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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Berkelium–carbon bonding in a tetravalent berkelocene

Interest in actinide–carbon bonds has persisted since actinide organometallics were first investigated for applications in isotope separation during the Manhattan Project. Transplutonium organometallics are rarely isolated and structurally characterized, likely owing to limited isotope inventories, a scarcity of suitable laboratory infrastructure, and intrinsic difficulties with the anaerobic conditions required. In this paper, we report the discovery of an organometallic “berkelocene” complex prepared from 0.3 milligrams of berkelium-249. Single-crystal x-ray diffraction shows a tetravalent berkelium ion between two substituted cyclooctatetraene ligands, resulting in the formation of berkelium–carbon bonds. The coordination in berkelocene resembles that of uranocene, and calculations show that the berkelium 5f orbitals engage in covalent overlap with the δ-symmetry orbitals of the cyclooctatetraenide ligand π system. Charge transfer from the ligands is diminished relative to uranocene and other actinocenes, which maximizes contributions from the stable, half-filled 5f 7 configuration of tetravalent berkelium.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Contemporary Chemistry of Berkelium and Californium

The merging of small-scale syntheses and rapid crystallization methods have provided access to crystalline samples of berkelium (Z=97) and californium (Z=98) coordination complexes and compounds that can be interrogated with a suite of spectroscopic tools and structural elucidation approaches that have come online over the last 20 years. The combination of this experimental data with relativistic theoretical methods that capture the effects of spin-orbit coupling and scalar relativistic effects have allowed us to understand the electronic structure of berkelium and californium compounds at a level of detail that was not previously possible. The harbinger of this new era of post-curium chemistry was the synthesis and characterization of [Cf{B 6 O 8 (OH) 5 }]. This compound possesses a structure type that is distinct from earlier actinide borates, a reduction in coordination number for californium, contracted Cf-O bond lengths, a substantially reduced magnetic moment with respect to the calculated free-ion moment and, most importantly, vibronically coupled broadband photoluminescence. Ligand-field analysis also showed that the splitting of the ground state was larger than typically found in the f-block elements, and when taken together places its overall electronic structure as a hybrid of d- and f-block components. The discovery of the unusual properties of this compound has led to the development of large families of 4f and 5f coordination complexes, in an effort to uncover the underlying origin of the electronic structure oddities, and whether there really is a sharp onset of these changes at californium. This in turn pushed the development of far more challenging berkelium chemistry (from a radiologic standpoint) because the half-life of the isotopes decreases from 351 years for 249 Cf to 330 days for 249 Bk. This short review details some of the chemistry that has been reported over the last 15 years, and its consequences for understanding the periodic table.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Theoretical examination of covalency in berkelium(IV) carbonate complexes

Experimental studies on the speciation of berkelium in carbonate media have shown that complexation of berkelium(III) by carbonate results in spontaneous oxidation to berkelium(IV) and that multiple species can be present in solution. We studied two proposed structures present in solution based on theoretical comparisons with spectroscopic data previously reported for Bk(IV) carbonate solutions. The multiconfigurational character of the ground and low-lying excited states in both complexes is demonstrated to result from the strong spin-orbit coupling. Although bonding in Bk(IV) carbonate and carbonate-hydroxide complexes is dominated by strong Coulombic forces, the presence of non-negligible covalent character is supported by ligand-field theory, natural localized orbitals, topological studies of the electron density, and energy transition state natural orbitals for chemical valence. Bond orders based on natural localized molecular orbitals show that Bk-OH bonds possess enhanced orbital overlap, which is reflected in the bond strength. This is also observed in the decomposition of the orbital interaction energy into individual deformation density pairs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Probing electronic structure in berkelium and californium via an electron microscopy nanosampling approach

Due to their rarity and radioactive nature, comparatively little is known about the actinides, particularly those with atomic numbers higher than that of plutonium, and their compounds. In this work, we describe how transmission electron microscopy can provide comprehensive, safe, and cost-effective characterization using only single nanogram amounts of highly-radioactive, solid compounds. Chlorides of the rare elements berkelium and californium are dropcast and then converted in situ to oxides using the electron beam. The f-band occupancies are probed using electron energy loss spectroscopy and an unexpectedly weak spin-orbit-coupling is identified for berkelium. In contrast, californium follows a jj coupling scheme. These results have important implications for the chemistries of these elements and solidify the status of californium as a transitional element in the actinide series.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Separation and Purification of Berkelium-249 and Einsteinium-254

