Chemical and elemental mapping of spent nuclear fuel sections by soft X-ray spectromicroscopy.

Soft X-ray spectromicroscopy at the O K-edge, U N-edges and Ce M-edges has been performed on focused ion beam sections of spent nuclear fuel for the first time, yielding chemical information on the sub-micrometer scale. To analyze these data, a modification to non-negative matrix factorization (NMF) was developed, in which the data are no longer required to be non-negative, but the non-negativity of the spectral components and fit coefficients is largely preserved. The modified NMF method was utilized at the O K-edge to distinguish between two components, one present in the bulk of the sample similar to UO and one present at the interface of the sample which is a hyperstoichiometric UO species.

Expanding the Nonaqueous Chemistry of Neptunium: Synthesis and Structural Characterization of [Np(NR)Cl], [Np(NR)Cl], and [Np{(R)(SiMeH)}(NR)] (R = SiMe).

Reaction of 3 equiv of NaNR (R = SiMe) with NpCl(DME) in THF afforded the Np(IV) silylamide complex, [Np(NR)Cl] (), in good yield. Reaction of with 1.5 equiv of KC in THF, in the presence of 1 equiv of dibenzo-18-crown-6, resulted in formation of [{K(DB-18-C-6)(THF)}(μ-Cl)][Np(NR)Cl] (), also in good yield.

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).

Uranium Uptake in Sea Urchin, Accumulation and Speciation.

Uranium speciation and bioaccumulation were investigated in the sea urchin . Through accumulation experiments in a well-controlled aquarium followed by ICP-OES analysis, the quantification of uranium in the different compartments of the sea urchin was performed. Uranium is mainly distributed in the test (skeletal components), as it is the major constituent of the sea urchin, but in terms of quantity of uranium per gram of compartment, the following rating: intestinal tract > gonads ≫ test, was obtained.

Chiral transcription in self-assembled tetrahedral EuL chiral cages displaying sizable circularly polarized luminescence.

Predictable stereoselective formation of supramolecular assembly is generally believed to be an important but complicated process. Here, we show that point chirality of a ligand decisively influences its supramolecular assembly behavior. We designed three closely related chiral ligands with different point chiralities, and observe their self-assembly into europium (Eu) tetrametallic tetrahedral cages.

Coordination Characteristics of Uranyl BBP Complexes: Insights from an Electronic Structure Analysis.

Organic ligand complexes of lanthanide/actinide ions have been studied extensively for applications in nuclear fuel storage and recycling. Several complexes of 2,6-bis(2-benzimidazyl)pyridine (H2BBP) featuring the uranyl moiety have been reported recently, and the present study investigates the coordination characteristics of these complexes using density functional theory-based electronic structure analysis. In particular, with the aid of several computational models, the nonplanar equatorial coordination about uranyl, observed in some of the compounds, is studied and its origin traced to steric effects.

Synthesis, Electrochemistry, and Reactivity of the Actinide Trisulfides [K(18-crown-6)][An(η(3)-S3)(NR2)3] (An = U, Th; R = SiMe3).

The reaction of [Th(I)(NR2)3] (R = SiMe3) with [K(18-crown-6)]2[S4] results in the formation of [K(18-crown-6)][Th(η(3)-S3)(NR2)3] (2). Oxidation of 2, or its uranium analogue, [K(18-crown-6)][U(η(3)-S3)(NR2)3] (1), with AgOTf, in an attempt to generate an [S3](•-) complex, results in the formation of [K(18-crown-6)][An(OTf)2(NR2)3] (3, An = U; 4, An = Th) as the only isolable products. These results suggest that the putative [S3](•-) ligand is only weakly coordinating and can be easily displaced by nucleophiles.

Use of (77)Se and (125)Te NMR Spectroscopy to Probe Covalency of the Actinide-Chalcogen Bonding in [Th(En){N(SiMe3)2}3](-) (E = Se, Te; n = 1, 2) and Their Oxo-Uranium(VI) Congeners.

Reaction of [Th(I)(NR2)3] (R = SiMe3) (1) with 1 equiv of either [K(18-crown-6)]2[Se4] or [K(18-crown-6)]2[Te2] affords the thorium dichalcogenides, [K(18-crown-6)][Th(η(2)-E2)(NR2)3] (E = Se, 2; E = Te, 3), respectively. Removal of one chalcogen atom via reaction with Et3P, or Et3P and Hg, affords the monoselenide and monotelluride complexes of thorium, [K(18-crown-6)][Th(E)(NR2)3] (E = Se, 4; E = Te, 5), respectively. Both 4 and 5 were characterized by X-ray crystallography and were found to feature the shortest known Th-Se and Th-Te bond distances.

