Pu Complex Research Articles

Bonding and Magnetic Trends in the [AnIII(DPA)3]3- Series Compared to the Ln(III) and An(IV) Analogues.

The crystal field parameters are determined from first-principles calculations in the [AnIII(DPA)3]3- series, completing previous work on the [LnIII(DPA)3]3- and [AnIV(DPA)3]2- series. The crystal field strength parameter follows the Ln(III) < An(III) < An(IV) trend. The parameters deduced at the orbital level decrease along the series, while J-mixing strongly impacts the many-electron parameters, especially for the Pu(III) complex. We further compile the available data for the three series. In some aspects, An(III) complexes are closer to Ln(III) than to An(IV) complexes with regard to the geometrical structure and bonding descriptors. At the beginning of the series, up to Pu(III), there is a quantitative departure from the free ion, especially for the Pa(III) complex. The magnetic properties of the actinides keep the trends of the lanthanides; in particular, the axial magnetic susceptibility follows Bleaney's theory qualitatively.

Local Structure and Magnetism of La1–xMxPO4 (M = Sm, 239Pu, 241Am) Explained by Experimental and Computational Analyses

With their high chemical and self-irradiation stability, crystalline monazites are among the most promising materials for the encapsulation of nuclear wastes. Yet, the local and magnetic structures of the matrices doped with low-content actinide cation, depicted as most resistant, are still unclear. This limits the development of theoretical approaches predicting their behavior under extreme conditions—self-irradiation and long-term leaching. Here, we characterize the model matrices La1–xMxPO4 (0 ≤ x ≤ 0.10)—with M = Sm, 239Pu, 241Am—by X-ray diffraction and solid-state 31P NMR. As an example, we confirm that La0.96241Am0.04PO4 has higher self-irradiation resistance compared to 241AmPO4. Further, computational analyses show that magnetic properties of the Pu complex are strongly affected by the J-mixing and the paramagnetic NMR shifts are dominated by the Fermi contact contribution, arising from delocalization of the spin density of the cation toward the phosphorus through the bonds.

A Single Small-Scale Plutonium Redox Reaction System Yields Three Crystallographically-Characterizable Organoplutonium Complexes.

An approach to obtaining substantial amounts of data from a hazardous starting material that can only be obtained and handled in small quantities is demonstrated by the investigation of a single small-scale reaction of cyclooctatetraene, C8H8, with a solution obtained from the reduction of Cp'3Pu (Cp' = C5H4SiMe3) with potassium graphite. This one reaction coupled with oxidation of a product has provided single-crystal X-ray structural data on three organoplutonium compounds as well as information on redox chemistry thereby demonstrating an efficient route to new reactivity and structural information on this highly radioactive element. The crystal structures were obtained from the reduction of C8H8 by a putative Pu(II) complex, (Cp'3PuII)1-, generated in situ, to form the Pu(III) cyclooctatetraenide complex, [K(crypt)][(C8H8)2PuIII], 1-Pu, and the tetra(cyclopentadienyl) Pu(III) complex, [K(crypt)][Cp'4PuIII], 2-Pu. Oxidation of the sample of 1-Pu with Ag(I) afforded a third organoplutonium complex that has been structurally characterized for the first time, (C8H8)2PuIV, 3-Pu. Complexes 1-Pu and 3-Pu contain Pu sandwiched between parallel (C8H8)2- rings. The (Cp'4PuIII)- anion in 2-Pu features three η5-Cp' rings and one η1-Cp' ring, which is a rare example of a formal Pu-C η1-bond. In addition, this study addresses the challenge of small-scale synthesis imparted by radiological and material availability of transuranium isotopes, in particular that of pure metal samples. A route to an anhydrous Pu(III) starting material from the more readily available PuIVO2 was developed to facilitate reproducible syntheses and allow complete spectroscopic analysis of 1-Pu and 2-Pu. PuIVO2 was converted to PuIIIBr3(DME)2 (DME = CH3OCH2CH2OCH3) and subsequently PuIIIBr3(THF)x, which was used to independently synthesize 1-Pu, 2-Pu, and 3-Pu.

Stabilization of Plutonium(V) Within a Crown Ether Inclusion Complex

Crystalline coordination complexes of actinides, especially in atypical oxidation states, are not only fundamentally important for expanding the notably limited knowledge on the bonding nature of a...

