Structure and Bonding Investigation of Plutonium Peroxocarbonate

Article pubs.acs.org/IC

Structure and Bonding Investigation of Plutonium Peroxocarbonate Complexes Using Cerium Surrogates and Electronic Structure Modeling Lucas E. Sweet,*,† Jordan F. Corbey,† Frédéric Gendron,‡ Jochen Autschbach,‡ Bruce K. McNamara,§ Kate L. Ziegelgruber,† Leah M. Arrigo,† Shane M. Peper,† and Jon M. Schwantes† †

Analytical Chemistry of Nuclear Materials Group, Signature Science & Technology Division, and §Actinide Science Group, Nuclear Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States ‡ Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14260-3000, United States S Supporting Information *

ABSTRACT: Herein, we report the synthesis and structural characterization of K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O. This is the second Pu-containing addition to the previously studied alkali-metal peroxocarbonate series M8[(CO3)3A]2(μ-η2-η2O2)2·xH2O (M = alkali metal; A = Ce or Pu; x = 8, 10, 12, or 18), for which only the M = Na analogue has been previously reported when A = Pu. The previously reported crystal structure for Na8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O is not isomorphous with its known Ce analogue. However, a new synthetic route to these M8[(CO3)3A]2(μ-η2-η2-O2)2·12H2O complexes, described below, has produced crystals of Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O that are isomorphous with the previously reported Pu analogue. Via this synthetic method, the M = Na, K, Rb, and Cs salts of M8[(CO3)3Ce]2(μ-η2-η2-O2)2·xH2O have also been synthesized for a systematic structural comparison with each other and the available Pu analogues using single-crystal X-ray diffraction, Raman spectroscopy, and density functional theory calculations. The Ce salts, in particular, demonstrate subtle differences in the peroxide bond lengths, which correlate with Raman shifts for the peroxide Op−Op stretch (Op = O atoms of the peroxide bridges) with each of the cations studied: Na+ [1.492(3) Å/847 cm−1], Rb+ [1.471(1) Å/854 cm−1], Cs+ [1.474(1) Å/859 cm−1], and K+ [1.468(6) Å/ 870 cm−1]. The trends observed in the Op−Op bond distances appear to relate to supermolecular interactions between the neighboring cations. alkaline nuclear waste.19 If released, they could potentially mediate radionuclide migration.20 Similarly, studtite (UO4· 4H2O) and metastudtite (UO4·2H2O) are examples of actinide compounds containing μ-η2 peroxide ligands that have been studied with respect to the environmental fate and transport of spent nuclear fuel,21−24 and research exploring the chemistry of similar uranyl peroxide moieties has become more popular in the field for this reason among others.25,26 There are also a number of lanthanide complexes that contain μ-η2 peroxide ligands.27−36 It is known that the radiolysis of water can form peroxides that can be incorporated into waste products as exemplified by the uranium species studtite and metastudtite, mentioned above.19,37,38 Additionally, because the carbonate anion is common in natural water environments,39,40 there has been an interest in understanding f-element carbonate speciation as it pertains to the environmental fate and transport of nuclear waste products for decades and, more recently, in relation to

1. INTRODUCTION Much work has been done to try and understand the chemistry and bonding that takes place in dioxygen metal complexes. The majority of work in this area has been focused on understanding O−O bond making and breaking processes that occur in biological systems.1−7 More recently, the search for alternative energy sources has promoted further interest in dioxygen metal complexes for the study of photocatalytic water splitting.8−10 Our interest is in the role that hydrogen peroxide may play in the environmental fate of f elements. Before the year 2000, relatively little research had targeted felement dioxygen moiety complexation. The vast majority of crystal structures published of f-element dioxygen complexes contain O2 bound in an η2 peroxide fashion. The peroxide ligands are found as μ-η2 bridges or simply as η2-O2 in monomeric molecular complexes. More recent examples of metal−peroxide bridging in actinide compounds include an array of hydroxide and peroxide uranium clusters.11−18 These nanoscale uranium complexes have fullerene-type topologies that consist of the μ-η2 peroxide bridges between U atoms and, given the appropriate conditions, could be formed in stored © XXXX American Chemical Society

Received: September 15, 2016

A

DOI: 10.1021/acs.inorgchem.6b02235 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

prepared. Upon the addition of 1.0 mL of 30% H2O2, a gray-green precipitate immediately formed. After 3−4 days, the solids dissolved, and the solution was layered with approximately 1 mL of MeOH. Dark-green X-ray-quality platelike crystals of K8[(CO3)3Pu]2(μ-η2-η2O2)2·12H2O formed in the transparent olive-green solution on the vial walls after 2 days and continued to grow for 1 week. Crystals outside of their mother liquor were found to be relatively unstable and decomposed after 1 h. Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O. A mixture of 1.7 mL of a 2.0 M Na2CO3 solution and 704 μL of a 0.33 M Ce(SO4)2 solution was pipetted into a 5 mL glass vial. Upon the addition of 115 μL of a 9.79 M H2O2 solution, a red-orange precipitate immediately formed. After 24−48 h, the solution appeared relatively homogeneous. Residual particulates were removed by filtering through a 0.2 μm syringe filter. Following clarification, the aqueous solution was layered with MeOH (∼1 mL). After 48 h at room temperature, red needle-shaped crystals were observed on the walls of the vial. One week later, red platelike crystals were also observed on the bottom of the vial, while the needleshaped crystals remained at the MeOH/aqueous layer interface. Both crystal habits were found to be Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O and, after washing with MeOH, were found to be stable at room temperature for several days. K8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O. Following the procedure described above for Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, 2.5 mL of a 2.0 M K2CO3 solution, 1.5 mL of a 0.33 M Ce(SO4)2 solution, and 60 μL of a 9.79 M H2O2 solution were pipetted into a 5 mL glass vial. Red platelike crystals formed, covering the walls of the vial within 48 h at room temperature. Unlike the aforementioned Na+ analogue but similar to the Pu analogue K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O, crystals of K8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O were relatively unstable outside of the mother liquor and decomposed after 1 h. Rb8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O. Similar to the procedures described above, 100 μL of a 0.33 M Ce(SO4)2 solution and 100 μL of a 9.79 M H2O2 solution were added to 185 mg of Rb2CO3. The solution changed from a light-orange to a dark-red solution within 24 h. Approximately 1 week after layering with MeOH, red rectangular platelike crystals of Rb8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O were observed to cover the walls of the vial. The crystals outside of the mother liquor were relatively unstable and decomposed after 1 h. Cs8[(CO3)3Ce]2(μ-η2-η2-O2)2·10H2O. Similar to the procedures described above, 404 mg of Cs2CO3 were dissolved in 200 μL of deionized water. A total of 100 μL of a 0.33 M Ce(SO4)2 solution and 100 μL of a 9.79 M H2O2 solution were added to the Cs2CO3 solution. The resulting solution was subsequently layered with MeOH (∼1 mL), and red rectangular platelike crystals of Cs8[(CO3)3Ce]2(μ-η2-η2O2)2·10H2O were observed within 1 week. Again, the crystals outside of the mother liquor were relatively unstable and decomposed quickly. 2.2. Raman Spectroscopy. An ExaminR 785 (Delta Nu, Laramie, WY) Raman spectrometer interfaced with an Olympus BX51 microscope (50×, 0.75 NA objective lens) was used to collect Raman spectra of single crystals. A 785 nm, 120 mW laser was used as the excitation source, and a CCD detector with a 1 cm−1 root-meansquare error in a calibration to a polystyrene standard was also used. Raman spectra were collected for each of the Ce salts; however, the same laser wavelength readily decomposed the Pu salts, and comparative spectra could not be recorded. Caution! In several cases, the spectacular decomposition of plutonium carbonate species induced by the intense 785 nm laser used to probe the Raman scattering was observed. Robust containment should be used when attempting to collect Raman spectra of radioactive and hazardous materials. 2.3. X-ray Structure Determination. The single-crystal X-ray diffraction data for the Pu salt K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O were collected at room temperature using a Bruker AXS SMART diffractometer equipped with an APEX II CCD detector at Argonne National Laboratory. Frame data were indexed and integrated using the APEX3 software suite.53,54 The structure solution was obtained using a Patterson method, and the structure was refined as a 29:71 two-component twin55 using full-matrix least-squares methods on F2 via SHELXTL.56