Berkelium-249 ( 249 Bk) and einsteinium-254 ( 254 Es) are isotopes of great importance for the investigation of berkelium and einsteinium chemical properties and super heavy element research. Therefore, it is necessary to be able to isolate acceptable, pure quantities of both isotopes to further research capabilities. These isotopes, along with californium-252 ( 252 Cf), are synthesized through the irradiation of mixed-curium targets in the High Flux Isotope Reactor (HFIR), which has the highest continuous thermal neutron flux in the world. Once irradiated, the targets are transferred to the Radiochemical Engineering Development Center for further chemical processing and final purification to separate 249 Bk and 254 Es from the remainder of isotopes present. Several methods of separation, such as the Berkex batch solvent extraction along with cation-exchange and alpha-hydroxy-isobutyrate (AHIB) columns, are employed to achieve a clean separation of the isotopes. Production Campaigns 74–77 are discussed in depth for 252 Cf, 249 Bk, and 254 Es production and isolation of 249 Bk and 254 Es. An attempt to isolate 257 Fm in Campaign 77 is discussed as well. Table 1 summarizes the total amount of material isolated in each campaign.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Transient Radiation-Induced Berkelium(III) and Californium(III) Redox Chemistry in Aqueous Solution

Despite the significant impact of radiation-induced redox reactions on the accessibility and lifetimes of actinide oxidation states, fundamental knowledge of aqueous actinide metal ion radiation chemistry is limited, especially for the late actinides. A quantitative understanding of these intrinsic radiation-induced processes is essential for investigating the fundamental properties of these actinides. We present here a picosecond electron pulse reaction kinetics study into the radiation-induced redox chemistry of trivalent berkelium (Bk(III)) and californium (Cf(III)) ions in acidic aqueous solutions at ambient temperature. New, and first of a kind, second-order rate coefficients are reported for the transient radical-induced reduction of Bk(III) and Cf(III) by the hydrated electron (eaq−) and hydrogen atom (H•), demonstrating significant reactivity (up to 1011M-1s-1) indicative of a preference of these metals to adopt divalent states. Additionally, we reportthe first-ever second-order rate coefficients for the transient radical-induced oxidation of these elements by reaction with hydroxyl (•OH) and nitrate (NO3•) radicals, which also exhibited fast reactivity (ca. 108 M-1s-1). Transient Cf(II), Cf(IV), and Bk(IV) absorption spectra are also reported. Overall, the presented data highlight the existence of rich, complex, intrinsic late actinide radiation-induced redox chemistry that has the potential to influence the findings of other areas of actinide science.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Applications of MP-1 anion exchange resin and Eichrom LN resin in berkelium-249 purification

Purification of berkelium-249 ( 249 Bk) at Oak Ridge National Laboratory requires a multi-step process with Bk Finishing as the final step. The current multi-process takes 6–7 months, including ~ 3 months spent on Bk Finishing. Recent trials of using columns of either LN resin or MP-1 anion exchange resin adsorbing the tetravalent 249 Bk4+ in 8M HNO 3 -0.5M NaBrO 3 , followed by eluting impurities (e.g. Ce 4+ , Cf 3+ ) and stripping 249 Bk resulted in a new dual column method of selectively separating 249 Bk from other trans-curium elements and fission product impurities, which is proposed to replace the current Bk Finishing with higher Bk purification efficiency and shorter processing period. This paper displays the experimental results and describes the dual column method with relevant chemistry issues.

Du, Miting (ORCID:0000000336741567)↗
DOE OSTI2025

Effects of the Inverse Trans-Influence in a Berkelium(III) Phosphine Oxide Complex

An example of a 249 Bk 3+ phosphine oxide complex has been prepared to examine and quantify the effects of the inverse trans-influence (ITI) on a late actinide complex. This has been accomplished through a comparison of cis and trans Bk-ligand bonds in the meridional berkelium(III) complex, BkBr 3 (OPCy 3 ) 3 (OPCy 3 = tricyclohexylphosphine oxide). A detailed bond metric analysis was completed that includes the shortest published distance for a Bk 3+ −O bond, attributed to the smaller coordination number of Bk 3+ of six in mer-BkBr 3 (OPCy 3 ) 3 . ITI calculations of the trans Bk 3+ −O bond provide an ITI value (98.5(2)%) comparable to that of mer-AmBr 3 (OPCy 3 ) 3 (98.2(2)%) and indicate a small 5f orbital contribution to bonding. This effect is discussed in the context of the isomorphous lanthanide(III) series where the ITI is calculated to be higher for mer-BkBr 3 (OPCy 3 ) 3 than in most Ln 3+ analogues.

