The use of lanthanide complexes for catalytic dinitrogen reduction is a new development in homogeneous catalysis. Density functional theory calculations on our recently reported cerium phenolate catalyst [K2Ce2(sol)4(mTP)2] (mTP = {(OC6H2-2-tBu-4-Me)2CH}2-1,3-C6H4; sol = OMe2 here; THF in the experiment) have been undertaken to elucidate the reduction, activation and silylation steps at the bound dinitrogen molecule, in the presence of the reductant, potassium metal (K0) and the electrophile Me3SiCl (TMSCl). Out of the total of six electron reductions required to cleave the N2, the first two-electron reduction step was found to be highly disfavoured unless potassium cations (K+) are included, upon which the step is rendered strongly exergonic; N-Si bond formation at the two-electron stage is predicted to be unfavourable. The three-electron-reduced N2-adduct is found to be at the reductive activation limit in the absence of added electrophiles, which can form N-element bonds and lower the overall charge. Added electron density beyond three-electron reduction no longer localises on N2, preventing formal N24- formation. A pathway in which both K0 and Me3SiCl work in concert was modelled, and six sequential reduction-silylation steps were calculated, showing how the N-N bond is cleaved after the third reduction, eventually releasing two equivalents of N(SiMe3)3, and regenerating the starting complex with the highest barrier of any step being 22 kcal mol-1. We establish alkali metal coordination and coupled electron-electrophile transfer as key factors in the design of rare-earth-mediated dinitrogen functionalisation.

p-Block complexes containing unsupported metal─metal bonds can activate small molecules via mechanisms that complement and contrast with those of d-block metal complexes. Here we report the synthesis of a new family of heterobimetallic Al─Zn complexes [(ArNacnac)Zn─Al(Cp*)(X)] (Ar = Dep, X = Cl, Br, I; Ar = Dipp, X = Cl, Br; ArNacnac = {HC[C(Me)N(Ar)]2}; Ar = Dep, C6H3Et2-2,6; Dipp, C6H3 iPr-2,6; Cp* = C5Me5), by insertion of in situ-generated "AlCp*" into the Zn─X bonds of parent dimeric zinc ArNacnac halide complexes [Zn(ArNacnac)(μ-X)]2. We find that the reactions of the newly formed Al─Zn complexes with N,N'-dicyclohexylcarbodiimide (DCC) proceed by migratory insertion into the Al─Zn bond to give [Zn(ArNacnac){μ2-C(NCy)2-κ1-C,κ2-N,N'}Al(Cp*)(X)] (Ar = Dep, X = Cl, Br, I; Ar = Dipp, X = Cl, Br) as expected, but for the DippNacnac derivatives a second equivalent of DCC inserts into the Al─Cp* moiety to afford [Zn(DippNacnac){μ2-C(NCy)2-κ1-C,κ2-N,N'}Al(Cl){κ2-(NCy)2C-η1-Cp*-κ2-N,N'}] or [Zn(DippNacnac)(Br){μ2-C(NCy)2-κ1-C,κ2-N,N'}Al{κ2-(NCy)2C-η1-Cp*-κ2-N,N'}], with concomitant halide migration giving a Zn─Br bond in the latter complex. These results show that non-innocent reactivity of Al─Cp*, widely assumed to be a spectator ligand in heterobimetallic complexes, can be switched on by subtly tuning ligand steric bulk about Al─Zn bonds.

The homogeneous conversion of ambient dinitrogen to amine products via the N2 reduction reaction (N2RR) remains a prized yet challenging feat for d-block complexes and is scarcely reported for f-block complexes. New, mononuclear TiIV and ZrIV aryloxide complexes Ti(DP)2 (1Ti), Zr(DP)2 (1Zr), and DP = [2-(OC6H2-2-tBu,4-Me)2CHPh] produce up to 51 eq. and up to 7.0 eq. of HN(SiMe3)2 per Ti/Zr, from N2, K0, weak acid, and chlorotrimethylsilane. Complex 1Ti exhibits more than double the activity toward N2-silylation of any previously reported Ti N2RR catalyst and can also catalyze the formation of up to 19 eq. of NH3, a new feature in early metal N2RR chemistry. The mononuclear 1Zr is the most active Zr catalyst for N2-silylation to date. [KSm(DP)2(THF)3] (1Sm), the mononuclear analogue of our previously reported dinuclear A-Sm complex, displays only stoichiometric N2-silylation due to its vulnerability to deleterious side reactions. DFT calculations confirm the catalysis can proceed via a monomeric Ti complex with a terminally bound, activated N2, agreeing with experimental 1H DOSY NMR measurements; the N-H bond is formed first, directing the catalyst selectivity. The isolable reduction product [K3(THF)Ti(DP)(DP-)(N2)] is also an active catalyst, and an intermediate in the calculated cycle.