hydrogen peroxide. Motivation for the current work was mainly incited as a call to explore potential new industrial routes to nuclear fuel processing after it was shown that concentrated carbonate solutions containing hydrogen peroxide can be used to completely dissolve spent uranium oxide fuel.41 These exploratory studies of alternate reprocessing methods highlighted two examples of monomeric f-element complexes, Na4UO2(CO3)3 and Na4UO2(O2)(CO3)2, of interest toward speciation and separation analyses.42−44 Currently, Pu and Ce are the only two f-elements known to form compounds containing double μ-η2 peroxide bridges in dimeric units.28,32,33,36,45 Some of the first syntheses of the cerium peroxocarbonate compounds were reported in the late 1800s and early 1900s.46−49 These compounds were not structurally characterized until 1976 when Butman et al. published the first crystal structure of [C(NH2)]8{[(CO3)3Ce]2(μ-η2-η2-O2)2}.32 Since then, the Na+,50 K+,51 Rb+,52 and Cs+ salts52 of the {[(CO3)3Ce]2(μ-η2η2-O2)2}8− dimer have been reported. Each analogue in this series is structurally unique, yet the Ce dimeric unit remains relatively unperturbed. This series of compounds forms an excellent set to study the supramolecular effects on the unusual double μ-η2 bonding mode of peroxide ligands and initiated our investigation of the analogous, but less forgiving, Pu compounds. Vibrational data have also been reported for the Rb+ and Cs+ analogues of the Ce series;52 however, an optical comparison over the whole series has not yet been made. The paramagnetism in the Pu complex Na8[(CO3)3Pu]2(μη2-η2-O2)245 makes it difficult to study by solution or solid-state NMR, and it presents a challenge for density functional theory (DFT) calculations. The availability of the {[(CO3)3Ce]2(μ-η2η2-O2)2}8− complexes and their structural similarities to the Pu complex provide an opportunity to investigate the role of the cation, at least in the solid-state structure. Additionally, the lack of paramagnetism in the Ce species allows for a more in-depth computational investigation at the DFT level. The previously reported structure of Na8[(CO3)3Pu]2(μ-η2-η2-O2)245 is not isomorphous with the previously reported Ce analogue,50 leaving the question as to whether Ce is a good chemical analogue to Pu in carbonate peroxide systems for comparison purposes. In this work, we show that Ce and Pu can form isomorphous crystalline species. The synthetic availability of the known set of isomorphous cerium and plutonium peroxocarbonate complexes, described below, provides a direct comparison to investigate the considerable role of the alkalimetal cations, which is manifest by differences in the volume, density, and packing arrangement in the solid-state structures. Understanding the complexation of Pu in peroxide carbonate systems is important for waste form studies and alternative routes to reprocessing spent nuclear fuels.39,40

2. EXPERIMENTAL SECTION 2.1. Syntheses. Na2CO3, K2CO3, Rb2CO3, Cs2CO3, Ce(SO4)2, H2O2 (30 wt %), and MeOH (99.8%) were purchased from SigmaAldrich and used as received. Aqueous stock solutions of the reagents were prepared using deionized water (18 MΩ·cm). Plutonium nitrate stock solutions were prepared from legacy samples at Pacific Northwest National Laboratory. Caution! Plutonium-239 is an α emitter (specif ic activity = 2.30 × 109 Bq/g) that presents both radioactivity and toxicity hazards. Manipulation and handling of these materials were performed only by qualif ied personnel in radiological facilities. K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O. A mixture of 5 mL of a 4.9 M K2CO3 solution and 500 μL of a 0.33 M 239Pu(NO3)4 solution was B


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Inorganic Chemistry

Table 1. Structure Data of Known Na+ and K+ Salts of {[(CO3)3Ce]2(μ-η2-η2-O2)2}8− (Ce Dimer) and {[(CO3)3Pu]2(μ-η2-η2O2)2}8− (Pu Dimer) cell parameters compound Na8(Pu dimer)·12H2O

Na8(Ce dimer)·12H2O

Na8(Ce dimer)·18H2O

K8(Pu dimer)·12H2O

K8(Ce dimer)·12H2O

K6Na2(Ce dimer)·8H2O

space group triclinic P1̅ (No. 2), Z = 1 triclinic P1̅ (No. 2), Z = 1 monoclinic P21/c (No. 14), Z = 2 triclinic P1̅ (No. 2), Z = 1 triclinic P1̅ (No. 2), Z = 1 triclinic P1̅ (No. 2), Z = 1

lengths (Å)

angles (deg)

a = 8.861(8) b = 8.889(8) c = 11.511(10) a = 8.8797(9) b = 8.8960(8) c = 11.5527(12) a = 7.53(3) b = 11.38(4) c = 22.17(4) a = 8.862(2) b = 10.330(2) c = 10.939(2) a = 8.887(1) b = 10.392(1) c = 10.958(1) a = 8.412(1) b = 9.789(2) c = 10.186(2)

α = 69.45(1) β = 67.99(1) γ = 64.69(2) α = 69.425(2) β = 68.114(2) γ = 64.829(2) β = 115.16(8) α = 66.787(3) β = 68.391(3) γ = 74.259(3) α = 66.85(1) β = 68.42(1) γ = 74.37(1) α = 96.20(2) β = 102.87(1) γ = 112.20(2)

Diffraction data for the new structure of the Ce compound Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O were collected using a Bruker Apex II diffractometer and Mo Kα radiation at room temperature. The crystal was mounted on a MiTeGen MicroMounts loop using Krytox (DuPont) grease. The initial unit cell was determined using the APEX353 program package. Data integration was performed using SAINT,54 and SADABS57 was used to determine the absorption correction. Subsequent data reduction, structure solution, and refinement were carried out using the SHELXTL56 program. The structure was solved by direct methods and refined on F2 by full-matrix least-squares techniques. 2.4. Computational Details. Most computations were performed with a 2014 developer’s version of the Amsterdam Density Functional (ADF) package58 using the scalar relativistic zeroth-order regular approximate (ZORA) relativistic all-electron Hamiltonian.59 Additional computational details and results can be found in the Supporting Information. All-electron Slater-type double-ζ-polarized (DZP) basis sets optimized for ZORA computations as supplied by the ADF basis set collection were employed. For Ce, Pu, and Cs, no DZP basis set was available, and the corresponding triple-ζ-polarized basis sets were used. The computations were carried out using a local density approximation (LDA) in the form of the Vosko−Wilk−Nusair (VWN) functional60 and the revised Perdew−Burke−Ernzerhof (PBE) generalized gradient approximation (GGA) functional.61 The latter predicted slightly longer Op−Op distances in the peroxo ligands of the Ce-containing dimers, leading to Op−Op stretching frequencies significantly closer to those observed experimentally. Starting from the crystal structure of the Na-containing Ce dimer, the structures of the free anionic dimer moiety {[(CO3)3Ce]2(μ-η2-η2-O2)2}8− and the corresponding complexes, including four alkali ions surrounding the peroxo ligands, were optimized. Similarly, the structures of the free anionic dimer moiety {[(CO3)3Pu]2(μ-η2-η2-O2)2}8− and the corresponding systems with four K and four Na ions were optimized. Subsequent calculations of the vibrational frequencies employed analytical or numerical derivatives of calculated analytical energy gradients, depending on the chosen program and version. The four alkali ions close to the peroxo ligands were chosen to be included in the calculations in order to test whether their presence had any impact on the calculated Op−Op vibrational frequencies. Typically, two to three very small imaginary frequencies between 0 and 20i cm−1 were obtained in the calculations, associated with torsional motions of the two Ce(CO3)3 or Pu(CO3)3 moieties, respectively, relative to each other. The imaginary frequencies arise from the very shallow potential

