Deviation between the Structural Chemistry of Barium and Radium Halides: Synthesis and Characterization of RaX·HO and RaX·2HO (X = Cl and Br).

To develop the structural chemistry of radium, the halide compounds RaX·HO and RaX·2HO (X = Cl and Br) have been synthesized and characterized and serve as benchmarks for comparisons with more complex compounds in the future. In contrast with historic reports on the structural chemistry of radium, the Ra chlorides differ from their Ba analogues. For MCl·HO (M = Ba, Ra), the variance between the metal coordination environments manifests as a small, local distortion that becomes more apparent in the extended structure.

Comparison of Americium(III) and Neodymium(III) Monothiophosphate Complexes.

Mixed-donor ligands, such as those containing a combination of O/N or O/S, have been studied extensively for the selective extraction of trivalent actinides, especially Am and Cm, from lanthanides during the recycling of used nuclear fuel. Oxygen/sulfur donor ligand combinations also result from the hydrolytic and/or radiolytic degradation of dithiophosphates, such as the Cyanex class of extractants, which are initially converted to monothiophosphates. To understand potential differences between the binding of such degraded ligands to Nd and Am, the monothiophosphate complexes [M(OPS(OEt))(HO)] (M = Nd, Am) were prepared and characterized by single-crystal X-ray diffraction and optical spectroscopy and studied as a function of pressure up to ca.

Investigation of Pressure Effects in the Bimetallic Transplutonium Tetrazolate Complexes [(An(pmtz)(HO))(μ-pmtz)](pmtz)·HO (An = Cm, Bk, and Cf).

Understanding the effects of pressure on actinide compounds is an integral part of safe nuclear waste storage in deep geologic repositories and provides a means of systematically altering the structure and properties. However, detailing how the effects of pressure evolve across the actinide series in the later elements is not typically undertaken because of the challenges of conducting research on these unstable isotopes. Here, a family of bimetallic actinide complexes, [(An(pmtz)(HO))(μ-pmtz)](pmtz)·HO (An = Cm, Bk, and Cf, pmtz = 5-(pyrimidyl)tetrazolate; , , and ), are reported and represent the first structurally characterized bimetallic berkelium and californium compounds.

Chemical Kinetics for the Oxidation of Californium(III) Ions with Select Radiation-Induced Inorganic Radicals (Cl and SO).

Despite the availability of transuranic elements increasing in recent years, our understanding of their most basic and inherent radiation chemistry is limited and yet essential for the accurate interpretation of their physical and chemical properties. Here, we explore the transient interactions between trivalent californium ions () and select inorganic radicals arising from the radiolytic decomposition of common anions and functional group constituents, specifically the dichlorine (Cl) and sulfate (SO) radical anions. Chemical kinetics, as measured using integrated electron pulse radiolysis and transient absorption spectroscopy techniques, are presented for the reactions of these two oxidizing radicals with ions.

Transformation of Mononuclear Plutonium(III) Tetrazolate Complexes into Dinuclear Complexes in the Solid State.

The salt metathesis reaction of Na(pmtz)·HO [pmtz 5-(pyrimidyl)tetrazolate] and PuBr·HO in an aqueous media leads to the formation of the mononuclear compound [Pu(pmtz)(HO)]·(3 + ) HO (, = ∼8) that is isotypic with the lanthanide compounds [Ln(pmtz)(HO)]·(3 + ) HO (Ln = Ce-Nd). Dissolution and recrystallization of in water yields the dinuclear compound {[Pu(pmtz)(HO)](μ-pmtz)}(pmtz)·14HO (), which is isotypic with the lanthanide compounds {[Ln(pmtz)(HO)](μ-pmtz)}(pmtz)·14HO (Ln = Nd and Sm). Like their nine-coordinate ionic radii, the M-O and M-N bond lengths in / and /, respectively, are within error of one another.

Stabilization of Pu(IV) in PuBr(OPCy) and Comparisons with Structurally Similar ThX(OPR) (R = Cy, Ph) Molecules.

The pursuit of a trivalent plutonium halide phosphine oxide compound, e.g., "PuBr(OPR)," instead led to the isolation of the tetravalent -PuBr(OPCy), , compound by spontaneous oxidation of Pu.

Co-Crystallization of Plutonium(III) and Plutonium(IV) Diglycolamides with Pu(III) and Pu(IV) Hexanitrato Anions: A Route to Redox Variants of [Pu(DGA)][Pu(NO)].