SmI2 has become a crucial reagent in organic chemistry due to its ability to facilitate single-electron transfer (SET) reactions under mild conditions, enabling the construction of complex molecular architectures. Its versatility can be further enhanced by the use of additives, particularly Lewis base (LB) additives. In this study, we provide a computational understanding of the multifaceted role of LB additives in SmI2 chemistry. We first identify the critical interplay between the basicity of the LB and the coordination geometry, which together dictate the reducing power of SmI2(LB)n complexes. For example, the relatively weak LB tetrahydrofuran (THF), a less bulky ligand than analogous ethers such as tetrahydropyran (THP), can achieve tight coordination to Sm, thereby enhancing electron donation and the reducing power of SmI2. Additionally, we investigate the SET reduction of various ketones by SmI2, showing that both steric and electronic effects from the LB and the substrate play pivotal roles in governing the SET reduction reactivity of SmI2, suggesting that SET reactivity cannot be solely determined by the commonly used reduction power of SmI2. In the final part of our study, we examine the influence of LB additives on practical SmI2-catalysed coupling reactions, finding a revised reaction mechanism that proceeds along a novel septet pathway that outperforms the conventional quintet route. We find that strongly coordinating additives can markedly reshape the reaction profile by accelerating key steps and altering the rate-determining stationary points. These results highlight how LB additives can intricately modulate reactivity and selectivity, offering valuable insights for the rational design of more efficient and selective SmI2-mediated transformations.

The Enhanced Actinide Removal Plant (EARP), at Sellafield in the UK, is tasked with separating waste actinide species from an aqueous waste stream via base-induced hydrolysis of Fe(III). During this flocculation process ferrihydrite forms and the actinides interact strongly with the surface. It has been shown that Pu remains sorbed in the solid state over long periods of time, during which ferrihydrite undergoes transformation into hematite. It is of critical importance to the operations of future Geological Disposal Facility (GDF) technologies that the Pu@hematite system is studied to understand the binding strength and sorption mechanism. Here we present a comprehensive study of Pu(IV) binding to two well-established basal terminations of hematite using periodic DFT+Ueff. First, we outline our methodology and demonstrate correct prediction of the bulk hematite lattice parameters and electronic band gap, then we generate the (001)-Fe and (001)-O3 terminations and demonstrate reasonable predictions of the surface energies, inter-layer spacings, and work functions. The (001)-Fe termination is then hydrated with a monolayer of water. We show that Pu(IV) forms multiple Pu-O bonds with both terminations at distances consistent with experimental EXAFS measurements. Density of states and charge density difference analysis reveals strong hybridisation between the Pu(5f) and O(2p) states supporting charge transfer as indicated by depleted charge density surrounding the Pu atom on the surface. Quantum Theory of Atoms in Molecules analysis shows that the Pu-O bonds are partially covalent, in agreement with our previous assessment of Pu bound to α-Fe13, a prenucleation cluster to ferrihydrite (Fh), and Pu bound to ferrihydrite surfaces. The reaction energies for surface binding are significantly exothermic, even more so than was found in our previous analysis of the Pu@Fh surfaces, indicating that Pu(IV) should remain immobile and bound to hematite, particularly in oxygenated conditions as may be found in the GDF or subterranean environments.