unit cell volume (Å3), density (g/cm3)

ref

739.9, 2.94

45

745.9, 2.441

this work

1719.5, 4.68

50

846.3, 2.820

this work

855.5, 2.39

51

739.7, 2.53

36

energy profile for these motions and concomitant numerical noise in the calculated second derivatives of the energy with respect to the nuclear coordinates. Given the total charges of 8− and 4− for the systems without and with alkali ions, a conductor-like screening model62 with a dielectric constant of 78 was used for embedding. This embedding does not represent the crystal environment in detail. Rather, the calculations were designed to study whether the observed properties of the dimer complexes are of “molecular” origin, in which case they should be reproducible by the embedded computations and (at least in principle) observable in solution, or whether they are dominated by short- and long-range intermolecular interactions in the crystal. The results of the calculations (vide infra) show that the trends in the observed Raman frequencies are reproduced by calculations for the individual clusters. To study the degree of bonding between Ce and the peroxo ligands, sets of “natural” localized molecular orbitals (LMOs) were generated with a locally modified version and parallelized with the NBO program, version 5,63 using a global hybrid version of the PBE functional with 25% exact exchange, PBE0.64 Additional bonding analyses were performed with the CAM-B3LYP and PBE functionals.65 The LMOs and selected canonical molecular orbitals (MOs) were visualized in the form of isosurfaces generated with the ADF graphical user interface.

3. RESULTS AND DISCUSSION 3.1. Structure. Structural details for the M8[(CO3)3A]2(μη2-η2-O2)2·xH2O (M = Na and/or K; A = Pu or Ce; x = 8, 12, or 18) series are shown in Table 1. Here, we report the first structure of the K salt of the {[(CO3)3Pu]2(μ-η2-η2-O2)2}8− dimer and a new structure for the Na salt of the {[(CO3)3Ce]2(μ-η2-η2-O2)2}8− dimer, which is isomorphous with the previously reported Pu analogue.50 Although crystal structures for the Na+ salts with Pu and Ce have been previously reported, they are not isomorphous, complicating experimental and theoretical comparisons. The Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O structure reported here differs from that in the literature in the arrangement of the dimers and the number of water molecules per dimeric unit. The K+, Rb+, and Cs+ analogues with Ce were synthesized using the method described in the Experimental Section, and the crystal structures obtained match those previously reported.50,52 C


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Inorganic Chemistry The packing arrangements in Na8[(CO3)3Pu]2(μ-η2-η2-O2)2· 12H2O50 and K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O were found to be identical with those observed in the new structure for Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O reported here (Figure 1)

Figure 2. ab plane of K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O. K is purple, Pu is green, O is red, and C is black. Cocrystallized water molecules have been omitted for clarity. The Ce analogue is isomorphous.51

Figure 1. Thermal ellipsoid plot of the anionic dimeric unit in Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O drawn at the 70% probability level. The Pu analogue is isomorphous.45

cation at a distance of 2.886 Å from the peroxo bridge, the packing is not as close as that achieved around the Na ions. Therefore, the closest contact between two neighbors in K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O is the interatomic distance between two terminal O atoms of carbonate ligands. This is referred to as a “carbonate-to-carbonate” interaction. The “carbonate-to-carbonate” interaction in the K salt does not allow for the more efficient packing that is observed with the “peroxo-to-carbonate” closest interactions of the Na salt. This is due in part to the larger ionic radius of K compared to that of Na.66 These differences in the packing can explain the differences in the density and unit cell volume between the Na and K salts of the Pu dimeric compounds. The interatomic distances and angles within the {[(CO3)3Ce]2(μ-η2-η2-O2)28− dimer unit are very similar in all of the salts that have been reported. As in the analogous Pu cases, the dimeric unit consists of two Ce(CO3)3 units linked by two μ-η2-peroxo units. For the Rb+, K+, Na+, and Na+/K+ salts of the dimeric compound, all of the compounds can crystallize in the P1̅ space group and contain one dimer per unit cell. The inversion center that relates the halves of the dimer is located in the center of the shared quadrilateral formed by the O atoms of the peroxo groups. Ranges of selected interatomic distances and angles for the Na and K analogues are shown in Table 2. The previously reported Na8[(CO3)3Ce]2(μ-η2-η2-O2)2· 18H2O50 differs from the structure of Na8[(CO3)3Ce]2(μ-η2η2-O2)2·12H2O, reported here, in the number of cocrystallized water molecules. The latter is isomorphous with the known Na8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O.45 Na, being the smallest cation in all of the known analogues, facilitates the tightest packing of the Ce dimeric compounds containing 12 water molecules and provides a unit c ell volume t o Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O of 745.9(1) Å3. This new version of the Na salt of the Ce dimer packs slightly more efficiently than the monoclinic structure containing more water molecules reported previously.50

and the previously reported structure of K8[(CO3)3Ce]2(μ-η2η2-O2)2·12H2O,51 respectively. This is reflected in their nearly identical unit cell parameters and volumes (Table 1). However, a comparison of the Na to K salts of these two sets of dimers highlights notable distinctions in the packing arrangements that facilitate differences in the volume and density values between the cation analogues. For the Pu dimers, the volume of the unit cell in the K salt is 846.3 Å3, while the Na salt displays a unit cell volume of 739.9 Å3. Na8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O is more dense (2.94 g/cm3) in contrast to 2.82 g/cm3 for the K+ salt. These differences can be explained by the position and coordination of the cations within the 2D sheets of the PuIV dimer cores, as discussed below. In the case of the Ce dimers, the unit cell of the Na analogue is again smaller in volume (745.9 Å3) than that of the K salt (855.5 Å3); however, the densities (2.441 g/cm3 for the Na analogue and 2.39 g/cm3 for the K analogue) are closer in value (Table 1) than those of the Pu analogues. Within the 2D sheets of dimeric anions in both the Pu and Ce analogues, “pockets” are formed by two neighboring dimers. In both the Na and K compounds of Pu and Ce, unique cations are located within or near the pockets formed by O atoms from peroxide and carbonate ligands. In Na8[(CO3)3Pu]2(μ-η2-η2O2)2·12H2O,45 these Na cations are able to coordinate close to the center of the PuIV dimer near the diperoxo bridge, with the shortest M−Op distance being 2.387 Å. This makes it possible for the Pu dimers to pack closer together in the Na salt. The closest contact between two neighboring dimers is the interatomic distance between a peroxide Op atom and a terminal O atom of a carbonate group. This is referred to as a “peroxo-to-carbonate” interaction and is facilitated by Na ions between the dimers. In the case of the K salt of the Pu analogue (Figure 2), only one K ion is able to fit into the pocket between two dimeric anions. This is similar to the arrangement of cations in the Na compound; however, with the nearest K D


