Charge Density Influence on Enthalpy of Formation of Uranyl Peroxide

Aug 29, 2018 - Peedikakkal, Quah, Chia, Jalilov, Shaikh, Al-Mohsin, Yadava, Ji, and Vittal. 2018 57 (18), pp 11341–11348. Abstract: Reaction of bpy ...
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Charge Density Influence on Enthalpy of Formation of Uranyl Peroxide Cage Cluster Salts Melika Sharifironizi,† Jennifer E. S. Szymanowski,† Jie Qiu,† Sarah Castillo,† Sarah Hickam,† and Peter C. Burns*,†,‡ †

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Department of Civil and Environmental Engineering and Earth Sciences, University of Notre Dame, Notre Dame, Indiana 46556, United States ‡ Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, United States S Supporting Information *

ABSTRACT: More than 60 unique uranyl peroxide cage clusters have been reported that contain as many as 124 uranyl ions and that have overall diameters extending to 4 nm. They self-assemble in water under ambient conditions, are models for understanding structure−size−property relations as well as testing computational models for actinides, and have potential applications in nuclear fuel cycles. High-temperature drop solution calorimetry has been used to derive the enthalpies of formation of the salts of seven topologically diverse uranyl peroxide cage clusters containing from 22 to 28 uranyl ions that are bridged by various combinations of peroxide, pyrophosphate, and phosphite. The enthalpies of formation of these seven salts, as well as three salts of other uranyl peroxide clusters reported earlier, are dominated by the interactions of the alkali countercations with the clusters. There is an approximately linear relationship between the enthalpies of formation of the cluster salts and the charge density of the corresponding uranyl peroxide cluster, wherein salts containing clusters with higher charge densities have more negative enthalpies of formation.

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INTRODUCTION Metal oxide clusters, including transition metal and actinide polyoxometalates, provide unique opportunities to study size− property relationships of nanoscale materials, and have numerous potential and realized applications.1−7 Beginning in 2005, a family of uranyl peroxide cage clusters has been developed,8 which now includes more than 60 published members9 that contain from 16 to 124 uranyl ions bridged through various linkers and that have diameters ranging to 4 nm.10−13 Uranyl peroxide clusters are a unique class of cage polyoxometalates that are stabilized on the inside and outside by uranyl ion “yl” oxygen atoms, which are invariably arranged in a trans configuration about the U(VI) cation.9,14 Uranyl peroxide cages encapsulate various cations and in a few cases oxyanions, and their overall negative charges are balanced by countercations that are most commonly alkalis.14 We note that there are other examples of uranium-containing polyoxometalates, including peroxo-bearing structures, that are structurally distinct from the uranyl peroxide cage clusters studied here.15−23 Uranyl peroxide cage clusters are typically stable and soluble in water,24 and under some conditions, they aggregate into hollow blackberries that persist in solution.25−27 They selfassemble in aqueous solution under ambient conditions, and can be crystallized for detailed characterization.28 Uranyl © XXXX American Chemical Society

peroxide clusters have potential applications in nuclear materials processing that include separating uranium from dissolved irradiated nuclear fuels by taking advantage of their size.29,30 They may also exist at radionuclide-contaminated sites such as Fukushima and Hanford.31,32 The thermodynamic properties of uranyl peroxide clusters are largely unstudied, owing to their relatively recent discovery and the rapid growth of this family of materials. Calorimetric studies have been reported for K, Na, and Li salts of noncluster uranyl peroxide compounds containing isolated UO2(O2)34− units,31 as well as studtite33 and metastudtite.26 Calorimetric studies for salts of uranyl peroxide clusters have been reported for K/Li-U60 and uranyl- and peroxotantalate-centered U28.31,34 The details of the interactions of alkali cations with uranyl peroxide cages are clearly important for the enthalpies of formation of these salts,31,34 but broader patterns in the energetics of uranyl peroxide cage clusters will be evident only with additional study. Here, seven uranyl peroxide cluster salts were chosen for calorimetric studies aimed at determining their enthalpies of formation. Clusters are abbreviated here as A-Un, A-UnPpm and A-UnPO3, where A lists the countercations in the salt in order Received: May 12, 2018