Actinides↗
DOE OSTI2017

Chelation and stabilization of berkelium in oxidation state +IV

Berkelium (Bk) has been predicted to be the only transplutonium element able to exhibit both +III and +IV oxidation states in solution, but evidence of a stable oxidized Bk chelate has so far remained elusive. Here, in this work, we describe the stabilization of the heaviest 4+ ion of the periodic table, under mild aqueous conditions, using a siderophore derivative. The resulting Bk(IV) complex exhibits luminescence via sensitization through an intramolecular antenna effect. This neutral Bk(IV) coordination compound is not sequestered by the protein siderocalin - a mammalian metal transporter - in contrast to the negatively charged species obtained with neighbouring trivalent actinides americium, curium and californium (Cf). The corresponding Cf(III)-ligand-protein ternary adduct was characterized by X-ray diffraction analysis. Finally, combined with theoretical predictions, these data add significant insight to the field of transplutonium chemistry, and may lead to innovative Bk separation and purification processes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Creation of an unexpected plane of enhanced covalency in cerium(III) and berkelium(III) terpyridyl complexes

Abstract Controlling the properties of heavy element complexes, such as those containing berkelium, is challenging because relativistic effects, spin-orbit and ligand-field splitting, and complex metal-ligand bonding, all dictate the final electronic states of the molecules. While the first two of these are currently beyond experimental control, covalent M‒L interactions could theoretically be boosted through the employment of chelators with large polarizabilities that substantially shift the electron density in the molecules. This theory is tested by ligating Bk III with 4’-(4-nitrophenyl)-2,2’:6’,2”-terpyridine (terpy*), a ligand with a large dipole. The resultant complex, Bk(terpy*)(NO 3 ) 3 (H 2 O)·THF, is benchmarked with its closest electrochemical analog, Ce(terpy*)(NO 3 ) 3 (H 2 O)·THF. Here, we show that enhanced Bk‒N interactions with terpy* are observed as predicted. Unexpectedly, induced polarization by terpy* also creates a plane in the molecules wherein the M‒L bonds trans to terpy* are shorter than anticipated. Moreover, these molecules are highly anisotropic and rhombic EPR spectra for the Ce III complex are reported.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Synthesis, characterization, and high-pressure studies of a 3D berkelium( III ) carboxylate framework material

Here, a berkelium(III) mellitate, Bk 2 [C 6 (CO 2 ) 6 ](H 2 O) 8 ·2H 2 O, was synthesized and rapidly crystallized by reacting mellitic acid, C 6 (CO 2 H) 6 , and BkBr 3 ·nH 2 O in an aqueous medium. Single crystal X-ray diffraction shows that the compound crystallizes as a three-dimensional framework isostructural with Pu(III), Am(III), and Cm(III) mellitates. UV-vis-NIR spectroscopic studies as a function of pressure were performed using a diamond anvil cell and show that the 5f → 5f transitions of Bk 3+ display enhanced hypsochromic shifting when compared to other An(III) mellitates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Remarkably High Stability of Late Actinide Dioxide Cations: Extending Chemistry to Pentavalent Berkelium and Californium

Actinyl chemistry is extended beyond Cm to BkO 2 + and CfO 2 + through transfer of an O atom from NO 2 to BkO + or CfO + , establishing a surprisingly high lower limit of 73 kcal mol -1 for the dissociation energies, D[O-(BkO + )] and D[O-(CfO + )]. CCSD(T) computations are in accord with the observed reactions, and characterize the newly observed dioxide ions as linear pentavalent actinyls; these being the first Bk and Cf species with oxidation states above IV. Computations of actinide dioxide cations AnO 2 + for An=Pa to Lr reveal an unexpected minimum for D[O-(CmO + )]. For CmO 2 + , and AnO 2 + beyond EsO 2 + , the most stable structure has side-on bonded η 2 -(O 2 ), as An III peroxides for An=Cm and Lr, and as An II superoxides for An=Fm, Md, and No. It is predicted that the most stable structure of EsO 2 + is linear [O=Es V =O] + , einsteinyl, and that FmO 2 + and MdO 2 + , like CmO 2 + , also have actinyl(V) structures as local energy minima. Finally, the results expand actinide oxidation state chemistry, the realm of the distinctive actinyl moiety, and the non-periodic character towards the end of the periodic table.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Pentavalent Curium, Berkelium, and Californium in Nitrate Complexes: Extending Actinide Chemistry and Oxidation States