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Inorganic Chemistry

Table 2. Selected Interatomic Distances (Å) and Angles (deg) of M8[A dimer]·12H2O, Where M = Nearest Na or K to the Peroxide Ligands, A = Ce or Pu, Op = O Atom of a Peroxide Ligand, and Oc = O Atom of a Carbonate Ligand A−Op A−Oc Op−Op A···A M−Op Op−M−Op A−Op−A

Na8[Ce dimer]·12H2O

Na8[Pu dimer]·12H2O

K8[Ce dimer]·12H2O

K8[Pu dimer]·12H2O

2.339(2)−2.383(2) 2.392(2)− 2.437(2) 1.492(3) 3.552(3) 2.390(2)−2.425(2) 36.09(7) 97.57(8)−97.78(7)

2.334(5)−2.368(5) 2.378(4)−2.483(4) 1.495(6) 3.528(4) 2.387(8)−2.420(7) 36.24(14) 97.14(16)−97.35(15)

2.345(4)−2.374(3) 2.390(4)−2.458(4) 1.468(6) 3.523(1) 2.908(6)−3.096(6) 27.62(1) 95.9(1)−97.8(1)

2.313(4)−2.371(4) 2.389(4)−2.449(4) 1.486(5) 3.502(6) 2.886(4)−3.064(4) 28.28(10) 95.71(14)−97.59(13)

η2-O2)2·12H2O, K8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, and Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O. Peaks between 1048 and 1060 cm−1 are attributed to the symmetric stretching of the CO3 groups [νs(O−C−O)]. The vibrational modes between 847 and 870 cm−1 correspond to peroxide groups and therefore are labeled as ν(Op−Op). Additional peaks between 379 and 404 cm−1 are observed in other known cerium peroxide complexes52 and are most likely due to a Op− Ce−Op vibrational mode, where Op is the O atom of a peroxide group. The vibrational modes around 733−744 and 285−301 cm−1 are present in compounds that contain CO3 bound to Ce such as Ce(CO3)3 and are therefore attributed to Ce−CO3 vibrations. The vibrational modes around 740 cm−1 appear to be nearly overlapping modes, which show up as clearly split peaks in all but the Na+ and Cs+ salts of the Ce dimers. The splitting of the peaks around 740 cm−1 is likely due to the chemical inequivalence of the CO3 groups and further supports the assignment of these modes being CO3 bending modes. See Table 3 for a list of the Raman shifts and assignments for each of the M8[(CO3)3Ce]2(μ-η2-η2-O2)2·xH2O compounds. The Raman spectra of these compounds, shown in Figure 4, indicate that the dimer unit has a signature pattern that is sensitive to the cation incorporated in the solid. While each analogue has similar observed vibrational modes, the frequency is slightly shifted in each structure, as shown in Table 3. A notable shift is in the ν(Op−Op) vibrational mode with values of 847, 870, 854, and 859 cm−1 for the Na+, K+, Rb+, and Cs+ salts, respectively. The shift of the Raman-active peroxide vibrational mode appears to correlate with the Op−Op bond distance within the peroxide group, as shown in Table 4. The longer the Op−Op bond length, the lower the ν(Op−Op) frequency. As ν(Op−Op) is shifted to higher frequencies, this corresponds to a stronger and therefore shorter Op−Op bond. The vibrational frequency/bond length correlation has been described previously.67−70 While the Rb and K analogues of the Ce dimer have the same structure type, there is still a significant shift of the ν(Op−Op) mode. The Op−Op bond must be influenced by the type of cation and its relative proximity. Although differences in the bond lengths and vibrational frequencies discussed are in some cases subtle, we believe the trend in the Raman data supports the X-ray data, indicating that these are real structural variances. There was no apparent trend in the Ce−Oc distances or in the Ce−Op lengths that correlates to the Op−Op peroxide distances. Interestingly, the Na+ compound possesses the smallest ν(Op−Op) frequency, the longest Op−Op bond, and the shortest (alkali metal−peroxide O) distance, once the Shannon radius of the alkali metal is taken into account, (M−Op)−SR (Table 4). Conversely, the K+ analogue possesses the largest ν(Op−Op) vibrational frequency for the shortest Op−Op bond and the farthest alkali metal−peroxide interaction. This trend is

The distinctive feature in the structure of Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O is the tongue and groove packing mode seen in Figure 3. One of the carbonate

Figure 3. ac plane of Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O. Na is green, Ce is yellow, O is red, and C is black. Cocrystallized water molecules have been omitted for clarity.

groups (tongue) points to the peroxide group (groove) of the neighboring dimer. The dimers form a small pocket that Na fits into. The packing arrangement results in a short M−Op distance. The K, Rb, and Cs salts of {[(CO3)3Ce]2(μ-η2-η2-O2)2}8− adopt a less dense packing of dimeric units than the Na analogue. The K+ and Rb+ analogues have similar packing arrangements. The Cs+ analogue crystallizes in the orthorhombic space group Pbca. Instead of having one dimeric unit per unit cell, the Cs+ analogue contains four dimeric units related by glide planes. All of the Ce crystals are red. For the Pu system, the structures of the Rb and Cs analogues are still unknown. The Na and K salts of the Pu analogues are green. 3.2. Raman Spectroscopy. Although Raman spectral measurements could not be performed on the Pu-containing compounds because of their physical instability when subjected to the Raman laser, data were collected for each of the Cecontaining analogues. Figure 4 shows the Raman spectra of Cs8[(CO3)3Ce]2(μ-η2-η2-O2)2·10H2O, Rb8[(CO3)3Ce]2(μ-η2E


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Inorganic Chemistry

Figure 4. Raman spectra of Cs8[(CO3)3Ce]2(μ-η2-η2-O2)2·10H2O, Rb8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, K8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, and Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O.

ligands in {[(CO3)3Ce]2(μ-η2-η2-O2)2}8− and M4{[(CO3)3Ce]2(μ-η2-η2-O2)2}4− with M = Na, K, and Cs are listed in Table 5. The peroxo group vibrations are given in terms of symmetric (in-phase) and antisymmetric (out-ofphase) collective vibrations. The results for the analogous complexes {[(CO3)3Pu]2(μ-η2-η2-O2)2}8− and M4{[(CO3)3Pu]2(μ-η2-η2-O2)2}4− with M = Na and K are also given in Table 5 for comparison. The Cs analogue with Ce was chosen because the Raman spectrum and crystal structure were reported previously52 and were confirmed in this study. The Na and K analogues afford the most extreme differences in the observed bond lengths and peroxide ν(Op−Op) vibrational frequencies. The VWN LDA functional gives too short peroxo Op−Op distances with concomitant high vibrational frequencies. The vibrational frequencies calculated with the PBE GGA functional are lower and in good agreement with the available experimental data. The optimized bond lengths for the Na, K, and Cs clusters with Ce agree quite well with the crystal structure data. The trend of increasing Op−Op stretching frequencies when going from Na to K, along with a slight decrease in the Op−Op distances, as seen in the Raman spectra and X-ray data of the solids, respectively, is also reproduced by calculations for the Ce analogues.

