Metal-Metal Bonding in Tri-Actinide Clusters: A DFT Study of [AnCl] (z=1-6) and [AnClCp] (z=-2-+3; An=Ac, Th, Pa, U, Np, Pu).

The actinide-actinide bonding in tri-actinide clusters [An₃Cl₆] (An=Ac-Pu, z=1-6) and [An₃Cl₆Cp₃] (z=-2-+3; Cp=(η-CH)) is studied using density functional theory. We find 3-centre bonding similar to the tri-thorium cluster [{Th(η⁸-C₈H₈)(μ₃-Cl)₂}₃{K(THF)₂}₂], as we previously reported (Nature 2021, 598, 72-75). The population of 3-centre molecular orbitals (3c-MOs) by zero, one or two electrons correlates with shortening of the An-An bond lengths, which also decrease with increasing actinide atomic number, consistent with the contraction of the actinide valence atomic orbitals.

Understanding covalency in molecular f-block compounds from the synergy of spectroscopy and quantum chemistry.

One of the most intensely studied areas of f-block chemistry is the nature of the bonds between the f-element and another species, and in particular the role played by covalency. Computational quantum chemical methods have been at the forefront of this research for decades and have a particularly valuable role, given the radioactivity of the actinide series. The very strong agreement that has recently emerged between theory and the results of a range of spectroscopic techniques not only facilitates deeper insight into the experimental data, but it also provides confidence in the conclusions from the computational studies.

Alkyl Cyclopropyl Ketones in Catalytic Formal [3 + 2] Cycloadditions: The Role of SmI Catalyst Stabilization.

Alkyl cyclopropyl ketones are introduced as versatile substrates for catalytic formal [3 + 2] cycloadditions with alkenes and alkynes and previously unexplored enyne partners, efficiently delivering complex, sp-rich products. The key to effectively engaging this relatively unreactive new substrate class is the use of SmI as a catalyst in combination with substoichiometric amounts of Sm; the latter likely acting to prevent catalyst deactivation by returning Sm to the catalytic cycle. In the absence of Sm, background degradation of the SmI catalyst can outrun product formation.

N-Heterocyclic Carbene to Actinide d-Based π-bonding Correlates with Observed Metal-Carbene Bond Length Shortening Versus Lanthanide Congeners.

Comparison of bonding and electronic structural features between trivalent lanthanide (Ln) and actinide (An) complexes across homologous series' of molecules can provide insights into subtle and overt periodic trends. Of keen interest and debate is the extent to which the valence f- and d-orbitals of trivalent Ln/An ions engage in covalent interactions with different ligand donor functionalities and, crucially, how bonding differences change as both the Ln and An series are traversed. Synthesis and characterization (SC-XRD, NMR, UV-vis-NIR, and computational modeling) of the homologous lanthanide and actinide N-heterocyclic carbene (NHC) complexes [M(CMe)(X)(I)] {X = I, M = La, Ce, Pr, Nd, U, Np, Pu; X = Cl, M = Nd; X = I/Cl, M = Nd, Am; and I = [C(NMeCMe)]} reveals consistently shorter An-C vs Ln-C distances that do not substantially converge upon reaching Am/Nd comparison.

Computational study of the interactions of tetravalent actinides (An = Th-Pu) with the α-Fe Keggin cluster.

In recent years, evidence has emerged that actinide (An) uptake at the enhanced actinide removal plant (EARP) at the UK's Sellafield nuclear site occurs An interactions with an α-Fe Keggin molecular cluster during ferrihydrite formation. We here study theoretically the substitution of aquo complexes of the actinides Th-Pu onto a Na-decorated α-Fe Keggin cluster using DFT at the PBE0 level. The optimised Pu-O and Pu-Fe distances are in good agreement with experiment and Na/An substitutions are significantly favourable energetically, becoming more so across the early 5f series, with the smallest and largest ° being for Th and Pu at -335.

DFT + Simulation of the X-ray Absorption Near-Edge Structure of Bulk UO and PuO.

Hubbard -corrected density functional theory within the periodic boundary condition model in the WIEN2k code is used to simulate the actinide and O edge X-ray absorption near-edge structure (XANES) for UO and PuO. Spin-orbit coupling effects are included, as are possible excitonic effects using supercells with a core hole on one of the atoms. Our calculations yield spectra in excellent agreement with previous experiments and superior to previous simulations.

A robust Zintl cluster for the catalytic reduction of pyridines, imines and nitriles.

Despite p-block clusters being known for over a century, their application as catalysts to mediate organic transformations is underexplored. Here, the boron functionalized [P] cluster [(BBN)P] ([1]; BBN = 9-borabicyclo[3.3.

