstract
Together with the synthesis and experimental characterization of 14 hybrid materials containing [UO2 X4 ]2- (X=Cl- and Br- ) and organic cations, we report on novel methods for determining correlation trends in their formation enthalpy (ΔHf ) and observed vibrational signatures. ΔHf values were analyzed through isothermal acid calorimetry and a Density Functional Theory+Thermodynamics (DFT+T) approach with results showing good agreement between theory and experiment. Three factors (packing efficiency, cation protonation enthalpy, and hydrogen bonding energy [E H , norm total ${{E}_{H,{\rm { norm}}}^{{\rm { total}}}}$ ]) were assessed as descriptors for trends in ΔHf . Results demonstrated a strong correlation betweenE H , norm total ${E_{{\rm{H}},{\rm{norm}}}^{{\rm{total}}} }$ and ΔHf , highlighting the importance of hydrogen bonding networks in determining the relative stability of solid-state hybrid materials. Lastly, we investigate how hydrogen bonding networks affect the vibrational characteristics of uranyl solid-state materials using experimental Raman and IR spectroscopy and theoretical bond orders and find that hydrogen bonding can red-shift U≡O stretching modes. Overall, the tightly integrated experimental and theoretical studies presented here bridge the trends in macroscopic thermodynamic energies and spectroscopic features with molecular-level details of the geometry and electronic structure. This modeling framework forms a basis for exploring 3D hydrogen bonding as a tunable design feature in the pursuit of supramolecular materials by rational design.
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Affiliation(s)
- Harindu Rajapaksha
- Department of Chemistry, University of Iowa, Chemistry Building W374, Iowa City, IA 52242, USA
| | - Logan J Augustine
- Department of Chemistry, University of Iowa, Chemistry Building W374, Iowa City, IA 52242, USA
| | - Sara E Mason
- Department of Chemistry, University of Iowa, Chemistry Building W374, Iowa City, IA 52242, USA
- Center for Funtional Nanomaterials (CFN), Brookhaven National Labotatory, Upton, NY 52242, USA
| | - Tori Z Forbes
- Department of Chemistry, University of Iowa, Chemistry Building W374, Iowa City, IA 52242, USA
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Kohlgruber TA, Surbella III RG. (NH 4) 2[UO 2Cl 4]·2H 2O, a new uranyl tetra-chloride with ammonium charge-balancing cations. Acta Crystallogr E Crystallogr Commun 2023; 79:702-706. [PMID: 37601403 PMCID: PMC10439412 DOI: 10.1107/s2056989023005753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Accepted: 06/29/2023] [Indexed: 08/22/2023]
Abstract
A new uranyl tetra-chloride salt with chemical formula, (NH4)2[UO2Cl4]·2H2O, namely, di-ammonium uranyl tetra-chloride dihydrate, 1, was prepared and crystallized via slow evaporation from a solution of 2 M hydro-chloric acid. As confirmed by powder X-ray diffraction, the title compound crystallizes with an ammonium chloride impurity that formed as a result of the breakdown of a triazine precursor. The (UO2Cl4)2- dianion is charge balanced by ammonium cations, while an extensive hydrogen-bond network donated from structural water mol-ecules stabilize the overall assembly. Compound 1 adds to the extensive collection of actinyl tetra-chloride salts, but it represents the first without an alkali cation for purely inorganic compounds. Diffuse reflectance and luminescence spectra show typical absorption and emission behavior, respectively, of uranyl materials.
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