Slow Magnetic Relaxation in a Californium Complex.

We report the synthesis and characterization of the macrocyclic californium derivative Na[Cf(HO)(DOTA)] (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate), , which was studied in comparison to its dysprosium counterpart, Na[Dy(HO)(DOTA)], . Divergent spectroscopic and magnetic behaviors were observed between and . Based upon spectroscopic measurements, we propose that accessible 5f → 6d transitions (potentially operating in tandem with charge-transfer transitions) are the major contributors to the observed broadband photoluminescence in .

The Counterintuitive Relationship between Orbital Energy, Orbital Overlap, and Bond Covalency in CeF and CeCl.

The 4f orbitals of Ce(IV) have shown appreciably enhanced covalent mixing with ligand orbitals relative to those of Ce(III). Here, X-ray spectroscopy, magnetic susceptibility measurements, and theoretical methods are used to investigate 4f covalency in CeF and CeCl. These techniques show covalent mixing between Ce 4f and F 2p orbitals to be about 25% less than mixing between Ce 4f and Cl 3p orbitals, placing CeF among the most ionic Ce(IV) compounds to-date.

4f-Orbital mixing increases the magnetic susceptibility of Cp'Eu.

Traditional models of lanthanide electronic structure suggest that bonding is predominantly ionic, and that covalent orbital mixing is not an important factor in determining magnetic properties. Here, 4f orbital mixing and its impact on the magnetic susceptibility of Cp'Eu (Cp' = CHSiMe) was analyzed experimentally using magnetometry and X-ray absorption spectroscopy (XAS) methods at the C K-, Eu M-, and L-edges. Pre-edge features in the experimental and TDDFT-calculated C K-edge XAS spectra provided unequivocal evidence of C 2p and Eu 4f orbital mixing in the π-antibonding orbital of a' symmetry.

Realization of Organocerium-Based Fullerene Molecular Materials Showing Mott Insulator-Type Behavior.

Electron-rich organocerium complexes (CMeH)Ce and [(CMe)Ce(-oxa)], with redox potentials = -0.82 V and = -0.86 V versus Fc/Fc, respectively, were reacted with fullerene (C) in different stoichiometries to obtain molecular materials.

Strengths of covalent bonds in LnO determined from O K-edge XANES spectra using a Hubbard model.

In LnO (Ln = Ce, Pr, and Tb), the amount of Ln 4f mixing with O 2p orbitals was determined by O K-edge X-ray absorption near edge (XANES) spectroscopy and was similar to the amount of mixing between the Ln 5d and O 2p orbitals. This similarity was unexpected since the 4f orbitals are generally perceived to be "core-like" and can only weakly stabilize ligand orbitals through covalent interactions. While the degree of orbital mixing seems incompatible with this view, orbital mixing alone does not determine the degree of stabilization provided by a covalent interaction.

Evaluation of Ce as a PET imaging surrogate for antibody drug conjugates incorporating Ac.

Introduction: The in vivo generator Ce/La has the potential to serve as a PET imaging surrogate for both alpha-emitting Ac and Th radionuclides due to the unique Ce/Ce redox couple and the relatively long half-life of Ce. The purpose of this study was to demonstrate the compatibility of Ce with DOTA-based antibody drug conjugates, which would act as therapeutic agents when incorporating Ac.

Methods: The in vivo biodistributions of [Ce]Ce-DOTA and [Ce]Ce-citrate were assayed by microPET imaging over 25 h in Swiss Webster mice to determine the in vivo stability of the [Ce]Ce-DOTA complex.

Electronic structure studies reveal 4f/5d mixing and its effect on bonding characteristics in Ce-imido and -oxo complexes.

This study presents the role of 5d orbitals in the bonding, and electronic and magnetic structure of Ce imido and oxo complexes synthesized with a tris(hydroxylaminato) [((2- BuNO)CHCH)N] (TriNO ) ligand framework, including the reported synthesis and characterization of two new alkali metal-capped Ce oxo species. X-ray spectroscopy measurements reveal that the imido and oxo materials exhibit an intermediate valent ground state of the Ce, displaying hallmark features in the Ce L absorption of partial f-orbital occupancy that are relatively constant for all measured compounds. These spectra feature a double peak consistent with other formal Ce(iv) compounds.

In situ beam reduction of Pu(IV) and Bk(IV) as a route to trivalent transuranic coordination complexes with hydroxypyridinone chelators.

The solution-state interactions of plutonium and berkelium with the octadentate chelator 3,4,3-LI(1,2-HOPO) (343-HOPO) were investigated and characterized by X-ray absorption spectroscopy, which revealed in situ reductive decomposition of the tetravalent species of both actinide metals to yield Pu(III) and Bk(III) coordination complexes. X-ray absorption near-edge structure (XANES) measurements were the first indication of in situ synchrotron redox chemistry as the Pu threshold and white-line position energies for Pu-343-HOPO were in good agreement with known diagnostic Pu(III) species, whereas Bk-343-HOPO results were found to mirror the XANES behavior of Bk(III)-DTPA. Extended X-ray absorption fine structure results revealed An-O bond distances of 2.