We present an investigation of one-photon valence-shell photoelectron spectroscopy and photoelectron circular dichroism (PECD) for the chiral molecule (1R,4R)-3-(heptafluorobutyryl)-(+)-camphor (HFC) and its europium complex Eu(III) tris[3-(heptafluorobutyryl)-(1R,4R)-camphorate] (Eu-HFC3), the latter of which constitutes the heaviest organometallic molecule for which PECD has yet been measured. We discuss the role of keto-enol tautomerism in HFC, both as a free molecule and complexed in Eu-HFC3. PECD is a uniquely sensitive probe of molecular chirality and structure such as absolute configuration, conformation, isomerization, and substitution, and is, in principle, well suited to unambiguously resolving tautomers; however, modeling remains challenging. For small organic molecules, theory is generally capable of accounting for experimentally measured PECD asymmetries, but significantly poorer agreement is typically achieved for the case of large open-shell systems. Here, we report PECD asymmetries, ranging up to ∼8% for HFC and ∼7% for Eu-HFC3, of similar magnitude to those reported previously for smaller isolated chiral molecules, indicating that PECD remains a practical experimental technique for the study of large, complicated chiral systems.

Exchange coupling in radical-bridged lanthanide complexes is a crucial aspect of their magnetic behavior, but it is challenging to model due to the interplay of strong electron correlation, spin-orbit coupling, and the localized nature of 4f orbitals. Here, we present a comprehensive ab initio analysis of isotropic and anisotropic exchange interactions in two families of radical-bridged dilanthanide complexes, [(Cp2*Ln)2(μ - bpym•)]+ and [(Cp2*Ln)2(μ - Co(pdt)2)], where Ln = Gd3+ and Dy3+; Cp* = pentamethylcyclopentadienyl; and the radical ligands are bpym = bipyrimidyl and pdt2- = 1,2-diphenylethylene-dithiolate. The microscopic contributions of direct and kinetic exchange to the isotropic exchange in the radical-bridged gadolinium complexes are disentangled, revealing that antiferromagnetic coupling in the μ-bpym•-bridged complex is dominated by virtual intersite electron hopping, largely facilitated by the delocalized radical orbitals, while ferromagnetic behavior in the μ-Co(pdt)2-bridged complex arises from direct exchange where virtual electron hopping is greatly hindered by localized d-orbitals. The finding thus explains the experimentally observed ferromagnetic coupling in a large number of gadolinium-transition metal complexes as well as observed antiferromagnetic coupling in the aromatic radical-bridged lanthanide complexes. Extending to radical-bridged dysprosium complexes, multiconfigurational spin-orbit calculations capture the full anisotropic exchange coupling, enabling the construction of effective exchange and crystal field Hamiltonians. The computed low-energy spectra and magnetic properties show close agreement with the experiment, clarifying the distinct ferro- versus antiferromagnetic ground states. This study provides a unified framework for quantifying and interpreting exchange in radical-bridged lanthanides, thereby advancing predictive design strategies for molecular magnetism.

Abstract In recent times all-metal aromaticity has arisen, challenging classical views of aromaticity. All-metal aromaticity invokes metal-metal bonding, but this remains rare for the actinides. Recently, one-electron trithorium superatom clusters exhibiting exalted diamagnetism and hence open-shell Jellium aromaticity have been reported. Those clusters complement closed-shell two-electron congeners, but computational assessments advanced conflicting interpretations. Here, we report one- and two-electron trithorium clusters that all exhibit exalted diamagnetism, demonstrating open- and closed-shell Jellium aromaticities. We show that these Jellium aromats exhibit non-linear magnetic responses, so a foundational assumption of ring current calculations is not met, accounting for the experimental-computational disagreement. This work suggests that while π-aromaticity results from preorganized coherent wave functions, for σ-aromats there may be an electronic reorganization barrier to cohesive wave functions and Jellium aromatic ring currents. This work demonstrates the importance of caution when using ring current calculations to assign aromatic character if the experimental magnetic response is not understood.

Zintl clusters have recently emerged as competent catalysts for a variety of organic transformations. Herein, we report the mechanism of functionalized Zintl-cluster-catalyzed hydroboration of pyridine and subsequent analysis of the energetic profile of this catalytic cycle, employing the energetic span model to identify key states that underpin the catalytic activity and observe how these states and other properties of the cycle change for several catalyst analogues. We also explore the effect of entropy, and how it is computed in solution, in determining the energetics and kinetics of the target systems.