A

DOI: 10.1021/acs.inorgchem.8b01300 Inorg. Chem. XXXX, XXX, XXX−XXX

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Table 1. Symbols and Chemical Formulae for Salts of Uranyl Peroxide Clusters and Their Determined Enthalpies of Formation from the Corresponding Oxides symbol

compound formula

Na/K-U24Pp12 Li/Na-U24Pp12 K/Li-U26Pp6 Li-U28 K-U28 K-U22PO3 K-U28PO3

Na43K8[(UO2)24(O2)24(P2O7)12]·123H2O Li36Na12[(UO2)24(O2)24(P2O7)12]·118H2O K31Li4[(UO2)26(O2)33(P2O7)6]·43H2O Li28[(UO2)28(O2)42]·68H2O K28[(UO2)28(O2)42]·46H2O K26[(UO2)22(O2)15(HPO3)20(H2O)10]·52H2O K32[(UO2)28(O2)20(HPO3)24(H2O)12]·77H2O

± ± ± ± ± ± ±

381.29 430.53 173.17 113.05 181.95 83.32 132.09

Crystals of K/Li-U26Pp6, reported here for the first time, were grown from an orange-yellow aqueous solution created by combining 0.1 mL of 0.5 M UO2(NO3)2·6H2O, 0.1 mL of 30% H2O2, 0.1 mL of 2.4 M LiOH, 0.4 mL of 0.1 M iminodiacetic acid (Aldrich), and 0.4 mL of 0.25 M K4P2O7 (Acros) in a 5 mL scintillation vial. The vial was then covered with Parafilm containing several small holes. Blockshaped orange crystals of U26Pp6 appeared within 3 days. Li-U28 crystals were grown from a bright yellow solution created by combining 30 mL of 0.5 M UO2(NO3)2·6H2O, 30 mL of 30% H2O2, and 18 mL of 2.4 M LiOH. The solution was distributed over six centrifuge tubes, each of which was centrifuged for 5 min, and the solutions were then separated from the solid. Methanol was slowly diffused into each, which produced bright yellow crystals in 3 days. To produce K-U28 crystals, 5 mL of 0.5 M uranyl nitrate and 5 mL of 30% H2O2 were combined to produce a pale yellow precipitate. While stirring, 3 mL of 2 M aqueous KOH was added to the mixture. The cloudy, pale green solution was transferred to falcon tubes and centrifuged for 5 min. The supernatant was divided into 5 mL glass vials and placed in beakers containing methanol, which were parafilmed for vapor diffusion. Green, acicular crystals formed in 1 day. Characterization. Single crystal X-ray diffraction data were used to determine the structure of K/Li-U26Pp6 (details in the Supporting Information). A crystal of suitable size and quality was selected using a polarized-light microscope, placed on a cryo-loop, and cooled to 100 K for data collection using a Bruker three-circle X-ray diffractometer equipped with an APEX II detector and monochromated Mo Kα Xradiation. A sphere of data was collected using frame widths of 0.5° in ω. Data were integrated and corrected for Lorentz, polarization, and background effects using the Bruker APEX II software. SADABS40 was used to correct for absorption, and structure solution and refinement was done using SHELXTL.41 Single crystal X-ray diffraction data were also collected for crystals of the other cluster salts to confirm their identifications. The compound crystallizes in space group Imm2 with Z = 2 and a = 19.284(4) Å, b = 35.001(7) Å, c = 17.011(4) Å, and was refined to R1 = 0.059. Chemical analyses for compounds prepared for calorimetry were done using a PerkinElmer Optima 8000 DV inductively coupled plasma-optical emission spectrometer (ICP-OES) with an analytical uncertainty of 3.5%. Crystals of each cluster salt were removed from their mother solution by vacuum-filtration, followed by lightly washing with 18 MΩ water. Recovered crystals were dissolved in 10 mL of diluted (5%) HNO3 prior to introduction into the ICP-OES instrument. Six standards containing 0.5−12 ppm of Na, K, Li, P, and U were prepared for calibration. All standards and samples were spiked with ∼0.5 ppm Y to monitor and correct for instrumental drift. In our previous experience, uranyl peroxide cage cluster compounds often become X-ray amorphous during grinding, making characterization by powder X-ray diffraction difficult. Electrospray ionization mass spectrometry (ESI-MS) was used to further characterize materials prepared for calorimetry. The mass spectra were collected using a Bruker-micro TOF-Q II high-resolution quadropole time-of-fight mass spectrometer in negative ion mode (3600 V capillary voltage, 0.8 bar nebulizer gas, 4 L/min dry gas, and 180 °C dry gas temperature). Samples were prepared by dissolving the salts in ultrapure water and were separately introduced into the instrument at a rate of 10 μL/min and scanned over a 500−5000 m/z