Actinide-Actinide Bonding: Electron Delocalisation and σ-Aromaticity in the Tri-Thorium Cluster [{Th(η -C H )(μ-Cl) } K ].

The tri-thorium cluster [{Th(η -C H )(μ -Cl) } {K(THF) } ] (Nature 2021, 598, 72-75) was reported to feature intriguing σ-aromatic bonding between the thorium atoms, a mode of metal-metal bonding unique in the actinide series. However, the presence of this bonding motif has since been challenged by others. Here, we computationally explore electron delocalisation in a molecular cluster fragment of [{Th(η -C H )(μ -Cl) } {K(THF) } ] and examine its responses to an applied magnetic field using a variety of methods.

A catalytic alkene insertion approach to bicyclo[2.1.1]hexane bioisosteres.

C(sp)-rich bicyclic hydrocarbon scaffolds, as exemplified by bicyclo[1.1.1]pentanes, play an increasingly high-profile role as saturated bioisosteres of benzenoids in medicinal chemistry and crop science.

Enhancing Hydrogen Evolution Reaction via Synergistic Interaction between the [MoS] Cluster Co-Catalyst and WSe Photocathode.

A thiomolybdate [MoS] nanocluster is a promising catalyst for hydrogen evolution reaction (HER) due to the high number of active edge sites. In this work, thiomolybdate cluster films are prepared by spin-coating of a (NH)MoS solution both on FTO glass substrates as hydrogen evolving electrodes and on highly 00.1-textured WSe for photoelectrochemical water splitting.

Covalent bond shortening and distortion induced by pressurization of thorium, uranium, and neptunium tetrakis aryloxides.

Covalency involving the 5f orbitals is regularly invoked to explain the reactivity, structure and spectroscopic properties of the actinides, but the ionic versus covalent nature of metal-ligand bonding in actinide complexes remains controversial. The tetrakis 2,6-di-tert-butylphenoxide complexes of Th, U and Np form an isostructural series of crystal structures containing approximately tetrahedral MO cores. We show that up to 3 GPa the Th and U crystal structures show negative linear compressibility as the OMO angles distort.

DFT + Study of Uranium Dioxide and Plutonium Dioxide with Occupation Matrix Control.

DFT + with occupation matrix control (OMC) is applied to study computationally bulk UO and PuO, the latter for the first time. Using the PBESol functional in conjunction with OMC locates AFM and NM ground states for UO and PuO, respectively, in agreement with experimental findings. By simulating the lattice parameter, magnetic moment, band gap, and densities of states, = 4.

Diastereoselective Radical 1,4-Ester Migration: Radical Cyclizations of Acyclic Esters with SmI.

Reductive cyclizations of carbonyl compounds, mediated by samarium(II) diiodide (SmI, Kagan's reagent), represent an invaluable platform to generate molecular complexity in a stereocontrolled manner. In addition to classical ketone and aldehyde substrates, recent advances in radical chemistry allow the cyclization of lactone and lactam-type substrates using SmI. In contrast, acyclic esters are considered to be unreactive to SmI and their participation in reductive cyclizations is unprecedented.

Contrasting behaviour under pressure reveals the reasons for pyramidalization in tris(amido)uranium(III) and tris(arylthiolate) uranium(III) molecules.

A range of reasons has been suggested for why many low-coordinate complexes across the periodic table exhibit a geometry that is bent, rather a higher symmetry that would best separate the ligands. The dominating reason or reasons are still debated. Here we show that two pyramidal UX molecules, in which X is a bulky anionic ligand, show opposite behaviour upon pressurisation in the solid state.

Uranium-nitride chemistry: uranium-uranium electronic communication mediated by nitride bridges.

Treatment of [U(N)(Tren)] (1, Tren = {N(CHCHNSiPr)}) with excess Li resulted in the isolation of [{U(μ-NLi)(Tren)}] (2), which exhibits a diuranium(IV) 'diamond-core' dinitride motif. Over-reduction of 1 produces [U(Tren)] (3), and together with known [{U(μ-NLi)(Tren)}] (4) an overall reduction sequence 1 → 4 → 2 → 3 is proposed. Attempts to produce an odd-electron nitride from 2 resulted in the formation of [{U(Tren)}(μ-NH)(μ-NLi)Li] (5).

Covalency in AnCl (An = Th-No).

A potential connection has previously been proposed between the emergence of unexpected covalent behaviour in various transcurium complexes and the increasing stability of the +2 oxidation state in the later members of the actinide series. We recently used computational methods to study AnCl, finding evidence for energy degeneracy driven covalency in the later actinides, and here present a comparative study of AnCl. The An-Cl bond lengths of the latter divide into two data sets; Th-Np, Cm, Bk and Pu, Am, Cf-No.

Accommodation of helium in PuO and the role of americium.