Interaction of Ozone with Actinides and Lanthanides in Aqueous Solutions

Specific features of the interaction of O3 in aqueous media with f-elements in a wide range of pH values are considered. In neutral solutions, O3 splits-off an O atom, which becomes the beginning of a chain process of O3 decomposition. NO3–, HSO4–, OH– anions initiate the decomposition by forming complexes with O3. The products of the subsequent transformations are OH, HO2, HO3, and H2O2. Phosphate and carbonate ions and HNO3 react with OH radicals and block the chain process. The peroxynitric acid formed from HNO3 serves both as an oxidizing agent and, as a result of hydrolysis, as reducing agent. In solutions of 1 M NaHCO3 or Na2CO3, ozone forms a complex with CO32– and its stability grows. In the alkaline medium, O3 is converted to O3–, but reducing agents are formed in the alkaline solution at a high concentration of O3 in the gas phase. The reactions of O3 with Ce, U, Np, Pu, Am, Bk, Ce, Tb, and Pr ions are analyzed. The reactions occur via a preliminary formation by cations of anion complexes and then complexes with O3. The formation constant of the Pu(IV) complex with O3 in a 4 M HNO3 solution is estimated to be 4.5 × 105 M–1. U(IV) and Pu(III) in an HClO4 solution, Np(IV) and Pu(IV) in an HNO3 solution, Np(IV) and Am(III) in a NaHCO3 solution are oxidized by ozone with transfer of the O. atom, Ce(III) and Bk(III) in an HNO3 solution, U(IV) and Am(III) in a solution of heteropolyanions, Np(IV, V) in a Na2CO3 solution, Np(V,VI), Pu(V, VI), and Am(V,VI) in alkaline media are oxidized with charge transfer to O3 or O3–.

Accessibility of Uranyl-Plutonium Complex Supported by a Polypyrrolic Macrocycle: An Implication for Experimental Synthesis.

The reaction of (THF)(H2L)(UVIO2) (L is a tetra-anion of polypyrrolic macrocycle) with AnIIICp3 (Cp = cyclopentadienyl) afforded two intriguing cation-cation interaction (CCI) complexes (i.e., uranyl-Np and -U), but did not yield the uranyl-Pu analogue. To complement and extend experimental results, a scalar relativistic density functional theory has been performed on the formation reactions and various relevant properties of (THF)(A2L)(OUO)-An(CpX)3 (A = Li and H; An = Pu, Np, and U; X = Me, H, Cl, and SiMe3). Inspired by a strategy that improves uranyl precursor reactivity, we utilized (THF)(Li2L)(UVIO2) instead to gain a uranyl-Pu complex. Reaction free energy is reduced even to be negative (i.e., undergoing an exergonic process), which provides the thermodynamic possibility for experimental synthesis. This manner is further rationalized by the lithiated precursor showing the increased Li-Oendo bond, uranium oxidation ability (VI → V), and exo-oxo basicity, as well as the lithiated uranyl-Pu product having more amount of electron transfer and a stronger Oexo-Pu bond (i.e., representing the CCI). Electronic structures and electron-transfer analyses reveal a UV-PuIV oxidation state for the new complex. Applying the more reactive lithiated precursor also decreases the formation reaction energies of uranyl-An (An = Np and U) complexes. The second strategy via exploiting substituted Cp to raise the reactivity of the plutonium reactant does not work well.

Skin absorption of actinides: influence of solvents or chelates on skin penetration ex vivo

Purpose: To evaluate skin penetration and retention of americium (Am) and plutonium (Pu), in different chemical forms relevant to the nuclear industry and to treatment by chelation.Materials and methods: Percutaneous penetration of different Am and Pu forms were evaluated using viable pig skin with the Franz cell diffusion system. The behavior of the complex Pu-tributyl phosphate (Pu-TBP), Am or Pu complexed to the chelator Diethylene triamine pentaacetic acid (DTPA) and the effect of dimethyl sulfoxide (DMSO) was assessed. Radioactivity was measured in skin and receiver compartments. Three approaches were used to visualize activity in skin including the recent iQID technique for quantification.Results: Transfer of Am was 24-fold greater than Pu and Pu-TBP complex penetration was enhanced by 500-fold. Actinide-DTPA transfer was greater than the Am or Pu alone (17-fold and 148-fold, respectively). The stratum corneum retained the majority of activity in all cases and both DMSO and TBP enhanced skin retention of Am and Pu, respectively. Histological and bioimaging data confirmed these results and the iQID camera allowed the quantification of skin activity.Conclusions: Skin penetration and fixation profiles are different depending on the chemical actinide form. Altered behavior of Pu-TBP and actinide-DTPA complexes reinforces the need to address decontamination protocols.