of abundance, n is the number of uranyl ions, Pp represents (P2O7)4−, and m the number of pyrophosphate units, and PO3 designates (HPO3)2−. The salts studied are Na/K-U24Pp12, Li/ Na-U24Pp12, K/Li-U26Pp6, Li-U28, K-U28, K-U22PO3, and KU28PO3 (Table 1, Figure 1). The crystal structure of each has

Figure 1. Polyhedral representations of uranyl peroxide cage clusters. Uranyl polyhedra are shown in yellow, and blue polyhedra represent [P2O7]4− and [HPO3]2−. Clusters are not drawn at the same scale.

been reported,8,35−39 except that of U26Pp6 that was determined in the current study by using single-crystal X-ray diffraction data. These clusters were selected for study because they present a range of topologies and sizes, as well as peroxide, pyrophosphate, and phosphite bridges, and because it is possible to synthesize pure materials in sufficient quantities for further study.

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ΔH (kJ/mol) −14672.35 −11331.23 −9640.65 −3342.11 −5048.56 −2867.71 −3716.55

EXPERIMENTAL METHODS

Synthesis. All reactions were conducted at room temperature. The K salts of U22PO3 and U28PO3 were synthesized using methods described previously.35 Crystals of Na/K-U24Pp12 were prepared by loading aqueous solutions into a 20 mL glass vial. First, 0.5 mL of 0.5 M UO2(NO3)2·6H2O (International Bio-Analytical Industries), 0.5 mL of 30% H2O2 (EMD Millipore), and 0.5 mL of 40% tetraethylammonium hydroxide (TEAH) (Sigma-Aldrich) were combined. Following cessation of off-gassing, 1.5 mL of 0.1 M Na4P2O7 (Spectrum) and 1.5 mL of 0.5 M H2C2O4 (Alfa Aesar) were added. The resulting orange solution was aged in a glass vial covered by Parafilm containing small holes, and orange crystals formed within 7 days. Li/Na-U24Pp12 crystals were synthesized by combining 1.5 mL of 0.5 M UO2(NO3)2·6H2O, 1.5 mL of 30% H2O2, 0.75 mL of 0.5 M H2C2O4, 0.55 mL of 0.2 M Na4P2O7, and 1.05 mL of 2.4 M LiOH (Alfa Aesar). The resulting orange solution was left to age in a glass vial covered by Parafilm with small holes for evaporation, and orange crystals were harvested after 7 days. B

