Thorium sits at a unique position on the periodic table. On one hand, there is little evidence that its 5f orbitals engage in bonding as they do in other early actinides; on the other hand, its ...chemistry is distinct from Lewis acidic transition metals. To gain insight into the underlying electronic structure of Th and develop trends across the actinide series, it is useful to study Th(iii) and Th(ii) systems with valence electrons that may engage in non-electrostatic metal-ligand interactions, although only a handful of such systems are known. To expand the range of low-valent compounds and gain deeper insight into Th electronic structure, we targeted actinide bimetallic complexes containing metal-metal bonds. Herein, we report the syntheses of Th-Al bimetallics from reactions between a di-
-butylcyclopentadienyl supported Th(iv) dihalide (Cp
ThCl
) and an anionic aluminum hydride salt K(H
AlC(SiMe
)
) (
). Reduction of the Th(iv)(Cl)-Al product resulted in a Th(iii)-Al complex Cp
Th(μ-H
)AlC(SiMe
)
(
). The U(iii) analogue Cp
U(μ-H
)AlC(SiMe
)
(
) could be synthesized directly from a U(iii) halide starting material. Electron paramagnetic resonance studies on
demonstrate hyperfine interactions between the unpaired electron and the Al atom indicative of spin density delocalization from the Th metal center to the Al. Density functional theory and atom in molecules calculations confirmed the presence of An→Al interactions in
and
, which represents the first examples of An→M interactions where the actinide behaves as an electron donor.
Reaction of (CpSiMe3)3U or (CpSiMe3)3Nd with (Cp*Al)4 or Cp*Ga (Cp* = C5Me5) afforded the isostructural complexes (CpSiMe3)3M−ECp* (M = U, E = Al (1); M = U, E = Ga (2); M = Nd, E = Al (3); M = Nd, E ...= Ga (4)). In the case of 1 and 2 the complexes were isolated in 39 and 90% yields, respectively, as crystalline solids and were characterized by single-crystal X-ray diffraction, variable-temperature 1H NMR spectroscopy, elemental analysis, variable-temperature magnetic susceptibility, and UV−visible−NIR spectroscopy. In the case of 3 and 4, the complexes were observed by variable-temperature 1H NMR spectroscopy but were not isolated as pure materials. Comparison of the equilibrium constants and thermodynamic parameters ΔH and ΔS obtained by 1H NMR titration methods revealed a much stronger U−Ga interaction in 2 than the Nd−Ga interaction in 4. Competition reactions between (CpSiMe3)3U and (CpSiMe3)3Nd indicate that Cp*Ga selectively binds U over Nd in a 93:7 ratio at 19 °C and 96:4 at −33 °C. For 1 and 3, comparison of 1H NMR peak intensities suggests that Cp*Al also achieves excellent U(III)/Nd(III) selectivity at 21 °C. The solution electronic spectra and solid-state temperature-dependent magnetic susceptibilities of 1 and 2, in addition to X-ray absorption near-edge structure (XANES) measurements from scanning transmission X-ray microscopy (STXM) of 1, are consistent with those observed for other U(III) coordination complexes. DFT calculations using five different functionals were performed on the model complexes Cp3M−ECp (M = Nd, U; E = Al, Ga), and empirical fitting of the values for Cp3M−ECp allowed the prediction of binding energy estimates for Cp*Al compounds 1 and 3. NBO/NLMO bonding analyses on Cp3U−ECp indicate that the bonding consists predominantly of a E→U σ-interaction arising from favorable overlap between the diffuse ligand lone pair and the primarily 7s/6d acceptor orbitals on U(III), with negligible U→E π-donation. The overall experimental and computational bonding analysis suggests that Cp*Al and Cp*Ga behave as good σ-donors in these systems.
We report the structural properties of ultra-small ThO
2
and UO
2
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. Characterization using electron microscopy and small-angle X-ray scattering indicates that growth of the ThO
2
and UO
2
NPs was confined by the pores of the COF template, resulting in sub-3 nm particles. X-ray absorption fine structure spectroscopy results indicate that the NPs are best described as ThO
2
and UO
2
materials with unpassivated surfaces. The surface layers of these particles compensate for high surface energy by exhibiting a broader distribution of Th-O and U-O bond distances despite retaining average bond lengths that are characteristic of bulk ThO
2
and UO
2
. The combined synthesis and physical characterization efforts provide a detailed picture of actinide oxide structure at the nanoscale, which remains highly underexplored compared to transition metal counterparts.