Long-chain nitrogen ions and radicals ([Nn]x+/[Nn]x-, n > 3) are naturally occurring under the intense radiative conditions of the Earth's ionosphere and those of other planetary bodies. However, the strong thermodynamic driving force to lose N2 renders these types of molecule extremely reactive under ambient conditions such that they can typically be studied only under extreme conditions, for example, at ultrahigh pressures (10 GPa to >200 GPa). Here we report the isolation of a series of five molecules featuring metal unsupported {N4}•- units under ambient conditions, with one derivative demonstrating remarkable multi-week long persistence in the solid state. Spectroscopic, crystallographic and computational studies provide insight into the bonding across the {N4}•- chain. Reactivity studies reveal that the chain can cleave into N1 and N3 fragments, and can act as a source of nitrene radical anions, an observation that such molecules could act as storable nitrogen group transfer reagents.

The concept of covalency in chemical bonding is well established, but there are few methods to experimentally measure covalency, and none is a panacea. Quantum crystallography X-ray charge density determination could be the most powerful method for experimentally visualizing chemical bonding, but its stringent requirements have prevented routine implementation. Hirshfeld atom refinement (HAR) has begun to emerge as an alternative, potentially more accessible quantum crystallography approach for experimentally visualizing covalency, but its use has remained limited with heavy elements such as actinides due to challenges in partitioning and modeling core and valence electron densities in relativistic regimes. Here, we apply HAR to two extreme test cases of clusters containing three proximate heavy actinides exhibiting multi-center thorium-thorium bonding. We demonstrate exceptional agreement between experimental HAR and purely density functional theory analyses, thus visualizing the thorium-thorium bonding and paving the way to more routine use of experimental HAR visualization of chemical bonding.

p-Block complexes containing unsupported metal–metal bonds can activate small molecules via mechanisms that complement and contrast with those of d-block metal complexes. Within this compound class, Al–Zn heterobimetallics have shown a remarkable ability to cooperatively activate heteroallenes by migratory insertion into the Al–Zn bond. Here we report the synthesis of a new family of heterobimetallic Al–Zn complexes [(ArNacnac)Zn–Al(Cp*)(X)] (Ar = Dep, X = Cl (2a), Br (2b), I (2c); Ar = Dipp, X = Cl (3a), Br (3b); ArNacnac = {HC[C(Me)N(Ar)]2}; Ar = Dep, C6H3Et2-2,6; Dipp, C6H3iPr-2,6), by insertion of in situ-generated “AlCp*” (Cp* = C5Me5) into the Zn–X bonds of parent dimeric zinc ArNacnac halide complexes [Zn(ArNacnac)(μ-X)]2. These complexes were characterized by NMR and ATR-IR spectroscopy, elemental analysis, single crystal X-ray diffraction, and density functional theory calculations. We find that the reactions of the newly formed Al–Zn complexes with N,Nʹ-dicyclohexylcarbodiimide (DCC) proceed by migratory insertion into the Al–Zn bond to give [Zn(ArNacnac){μ2-C(NCy)2-κ1-C,κ2-N,Nʹ}Al(Cp*)(X)] (Ar = Dep, X = Cl (4a), Br (4b), I (4c); Ar = Dipp, X = Cl (5a), Br (6a)) as expected, but surprisingly for the DippNacnac derivatives a second equivalent of DCC inserts into the Al–Cp* moiety to afford [Zn(DippNacnac){μ2-C(NCy)2-κ1-C,κ2-N,Nʹ}Al(Cl){κ2-(NCy)2C-η1-Cp*-κ2-N,Nʹ}] (5b) or [Zn(DippNacnac)(Br){μ2-C(NCy)2-κ1-C,κ2-N,Nʹ}Al{κ2-(NCy)2C-η1-Cp*-κ2-N,Nʹ}] (6b); for 6b concomitant halide migration gives a Zn–Br bond. These surprising results show that non-innocent reactivity of Al–Cp*, widely assumed to be a spectator ligand in heterobimetallic complexes, can be switched on by subtly tuning ligand steric bulk about Al–Zn bonds.

Nitrous oxide (N2O) is sometimes referred to as the forgotten greenhouse gas, but ignoring it would be a mistake. N2O has a greenhouse warming potential 300× that of CO2, and anthropogenic emissions are increasing. Yet, compared to CO2, homogeneous catalysts that mediate its reduction are scarce. We present a range of cluster catalysts based on abundant and inexpensive p-block elements that mediate the conversion of N2O to environmentally benign N2. The catalysts studied offer many critical advantages, and systems can be tuned for performance, recyclability, selectivity, air stability, and commercial availability. Pnictogen clusters present themselves as a general platform in N2O reduction chemistry, and control reactions confirm that these clusters offer access to reactivity that simple monopnictogen molecules do not. Mechanistic investigations reveal that the low-valent clusters can access a -1/+1 redox couple, which goes beyond classical main group redox couples and will unlock a vault of hitherto unknown chemical space.