Pentavalent actinyl nitrate complexes An V O 2 (NO 3 ) 2 - were produced by elimination of two NO 2 from An III (NO 3 ) 4 - for An = Pu, Am, Cm, Bk, and Cf. Density functional theory (B3LYP) and relativistic multireference (CASPT2) calculations confirmed the AnO 2 (NO 3 ) 2 - as AnVO 2 + actinyl moieties coordinated by nitrates. Computations of alternative An III O 2 (NO 3 ) 2 - and AnI V O 2 (NO 3 ) 2 - revealed significantly higher energies. Previous computations for bare AnO 2 + indicated AnVO 2 + for An = Pu, Am, Cf, and Bk, but Cm III O 2 + : electron donation from nitrate ligands has here stabilized the first Cm V complex, Cm V O 2 (NO 3 ) 2 - . Structural parameters and bonding analyses indicate increasing An-NO 3 bond covalency from Pu to Cf, in accordance with principles for actinide separations. Atomic ionization energies effectively predict relative stabilities of oxidation states; more reliable energies are needed for the actinides.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Streamlining and Simplifying the Chemical Separationof Berkelium (249Bk) from Other Actinides/Lanthanides andFission Products

Abstract Separation of an individual heavy actinide from other actinides, lanthanides, and coproduced fission products is challenging not only because of their similarity in chemistry but also because the chemistry of heavy actinides is largely unknown. At present, the cation-exchange chromatography with α-hydroxyisobutyric acid (CX-AHIB) method is used to isolate milli- to picogram quantities of heavy actinides (i.e., 249Bk, 252Cf, 254Es, and 257Fm). This method allows simultaneous separation of these actinides; however, isolating a clean individual product with a high yield has proven challenging. The process is also very slow and labor-intensive and requires precise control of various chemical conditions, such as pH, temperature, and AHIB concentration. Developing a separation scheme for heavy actinides requires identifying their unique feature and then harnessing this feature in the separation process design. The unique characteristic of Bk4+ is that it does not adsorb onto anion exchange resin columns, unlike other tetravalent actinides. This article discusses what makes Bk unique and how this discovery led to a new method for separating Bk from adjacent actinides, lanthanides, and coproduced fission products. The method employed two different resin columns in tandem to separate unwanted actinides from 249Bk, followed by fine cleanup of 249Bk. The advantages of the new Bk method over the CX-AHIB method in Bk production are discussed, and the performance and robustness of the proposed method were assessed in two recent production campaigns.

Chemistry↗
DOE OSTI2017

Electronic Structure and Properties of Berkelium Iodates

The reaction of 249 Bk(OH) 4 with iodate under hydrothermal conditions results in the formation of Bk(IO 3 ) 3 as the major product with trace amounts of Bk(IO 3 ) 4 also crystallizing from the reaction mixture. The structure of Bk(IO 3 ) 3 consists of nine-coordinate Bk III cations that are bridged by iodate anions to yield layers that are isomorphous with those found for Am III , Cf III , and with lanthanides that possess similar ionic radii. Bk(IO 3 ) 4 was expected to adopt the same structure as M(IO 3 ) 4 (M = Ce, Np, Pu), but instead parallels the structural chemistry of the smaller Zr IV cation. Bk III –O and Bk IV –O bond lengths are shorter than anticipated and provide further support for a postcurium break in the actinide series. Photoluminescence and absorption spectra collected from single crystals of Bk(IO 3 ) 4 show evidence for doping with Bk III in these crystals. In addition to luminescence from Bk III in the Bk(IO 3 ) 4 crystals, a broad-band absorption feature is initially present that is similar to features observed in systems with intervalence charge transfer. However, the high-specific activity of 249 Bk ( t 1/2 = 320 d) causes oxidation of Bk III and only Bk IV is present after a few days with concomitant loss of both the BkIII luminescence and the broadband feature. The electronic structure of Bk(IO 3 ) 3 and Bk(IO 3 ) 4 were examined using a range of computational methods that include density functional theory both on clusters and on periodic structures, relativistic ab initio wave function calculations that incorporate spin–orbit coupling (CASSCF), and by a full-model Hamiltonian with spin–orbit coupling and Slater–Condon parameters (CONDON). Some of these methods provide evidence for an asymmetric ground state present in Bk IV that does not strictly adhere to Russel–Saunders coupling and Hund’s Rule even though it possesses a half-filled 5 f 7 shell. Multiple factors contribute to the asymmetry that include 5 f electrons being present in microstates that are not solely spin up, spin–orbit coupling induced mixing of low-lying excited states with the ground state, and covalency in the Bk IV –O bonds that distributes the 5f electrons onto the ligands. These factors are absent or diminished in other f 7 ions such as Gd III or Cm III .