ThO
2
and UO
2
nanoparticles synthesized using a COF-5 template exhibit unpassivated surfaces and provide insight into nanoscale properties of actinides.
C-term magnetic circular dichroism (MCD) spectroscopy is a powerful method for probing d-d and f-f transitions in paramagnetic metal complexes. However, this technique remains underdeveloped both ...experimentally and theoretically for studies of U(v) complexes of Oh symmetry, which have been of longstanding interest for probing electronic structure, bonding, and covalency in 5f systems. In this study, C-term NIR MCD of the Laporte forbidden f-f transitions of UCl6- and UF6- are reported, demonstrating the significant fine structure resolution possible with this technique including for the low energy Γ7 → Γ8 transitions in UF6-. The experimental NIR MCD studies were further extended to U(OC6F5)6-, U(CH2SiMe3)6-, and U(NC(tBu)(Ph))6- to evaluate the effects of ligand-type on the f-f MCD fine structure features. Theoretical calculations were conducted to determine the Laporte forbidden f-f transitions and their MCD intensity experimentally observed in the NIR spectra of the U(v) hexahalide complexes, via the inclusion of vibronic coupling, to better understand the underlying spectral fine structure features for these complexes. These spectra and simulations provide an important platform for the application of MCD spectroscopy to this widely studied class of U(v) complexes and identify areas for continued theoretical development.
We report the synthesis of four homoleptic thorium(
iv
) amidate complexes as single-source molecular precursors for thorium dioxide. Each can be sublimed at atmospheric pressure, with the ...substituents on the amidate ligands significantly impacting their volatility and thermal stability. These complexes decompose
via
alkene elimination to give ThO
2
without need for a secondary oxygen source. ThO
2
samples formed from pyrolysis of
C
-alkyl amidates were found to have higher purity and crystallinity than ThO
2
samples formed from
C
-aryl amidates.
Volatile thorium amidates can be converted to ThO
2
in the absence of an external oxygen source, and the thermal properties of these precursors can be readily tuned by modifying the ligand substituents.
In the ocean, complex interactions between natural and anthropogenic radionuclides, seawater, and diverse marine biota provide a unique window through which to examine ecosystem and trophic transfer ...mechanisms in cases of accidental dissemination. The nature of interaction between radionuclides, the marine environment, and marine species is therefore essential for better understanding transfer mechanisms from the hydrosphere to the biosphere. Although data pertaining to the rate of global transfer are often available, little is known regarding the mechanism of environmental transport and uptake of heavy radionuclides by marine species. Among marine species, sponges are immobile active filter feeders and have been identified as hyperaccumulators of several heavy metals. We have selected the Mediterranean sponge Aplysina cavernicola as a model species for this study. Actinide elements are not the only source of radioactive release in cases of civilian nuclear events; however, their physicochemical transfer mechanisms to marine species remain largely unknown. We have targeted europium(III) as a representative of the trivalent actinides such as americium or curium. To unravel biological uptake mechanisms of europium in A. cavernicola, we have combined radiometric (γ) measurements with spectroscopic (time-resolved laser-induced fluorescence spectroscopy, TRLIFS, and X-ray absorption near-edge structure, XANES) and imaging (transmission electron microscopy, TEM, and scanning transmission X-ray microscopy, STXM) techniques. We have observed that the colloids of NaEu(CO3)2·nH2O formed in seawater are taken up by A. cavernicola with no evidence that lethal dose has been reached in our working conditions. Spectroscopic results suggest that there is no change of speciation during uptake. Finally, TEM and STXM images recorded at different locations across a sponge cross section, together with differential cell separation, indicate the presence of europium particles (around 200 nm) mainly located in the skeleton and toward the outer surface of the sponge.