Table 3. Raman Assignments (cm−1) of Na8[(CO3)3Ce]2(μη2-η2-O2)2·12H2O, K8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, Rb8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, and Cs8[(CO3)3Ce]2(μ-η2-η2-O2)2·10H2O, Where Op = O Atom of a Peroxide Group and Oc = O Atom of a Carbonate Group assignment

Na+

K+

Rb+

Cs+

νs(Oc−C−Oc) ν(Op−Op) δ(Oc−C−Oc) ν(Ce−Op) δ(Oc−C−Oc)

1060 847 744 404 285

1048 870 733 393 301

1058 854 733 386 294

1053 859 735 379 287

consistent with the way we understand the vibrational frequency/bond length correlation and suggests that the distance of the nearest alkali-metal cation to each peroxide bridge, respectively, could affect the strength of the peroxide bond. These parameters for the Rb and Cs analogues fall between the extremes of the Na and K analogues. Figure 5 shows the locations of the nearest cations to the μ-η2 peroxide bridge for each of the Ce analogues. 3.3. Electronic Structure. The calculated vibrational frequencies and optimized Op−Op distances for the peroxo

Table 4. Peroxide Symmetric Stretching Frequency (cm−1) and Interatomic Distances (Å) for the Na+, K+, Rb+,52 and Cs+ Salts52 of the Ce Dimer {[(CO3)3Ce]2(μ-η2-η2-O2)2}8−, Where M = Respective Alkali-Metal Cations Nearest to the Peroxide Bridges compound

ν(Op−Op)

Op−Op

avg. Ce−Op

M−Op

(M−Op)−SRa,66

Na8[Ce dimer]·12H2O Rb8[Ce dimer]·12H2O Cs8[Ce dimer]·10H2O K8[Ce dimer]·12H2O

847 854 859 870

1.492(3) 1.471(1) 1.474(1) 1.468(6)

2.359(2) 2.361(7) 2.362(7) 2.354(4)

2.390(2) 2.979(7) 3.016(7) 2.908(6)

1.220 1.369 1.276 1.398

a

The Shannon radius for each cation was subtracted from the respective cation−Op distance. This gives the radius of Op for each cation−Op interaction. F


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Inorganic Chemistry

Figure 5. Interatomic distances (Å) between the cations and O atoms of the peroxide ligands (Op) for (A) Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, (B) K8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, (C) Rb8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, and (D) Cs8[(CO3)3Ce]2(μ-η2-η2-O2)2·10H2O.

Table 5. Calculated Frequencies (cm−1, Unscaled) for the Symmetric (s) and Asymmetric (a) Peroxo Op−Op Stretching Modes and Optimized Peroxo Op−Op Distances (Å) of {[(CO3)3A]2(μ-η2-η2-O2)2}8− and M4{[(CO3)3A]2(μη2-η2-O2)2}4−, Where A = Ce or Pu and M = Na, K, or Cs. Available experimental data for the corresponding 2 2 M8{[(CO3)3A]2(μ-η -η -O2)2} species are provided in a parentheses compound [Ce dimer]

8−

ν(Op−Op)a ν(Op-Op)s

VWN PBE VWN PBE

914 853 907 840

K4[Ce dimer]4−

VWN PBE

913 859

Cs4[Ce dimer]4−

VWN PBE

913 855

[Pu dimer]8− a

VWN PBE VWN PBE

888 841 883 844

930 868 919 852 (847) 926 872 (870) 926 867 (859) 902 855 893 853

VWN PBE

882 842

893 853

Na4[Ce dimer]4−

[Na4[Pu dimer]]4− a

K4[Pu dimer]4− a

a

functional

the Na and K analogues with Pu are also in a region similar to that for both the experimental and theoretical ν(Op−Op) frequencies of the Ce analogues (850−870 cm−1). However, in the Pu case, these values do not indicate any increasing or decreasing trends in the Op−Op distances or their predicted Raman vibrational modes, which could suggests that, if experimentally attainable, the ν(O−Op−Op) vibrational frequencies for Na8{[(CO3)3Pu]2(μ-η2-η2-O2)2}·12H2O and K8{[(CO3)3Pu]2(μ-η2-η2-O2)2}·12H2O would be indistinguishable. However, we note that the results of the calculations on the Pu compounds are more approximate because of the partially filled 5f shell of the Pu4+ ion. Figure 6 displays selected LMOs, as well as selected canonical (the usual self-consistent field) MOs, of the {[(CO3)3Ce]2(μ-η2-η2-O2)2}8− moiety. There is a minor degree of Op → Ce donation bonding visible in a set of eight approximately equivalent LMOs that represent oxygen lone pairs, with about 5% contribution to the density of each LMO from the Ce orbitals. On the Ce side, the composition of these orbitals is predominantly Ce 4f (ca. 60/30/10% f/d/s). Overall, however, the Ce contributions in the O lone-pair LMOs are small, and therefore the Ce−peroxide interactions should be characterized as predominantly ionic with a secondary contribution from Op-to-Ce donation bonding. The assignment of the Op−Ce interactions is confirmed by the MOs displayed in Figure 6. There are two ways to represent the peroxo ligands in the complex: The LMO description of Figure 6 tends to represent a quantum-mechanical analogue of the Lewis structure more directly. Here, each peroxo ligand is described by an Op−Op σ bond and three lone pairs per O. This is not surprising because O22− is isoelectronic with F2. In the LMO description, the donation bonding involves the O lone pairs. In the canonical MO description, the peroxo ligand is described by a filled bonding σ orbital, and pairs of filled bonding and antibonding π orbitals, along with ± sets of linear combinations of O σ lone pairs. The formal π bond order is zero. Therefore,

Op−Op 1.447 1.482 1.457 1.493 [1.492(3)] 1.450 1.482 [1.468(6)] 1.448 1.483 [1.474(1)] 1.457 1.490 1.465 1.495 [1.495(6)] 1.462 1.493 [1.486(5)]

Results obtained for a non-spin polarized electronic state.

For the Pu analogues, Raman data could not be obtained for comparison with the computational model. To model these systems, non-spin-polarized electronic states were used. The predicted Op−Op bond lengths for the Pu analogues are very similar to their experimental values obtained by X-ray diffraction (Table 5). The ν(Op−Op) modes predicted for G


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Inorganic Chemistry

Figure 6. (a) Isosurfaces (±0.03 atomic units) of selected LMOs and (b) selected canonical MOs of {[(CO3)3Ce]2(μ-η2-η2-O2)2}8−.

antibonding Op−Op σ* orbital for the Na analogue compared to the K and Cs complexes. On the basis of these findings, the effect on the vibrational frequencies is mainly attributed to electrostatic effects, leading to a minor degree of charge reorganization in the dimer complexes upon the addition of alkali ions.

the LMO and canonical MO descriptions are different, but equally valid, representations of the same bonding situation. There is also the possibility of an LMO description of the complex in which the doubly occupied σ orbitals and pairs of bonding and antibonding π orbitals of the peroxo ligands are retained, as shown in Figure S2 in the Supporting Information. (Among the full set of calculations, this LMO set was found only for the K analogue.) In this case, the canonical MOs of “gas-phase free O22−” (an unstable species) underlie the peroxo-centered LMOs in the complex but with a lesser degree of localization than the localized orbitals shown in Figure 6. In the canonical description, the highest occupied molecular orbital of the anionic Ce dimer reveals a small bonding interaction between the π* fragment orbitals of the peroxide ligands and the Ce 4f orbitals. Calculations with different functionals were performed in order to test whether there is a pronounced sensitivity of the Ce contributions in these orbitals to approximations made in the calculations. The rangeseparated hybrid functional CAM-B3LYP produced natural bond order (NBO) data very similar to those of the PBE0 global hybrid (Figure 6). In calculations with the nonhybrid functional PBE, the Ce contributions in the peroxide lone pairs were slightly larger, on average 7%, compared to PBE0 and CAM-B3LYP (5−6%). This is very likely a manifestation of the larger DFT delocalization error (DE) in the calculations with the PBE functional.71 Sizable Ce 4f (and 5d) orbital populations in CeIV complexes have been noted previously.72,73 A recent computational analysis has shown that these populations are present in calculations with a variety of hybrid functionals with varying degrees of DE as well as in wave-function calculations and that GGA functionals overestimate these populations.74 The PBE0 hybrid functional underlying the orbitals of Figure 6 should provide a physically reasonable extent of peroxo−Ce donation bonding. Additional NBO calculations for the −4-charged systems with alkali metals indicated no covalent interactions between the alkali ions and the Ce dimer moieties. Further, no obvious trends in the change of the LMO compositions of the complexes were observed upon the addition of alkali-metal ions, apart from a slight increase of the occupation of the