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Figure 2. Enthalpy of formation of uranyl peroxide cluster salts from oxides as a function of the number of alkali cations per formula unit. Data for the K, Na, and Li monomer salts, as well as Cs/K/U-U28, Cs/K/Ta-U28, and Li/K-U60, are from the literature.31,34 range. Deconvolution of data was done using the MaxEnt software (Figure S2 in the Supporting Information). Thermogravimetric analyses (TGA) were conducted for aliquots of each salt using a Netzsch TG209 F1 Iris thermal analyzer. For each sample, a 25 mg pellet was placed in an Al crucible and heated from room temperature to 900 °C at a rate of 5 °C/min under Ar gas flowing at 50 mL/min (Figure S3 in the Supporting Information). High-Temperature Calorimetry. Calorimetry measurements were conducted using a Calvet-type Setaram AlexSYS high-temperature oxide melt drop solution calorimeter. High-temperature solution calorimetry is a well-established method for measurement of the heat of formation of hydrous uranyl compounds and is generally problemfree.26,31,33,34,42−49 The enthalpy of formation of each compound from its elements and its binary oxides was calculated from the measured heat of drop solution by applying thermochemical cycles, as detailed in the Supporting Information. Prior to each experiment, the instrument was calibrated using the well-known heat capacity of αAl2O3. 4−6 mg pressed pellets of crystals of each cluster were dropped from room temperature into the molten 3Na2O-4MoO3 solvent at 700 °C. In order to sweep away any evolved gas or water vapor associated with sample dissolution, O2 gas was flushed over the solvent at 45 mL/min. O2 gas was also continuously bubbled through the solvent at 7 mL/min to promote mixing and to ensure an oxidizing environment. Complete dissolution of each synthetic phase in 3Na2O-4MoO3 was documented at 700 °C by dropping 5 mg pellets into molten solvent in a furnace. The resulting clear solutions confirmed dissolution.

balanced by Li and K cations distributed inside and between the clusters. Crystallographic details are in the Supporting Information. The results of the crystal structure, thermogravimetric, and elemental composition analyses of the cluster salts studied here yield the formulas listed in Table 1.8,24,35 In each case, the single-crystal structure determination defines the makeup of the uranyl peroxide cage, including the ligands that bridge uranyl ions. However, owing to omnipresent disorder of the countercations and H2O, the X-ray data do not provide full details of the quantity of countercations and H2O. The quantity of countercations was determined from ICP-OES analysis, and for K-U22PO3, K-U28PO3, Li-U28, K-U28, and Li/ Na-U24Pp12, the determined quantity matches well with that needed to balance the charge of the uranyl peroxide cage. For K/Li-U26Pp6, the chemical analysis indicated 35 countercations per formula unit, whereas the charge of the uranyl peroxide cage is −38. This possibly indicates that three of the terminal oxygen atoms of the pyrophosphate groups are protonated (on average), and the X-ray data did not provide H atom positions. For Na/K-U24Pp12, the ICP-OES analysis yielded 51 countercations per formula unit, whereas the uranyl peroxide cage has a charge of −48. The TGA analysis indicated 123 H2O groups per formula unit, but some of these could correspond to hydroxyl, giving charge balance. Specifically, some encapsulated countercations are in configurations that could be compatible with the presence of hydroxyl. The thermochemical cycles used to determine the enthalpies of formation of the cluster salts were calculated using the quantities of Li and K determined for K/Li-U26Pp6 and Na/K-U24Pp12 by ICP-OES analyses (Supporting Information). The determination of H2O for the compounds under study using thermogravimetric analyses is difficult because mass loss during heating may correspond to loss of H2O bonded to countercations or held in interstitial spaces by H bonding, as well as loss of hydroxyl and peroxide that are components of the uranyl peroxide cages. At high temperatures, loss of oxygen,

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RESULTS AND DISCUSSION The structure determination for K/Li-U26Pp6 revealed that the uranyl peroxide cage contains 26 uranyl ions, each of which is present in a hexagonal bipyramidal coordination environment (Figure 1). Bridges between the uranyl ions are 33 bidentate peroxide ligands and six bidentate “side on” pyrophosphate groups. The U26Pp6 cage has the composition [(UO2)26O2)33P2O7)6]38− and consists of a bowl-shaped unit containing 18 uranyl ions bridged through peroxide, and a second unit made from eight uranyl ions that are also bridged through peroxide. The 18- and 8-membered uranyl units are linked to each other through pyrophosphate. The charge of the U26Pp6 cage is C