The high alpha-activity of plutonium dioxide (PuO) results in significant ingrowth of radiogenic helium (He) in the aged material. To safely store/dispose PuO or use in applications such as space exploration, the impact of He accumulation needs to be understood. In this work, defect energies obtained using a density functional theory (DFT) + + D3 scheme are used in a point defect model constructed for PuO to predict the method of He incorporation within the PuO lattice.

Exceptional uranium(VI)-nitride triple bond covalency from N nuclear magnetic resonance spectroscopy and quantum chemical analysis.

Determining the nature and extent of covalency of early actinide chemical bonding is a fundamentally important challenge. Recently, X-ray absorption, electron paramagnetic, and nuclear magnetic resonance spectroscopic studies have probed actinide-ligand covalency, largely confirming the paradigm of early actinide bonding varying from ionic to polarised-covalent, with this range sitting on the continuum between ionic lanthanide and more covalent d transition metal analogues. Here, we report measurement of the covalency of a terminal uranium(VI)-nitride by N nuclear magnetic resonance spectroscopy, and find an exceptional nitride chemical shift and chemical shift anisotropy.

A crystalline tri-thorium cluster with σ-aromatic metal-metal bonding.

Metal-metal bonding is a widely studied area of chemistry, and has become a mature field spanning numerous d transition metal and main group complexes. By contrast, actinide-actinide bonding, which is predicted to be weak, is currently restricted to spectroscopically detected gas-phase U and Th (refs. ), UH and UH in frozen matrices at 6-7 K (refs.

Synthesis, structure, and reactivity of uranium(vi) nitrides.

Uranium nitride compounds are important molecular analogues of uranium nitride materials such as UN and UN which are effective catalysts in the Haber-Bosch synthesis of ammonia, but the synthesis of molecular nitrides remains a challenge and studies of the reactivity and of the nature of the bonding are poorly developed. Here we report the synthesis of the first nitride bridged uranium complexes containing U(vi) and provide a unique comparison of reactivity and bonding in U(vi)/U(vi), U(vi)/U(v) and U(v)/U(v) systems. Oxidation of the U(v)/U(v) bis-nitride [K{U(OSi(O Bu))(μ-N)}], , with mild oxidants yields the U(v)/U(vi) complexes [K{U(OSi(O Bu))(μ-N)}], and [K{U(OSi(O Bu))}(μ-N)(μ-I)], while oxidation with a stronger oxidant ("magic blue") yields the U(vi)/U(vi) complex [{U(OSi(O Bu))}(μ-N)(μ-thf)], .

Si NMR Spectroscopy as a Probe of s- and f-Block Metal(II)-Silanide Bond Covalency.

We report the use of Si NMR spectroscopy and DFT calculations combined to benchmark the covalency in the chemical bonding of s- and f-block metal-silicon bonds. The complexes [M(SiBu)(THF)(THF)] (: M = Mg, Ca, Yb, = 0; M = Sm, Eu, = 1) and [M(SiBuMe)(THF)(THF)] (: M = Mg, = 0; M = Ca, Sm, Eu, Yb, = 1) have been synthesized and characterized. DFT calculations and Si NMR spectroscopic analyses of and (M = Mg, Ca, Yb, No, the last due to experimental unavailability) together with known {Si(SiMe)}-, {Si(SiMeH)}-, and {SiPh}-substituted analogues provide 20 representative examples spanning five silanide ligands and four divalent metals, revealing that the metal-bound Si NMR isotropic chemical shifts, δ, span a wide (∼225 ppm) range when the metal is kept constant, and direct, linear correlations are found between δ and computed delocalization indices and quantum chemical topology interatomic exchange-correlation energies that are measures of bond covalency.

High coordination number actinide-noble gas complexes; a computational study.

The geometries, electronic structures and bonding of early actinide-noble gas complexes are studied computationally by density functional and wavefunction theory methods, and by ab initio molecular dynamics. AcHe183+ is confirmed as being an 18-coordinate system, with all of the He atoms accommodated in the primary coordination shell, and this record coordination number is reported for the first time for Th4+ and Th3+. For Pa and U in their group valences of 5 and 6 respectively, the largest number of coordinated He atoms is 17.

Covalency in AnCl (An = Th-No).

The geometric and electronic structures of AnCl3 are studied computationally using scalar relativistic, hybrid density functional theory (PBE0). The An-Cl bond lengths generally decrease across the 5f series, although there is a slight lengthening from Fm-Cl to No-Cl as the metal ions display increasing M(ii) character. Covalency in the An-Cl bond is studied using a wide range of metrics drawn from the Natural Bond Orbital, Natural Resonance Theory and Quantum Theory of Atoms-in-Molecules (QTAIM) methods, including bond order, orbital composition, orbital overlap and electron density topology data.