Correction: Enhanced 5f-δ bonding in [U(CH)]: C K-edge XAS, magnetism, and calculations.

Correction for 'Enhanced 5f-δ bonding in [U(CH)]: C K-edge XAS, magnetism, and calculations' by Yusen Qiao , , 2021, , 9562-9565, DOI: 10.1039/D1CC03414F.

Enhanced 5f-δ bonding in [U(CH)]: C K-edge XAS, magnetism, and calculations.

5f covalency in [U(CH)] was probed with carbon K-edge X-ray absorption spectroscopy (XAS) and electronic structure theory. The results revealed U 5f orbital participation in δ-bonding in both the ground- and core-excited states; additional 5f ϕ-mixing is observed in the core-excited states. Comparisons with U(CH) show greater δ-covalency for [U(CH)].

Cerium(iv) complexes with guanidinate ligands: intense colors and anomalous electronic structures.

A series of cerium(iv) mixed-ligand guanidinate-amide complexes, {[(MeSi)NC(N Pr)] Ce[N(SiMe)] } ( = 0-3), was prepared by chemical oxidation of the corresponding cerium(iii) complexes, where = 1 and 2 represent novel complexes. The Ce(iv) complexes exhibited a range of intense colors, including red, black, cyan, and green. Notably, increasing the number of the guanidinate ligands from zero to three resulted in significant redshift of the absorption bands from 503 nm (2.

Probing Multiconfigurational States by Spectroscopy: The Cerium XAS L -edge Puzzle.

Invited for the cover of this issue are Prof. Jochen Autschbach and Dr. Dumitru-Claudiu Sergentu of State University of New York at Buffalo, and Dr.

Complexation of Lanthanides and Heavy Actinides with Aqueous Sulfur-Donating Ligands.

The separation of trivalent lanthanides and actinides is challenging because of their similar sizes and charge densities. S-donating extractants have shown significant selectivity for trivalent actinides over lanthanides, with single-stage americium/lanthanide separation efficiencies for some thiol-based extractants reported at >99.999%.

Amidinate Supporting Ligands Influence Molecularity in Formation of Uranium Nitrides.

Uranium nitride complexes are attractive targets for chemists as molecular models for the bonding, reactivity, and magnetic properties of next-generation nuclear fuels, but these molecules are uncommon and can be difficult to isolate due to their high reactivity. Here, we describe the synthesis of three new multinuclear uranium nitride complexes, [U(BCMA)](μ-N)(μ-κ:κ-BCMA) (), [(U(BIMA))(μ-N)(μ-NPr)(K(μ-η:η-CHCHNPr)] (), and [U(BIMA)](μ-N)(μ-κ:κ-BIMA) () (BCMA = ,-bis(cyclohexyl)methylamidinate, BIMA = ,-bis(-propyl)methylamidinate), from U(III) and U(IV) amidinate precursors. By varying the amidinate ligand substituents and azide source, we were able to influence the composition and size of these nitride complexes.

Combining the Best of Two Chelating Titans: A Hydroxypyridinone-Decorated Macrocyclic Ligand for Efficient and Concomitant Complexation and Sensitized Luminescence of f-Elements.

An ideal chelator for f-elements features rapid kinetics of complexation, high thermodynamic stability, and slow kinetics of dissociation. Here we present the facile synthesis of a macrocyclic ligand bearing four 1-hydroxy-2-pyridinone units linked to a cyclen scaffold that rapidly forms thermodynamically stable complexes with lanthanides (Sm , Eu , Tb , Dy ) and a representative late actinide (Cm ) in aqueous media and concurrently sensitizes them. Extended X-ray absorption fine structure (EXAFS) spectroscopy revealed an increase in the Ln/An-O bond lengths following the trend Cm>Eu>Tb and EXAFS data were compatible with time-resolved luminescence studies, which indicated one to two water molecules in the inner metal coordination sphere of Eu(III) and two water molecules for the Cm(III) complex.

Probing Multiconfigurational States by Spectroscopy: The Cerium XAS L -edge Puzzle.

The Ce L edge XAS spectra of CeO and cerocene [Ce(C H ) ] were calculated with relativistic ab-initio multireference wavefunction approaches capable of reproducing the observed spectra accurately. The study aims to resolve the decades-long puzzle regarding the relationship between the number and relative intensities of the XAS peaks and the 4f electron occupation in the ground state (GS) versus the core-excited states (ESs). CeO and cerocene exemplify the different roles of covalent bonding and wavefunction configurational composition in the observed intensity patterns.

Structural and spectroscopic characterization of an einsteinium complex.

The transplutonium elements (atomic numbers 95-103) are a group of metals that lie at the edge of the periodic table. As a result, the patterns and trends used to predict and control the physics and chemistry for transition metals, main-group elements and lanthanides are less applicable to transplutonium elements. Furthermore, understanding the properties of these heavy elements has been restricted by their scarcity and radioactivity.

