Molecular single-bond covalent radii for elements 1-118

Synthesis of heteropnictogen ligands via PI transfer

The heterodipnictogen complexes [{CpMo(CO)2}2(μ,η2:2-PE)] (E = P, As, Sb) react with the phosphorus(I) transfer reagent [(BZIMPY)P][CF3SO3] (BZIMPY = 2,6-bis(benzimidazole-2-yl)pyridine) in a transmetallation reaction forming the unprecedented [CpMo(CO)2(η3-P2E)] complexes.

Neutral All-Metal σ-Aromaticity in a Rhombic Cluster

Aromaticity is a cornerstone concept in chemistry, playing a crucial role in understanding molecular stability and reactivity. Traditionally, aromaticity has been primarily associated with cyclic planar conjugated organic molecules composed solely of carbon, but it has recently expanded to include metal-containing systems. However, metal-only aromatics remain extremely scarce. Here, we present the first neutral all-metal aromatic cluster with a rhombic geometry. X-ray crystallography reveals that the rhombic Al2Pd2 core is stabilized by an innovative double-layer N-P ligand framework, featuring essentially the same Al-Pd bond lengths (2.4706(4) and 2.4636(4) Å) and two planar tetracoordinate Al centers. Quantum chemical calculations provide compelling evidence for the two-electron σ-aromaticity in this molecule. Further research on the reactivity of the σ-aromatic Al2Pd2 cluster reveals that it can accept lone-pair electron coordination and act as a two-electron reducing agent. This study not only extends the concept of aromaticity to neutral all-metal rhombic systems but also opens new horizons for the synthesis and exploration of novel all-metal aromatic clusters.

Reactivity of an arsanyl-phosphagallene: decarbonylation of CO2 and COS to form phosphaketenes

The synthesis of an arsanyl-phosphagallene [H2CN(Dipp)]2AsP[double bond, length as m-dash]Ga(NacNac) (NacNac = HC[C(Me)N(Dipp)]2; Dipp = diisopropylphenyl) and its reactivity towards heterocumulenes and ketones is described. Reactions with azides, carbodiimides, isocyanates and ketones give rise to heterocycles via cyclization reactions involving the Ga[double bond, length as m-dash]P π-bond (with the Ga-P σ-bond remaining unperturbed in the final products). By contrast, reactions with CO2, CS2 and COS are more intriguing, revealing a reactivity profile in which the phosphorus atom can abstract carbon monoxide from the oxygen-containing heterocumulenes. These reactions result in the formation of gallium phosphaethynolate compounds. Such reactivity is enabled by the presence of a weakly Lewis basic arsanyl moiety which, in contrast to other related compounds featuring phosphanyl groups, is insufficiently nucleophilic to play a role in frustrated Lewis-pair like reactivity.

Transient Dangling Active Sites of Fe(III)-N-C Single-Atom Catalyst for Efficient Electrochemical CO2 Reduction Reaction

The Fe single-atom catalyst (SAC) with an oxidation state of III anchored on the N-doped carbon substrate (Fe(III)-N-C) delivers superior activity for catalyzing the electrochemical CO2 reduction reaction (eCO2RR) to produce CO, but its mechanism remains contentious and the commonly adopted FeN4-C model is not a conformant model for Fe(III)-N-C but for Fe(II)-N-C. Herein, employing the grand-canonical ensemble modeling with the density functional theory method benchmarked against the high-level wavefunction theory method, we first identify the conformant model for Fe(III)-N-C to be FeN1C3-C, and we then unveil that the Fe(III)N1C3-C SAC generates a novel type of dangling active site transiently under working conditions, in which the Fe single-atom leaves from the anchoring site by breaking all the Fe-C bonds but retains a stable binding to the substrate by the Fe-N bond. Thus, we further elucidate that this flexible dangling active site of Fe(III)-N-C renders a convoluted reaction network with facile CO2 activation, which delivers superior activity for eCO2RR. Our findings provide a novel understanding of the structure-activity relationship for Fe-N-C and concrete insights into the design of highly active SACs.