4. CONCLUSIONS Using the simplified preparation method described here, the Na, K, Rb, and Cs salts of the {[(CO3)3A(μ-η2-η2-O2)2}8− dimers, where A = Ce (Na, K, Rb, Cs) or Pu (K), were synthesized. With this new method of crystal preparation, two new structures, namely, K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O and Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O, were obtained. The size of the cation used in the synthesis seems to dictate the packing of the f-element dimers. In the case of the Ce analogues, the Raman shift of the ν(Op−Op) vibrational mode correlates with the Op−Op bond length of the peroxide ligand. Electronic structure calculations gave insight into the nature of the Ce−peroxide interactions. Because the molecular-based electronic structure calculations were able to reproduce the observed Raman shifts for the peroxide groups in the Na, K, and Cs analogues of Ce, it can be deduced that the shifts are due to cation−peroxide group interactions mainly of the electrostatic nature. The structure calculations also indicate that the Ce−peroxide bond is predominantly ionic with a minor covalent peroxo-to-cerium donation-bonding contribution. The trends in the peroxide vibrational frequencies of the dimeric structures are reproduced by the calculations, indicating that the properties of this system can be meaningfully interpreted as that of a molecule surrounded by the nearest alkali ions rather than as a consequence of more complex short- and long-range interactions within the crystals. Although Raman data could not be obtained for the Pu analogues because of their physical instability when irradiated by the Raman laser, computational modeling of the open-shell 5f system was performed. The predicted bond lengths of the Op−Op bridges are in relatively good agreement with their experimental values. The corresponding theoretical ν(O−O) H


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Inorganic Chemistry

(3) Aboelella, N. W.; Reynolds, A. M.; Tolman, W. B. Catching copper in the act. Science 2004, 304, 836. (4) Lewis, E. A.; Tolman, W. B. Reactivity of dioxygen−copper systems. Chem. Rev. 2004, 104, 1047. (5) Betley, T. A.; Wu, Q.; Van Voorhis, T.; Nocera, D. G. Electronic design criteria for O−O bond formation via metal−oxo complexes. Inorg. Chem. 2008, 47, 1849. (6) Momenteau, M.; Reed, C. A. Synthetic heme-dioxygen complexes. Chem. Rev. 1994, 94, 659. (7) Vaska, L. Dioxygen-metal complexes: Toward a unified view. Acc. Chem. Res. 1976, 9, 175. (8) Lewis, N. S.; Nocera, D. G. Powering the planet: Chemical challenges in solar energy utilization. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 15729. (9) Du, P.; Eisenberg, R. Catalysts made of earth-abundant elements (Co, Ni, Fe) for water splitting: Recent progress and future challenges. Energy Environ. Sci. 2012, 5, 6012. (10) Kohl, S. W.; Weiner, L.; Schwartsburd, L.; Konstantinovski, L.; Shimon, L. J. W.; Ben-David, Y.; Iron, M. A.; Milstein, D. Consecutive thermal H2 and light-induced O2 evolution from water promoted by a metal complex. Science 2009, 324, 74. (11) Sigmon, G. E.; Burns, P. C. Rapid self-assembly of uranyl polyhedra into crown clusters. J. Am. Chem. Soc. 2011, 133, 9137. (12) Unruh, D. K.; Ling, J.; Qiu, J.; Pressprich, L.; Baranay, M.; Ward, M.; Burns, P. C. Complex nanoscale cage clusters built from uranyl polyhedra and phosphate tetrahedra. Inorg. Chem. 2011, 50, 5509. (13) Ling, J.; Wallace, C. M.; Szymanowski, J. E. S.; Burns, P. C. Hybrid uranium−oxalate fullerene topology cage clusters. Angew. Chem., Int. Ed. 2010, 49, 7271. (14) Vlaisavljevich, B.; Gagliardi, L.; Burns, P. C. Understanding the structure and formation of uranyl peroxide nanoclusters by quantum chemical calculations. J. Am. Chem. Soc. 2010, 132, 14503. (15) Sigmon, G. E.; Ling, J.; Unruh, D. K.; Moore-Shay, L.; Ward, M.; Weaver, B.; Burns, P. C. Uranyl−peroxide interactions favor nanocluster self-assembly. J. Am. Chem. Soc. 2009, 131, 16648. (16) Sigmon, G. E.; Unruh, D. K.; Ling, J.; Weaver, B.; Ward, M.; Pressprich, L.; Simonetti, A.; Burns, P. C. Symmetry versus minimal pentagonal adjacencies in uranium-based polyoxometalate fullerene topologies. Angew. Chem., Int. Ed. 2009, 48, 2737. (17) Kubatko, K.-A.; Burns, P. C. Expanding the crystal chemistry of actinyl peroxides: Open sheets of uranyl polyhedra in Na5[(UO2)3(O2)4(OH)3](H2O)13. Inorg. Chem. 2006, 45, 6096. (18) Burns, P. C.; Kubatko, K.-A.; Sigmon, G.; Fryer, B. J.; Gagnon, J. E.; Antonio, M. R.; Soderholm, L. Actinyl peroxide nanospheres. Angew. Chem., Int. Ed. 2005, 44, 2135. (19) Douglas, M.; Clark, S. B.; Friese, J. I.; Arey, B. W.; Buck, E. C.; Hanson, B. D. Neptunium(V) partitioning to uranium(VI) oxide and peroxide solids. Environ. Sci. Technol. 2005, 39, 4117. (20) Nyman, M.; Burns, P. C. A comprehensive comparison of transition-metal and actinyl polyoxometalates. Chem. Soc. Rev. 2012, 41, 7354. (21) Kubatko, K.-A. H.; Helean, K. B.; Navrotsky, A.; Burns, P. C. Stability of peroxide-containing uranyl minerals. Science 2003, 302, 1191. (22) Hanson, B. D.; McNamara, B.; Buck, E.; Friese, J.; Jenson, E.; Krupka, K.; Arey, B. Corrosion of commercial spent nuclear fuel. 1. Formation of studtite and metastudtite. Radiochim. Acta 2005, 93, 159. (23) McNamara, B.; Hanson, B. D.; Buck, E. C.; Soderquist, C. Corrosion of commercial spent nuclear fuel. 2. Radiochemical analyses of metastudtite and leachates. Radiochim. Acta 2005, 93, 169. (24) Amme, M.; Svedkauskaite, J.; Bors, W.; Murray, M.; Merino, J. A kinetic study of UO2 dissolution and H2O2 stability in the presence of groundwater ions. Radiochim. Acta 2007, 95, 683. (25) Thangavelu, S. G.; Cahill, C. L. Uranyl-promoted peroxide generation: Synthesis and characterization of three uranyl peroxo [(UO2)2(O2)] complexes. Inorg. Chem. 2015, 54, 4208. (26) Wahu, S.; Berthet, J.-C.; Thuéry, P.; Guillaumont, D.; Ephritikhine, M.; Guillot, R.; Cote, G.; Bresson, C. Structural versatility of uranyl(VI) nitrate complexes that involve the diamide

vibrational frequencies for the Na and K analogues with Pu are predicted to be very similar, which could suggest that, if experimental values could be acquired, they may be indistinguishable despite variation in the alkali-metal cations. With the discovery of the sodium and potassium peroxocarbonate dimers of Ce, which are isomorphous with their Pu analogues, there is direct evidence that the speciation of Ce in carbonate peroxide systems closely resembles that of Pu. However, more analysis is currently underway to fully compare these two series of peroxocarbonate complexes. CCDC 1501556 and 1501557 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif and are also available in the Supporting Information.