Nanoparticulate ferrihydrite (Fh) has a strong affinity towards environmental contaminants, particularly radionuclides. Recently, Pu(IV) was found experimentally to form a tetradentate inner-sphere surface complex with Fh, motivating the present study of the interaction of Pu(IV) with Fh(100), Fh(110) and Fh(120) surfaces using DFT+Ueff. Prior to introduction of Pu(IV), we first discuss the effects of spin arrangement and the choice of Ueff on bulk Fh. The relaxed lattice parameters agree well with previous experiments and simulations, and band gaps (direct/indirect) are determined. The work function, bare and hydrated surface energies of the three terminations are in agreement with previous studies, though we highlight the need for further experimental work in this area. Multidentate binding to the Fh surfaces is highly favorable, with Pu(IV) surface complexation energies significantly exothermic (-3.01 to -6.24 eV). Average Pu-O and Pu-Fe distances are within 0.31 Å of EXAFS measurements, for the lowest energy complexes. Pu(IV) binding is tetradentate on Fh(110) and Fh(120) and tridentate on Fh(100). Surface complex stability depends on the charge of the Pu, indicating primarily ionic Pu-O bonds, though Pu(f) and O(p) states hybridise in the bonding region of the valence band. The Pu-O interactions are determined as partially covalent using the quantum theory of atoms in molecules, consistent with our previous findings for Pu(IV) bound to the Fe13 Keggin cluster. Our work supports recent experimental evidence that Pu(IV) uptake begins via the Keggin and remains bound through transformation to Fh.

Incorporation of actinide species into iron (oxyhydr)oxides could present an environmentally secure method for preventing the release of actinides over an extended period, as would be the case in a number of radioactively contaminated land situations including surface, near-surface, and subsurface disposal and storage. Uranium is known to incorporate into iron (oxyhydr)oxides, including goethite, in a number of valence states, but the atomistic structures of these processes are unclear. In particular, it is increasingly reported that iron-containing minerals can reductively incorporate and stabilize the +V state of uranium, an oxidation state that is known to be unstable with respect to disproportionation. Here, we use density functional theory within the Periodic Electrostatic Embedded Cluster Method to model U(IV), U(V), and U(VI) incorporation into the pristine and iron-vacancy [010] surface and near-surface region of goethite. Solvated and unsolvated surfaces are studied, and the role of electron transfer from the lattice to uranium ions is explored. Comparisons are made with published X-ray absorption spectroscopic data, and we conclude that, based on the expected conditions for surface and near surface storage sites, both U(VI) and U(V) would incorporate into goethite as it transforms from ferrihydrite, forming two distinct structural types. We find that U(VI) incorporated into goethite may be reduced to U(V), where electron transfer occurs from oxygens surrounding iron vacancies and the incorporated uranium, reducing the U(VI) species to U(V). Both U(VI) and U(V) can incorporate into the surface of goethite with an adjacent iron vacancy, or U(V) can uniquely incorporate into the structure within the near-surface region, containing local but not immediately adjacent iron vacancies for charge compensation. Both of these incorporation schemes are little affected by the presence of a monolayer of surface water, suggesting that incorporation into goethite is a viable method to prevent uranium release into the aqueous surroundings.

Np- and Am-substituted surfaces were constructed from the stoichiometric PuO2 {110} surface. Density functional theory simulations reveal the effects of neighboring Np and Am atoms, and their influence on the Pu 5f-band properties is analyzed. Linear relationships are observed between the 5f-band properties and the number of neighboring Np or Am atoms. Small molecules (water and nitric oxide) were used as probes, and their adsorption behaviors were compared across the substituted surfaces. Notable correlations are found between the 5f-band properties and adsorption energies. These findings suggest the potential to develop an f-band theory for actinides analogous to the well-established d-band theory for transition metals.