DOI: 10.1021/acs.inorgchem.8b01300 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 3. Determined enthalpy of formation of each uranyl peroxide cluster salt from the corresponding oxides plotted against the cluster charge density. Data for Cs/K/U-U28, Cs/K/Ta-U28, and Li/K-U60 are from the literature.31,34

the data suggests significant complexity of the enthalpy landscape. Given the compositional complexity of the clusters under study here, there is no simple way to normalize the enthalpies of formation for more direct comparison. Assembly of uranyl peroxide clusters is spontaneous and exothermic in water.9 Fully formed clusters crystallize in combination with countercations sufficient to balance the cluster charge, and numerous water molecules that are mostly located outside the clusters.8 The enthalpy of formation of cluster salts includes the enthalpy of cluster assembly, as well as crystallization. The enthalpy of formation of cluster salts per formula unit will be impacted by the number of uranyl ions and the number and type of the ligands that bridge between them, and grows with cluster size, as shown in Figure 2. Li/Na-U24Pp12 and K/Na-U24Pp12 cluster salts studied here contain chemically identical U24Pp12 clusters, but their determined heats of formation are very different (Table 1). Li/Na-U24Pp12 and K/Na-U24Pp12 salts contain similar quantities of water; thus the differences in their heats of formation relate to the countercations, their enthalpies of hydration, and their interactions with the uranyl peroxide cages. An earlier study reported the heats of formation of the simple alkali uranyl peroxide salts Li4[UO2(O2)3](H2O)10 and Na4[UO2(O2)3](H2O)9 from the oxides to be −260.9 ± 13.2 and −515.5 ± 8.9 kJ/mol, respectively.31 As these compounds contain the same [UO2(O2)3]4− species and similar amounts of H2O, the substantial differences in their heats of formation are attributed to interactions between the alkali cations and [UO2(O2)3]4− as well as H2O. For U24Pp12 cluster salts, that with Li as the dominant countercation has a less negative enthalpy of formation than the salt in which Na is the major countercation. However, despite their chemically identical makeups, the clusters in these two compounds are different sizes, and the potential importance of this is explored further below. Salts of K-U28 and Li-U28 contain the same uranyl peroxide cage cluster, but different countercations. The Li salt contains

together with reduction of U(VI), is likely. Thermogravimetric analysis of studtite, [(UO2)O2(H2O)2](H2O)2, which is compositionally and structurally much simpler than the compounds under study here, demonstrated that, whereas most water loss was complete by ∼200 °C, some of the peroxide persisted in the structure until close to 500 °C.50 As the TGA curves for the different compounds under study are quite different and all lose mass over an extended range of temperature (Supporting Information), we have taken the total mass loss by 450 °C to represent destruction of all H2O and peroxide in each case. Mass loss due to volatilization of lithium appears to occur by about 500 °C (Figure S3). The quantities of hydroxyl and peroxide from the crystal structure analyses were used to calculate the H2O content of each compound. ESI-MS data for solutions resulting from dissolution of cluster salts in water are consistent with the specific cluster in the material (Figure S2 in the Supporting Information). Identification of the charge state associated with broad signals in the ESI-MS data allowed calculation of the average mass of each cluster including countercations. The measured mass corresponds to the uranyl peroxide cage as well as chargebalancing cations needed to yield the observed charge state, at a minimum. The average of the measured mass for different observed charge states for each cluster is compared to its theoretical mass calculated from the crystallographic data in Table S1 in the Supporting Information. The enthalpies of formation of the cluster salts from oxides (Table 1) as a function of the number of alkali cations per formula unit are shown in Figure 2, as has been done previously for compounds containing uranyl peroxide clusters.31,34 The enthalpies of formation of the cluster salts from oxides generally become more negative as the charge on the cluster increases and more alkali cations are required to achieve charge balance, as noted previously for uranyl peroxide compounds in general.31,34 This is expected given that the enthalpies of formation are plotted per formula unit and the formula units are becoming larger, but the fairly large scatter of D

DOI: 10.1021/acs.inorgchem.8b01300 Inorg. Chem. XXXX, XXX, XXX−XXX

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combination with the current results, will provide the enthalpies of formation of the clusters in solution.