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Application of a Dual-Column Method to Selectively Extract and Purify Berkelium-249 from Other Actinides and Impurities

The super heavy element (SHE) Tennessine (Ts, Element 117) was discovered in 2016 a collaboration of US and Russian scientists vis bombardment reaction of 249 Bk + 48 Ca $\rightarrow$ 117 Ts, while the target element 249 Bk (half-life 330d) was produced and provided by the Radiochemical Engineering Development Center (REDC), Oak Ridge National Laboratory (ORNL). The production of 249 Bk at REDC, ORNL requires a multi-step chemical process of irradiated curium feedstock target to remove all fission product (FP) elements and to separate 249 Bk from other actinide (An) elements (Am, Cm, Cf, Fm and Es), including: Caustic Dissolution, Acid Dissolution, Cleanex, two LiCl Anion Exchanges, LiOH Precipitation, Cation Exchange with AHIB, and with Bk Finishing as the final Bk purification step. The major product of this campaign is 252 Cf, while 249 Bk is one of important by-products. The current Cf campaign for recovery of c.a. 15 mg of 249 Bk per campaign (not including the time for Finishing of Cf, Fm and Es) takes 6 or 7 months, including ~3 months spent on Bk Finishing. Bk Finishing includes two major processes: (1) BERKEX, operated inside a hot cell with two cycles of batch solvent extraction (SX) using di-2-ethylhexyl phosphoric acid (HDEHP) as the extractant for tetravalent 249 Bk from an 8 $M$ HNO 3 -0.3 $M$ NaBrO 3 solution; and (2) Cation Exchange (CX) with AHIB (α-Hydroxy isobutyric acid), operated inside a glove box laboratory. Entire Bk Finishing takes five SX, more than five column runs and several drying down processes for aqueous solutions including one from 500 mL to 1 mL for volume reduction. To shorten the Bk Finishing period and simplify the Bk purification operation steps, possibilities of using other resin columns were explored.Recent trials using columns of either $LN$ resin or $MP$-1 anion exchange resin adsorbing the tetravalent 249 Bk 4+ in 8 $M$ HNO 3 -0.5 $M$ NaBrO 3 , followed by eluting impurities (e.g. Ce 4+ ,Cf 3+ ) and stripping 249 Bk resulted in a new Dual Column Method of selectively separating 249 Bk from other trans-plutonium elements and fission product (FP) impurities. This new method is proposed to replace the current Bk Finishing and provide increased Bk purification effeciency and a shorter processing period of 4 to 5 months (less decay loss for higher 249 Bk productivity). This TM Report discusses the trial experimental results, describes the dual column method with relevant chemistry issues and possibilities being used in further process steps ahead of the Bk Finishing.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2019

Synthesis and Characterization of Tris-chelate Complexes for Understanding f -Orbital Bonding in Later Actinides

An isostructural family of f-element compounds (Ce, Nd, Sm, Gd; Am, Bk, Cf) of the redox-active dioxophenoxazine ligand (DOPOq; DOPO = 2,4,6,8-tetra-tert-butyl-1-oxo-1H-phenoxazin-9-olate) was prepared. This family, of the form M(DOPOq)3, represents the first nonaqueous isostructural series, including the later actinides berkelium and californium. The lanthanide derivatives were fully characterized using 1H NMR spectroscopy and SQUID magnetometry, while all species were structurally characterized by X-ray crystallography and electronic absorption spectroscopy. In order to probe the electronic structure of this new family, CASSCF calculations were performed and revealed these systems to be largely ionic in contrast to previous studies, where berkelium and californium typically have a small degree of covalent character. To validate the zeroth order regular approximation (ZORA) method, the same CASSCF analysis using experimental structures versus UDFT-ZORA optimized structures does not exhibit sizable changes in bonding patterns. This shows that UDFT-ZORA combined with CASSCF could be a useful first approximation to predict and investigate the structure and electronic properties of actinides and lanthanides that are difficult to synthesize or characterize.

Chemistry↗