Polarized aluminum K-edge X-ray absorption near edge structure (XANES) spectroscopy and first-principles calculations were used to probe electronic structure in a series of (BDI)Al, (BDI)AlX2, and ...(BDI)AlR2 coordination compounds (X = F, Cl, I; R = H, Me; BDI = 2,6-diisopropylphenyl-β-diketiminate). Spectral interpretations were guided by examination of the calculated transition energies and polarization-dependent oscillator strengths, which agreed well with the XANES spectroscopy measurements. Pre-edge features were assigned to transitions associated with the Al 3p orbitals involved in metal–ligand bonding. Qualitative trends in Al 1s core energy and valence orbital occupation were established through a systematic comparison of excited states derived from Al 3p orbitals with similar symmetries in a molecular orbital framework. These trends suggested that the higher transition energies observed for (BDI)AlX2 systems with more electronegative X1– ligands could be ascribed to a decrease in electron density around the aluminum atom, which causes an increase in the attractive potential of the Al nucleus and concomitant increase in the binding energy of the Al 1s core orbitals. For (BDI)Al and (BDI)AlH2 the experimental Al K-edge XANES spectra and spectra calculated using the eXcited electron and Core–Hole (XCH) approach had nearly identical energies for transitions to final state orbitals of similar composition and symmetry. These results implied that the charge distributions about the aluminum atoms in (BDI)Al and (BDI)AlH2 are similar relative to the (BDI)AlX2 and (BDI)AlMe2 compounds, despite having different formal oxidation states of +1 and +3, respectively. However, (BDI)Al was unique in that it exhibited a low-energy feature that was attributed to transitions into a low-lying p-orbital of b1 symmetry that is localized on Al and orthogonal to the (BDI)Al plane. The presence of this low-energy unoccupied molecular orbital on electron-rich (BDI)Al distinguishes its valence electronic structure from that of the formally trivalent compounds (BDI)AlX2 and (BDI)AlR2. The work shows that Al K-edge XANES spectroscopy can be used to provide valuable insight into electronic structure and reactivity relationships for main-group coordination compounds.
Oxygen and aluminum K-edge X-ray absorption spectroscopy (XAS), imaging from a scanning transmission X-ray microscope (STXM), and first-principles calculations were used to probe the composition and ...morphology of bulk aluminum metal, α- and γ-Al2O3, and several types of aluminum nanoparticles. The imaging results agreed with earlier transmission electron microscopy studies that showed a 2 to 5 nm thick layer of Al2O3 on all the Al surfaces. Spectral interpretations were guided by examination of the calculated transition energies, which agreed well with the spectroscopic measurements. Features observed in the experimental O and Al K-edge XAS were used to determine the chemical structure and phase of the Al2O3 on the aluminum surfaces. For unprotected 18 and 100 nm Al nanoparticles, this analysis revealed an oxide layer that was similar to γ-Al2O3 and comprised of both tetrahedral and octahedral Al coordination sites. For oleic acid-protected Al nanoparticles, only tetrahedral Al oxide coordination sites were observed. The results were correlated to trends in the reactivity of the different materials, which suggests that the structures of different Al2O3 layers have an important role in the accessibility of the underlying Al metal toward further oxidation. Combined, the Al K-edge XAS and STXM results provided detailed chemical information that was not obtained from powder X-ray diffraction or imaging from a transmission electron microscope.
Use of an alternative aluminium(III) starting material has led to the isolation of a new aluminium(II) diiododialane, which functions as an intermediate in the synthesis of (Cp*Al)4, reacts ...oxidatively with methyllithium, and undergoes oxidative cleavage of the Al-Al bond with an aryl azide.
Advancing theories of how metal–oxygen bonding influences metal oxo properties can expose new avenues for innovation in materials science, catalysis, and biochemistry. Historically, spectroscopic ...analyses of the transition metal MO4 x– anions have formed the basis for new M–O bonding theories. Herein, relative changes in M–O orbital mixing in MO4 2– (M = Cr, Mo, W) and MO4 – (M = Mn, Tc, Re) are evaluated for the first time by nonresonant inelastic X-ray scattering, X-ray absorption spectroscopy using fluorescence and transmission (via a scanning transmission X-ray microscope), and time-dependent density functional theory. The results suggest that moving from Group 6 to Group 7 or down the triads increases M–O e* (π*) mixing; for example, it more than doubles in ReO4 – relative to CrO4 2–. Mixing in the t 2* orbitals (σ* + π*) remains relatively constant within the same Group, but increases on moving from Group 6 to Group 7. These unexpected changes in orbital energy and composition for formally isoelectronic tetraoxometalates are evaluated in terms of periodic trends in d orbital energy and radial extension.
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