68 H2O, whereas the K salt has 46 H2O per formula unit. The enthalpy of formation of the salt of K-U28 was found to be 1706.49 kJ/mol more negative than that of Li-U28, again consistent with the trend seen for simple alkali peroxide salts. Salts of K-U22PO3 and K-U28PO3 contain the same countercation, although the latter contains more H2O. The clusters in these two salts are topologically similar, with belts of edge-sharing uranyl hexagonal bipyramids bridged through uranyl pentagonal bipyramids and phosphite groups (Figure 1). Normalizing their enthalpies of formation to the number of uranyl ions per cluster in each salt yields values of −130.35 and −132.73 kJ/mol for K-U22PO3 and K-U28PO3, respectively. The enthalpy of formation of salts of uranyl peroxide clusters is likely impacted by the strengths of interactions between the uranyl peroxide cages and the countercations, as well as countercation size and cation hydration enthalpies.31,34 We therefore calculated charge densities for spheres representing the sizes of the various clusters. Crystallographic data provided the minimum and maximum diameters of each cluster, as measured from the outer edges of bounding oxygen atoms. The radius calculated from the average of the maximum and minimum diameters was used to compute the charge density as CD = ne/((4/3)πr3). Here, n is the charge of the cluster (excluding encapsulated species), e is the electron charge, and r is the average radius of the sphere representing the cluster. The calculated charge density of each cluster is compared with the enthalpy of formation of its salt from the oxides in Figure 3. The enthalpies of formation of cluster salts become more negative as the charge density increases in a roughly linear fashion (R2 = 0.75). The largest cluster, U60, which also has the highest charge and contains the most uranyl ions, does not have the highest charge density of this family of clusters, and the enthalpy of formation of the Li/K-U60 salt is midway through the range observed for the various clusters. The two cluster salts with the most negative enthalpies of formation from the oxides are Li/Na-U24Pp12 and K/Na-U24Pp12. The clusters in these compounds have the same composition, charge, and topologies, but they differ in size. Each consists of six four-membered rings of uranyl ions, and in Li/Na-U24Pp12 each of these rings is linked into a spherical cluster. In the cluster of K/Na-U24Pp12, two of the tetramer rings are in the opposite orientation relative to Li/Na-U24Pp12, which results in a smaller oblong cluster (Figure 1), as reflected by the higher charge density shown in Figure 3. We plan to use calorimetry to derive the enthalpies of formation of various uranyl peroxide clusters to probe the energy landscape of different cluster sizes and topologies, and to compare these enthalpies with those predicted from density functional theory calculations. The current study represents an important step toward this goal by providing enthalpies of formation of cluster salts. The enthalpies of formation of uranyl peroxide cluster salts are impacted by interactions of countercations with anionic clusters having different charge densities, rather than the energetics of formation of the clusters themselves. Measurements of the enthalpies of formation of cluster salts therefore provide no insight into the relative energetics of various clusters. As such, we are developing methodologies for measurement of the enthalpies of dissolution of uranyl peroxide cluster salts in water at near ambient temperatures, as the clusters will remain intact as dissolved species in water24 and the measurement will yield the enthalpy of their crystallization. These measurements, in

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b01300. Illustration of U26Pp6, results of ESI-MS measurements, ESI-MS spectra, thermogravimetric curves of each compound, thermochemical cycles for the calculation of enthalpy of formation of each compound, ICP-OES analysis, and crystallographic tables for U26Pp6 (PDF) Accession Codes

CCDC 1841870 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Jie Qiu: 0000-0001-7131-4881 Peter C. Burns: 0000-0002-2319-9628 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This material is based upon research supported by the Materials Science of Actinides, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award DESC0001089. ICP-OES analyses were done in the Center for Environmental Science and Technology (CEST) at the University of Notre Dame. ESI-MS spectra were collected in the Mass Spectrometry and Proteomics Facility at the University of Notre Dame. Calorimetry and TGA measurements were done in the Materials Characterization Facility (MCF) of the Center for Sustainable Energy at Notre Dame (ND Energy).