We present a detailed comparative study of the lattice thermal conductivity κ_latt of ten reported phases of the IV-VI chalcogenides GeSe, GeTe, SnSe and SnTe, calculated within the single-mode relaxation-time approximation based on third-order interatomic force constants. Differences in κ_latt are attributed quantitatively to the phonon group velocities and lifetimes, and differences in the lifetimes are further attributed to the averaged three-phonon interaction strengths and the “phase space” of allowed energy- and momentum-conserving scattering pathways. Our analysis reveals a complex dependence of the κlatt on the crystal structure: structures that constrain the tetrel atoms to locally-symmetric environments show strong phonon anharmonicity and short lifetimes, but in simple structures such as the rocksalt phase these are counterbalanced by large group velocities and a smaller phase space. We find that these competing effects are optimised for orthorhombic Cmcm SnSe, resulting in the lowest predicted κlatt across the ten systems examined. Our findings provide new insight into the interplay between crystal structure and lattice thermal conductivity, and allow us to propose some new guidelines for how to optimise the thermal transport of the IV-VI chalcogenides through crystal engineering.

Cross-coupling strategies involving strain release have gained significant recent attention for the construction of complex molecular frameworks, particularly in the context of preparing bioisosteres for medicinal chemistry. While the reactivity of cyclopropanes and bicyclo[1.1.0]butanes (BCBs) has been extensively studied, higher homologues are emerging as valuable substrates for synthesis. For example, methods for the fragmentation and coupling of bicyclo[2.1.0]pentane, or housane, ketones show promise but are currently limited in substrate scope. Here, we describe a mild, atom-economical, samarium diiodide (Sml2)-catalyzed fragmentation and coupling of alkyl and aryl housane ketones with alkenes that grants access to functionalized norbornane structural motifs, not easily accessible by classical cycloaddition approaches, and with considerable potential for further manipulation.

We report quantum chemical investigations of metal-metal bonding in molecular thorium clusters and compare them with cerium and group IV transition metal analogues. We explore periodic trends in metal-metal bonding and the roles of electron delocalization, orbital diffuseness, and oxidation state. As cluster size increases in the series [{Th(η8-COT)Cl2}nK2] (COT = C8H8, n = 2-5, 2-5) and [Th4Cl4(η8-COT)4]2+ (T), n-center-2-electron bonding weakens. Quantum theory of atoms in molecules (QTAIM) analysis finds Th-Th bond paths only in 2 and 3, while T exhibits a non-nuclear attractor, indicating charge concentration in the [Th4Cl4]10+ core. In the Ce analogues, Ce-Ce bonding is observed only in oxidation states below +3. Calculations on [Ce3Cl6]z (z = 1-3) and Cp-stabilized analogues show Ce-Ce bond shortening with increasing population of the 3-center MOs. The QTAIM confirms Ce-Ce bond paths in [Ce3Cl6]+, [Ce3Cl6(η5-Cp)3]-, and [Ce3Cl6(η5-Cp)3K2]. Group IV analogues reveal variations in metal-metal bonding on progressing from the contracted 3d AOs of Ti to the more diffuse 6d AOs of Rf. In [M3Cl6(η8-COT)3K2] (3-M), only 3-Rf exhibits QTAIM bond paths similar to the Th analogue, suggesting that only the 6d orbitals are sufficiently diffuse as to support such interactions.

Quantum-confined nanoclusters can be described by the jellium model, which emphasizes closed-shell electron configurations, but an open-shell variation with jellium aromaticity has been proposed. Such clusters are termed superatoms because they behave like an atom, and they exhibit unusual properties. Superatoms feature metal-metal bonding; hence, since their discovery 40 years ago, superatoms have exclusively involved main group or transition metals, with actinides only considered computationally as dopants owing to actinide-actinide bonding being exceedingly rare. Here we report trithorium nanoclusters exhibiting three-centre-one-electron actinide-actinide bonding. Experimental and computational analysis demonstrates Robin-Day Class III 6d-orbital valence delocalization in these clusters. These S = 1/2 clusters are paramagnetic, but in external applied magnetic fields they exhibit exalted diamagnetism, evidencing actinide open-shell jellium aromaticity superatom character. Exalted diamagnetism is not normally associated with a single unpaired electron, but with a 1S1 magic number, the valence delocalization enables exalted diamagnetism, which is aromaticity, via superatom ring currents.