Self-assembled hybrid nanoarchitectures deposited on poly(urethane) foams capable of chemically adapting to extreme heat

In the present paper the layer by layer (LbL) technique has been adopted for the construction of hybrid organic–inorganic nanoarchitectures capable of adapting to extreme heat or flame exposure and chemically evolving into thermally-stable carbon based structures. More specifically, the LbL technique has been applied to an open cell poly(urethane) (PU) foam in order to increase its thermal and flame stability. Scanning electron microscopy showed that the LbL assembly covered each surface of the PU complex three-dimensional structure without altering its open cell morphology. When exposed to a direct flame, the treated PU foam was capable of stopping combustion within a few seconds after ignition, unlike the untreated foam that burned completely. Under different irradiative heat fluxes (from 35 up to 75 kW m2), the coating demonstrated exceptional performances by reducing the rate of heat release up to 60% with respect to the untreated counterpart. Finally, when subjected to a flame torch penetration (Tflame ≈ 1300 °C), the LbL-coated PU foam was capable of maintaining its three-dimensional structure, thus successfully insulating the unexposed side (T below 100 °C after two flame torch applications) with temperature drops of 800 °C achieved with a specimen thickness of only 10 mm.

Oxidation States, Geometries, and Electronic Structures of Plutonium Tetroxide PuO4 Isomers: Is Octavalent Pu Viable?

In neutral chemical compounds, the highest known oxidation state of all elements in the Periodic Table is +VIII. While PuO4 is viewed as an exotic Pu(+VIII) complex, we have shown here that no stable electronic homologue of octavalent RuO4 and OsO4 exists for PuO4, even though Pu has the same number of eight valence electrons as Ru and Os. Using quantum chemical approaches at the levels of quasi-relativistic DFT, MP2, CCSD(T), and CASPT2, we find the ground state of PuO4 as a quintet (5)C2v-(PuO2)(+)(O2)(-) complex with the leading valence configuration of an (f(3))plutonyl(V) unit, loosely coupled to a superoxido (π*(3))O2(-) ligand. This stable isomer is likely detectable as a transient species, while the previously suggested planar (1)D4h-Pu(VIII)O4 isomer is only metastable. Through electronic structure analyses, the bonding and the oxidation states are explained and rationalized. We have predicted the characteristics of the electronic and vibrational spectra to assist future experimental identification of (PuO2)(+)(O2)(-) by IR, UV-vis, and ionization spectroscopy.

Plutonium(iv) complexation by diglycolamide ligands—coordination chemistry insight into TODGA-based actinide separations

Complexation of Pu(IV) with TMDGA, TEDGA, and TODGA diglycolamide ligands was followed by vis-NIR spectroscopy. A crystal structure determination reveals that TMDGA forms a 1 : 3 homoleptic Pu(IV) complex with the nitrate anions forced into the outer coordination sphere.

Dimethyl sulfoxide as an O-donor ligand in tetravalent actinide complexes

Four new perchlorate complexes of tetravalent actinides with dimethyl sulfoxide (DMSO) molecules (An4+ = Th, U, Np, Pu) are synthesized and studied. According to the X-ray diffraction data, compounds [Th(DMSO)9](ClO4)4 · 2CH3CN (I), [U(DMSO)8](ClO4)4 · CH3CN (II), [Np(DMSO)8](ClO4)4 · CH3CN (III), and [Pu(DMSO)8](ClO4)4 · CH3CN (IV) crystallize in the triclinic crystal system (space group P1). The crystals of compounds II–IV are isostructural. The absorption spectra of the complexes in the IR and visible regions are measured. All compounds exhibit a decrease in the frequencies of stretching vibrations ν(SO) over the spectrum of free DMSO, indicating the formation of the O-bonded complexes of An4+. The optical spectra of the crystalline compounds exhibit shifts of the bands of electronic f-f transitions of the An4+ ions relative to the hydrated ions: the bathochromic shifts for the U and Np complexes and the hypsochromic shift for the Pu complex. The first coordination sphere of the actinide atoms in the studied complexes is highly stable.