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REFERENCES

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DOI: 10.1021/acs.inorgchem.8b01300 Inorg. Chem. XXXX, XXX, XXX−XXX

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Peroxide Cage Cluster Solubility in Water and the Role of the Electrical Double Layer. Inorg. Chem. 2017, 56, 1333−1339. (25) Guo, X.; Szenknect, S.; Mesbah, A.; Clavier, N.; Poinssot, C.; Ushakov, S. V.; Curtius, H.; Bosbach, D.; Ewing, R. C.; Burns, P. C.; Labs, S.; Dacheux, N.; navrotsky, A. Thermodynamics of formation of coffinite, USiO4. Proc. Natl. Acad. Sci. U. S. A. 2015, 112, 6551−6555. (26) Guo, X.; Ushakov, S. V.; Curtius, H.; Bosbach, D.; Navrotsky, A.; Labs, S. Energetics of metastudtite and implications for nuclear waste alteration. Proc. Natl. Acad. Sci. U. S. A. 2014, 111, 17737− 17742. (27) Soltis, J. A.; Wallace, C. M.; Penn, R. L.; Burns, P. C. Cationdependent hierarchical assembly of U60 nanoclusters into macro-ion assemblies imaged via cryogenic transmission electron microscopy. J. Am. Chem. Soc. 2016, 138, 191−198. (28) Burns, P. C. Nanoscale uranium-based cage clusters inspired by uranium mineralogy. Mineral. Mag. 2011, 75, 1−25. (29) Wylie, E. M.; Peruski, K. M.; Weidman, J. L.; Phillip, W. A.; Burns, P. C. Ultrafiltration of uranyl peroxide nanoclusters for the separation of uranium from aqueous solution. ACS Appl. Mater. Interfaces 2014, 6, 473−479. (30) Wylie, E. M.; Peruski, K. M.; Prizio, S. E.; Bridges, A. N.; Rudisill, T. S.; Hobbs, D. T.; Phillip, W. A.; Burns, P. C. Processing used nuclear fuel with nanoscale control of uranium and ultrafiltration. J. Nucl. Mater. 2016, 473, 125−130. (31) Armstrong, C. R.; Nyman, M.; Shvareva, T.; Sigmon, G. E.; Burns, P. C.; Navrotsky, A. Uranyl peroxide enhanced nuclear fuel corrosion in seawater. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 1874− 1877. (32) Peterson, R. A.; Buck, E. C.; Chun, J.; Daniel, R. C.; Herting, D. L.; Ilton, E. S.; Lumetta, G. J.; Clark, S. B. Review of the scientific understanding of radioactive waste at the U.S. DOE Hanford Site. Environ. Sci. Technol. 2018, 52, 381−396. (33) Kubatko, K.-A. H.; Helean, K. B.; Navrotsky, A.; Burns, P. C. Stability of peroxide-containing uranyl minerals. Science 2003, 302, 1191−1193. (34) Tiferet, E.; Gil, A.; Bo, C.; Shvareva, T. Y.; Nyman, M.; Navrotsky, A. The Energy Landscape of Uranyl−Peroxide Species. Chem. - Eur. J. 2014, 20, 3646−3651. (35) Qiu, J.; Nguyen, K.; Jouffret, L.; Szymanowski, J. E.; Burns, P. C. Time-Resolved Assembly of Chiral Uranyl Peroxo Cage Clusters Containing Belts of Polyhedra. Inorg. Chem. 2013, 52, 337−345. (36) Ling, J.; Qiu, J.; Sigmon, G. E.; Ward, M.; Szymanowski, J. E.; Burns, P. C. Uranium pyrophosphate/methylenediphosphonate polyoxometalate cage clusters. J. Am. Chem. Soc. 2010, 132, 13395− 13402. (37) Dembowski, M.; Colla, C. A.; Hickam, S.; Oliveri, A. F.; Szymanowski, J. E. S.; Oliver, A. G.; Casey, W. H.; Burns, P. C. Hierarchy of Pyrophosphate-Functionalized Uranyl Peroxide Nanocluster Synthesis. Inorg. Chem. 2017, 56, 5478−5487. (38) Dembowski, M.; Colla, C. A.; Yu, P.; Qiu, J.; Szymanowski, J. E. S.; Casey, W. H.; Burns, P. C. The Propensity of Uranium-Peroxide Systems to Preserve Nanosized Assemblies. Inorg. Chem. 2017, 56, 9602−9608. (39) Dembowski, M.; Olds, T. A.; Pellegrini, K. L.; Hoffmann, C.; Wang, X. P.; Hickam, S.; He, J. H.; Oliver, A. G.; Burns, P. C. Solution P-31 NMR Study of the Acid-Catalyzed Formation of a Highly Charged {U24Pp12} Nanocluster, (UO2)24(O2)24(P2O7)12 48‑, and Its Structural Characterization in the Solid State Using Single-Crystal Neutron Diffraction. J. Am. Chem. Soc. 2016, 138, 8547−8553. (40) Sheldrick, G. SADABS-2008/1-Bruker AXS: Area detector scaling and absorption correction; Bruker AXS Inc.: Madison, WI, 2008. (41) Sheldrick, G. SHELXTL; Bruker AXS Inc.: Madison, WI, 1997. (42) Gorman-Lewis, D.; Mazeina, L.; Fein, J. B.; Szymanowski, J. E.; Burns, P. C.; Navrotsky, A. Thermodynamic properties of soddyite from solubility and calorimetry measurements. J. Chem. Thermodyn. 2007, 39, 568−575. (43) Gorman-Lewis, D.; Shvareva, T.; Kubatko, K.-A.; Burns, P. C.; Wellman, D. M.; McNamara, B.; Szymanowski, J. E.; Navrotsky, A.; Fein, J. B. Thermodynamic properties of autunite, uranyl hydrogen F