Titanium Phosphinidene and Phosphide Moieties from Oxidative Phosphorylation and Desilylation

A unique entry into mononuclear titanium complexes bearing phosphinidene and phosphide ligand moieties is reported. Reaction of [K(crypt)][(PN)2TiCl] (1, crypt = 2.2.2-cryptand) with [Na(OCP)] results in [K(crypt)][(PN)2Ti(OCP)] (2) and such species can be oxidized to the derivative [(PN)2Ti(OCP)] (3), both of which do not undergo decarbonylation. However, the reaction of 1 and [NaP(SiMe3)2] leads to an unprecedented TiIII phosphinidene, [K(crypt)][(PN)2Ti═PSiMe3] (4), through an oxidative phosphorylation reaction. To promote the formation of a Ti≡P bond, complex 4 was treated with 0.5 equivalent XeF2, resulting in an oxidative desilylation step forming a molecular titanium phosphide complex, [K(crypt)][(PN)2Ti≡P] (5), which showed a characteristic downfield chemical shift at 1449.8 pmm in the 31P NMR spectrum. Complex 5 can be further functionalized to generate a terminal TiIV phosphinidene, [(PN)2Ti═PSiMe3] (6), and the latter can be independently accessed through oxidation of 4. All new complexes were characterized structurally and as appropriate by multinuclear NMR, CW X-band EPR (for TiIII), and HFEPR (for TiII) spectroscopies.

Facet-dependent polaron stability in photocatalysis by SrTiO3: a constrained DFT study

Strontium titanate (SrTiO3 or STO) is one of the promising photocatalysts for sustainable energy applications. Using the density functional theory (DFT) calculations, we herein study the structural and electronic factors contributing to its high photocatalytic activity and facet dependence. The constrained DFT method revealed that the hole polarons in bulk and surface STO are localized primarily on oxygen atoms. In contrast, electron polarons in bulk STO tend to delocalize over oxygen atoms unless stabilized by oxygen vacancies. The stability of hole polarons is higher at the surface O site of the (110) surface compared to the (001) surfaces. In addition, the oxygen vacancy is stable specifically at the TiO2-terminated (001) surface. These findings provide an atomic-level insight into the relationship between polaron stability and facet dependence of photocatalysis, paving the way for the design of more efficient STO-based photocatalysts.

SUF4: A Terminal Monosulfido Complex of Uranium(VI) with a Linear SUF Moiety

Although there have been a few terminal sulfido complexes of uranium(VI) with either SUO or SUN moiety, it remains a question whether the terminal sulfido ligand can be stabilized in the absence of such multiply bound oxo or nitrido ligands. Herein, we report a terminal monosulfide complex of uranium(VI) in the form of SUF4 bearing a linear SUF moiety that was prepared via the reaction of laser-ablated uranium atoms with SF4 in cryogenic matrixes. On the basis of the results from infrared spectroscopy combined with density functional theory calculations at the B3LYP level, the SUF4 complex possesses a trigonal bipyramid structure with singlet ground state and nonplanar C3v symmetry where the terminal sulfido ligand is stabilized by the monovalent fluoro ligand trans to sulfur. A triple U-S bond with a positively charged sulfur atom was identified according to the natural bond orbital analysis. Inverse trans influence is present in SUF4 as revealed by the difference in bond length between U-Faxial from the linear SUF moiety and U-Fequatorial from the UF3 equatorial plane, which is further supported by bonding analysis.

Harnessing transient CAAC-stabilized mesitylborylenes for chalcogen activation

Newly synthesized adducts of CAAC-bound mesitylborylene with carbon monoxide (CO) and trimethylphosphine (PMe3) are established as efficient precursors for the in situ generation of the dicoordinate borylene [(CAAC)BMes] (CAAC = cyclic(alkyl)(amino)carbene), as demonstrated by their ability to activate elemental chalcogens. Upon thermal or photolytic activation, these precursors readily react with sulfur and selenium, yielding boron chalcogenides characterized by terminal boron-chalcogen double bonds. In contrast, the reaction with tellurium leads to the formation of an unusual diradical ditelluride species with a Te-Te bond. Quantum chemical calculations of its electronic structure indicate an open-shell singlet ground state characterized by significant diradical character. Further investigations into the redox behavior of these boron chalcogenides reveal intriguing transformations, including the redox-induced formation and cleavage of E-E bonds.