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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.6b02235. X-ray crystallographic data in CIF format (CIF) X-ray crystallographic data in CIF format (CIF) Additional computational and crystallographic details for K8[(CO3)3Pu]2(μ-η2-η2-O2)2·12H2O and Na8[(CO3)3Ce]2(μ-η2-η2-O2)2·12H2O (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +1 (949) 375-7248. ORCID

Jordan F. Corbey: 0000-0002-3273-3044 Jochen Autschbach: 0000-0001-9392-877X Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This research was conducted at the U.S. Department of Energy (DOE)’s Pacific Northwest National Laboratory, which is operated for the DOE by Battelle Memorial Institute under Contract DE-AC05-76RL1830. We thank and acknowledge the Department of Homeland Security’s Nuclear Forensics Postdoctoral Fellowship Program run by the National Technical Nuclear Forensics Center within the Domestic Nuclear Detection Office for providing support for Dr. Jordan Corbey. We thank our sponsors for their support as well as Dr. Richard E. Wilson and Argonne National Laboratory for assistance with crystallography. L.E.S. and J.F.C. also thank Dr. David G. Abrecht for technical discussion. F.G. and J.A. acknowledge financial support of the computational part of this study from the DOE, Office of Basic Energy Sciences, Heavy Element Chemistry Program, under Grant DE-SC0001136 (formerly Grant DE-FG02-09ER16066) and thank the Center for Computational Research at The State University of New York at Buffalo for providing computing resources.

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REFERENCES

(1) Borovik, A. S. Bioinspired hydrogen bond motifs in ligand design: The role of noncovalent interactions in metal ion mediated activation of dioxygen. Acc. Chem. Res. 2005, 38, 54. (2) Meunier, B. Biomimetic oxidations catalyzed by transition metal complexes; Imperial College Press: London, 2000. I


Article

Inorganic Chemistry ligand Et2N(CO) (CH2)n(CO)NEt2 (0 ≤ n ≤ 6). Eur. J. Inorg. Chem. 2012, 2012, 3747. (27) Radecka-Paryzek, W.; Patroniak, V.; Kubicki, M. First example of template synthesis of pentaaza macrocyclic ytterbium(III) complex and solvent-controlled supramolecular self-assembly of its dimeric μη2:H2 peroxo-bridged derivative. Inorg. Chem. Commun. 2004, 7, 455. (28) Wang, G.-C.; Sung, H. H. Y.; Williams, I. D.; Leung, W.-H. Tetravalent titanium, zirconium, and cerium oxo and peroxo complexes containing an imidodiphosphinate ligand. Inorg. Chem. 2012, 51, 3640. (29) Mustapha, A.; Reglinski, J.; Kennedy, A. R. The use of hydrogenated schiff base ligands in the synthesis of multi-metallic compounds. Inorg. Chim. Acta 2009, 362, 1267. (30) Niemeyer, M. Synthesis and structural characterization of several ytterbium bis(trimethylsilyl)amides including base-free [Yb{N(SiMe3)2}2(μ-Cl)]2  a coordinatively unsaturated complex with additional agostic Yb···(H3CSi) interactions. Z. Anorg. Allg. Chem. 2002, 628, 647. (31) Coles, M. P.; Hitchcock, P. B.; Khvostov, A. V.; Lappert, M. F.; Li, Z.; Protchenko, A. V. Crystalline amidocerium(IV) oxides and a side-on bridging dioxygen complex. Dalton Transactions 2010, 39, 6780. (32) Butman, L. A.; Sokol, V. I.; Porai-Koshits, M. A. Koord. Khim. 1976, 2, 265. (33) Pook, N.-P.; Adam, A. Synthesis, crystal structure, and vibrational spectra of five novel peroxidocerates(IV) and the occurrence of a new complex unit in K8[Ce2(O2)3(nta)2]2·20H2O. Z. Anorg. Allg. Chem. 2014, 640, 2931. (34) Deacon, G. B.; Forsyth, C. M.; Freckmann, D.; Junk, P. C.; Konstas, K.; Luu, J.; Meyer, G.; Werner, D. Adventitiously obtained rare-earth peroxide complexes and their structural characterisation. Aust. J. Chem. 2014, 67, 1860. (35) Farnaby, J. H.; Fang, M.; Ziller, J. W.; Evans, W. J. Expanding yttrium bis(trimethylsilylamide) chemistry through the reaction chemistry of (N2)2−, (N2)3−, and (NO)2− complexes. Inorg. Chem. 2012, 51, 11168. (36) Barnes, J. C.; Blyth, C. S.; Paton, J. D.; Smith, I. G. B. Dimeric cerium (iv) peroxide complexes. Crystal structures of hexapotassium disodium bis-μ-peroxohexacarbonatodicerate (IV) 8-hydrate and dipotassium disodium bis-μ-peroxobis (ethylene-diamine-n, n, n′, n′tetra-acetato) dicerate (IV) 13-hydrate. Lanth. Actin. Res. 1990, 3, 181. (37) Štefanić, I.; LaVerne, J. A. Temperature dependence of the hydrogen peroxide production in the γ-radiolysis of water. J. Phys. Chem. A 2002, 106, 447. (38) Felmy, A. R.; Cantrell, K. J.; Conradson, S. D. Plutonium contamination issues in hanford soils and sediments: Discharges from the z-plant (pfp) complex. Physics and Chemistry of the Earth, Parts A/ B/C 2010, 35, 292. (39) Clark, D. L.; Hobart, D. E.; Neu, M. P. Actinide carbonte complexes and their importance in actinide environmental chemistry. Chem. Rev. 1995, 95, 25. (40) Clark, D. L.; Conradson, S. D.; Keogh, D. W.; Palmer, P. D.; Scott, B. L.; Tait, C. D. Identification of the limiting species in the plutonium(IV) carbonate system. Solid state and solution molecular structure of the [Pu(CO3)5]6‑ ion. Inorg. Chem. 1998, 37, 2893. (41) Soderquist, C.; Hanson, B. Dissolution of spent nuclear fuel in carbonate-peroxide solution. J. Nucl. Mater. 2010, 396, 159. (42) Chung, D.-Y.; Seo, H.-S.; Lee, J.-W.; Yang, H.-B.; Lee, E.-H.; Kim, K.-W. Oxidative leaching of uranium from simfuel using Na2CO3−H2O2 solution. J. Radioanal. Nucl. Chem. 2010, 284, 123. (43) Soderquist, C.; Hanson, B. Dissolution of spent nuclear fuel in carbonate−peroxide solution. J. Nucl. Mater. 2010, 396, 159. (44) Smith, S. C.; Peper, S. M.; Douglas, M.; Ziegelgruber, K. L.; Finn, E. C. Dissolution of uranium oxides under alkaline oxidizing conditions. J. Radioanal. Nucl. Chem. 2009, 282, 617. (45) Runde, W.; Brodnax, L. F.; Goff, G. S.; Peper, S. M.; Taw, F. L.; Scott, B. L. Synthesis and structural characterization of a molecular plutonium(IV) compound constructed from dimeric building blocks. Chem. Commun. 2007, 1728.