DOI: 10.1021/acs.inorgchem.8b01300 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry phosphate, and uranyl orthophosphate from solubility and calorimetric measurements. Environ. Sci. Technol. 2009, 43, 7416−7422. (44) Kubatko, K.-A.; Helean, K.; Navrotsky, A.; Burns, P. C. Thermodynamics of uranyl minerals: Enthalpies of formation of uranyl oxide hydrates. Am. Mineral. 2006, 91, 658−666. (45) Kubatko, K.-A.; Helean, K. B.; Navrotsky, A.; Burns, P. C. Thermodynamics of uranyl minerals: Enthalpies of formation of rutherfordine, UO2CO3, andersonite, Na2CaUO2(CO3)3(H2O)5, and grimselite, K3NaUO2(CO3)3H2O. Am. Mineral. 2005, 90, 1284− 1290. (46) Navrotsky, A. Progress and New Directions in Calorimetry: A 2014 Perspective. J. Am. Ceram. Soc. 2014, 97, 3349−3359. (47) Sharifironizi, M.; Szymanowski, J. E.; Sigmon, G. E.; Navrotsky, A.; Fein, J. B.; Burns, P. C. Thermodynamic studies of zippeite, a uranyl sulfate common in mine wastes. Chem. Geol. 2016, 447, 54−58. (48) Shvareva, T. Y.; Fein, J. B.; Navrotsky, A. Thermodynamic properties of uranyl minerals: constraints from calorimetry and solubility measurements. Ind. Eng. Chem. Res. 2012, 51, 607−613. (49) Shvareva, T. Y.; Mazeina, L.; Gorman-Lewis, D.; Burns, P. C.; Szymanowski, J. E.; Fein, J. B.; Navrotsky, A. Thermodynamic characterization of boltwoodite and uranophane: Enthalpy of formation and aqueous solubility. Geochim. Cosmochim. Acta 2011, 75, 5269−5282. (50) Odoh, S. O.; Shamblin, J.; Colla, C. A.; Hickam, S.; Lobeck, H. L.; Lopez, R. A. K.; Olds, T.; Szymanowski, J. E. S.; Sigmon, G. E.; Neuefeind, J.; Casey, W. H.; Lang, M.; Gagliardi, L.; Burns, P. C. Structure and Reactivity of X-ray Amorphous Uranyl Peroxide. Inorg. Chem. 2016, 55, 3541−3546.

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DOI: 10.1021/acs.inorgchem.8b01300 Inorg. Chem. XXXX, XXX, XXX−XXX