Experimental evaluation of the stabilization of the COT orbitals by 4f orbitals in COTCe using a Hubbard model.

Significant orbital mixing is rare in lanthanide complexes because of the limited radial extent of the 4f orbitals, which results in a generally small stabilization due to 4f orbital interactions. Nevertheless, even a small amount of additional stabilization could enhance lanthanide separations. One lanthanide complex in which orbital mixing has been extensively studied both experimentally and computationally is cerocene, COTCe, where COT is cyclooctatetraene.

Controlling the Reduction of Chelated Uranyl to Stable Tetravalent Uranium Coordination Complexes in Aqueous Solution.

The solution-state interactions between octadentate hydroxypyridinone (HOPO) and catecholamide (CAM) chelating ligands and uranium were investigated and characterized by UV-visible spectrophotometry and X-ray absorption spectroscopy (XAS), as well as electrochemically via spectroelectrochemistry (SEC) and cyclic voltammetry (CV) measurements. Depending on the selected chelator, we demonstrate the controlled ability to bind and stabilize U, generating with 3,4,3-LI(1,2-HOPO), a tetravalent uranium complex that is practically inert toward oxidation or hydrolysis in acidic, aqueous solution. At physiological pH values, we are also able to bind and stabilize U to a lesser extent, as evidenced by the mix of U and U complexes observed via XAS.

Structure and magnetism of a tetrahedral uranium(iii) β-diketiminate complex.

We describe the functionalisation of the previously reported uranium(iii) β-diketiminate complex (BDI)UI(THF) (1) with one and two equivalents of a sterically demanding 2,6-diisopropylphenolate ligand (ODipp) leading to the formation of two heteroleptic complexes: [(BDI)UI(ODipp)] (2) and (BDI)U(ODipp) (3). The latter is a rare example of a tetrahedral uranium(iii) complex, and it shows single-molecule magnet behaviour.

Structural properties of ultra-small thorium and uranium dioxide nanoparticles embedded in a covalent organic framework.

We report the structural properties of ultra-small ThO and UO nanoparticles (NPs), which were synthesized without strong binding surface ligands by employing a covalent organic framework (COF-5) as an inert template. The resultant NPs were used to observe how structural properties are affected by decreasing grain size within bulk actinide oxides, which has implications for understanding the behavior of nuclear fuel materials. Through a comprehensive characterization strategy, we gain insight regarding how structure at the NP surface differs from the interior.

The duality of electron localization and covalency in lanthanide and actinide metallocenes.

Previous magnetic, spectroscopic, and theoretical studies of cerocene, Ce(CH), have provided evidence for non-negligible 4f-electron density on Ce and implied that charge transfer from the ligands occurs as a result of covalent bonding. Strong correlations of the localized 4f-electrons to the delocalized ligand π-system result in emergence of Kondo-like behavior and other quantum chemical phenomena that are rarely observed in molecular systems. In this study, Ce(CH) is analyzed experimentally using carbon K-edge and cerium M-edge X-ray absorption spectroscopies (XAS), and computationally using configuration interaction (CI) calculations and density functional theory (DFT) as well as time-dependent DFT (TDDFT).

Spontaneous Chelation-Driven Reduction of the Neptunyl Cation in Aqueous Solution.

Octadentate hydroxypyridinone (HOPO) and catecholamide (CAM) siderophore analogues are known to be efficacious chelators of the actinide cations, and these ligands are also capable of facilitating both activation and reduction of actinyl species. Utilizing X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies, as well as cyclic voltammetry measurements, herein, we elucidate chelation-based mechanisms for driving reactivity and initiating redox processes in a family of neptunyl-HOPO and CAM complexes. Based on the selected chelator, the ability to control the oxidation state of neptunium and the speed of reduction and concurrent oxo group activation was demonstrated.

Dicerium letterbox-shaped tetraphenolates: f-block complexes designed for two-electron chemistry.

Rare examples of molecular, dinuclear CeIII and PrIII complexes with robust Ln-coordination are accessible by use of the tetraphenolate pTP as a supporting, chelating O-donor ligand platform, pTP = [{2-(OC6H2R2-2,4)2CH}-C6H4-1,4]4- that favours the higher formal oxidation states accessible to rare earths. Two classes of complexes have been made from the platforms; one metallacyclic 2 + 2 [Ln2(pTP)2] framework with a rigid, letterbox-shaped geometry and [Ln(aryloxide)4] core, and one more flexible [(LnX)2(pTP)] with one rare earth ion at either end of the platform. The LnIII letterbox complexes have two K+ counter-cations, one of which sits inside the letterbox, binding the two central arenes of the platform sufficiently strongly that it cannot be displaced by solvent molecules (THF and pyridine) or crown ethers.

NpSe : a Binary Chalcogenide Containing Modulated Selenide Chains and Ambiguous-Valent Metal.

A new binary compound, NpSe possesses metal-chalcogen and chalcogen-chalcogen interactions different from those reported for other metal dichalcogenides. Its structure is incommensurately modulated and features linear Se chains and valence-ambiguous Np cations.