(46) Job, P. Compt. rend. 1899, 128, 1098. (47) Job, P. Ann. Chim. Phys., 1900, 7. (48) Meloche, C. C. The derivatives of perceric oxide - [second paper]. J. Am. Chem. Soc. 1915, 37, 2645. (49) Meloche, C. C. The derivatives of perceric oxide - [first paper]. J. Am. Chem. Soc. 1915, 37, 2338. (50) Barnes, J. C.; Blyth, C. S.; Knowles, D. Sodium-salts of the bismu-peroxohexacarbonatodicerate(IV) anion - crystal-structure of Na8[Ce(O2)-(CO3)3]2-mu-18H2O. Inorg. Chim. Acta 1987, 126, L3. (51) Barnes, J. C.; Blyth, C. S. Structure and thermal-decomposition of potassium bis-mu-peroxo hexacarbonatodicerate(IV) dodecahydrate. Inorg. Chim. Acta 1985, 110, 133. (52) Pook, N. P.; Adam, A. Synthesis, crystal structure and vibrational characterization of bis-mu-peroxo-hexacarbonatodicerate(IV) complexes of rubidium and cesium. Cryst. Res. Technol. 2008, 43, 1197. (53) APEX3, 2016.1-0 ed.; Bruker AXS, Inc.: Madison, WI, 2016. (54) SAINT, 8.34a ed.; Bruker AXS, Inc.: Madison, WI, 2014. (55) SHELXTL, 2012/1 ed.; Bruker AXS, Inc: Madison, WI, 2012. (56) Sheldrick, G. M.SHELXTL, 2014/7 ed.; Bruker AXS, Inc.: Madison, WI, 2014. (57) Sheldrick, G. M. SADABS, 2014/5 ed.; Bruker AXS, Inc.: Madison, WI, 2014. (58) Baerends, E. J. Z. T.; Autschbach, J.; Bashford, D.; Bérces, A.; Bickelhaupt, F. M.; Bo, C.; Boerrigter, P. M.; Cavallo, L.; Chong, D. P.; Deng, L.; Dickson, R. M.; Ellis, D. E.; van Faassen, M.; Fan, L.; Fischer, T. H.; Fonseca Guerra, C.; Ghysels, A.; Giammona, A.; van Gisbergen, S. J. A.; Götz, A. W.; Groeneveld, J. A.; Gritsenko, O. V.; Grüning, M.; Gusarov, S.; Harris, F. E.; van den Hoek, P.; Jacob, C. R.; Jacobsen, H.; Jensen, L.; Kaminski, J. W.; van Kessel, G.; Kootstra, F.; Kovalenko, A.; Krykunov, M. V.; van Lenthe, E.; McCormack, D. A.; Michalak, A.; Mitoraj, M.; Neugebauer, J.; Nicu, V. P.; Noodleman, L.; Osinga, V. P.; Patchkovskii, S.; Philipsen, P. H. T.; Post, D.; Pye, C. C.; Ravenek, W.; Rodríguez, J. I.; Ros, P.; Schipper, P. R. T.; Schreckenbach, G.; Seldenthuis, J. S.; Seth, M.; Snijders, J. G.; Solà, M.; Swart, M.; Swerhone, D.; te Velde, G.; Vernooijs, P.; Versluis, L.; Visscher, L.; Visser, O.; Wang, F.; Wesolowski, T. A.; van Wezenbeek, E. M.; Wiesenekker, G.; Wolff, S. K.; Woo, T. K.; Yakovlev, A. L. Amsterdam Density Functional, SCM, Theoretical Chemistry; Vrije Universiteit: Amsterdam, The Netherlands, http://www.scm.com. (59) van Lenthe, E.; Baerends, E. J.; Snijders, J. G. J. Relativistic regular two-component Hamiltonians. J. Chem. Phys. 1993, 99, 4597. (60) Vosko, S. H.; Wilk, L.; Nusair, M. Accurate spin-dependent electron liquid correlation energies for local spin density calculations: a critical analysis. Can. J. Phys. 1980, 58, 1200. (61) Perdew, J. P.; Burke, K.; Ernzerhof, M. Perdew, Burke, and Ernzerhof Reply. Phys. Rev. Lett. 1998, 80, 891. (62) Pye, C. C.; Ziegler, T. An implementation of the conductor-like screening model of solvation within the Amsterdam density functional package. Theor. Chem. Acc. 1999, 101, 396. (63) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.; Bohmann, J. A.; Morales, C. M.; Weinhold, F. NBO 5.0; Theoretical Chemistry Institute, University of Wisconsin: Madison, WI, 2001; http://nbo.chem.wisc.edu/. (64) Adamo, C.; Barone, V. J. Toward reliable density functional methods without adjustable parameters: The PBE0 model. J. Chem. Phys. 1999, 110, 6158. (65) Yanai, T.; Tew, D. P.; Handy, N. C. A new hybrid exchange− correlation functional using the coulomb-attenuating method (CAMB3LYP). Chem. Phys. Lett. 2004, 393, 51. (66) Shannon, R. D. Revised effective ionic-radii and systematic studies of interatomic distances in halides and chalcogenides. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 751. (67) Cioslowski, J.; Liu, G.; Mosquera Castro, R. A. Badger’s rule revisited. Chem. Phys. Lett. 2000, 331, 497. (68) Gordy, W. A relation between bond force constants, bond orders, bond lengths, and the electronegativities of the bonded atoms. J. Chem. Phys. 1946, 14, 305. J


Article

Inorganic Chemistry (69) Herschbach, D. R.; Laurie, V. W. Anharmonic potential constants and their dependence upon bond length. J. Chem. Phys. 1961, 35, 458. (70) Fieser, M. E.; Woen, D. H.; Corbey, J. F.; Mueller, T. J.; Ziller, J. W.; Evans, W. J. Raman spectroscopy of the N-N bond in rare earth dinitrogen complexes. Dalton Trans. 2016, 45, 14634. (71) Autschbach, J.; Srebro, M. Delocalization error and “functional tuning” in kohn−sham calculations of molecular properties. Acc. Chem. Res. 2014, 47, 2592. (72) Bogart, J. A.; Lewis, A. J.; Medling, S. A.; Piro, N. A.; Carroll, P. J.; Booth, C. H.; Schelter, E. J. Homoleptic cerium(III) and cerium(IV) nitroxide complexes: Significant stabilization of the 4+ oxidation state. Inorg. Chem. 2013, 52, 11600. (73) Löble, M. W.; Keith, J. M.; Altman, A. B.; Stieber, S. C. E.; Batista, E. R.; Boland, K. S.; Conradson, S. D.; Clark, D. L.; Lezama Pacheco, J.; Kozimor, S. A.; Martin, R. L.; Minasian, S. G.; Olson, A. C.; Scott, B. L.; Shuh, D. K.; Tyliszczak, T.; Wilkerson, M. P.; Zehnder, R. A. Covalency in lanthanides. An x-ray absorption spectroscopy and density functional theory study of LnCl6x− (x = 3, 2). J. Am. Chem. Soc. 2015, 137, 2506. (74) Duignan, T. J.; Autschbach, J. Impact of the kohn−sham delocalization error on the 4f shell localization and population in lanthanide complexes. J. Chem. Theory Comput. 2016, 12, 3109.

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