Flash Communication: Pd2Zn2 Clusters from the Reduction of Palladium(II) Dichloride Precursors with Metallic Zinc

We report the synthesis and solid-state characterization of two unusual Pd2Zn2 clusters formed from the partial reduction of [PdL2Cl2] precursors (L2 = dcpe or dppe) with metallic zinc. The new clusters have been characterized by single crystal X-ray diffraction and contain a Pd2Zn2Cl3 core capped by two chelating phosphine ligands with Zn in the formal +1.5 oxidation state. While they possess a near tetrahedral arrangement of metal ions, calculations and bonding analysis (NBO, AIM) suggest that there is limited Zn- - -Zn bonding in these species. Characterization in the solution state is suggestive of dynamic behavior on dissolution, with both diamagnetic and paramagnetic species observed by NMR and EPR spectroscopy. One of these Pd2Zn2 clusters was shown to be an effective precursor for the homocoupling of an aryl bromide.

Crystalline Arylstibinidene Chalcogenides: Heavier Congeners of Aromatic Nitroso Compounds

Nitroso compounds, R-N═O, containing N═O double bonds are ubiquitous and widely utilized in organic synthesis. In contrast, heavier congeners of nitroso compounds, namely pnictinidene chalcogenides R-Pn = E (Pn = P, As, Sb, Bi; E = O, S, Se, Te), are highly reactive and scarce. They have been stabilized in the coordination sphere of Lewis acid/base or by pronounced contribution from resonance structures, whereas free species with unperturbed pnictogen-chalcogen double bonds remains elusive. In this work, we report the isolation and characterization of arylstibinidene chalcogenides, which are the first heavier congeners of aromatic nitroso compounds. They are facilely synthesized through the salt metathesis reactions of aryldichlorostibane and dilithium chalcogenides. They bear unperturbed Sb═E (E = S, Se and Te) double bonds due to poor orbital overlap between the C 2p orbitals of the phenyl ring of the substituent and the Sb 5p orbitals. Moreover, they show versatile reactivity, including acting as chalcogen atom transfer reagents and reacting with small molecules via (cyclo)addition.

[Co3@Ge6Sn18]5-: A Giant σ-Aromatic Cluster Analogous to H3+ and Li3. J Am Chem Soc 2025;147:9407-9414. [PMID: 40042471 DOI: 10.1021/jacs.4c16401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Aromaticity is one of the most important concepts in chemistry and has been successfully extended to all-metal clusters. However, the study of all-metallic aromatic clusters remains in its early stages, with σ-aromatic clusters mostly limited to small sizes (≤12) that often require external stabilization. In this work, we report the first Ge/Sn-based trimer, [Co3@Ge6Sn18]5-, which can be rationalized as the fusion of three [Co-@Ge3Sn64-] units via a Ge3 face. Theoretical studies have revealed that two σ-electrons are delocalized across the entire trimer, with the spherical aromaticity of each [Co@Ge3Sn6] unit and the global σ-aromaticity of [Co3@Ge6Sn18]5- further supported by its electron delocalization and magnetic behavior. As a result, this trimer can be viewed as a giant σ-aromatic counterpart to triatomic H3+ and Li3+. Our findings suggest the potential for synthesizing cluster-of-cluster analogs of discrete all-metallic aromatic species, such as Al42-, and further enhance our understanding of chemical bonding.

Stabilization of Sb4 Tetrahedra in Paramagnetic Transition Metal Carbonyl Complexes

We present a straightforward synthetic route to the novel chromium carbonyl-stabilized paramagnetic Sb4-based cluster [Et4N]4[Sb4Cr6(CO)28] ([Et4N]4[1]), which represented a rare example of the intact Sb4 tetrahedron structurally characterized in the solid state. Complex 1 exhibited versatile reactivities toward groups 7-9 metal carbonyls, dioxygen, or [Cu(MeCN)4][BF4] to form selective orbital-controlled Sb4-based products, including transmetalated paramagnetic complexes [Et4N]4[Sb4Cr5Mn(CO)28]Br ([Et4N]4[1-Mn]Br), [Et4N]4[Sb4Cr2Fe6(CO)30] ([Et4N]4[1-Fe]), and [Et4N]2[Sb4Cr4Co4(CO)31] ([Et4N]2[1-Co]), the dioxygen-activated paramagnetic cluster [Et4N]4[O2Sb4Cr6(CO)28] ([Et4N]4[1-O2]), or the spin-quenched complex [Et4N]2[Sb4Cr6(CO)28] ([Et4N]2[2]), respectively. The structural nature, bonding properties, paramagnetism, and semiconductivity of these unprecedented transition metal carbonyl-protected Sb4-based clusters were further realized with DFT calculations.