Low-Valent Molecular Plutonium Halide Complexes

Treatment of plutonium metal with 1.5 equiv of bromine in tetrahydrofuran (thf) led to isolation of PuBr3(thf)4 (1), which is a new versatile synthon for exploration of non-aqueous Pu(III) chemistry. Adventitious water in the system resulted in structural characterization of the eight-coordinate complex [PuBr2(H2O)6][Br] (2). The crystal structure of PuI3(thf)4 (3) has been determined for the first time and is isostructural with UI3(thf)4. Attempts to form a bis(imido) plutonyl(VI) moiety ([Pu(NR)2](2+)) by oxidation of PuI3(py)4 with iodine and (t)BuNH2 resulted in crystallization of the Pu(III) complex [PuI2(thf)4(py)][I3] (4). Dissolution of a Pu(IV) carbonate with a HCl/Et2O solution in thf gave the mixed valent (III/IV) complex salt [PuCl2(thf)5][PuCl5(thf)] (5) as the only tractable product. Oxidation of Pu[N(SiMe3)2]3 with TeCl4 afforded the Pu(IV) complex Pu[N(SiMe3)2]3Cl (6), which may prove to be a useful entry route for investigation of organometallic/non-aqueous tetravalent plutonium chemistry.

Thermodynamic studies of actinide complexes. 1. A reappraisal of the solution equilibria between plutonium(IV) and ethylenediaminetetraacetic acid (EDTAH4) in nitric media

Abstract A detailed reevaluation of the complexation equilibria of plutonium(IV) with the polyaminocarboxylic sequestering agent EDTA4− has been performed in 1 M (H,K)NO3 media at 298 K by means of visible absorption spectrophotometry and glass-electrode potentiometry at millimolar concentration levels. The high binding affinity even under strongly acidic conditions supports the exclusive formation of the neutral Pu(EDTA) complex over the range 0.01 ≤ [H+] ≤ 0.9 M with an apparent formation constant of log β110 = 25.8(1) at 0.9 M HNO3. Extrapolation to zero ionic strength using the SIT approach provides the first ever-reported NEA–TDB compliant estimate of β 110 0 ( log β 110 0 = 32.2 ( 3 ) ) . A global modeling procedure of the potentiometric data collected for three different metal over ligand ratios (1:1, 1:1.5, and 1:2) ascertained the formation of four additional species for pH values comprised between 2 and 6.5, namely [Pu(EDTA)(OH)]−, [Pu(EDTA)2H2]2−, [Pu(EDTA)2H]3−, and [Pu(EDTA)2]4−. The visible absorption spectra for the first three complexes have also been determined. Data recorded above pH 3.5 (for a 1:1 molar ratio) or 6.5 (for a 1:2 molar ratio) were finally excluded from the global fitting procedure as speciation calculations suggested the precipitation of amorphous Pu(OH)4(am) according to the latest critical value quoted in the literature for its solubility product.

Long-Term Modeling of Plutonium Solubility at a Desert Disposal Site, Including CO2 Diffusion, Cellulose Decay, and Chelation

The solubility of plutonium was estimated for waste buried at the Greater Confinement Disposal site in Nevada. The EQ3/6 thermochemical database was modified to include recent data on Pu complex formation, and the solubilities of two critical phases (probertite (CaNaB5O9·5H2O), added as a backfill material; and Ca sac-charate) were determined by experiment. Reaction path runs were used to model effects of cellulose degradation, including complexation of actinides by organic acids and carbonate, decay of the complexing agents, and the buildup and diffusive loss of CO2 through the permeable alluvium. For most waste interaction scenarios, long-term (≈103 years) concentrations of Pu in pore waters are ≤10−7 molal and are dominated by carbonate complexes, although organic complexes could dominate in the first ≈103 years. In unusual circumstances, carbonation of buried lithium could produce very high Pu solubilities; however, even in such a system, a slight lowering of the effective redox potential dramatically lowers Pu solubility. A sensitivity analysis suggests that the “base case” calculations are conservative, tending to overestimate long-term solubility, with the system redox and the identity of the organic acids the major sources of uncertainty.