-tetramethyl diglycolamide (TMDGA), a methylated variant of the diglycolamide extractants being proposed as curium holdback reagents in advanced used nuclear fuel reprocessing technologies, has been crystallized with plutonium, a transuranic actinide that has multiple accessible oxidation states. Two plutonium TMDGA complexes, [Pu(TMDGA)][Pu(NO)] and[Pu(TMDGA)][Pu(NO)]·0.75MeOH, were crystallized through solvent diffusion of a reaction mixture containing plutonium(III) nitrate and TMDGA.

Altering the spectroscopy, electronic structure, and bonding of organometallic curium(III) upon coordination of 4,4'-bipyridine.

Structural and electronic characterization of (Cp'Cm)(μ-4,4'-bpy) (Cp' = trimethylsilylcyclopentadienyl, 4,4'-bpy = 4,4'-bipyridine) is reported and provides a rare example of curium-carbon bonding. Cp'Cm displays unexpectedly low energy emission that is quenched upon coordination by 4,4'-bipyridine. Electronic structure calculations on Cp'Cm and (Cp'Cm)(μ-4,4'-bpy) rule out significant differences in the emissive state, rendering 4,4'-bipyridine as the primary quenching agent.

Free Energy Calculations and Conformational Analysis of Dibenzo-30-crown-10 with Sm, Eu, and Three Halide Salts in THF Using the AMOEBA Force Field.

Crown ether complexes have been tailored for use in industrial separations of lanthanides (Ln) as a part of rare earth mining and refining. Dibenzo-30-crown-10 (DB30C10) is one of the most efficient complexants for the separation of rare earth mixtures based on the cation size. To understand the origin of this complexation, molecular dynamics (MD) simulations of DB30C10 have been performed using different combinations of divalent Sm and Eu and three halide salts Cl, Br, and I in tetrahydrofuran (THF) solvent.

Radium Revisited: Revitalization of the Coordination Chemistry of Nature's Largest +2 Cation.

The crystallization, single crystal structure, and Raman spectroscopy of Ra(NO) have been investigated by experimentation and theory, which represent the first pure radium compound characterized by single crystal X-ray diffraction. The Ra centers are bound by six chelating nitrate anions to form an anticuboctahedral geometry. The Raman spectrum acquired from a single crystal of Ra(NO) generally occurs at a lower frequency than found in Ba(NO), as expected.

Expanding Transuranium Organoactinide Chemistry: Synthesis and Characterization of (Cp'M)(μ-4,4'-bpy) (M = Ce, Np, Pu).

Dinuclear, organometallic, transuranium compounds, (Cp'M)(μ-4,4'-bpy) (Cp' = trimethylsilylcyclopentadienide, 4,4'-bpy = 4,4'-bipyridine, M = Ce, Np, Pu), reported herein provide a rare opportunity to probe the nature of actinide-carbon bonding. Significant splitting of the f-f transitions results from the unusual coordination environment in these complexes and leads to electronic properties that are currently restricted to organoactinide systems. Structural and spectroscopic characterization in the solid state and in solution for (Cp'M)(μ-4,4'-bpy) (M = Np, Pu) are reported, and their structural metrics are compared to a cerium analogue.

Isolation of a californium(II) crown-ether complex.

The actinides, from californium to nobelium (Z = 98-102), are known to have an accessible +2 oxidation state. Understanding the origin of this chemical behaviour requires characterizing Cf materials, but investigations are hampered by the fact that they have remained difficult to isolate. This partly arises from the intrinsic challenges of manipulating this unstable element, as well as a lack of suitable reductants that do not reduce Cf to Cf°.

Neptunium Alkoxide Chemistry: Expanding Alkoxides to the Transuranium Elements.

Two oxo-containing neptunium(IV) -butoxides, [NpO(OBu)] () and [KNpO(OBu)] (), were synthesized using the ligand substitution between neptunium(IV) silylamides and HOBu, whereas the salt metathesis between [NpCl(DME)] (DME = dimethoxyethane) and various amounts of LiOBu resulted in the formation of oxo-free alkoxides [Np(OBu)(py)] (; py = pyridine) and [Li(THF)][Np(OBu)] (; THF = tetrahydrofuran). These complexes are the first structurally characterized neptunium(IV) alkoxides using single-crystal X-ray diffraction and solid-state absorption spectroscopy, which provide data for the development of anhydrous metal-organic neptunium chemistry.

Molecular Dynamics and Free Energy Calculations of Dicyclohexano-18-crown-6 Diastereoisomers with Sm, Eu, Dy, Yb, Cf, and Three Halide Salts in Tetrahydrofuran and Acetonitrile Using the AMOEBA Force Field.