Thorium-ligand multiple bonds reductive deprotection of a trityl group.

Reaction of [Th(I)(NR)] (R = SiMe) () with KECPh (E = O, S) affords the thorium chalcogenates, [Th(ECPh)(NR)] (, E = O; , E = S), in moderate yields. Reductive deprotection of the trityl group from and by reaction with KC, in the presence of 18-crown-6, affords the thorium oxo complex, [K(18-crown-6)][Th(O)(NR)] (), and the thorium sulphide complex, [K(18-crown-6)][Th(S)(NR)] (), respectively. The natural bond orbital and quantum theory of atoms-in-molecules approaches are employed to explore the metal-ligand bonding in and and their uranium analogues, and in particular the relative roles of the actinide 5f and 6d orbitals.

Reversible chalcogen-atom transfer to a terminal uranium sulfide.

The reaction of elemental S or Se with [K(18-crown-6)][U(S)(NR2)3] (1) results in the formation of the new uranium(IV) dichalcogenides [K(18-crown-6)][U(η(2)-S2)(NR2)3] (2) and [K(18-crown-6)][U(η(2)-SSe)(NR2)3] (5). The further addition of elemental S to 2 results in the formation of [K(18-crown-6)][U(η(3)-S3)(NR2)3] (3). Complexes 2, 3, and 5 can be reconverted into 1 via the addition of R3P (R = Et, Ph), concomitant with the formation of R3P═E (E = S, Se).

Synthesis of terminal monochalcogenide and dichalcogenide complexes of uranium using polychalcogenides, [E(n)]²⁻ (E = Te, n = 2; E = Se, n = 4), as chalcogen atom transfer reagents.

Reaction of KH with elemental tellurium, in the presence of 18-crown-6, results in the formation of the ditelluride, [K(18-crown-6)]2[Te2] (1), in good yield. Similarly, reaction of KH with elemental selenium, in the presence of 18-crown-6, results in the formation of [K(18-crown-6)]2[Se4] (4). Both 1 and 4 are capable of chalcogen atom transfer to U(III).

Synthesis of uranium-ligand multiple bonds by cleavage of a trityl protecting group.

Addition of KSCPh3 to [U(NR2)3] (R = SiMe3) in tetrahydrofuran, followed by addition of 18-crown-6, results in formation of the U(IV) sulfide, [K(18-crown-6)][U(S)(NR2)3] (1) and Gomberg's dimer. Similarly, addition of KOCPh3 to [U(NR2)3] in tetrahydrofuran, followed by addition of 18-crown-6, results in formation of the U(IV) oxide, [K(18-crown-6)][U(O)(NR2)3] (3). Also observed in this transformation are the triphenylmethyl anion, [K(18-crown-6)(THF)2][CPh3] (5), and the U(IV) alkoxide, [U(OCPh3)(NR2)3] (4).

Reactivity and Mössbauer spectroscopic characterization of an Fe(IV) ketimide complex and reinvestigation of an Fe(IV) norbornyl complex.

Thermolysis of Fe(N═C(t)Bu2)4 (1) for 8 h at 50 °C generates the mixed valent Fe(III)/Fe(II) bimetallic complex Fe2(N═C(t)Bu2)5 (2) in moderate yield. Also formed in this reaction are tert-butyl cyanide, isobutane, and isobutylene, the products of ketimide oxidation by the Fe(4+) center. Reaction of 1 with 1 equiv of acetylacetone affords the Fe(III) complex, Fe(N═C(t)Bu2)2(acac) (3), concomitant with formation of bis(tert-butyl)ketimine, tert-butyl cyanide, isobutane, and isobutylene.

Improving T₁ and T₂ magnetic resonance imaging contrast agents through the conjugation of an esteramide dendrimer to high-water-coordination Gd(III) hydroxypyridinone complexes.

Commercial gadolinium magnetic resonance imaging (MRI) contrast agents are limited by low relaxivity (r₁) and coordination to only a single water molecule (q = 1). Consequently, gram quantities of these agents must be injected to obtain sufficient diagnostic contrast. In this study, MRI contrast agents for T(1) and T₂ relaxivity were synthesized using hydroxypyridinone and terephthalamide chelators with mesityl and 1,4,7-triazacyclononane capping moieties.

Conjugation effects of various linkers on Gd(III) MRI contrast agents with dendrimers: optimizing the hydroxypyridinonate (HOPO) ligands with nontoxic, degradable esteramide (EA) dendrimers for high relaxivity.

One essential requirement for more sensitive gadolinium-based MRI contrast agents is to slow the molecular tumbling of the gadolinium(III) ion, which increases the gadolinium's relaxivity (i.e., its ability to speed up the NMR relaxation of nearby water molecules).