Chelation of 238Pu(IV) in vivo by 3,4,3-LICAM(C): effects of ligand methylation and pH.

The linear tetracarboxycatecholate ligand, 3,4,3-LICAM(C) (N1,N5,N10,N14-tetrakis(2,3-dihydroxy-4-carboxybenzoyl-tetraaza tet radecane, tetra sodium salt) injected within 1 h after injection of Pu(IV) citrate, removes about the same fraction of Pu from animals as CaNa3-DTPA (diethylenetriaminepentaacetate, calcium, sodium salt) but removes less inhaled Pu than CaNa3-DTPA and leaves a Pu residue in the renal cortex. However, the formation constant of the expected Pu-3,4,3-LICAM(C) complexes are orders of magnitude greater than that of Pu-DTPA, and 3,4,3-LICAM(C) is 100 times more efficient than CaNa3-DTPA for removing Pu from transferrin in vitro. Because the formation constants of their actinide complexes are central to in vivo actinide chelation, ligand design strategies are dominated by the search for ligands with large Pu complex stabilities, and it was necessary to explain the failure of 3,4,3-LICAM(C) to achieve its thermodynamic potential in vivo. All the batches of 3,4,3-LICAM(C) prepared at Berkeley or in France [Euro-LICAM(C)] were found by high-pressure liquid chromatography to be mixtures of the pure ligand [55% in Berkeley preparations, 8.5% in Euro-LICAM(C)] and its four methylesters. A revised synthesis for 3,4,3-LICAM(C) is appended to this report. All of the incompletely hydrolyzed 3,4,3-LICAM(C) preparations and the pure ligand were tested for removal of Pu from mice [238Pu(IV) citrate intravenous, 30 mumol kg-1 of ligand at 1 h, kill at 24 h, radioanalyze tissues and separated excretal]. The presence of methylesters did not significantly impair the ability of the ligands to remove Pu from mice, and it did not alter the fraction of injected Pu deposited in kidneys. Temporary elevation (reduction) of plasma and urine pH of mice by 0.5 mL of 0.1 M NaHCO3 (NH4Cl) injected before or simultaneously with pure 3,4,3-LICAM(C) somewhat improved (significantly reduced) Pu excretion but had little influence on Pu deposition in kidneys. Review of the investigations of Pu removal from animals by 3,4,3-LICAM(C) revealed that the fractional renal Pu deposit was characteristic of the species and that it could be reduced by vigorous alkalinization which indicated the need to examine the details of the pH dependence of Pu complexation by 3,4,3-LICAM(C).(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of Plutonium on Soil Microorganisms

As a first phase in an investigation of the role of the soil microflora in Pu complex formation and solubilization in soil, the effects of Pu concentration, form, and specific activity on microbial types, colony-forming units, and CO(2) evolution rate were determined in soils amended with C and N sources to optimize microbial activity. The effects of Pu differed with organism type and incubation time. After 30 days of incubation, aerobic sporeforming and anaerobic bacteria were significantly affected by soil Pu levels as low as 1 mug/g when Pu was added as the hydrolyzable Pu(NO(3))(4) (solubility, <0.1% in soil). Other classes of organisms, except the fungi, were significantly affected at soil Pu levels of 10 mug/g. Fungi were affected only at soil Pu levels of 180 mug/g. Soil CO(2) evolution rate and total accumulated CO(2) were affected by Pu only at the 180 mug/g level. Because of the possible role of resistant organisms in complex formation, the mechanisms of effects of Pu on the soil fungi were further evaluated. The effect of Pu on soil fungal colony-forming units was a function of Pu solubility in soil and Pu specific activity. When Pu was added in a soluble, complexed form [Pu(2)(diethylenetriaminepentaacetate)(3)], effects occurred at Pu levels of 1 mug/g and persisted for at least 95 days. Toxicity was due primarily to radiation effects rather than to chemical effects, suggesting that, at least in the case of the fungi, formation of Pu complexes would result primarily from ligands associated with normal (in contrast to chemically-induced) biochemical pathways.