With the continual development of lanthanides (Ln) in current technological devices, an efficient separation process is needed that can recover greater amounts of these rare elements. Dicyclohexano-18-crown-6 (DCH18C6) is a crown ether that may be a promising candidate for Ln separation, but additional research is required. As such, molecular dynamics (MD) simulations have been performed on four divalent lanthanide halide salts (Sm, Eu, Dy, and Yb) and one divalent actinide halide salt (Cf) bound to three diastereoisomers of DCH18C6.

Syntheses and Characterization of Tetrazolate-Based Lanthanide Compounds and Selective Crystallization Separation of Neodymium and Dysprosium.

Selective crystallization offers new opportunities for separating neodymium and dysprosium, which are considerably important in permanent magnets. Two water-soluble nitrogen-rich tetrazolate-based ligands, dtp (Hdtp = 2,3-di-1-tetrazol-5-ylpyrazine) and Hibt [Hibt = 4,5-bis(tetrazol-5-yl)imidazole], allow the separation of Nd and Dy through selective crystallization. The reactions of Ln with the ligand Na(dtp)·2HO lead to two distinct phases, Na[Ln(dtp)(HO)](dtp)·HO (; Ln = La-Pr) and [Ln(HO)](Hdtp)(dtp)·HO (; Ln = Nd and Sm-Lu).

Two Neptunium(III) Mellitate Coordination Polymers: Completing the Series Np-Cf of Trans-Uranic An(III) Mellitates.

Two neptunium(III) mellitates, Np(mell)(HO)·1.5HO () and Np(mell)(HO)·2HO (), have been synthesized from NpCl(dme) by reduction with KC and subsequent reaction with an aqueous solution of mellitic acid (Hmell). Characterization by single-crystal X-ray crystallography and UV-vis-NIR spectroscopy confirms that the neptunium is in its +3 oxidation state and both polymorphs are isostructural to the previously reported plutonium mellitates.

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.

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

A berkelium(III) mellitate, Bk[C(CO)](HO)·2HO, was synthesized and rapidly crystallized by reacting mellitic acid, C(COH), and BkBr·HO 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 display enhanced hypsochromic shifting when compared to other An(III) mellitates.

Cyclopentadienyl coordination induces unexpected ionic Am-N bonding in an americium bipyridyl complex.

Variations in bonding between trivalent lanthanides and actinides is critical for reprocessing spent nuclear fuel. The ability to tune bonding and the coordination environment in these trivalent systems is a key factor in identifying a solution for separating lanthanides and actinides. Coordination of 4,4'-bipyridine (4,4'-bpy) and trimethylsilylcyclopentadienide (Cp') to americium introduces unexpectedly ionic Am-N bonding character and unique spectroscopic properties.

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

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 with 4'-(4-nitrophenyl)-2,2':6',2"-terpyridine (terpy*), a ligand with a large dipole.

Isolation and characterization of a californium metallocene.

Californium (Cf) is currently the heaviest element accessible above microgram quantities. Cf isotopes impose severe experimental challenges due to their scarcity and radiological hazards. Consequently, chemical secrets ranging from the accessibility of 5f/6d valence orbitals to engage in bonding, the role of spin-orbit coupling in electronic structure, and reactivity patterns compared to other f elements, remain locked.

Synthesis, characterization, and theoretical analysis of a plutonyl phosphine oxide complex.

The interplay of bond strength and covalency are examined in AnOCl(OPcy) (An = Pu, U) complexes. The synthesis of -PuOCl(OPcy), 1-Pu, has been carried out and confirmed by single crystal X-ray diffraction along with UV-vis-NIR, and P NMR spectroscopies. Theoretical analysis finds that despite a higher calculated covalency for the Pu-Cl interaction, the Pu-OPcy interaction is stronger due to the accumulation of electron density in the interatomic region.

Using Redox-Active Ligands to Generate Actinide Ligand Radical Species.

Using a redox-active dioxophenoxazine ligand, DOPO (DOPO = 2,4,6,8-tetra--butyl-1-oxo-1-phenoxazine-9-olate), a family of actinide (U, Th, Np, and Pu) and Hf tris(ligand) coordination compounds was synthesized. The full characterization of these species using H NMR spectroscopy, electronic absorption spectroscopy, SQUID magnetometry, and X-ray crystallography showed that these compounds are analogous and exist in the form M(DOPO)(DOPO), where two ligands are of the oxidized quinone form (DOPO) and the third is of the reduced semiquinone (DOPO) form. The electronic structures of these complexes were further investigated using CASSCF calculations, which revealed electronic structures consistent with metals in the +4 formal oxidation state and one unpaired electron localized on one ligand in each complex.