Carbene-activated stannylenes to access selective C(sp3)-H bond scission at the steric limit

The ubiquity of N-heterocyclic carbenes (NHCs) in diverse areas of chemical research typically arises from their potent stabilising capabilities and role as innocent spectators to stabilise otherwise non-bottleable compounds and complexes. This has, until now, been particularly true for NHC-stabilised stannylenes, with no exceptions reported thus far. Herein, we demonstrate that the combination of heteroleptic terphenyl-/amido-based stannylenes and tetra-alkyl substituted NHCs renders the corresponding NHC-ligated stannylenes highly reactive, yet isolable. In solution, this induces sterically controlled inter- and intramolecular C(sp3)-H bond scissions, resulting in the selective formation of stannylene metallocycles that depend on both the NHC source and the meta-terphenyl ligand coordinated to tin.

Matrix Isolation of the Arsinoborene F2B-As═BF with an As═B Double Bond Character

We report on the generation of F2B-As═BF, an arsinoborene (boranylidenearsane) with a genuine As═B double bond, where both the As and B atoms are two-coordinate. It was obtained from the reaction of AsF3 with laser-ablated boron atoms under cryogenic conditions in neon and argon matrices. In addition, the single-bonded arsenic-boron radicals FB-AsF2 and F2B-AsF were characterized. These species were identified by infrared spectroscopy and 10/11B isotope substitution in conjunction with quantum-chemical calculations at the B3LYP and CCSD(T) levels of theory. The isomerization from FB-AsF2 to F2B-AsF can be triggered by irradiation with ultraviolet light (λ = 275 nm) in argon. This discovery of the arsinoborene F2B-As═BF further extends the series of multiple-bonded systems between heavy main group elements and boron.

Noble metal (Pd, Pt)-functionalized WSe2 monolayer for adsorbing and sensing thermal runaway gases in LIBs: A first-principles investigation

This research using the first-principles theory introduces Pd- and Pt-functionalized WSe2 monolayers as promising materials for detecting three critical gases (H2, CO, and C2H4), to evaluate the health of Li-ion battery (LIBs). Various sites on the pristine WSe2 monolayer are considered for the functionalization with Pd and Pt atoms. The adsorption performances of the determined Pd- and Pt-WSe2 monolayers upon the three gases are analyzed by the comparative highlight of the adsorption energy, bonding behavior and electron transfer. Subsequently, an examination of the electronic properties of these monolayers uncovers their semiconducting nature and sensing mechanisms, while the sensing responses are quantified based on variations in their bandgaps. Furthermore, the practical applications of these monolayers are confirmed by assessing their recovery properties. The findings in this study concretely serve the Pd-WSe2 monolayer as a promising CO and C2H4 gas sensor, and the Pt-WSe2 monolayer as an optimal for H2 gas sensor. These findings not only underscore the promising sensing potential of WSe2-based materials for indicating thermal runaway in LIBs, but also emphasize the critical importance of metal selection for surface-functionalization on the nano-surface in the gas sensing technologies.

A first-principles study of SOF2 and SO2F2 adsorption onto PdSe2-based monolayers: Favorable sensitivity and selectivity by doping single Cu or Rh atom

In this first-principles study, we simulate the adsorption of SOF2 and SO2F2 molecules on the pristine, Cu- and Rh-doped PdSe2 monolayer, in order to explore their potentials as novel gas sensors for status evaluation of the SF6-insulation devices. Single Cu or Rh atom is doped by the replacement of a Se atom within the PdSe2 surface, with the formation energy of 0.40 and -0.62 eV, respectively. Compared with the weak interactions between the pristine PdSe2 monolayer and two gas species with little potential for gas sensing application, Cu-PdSe2 monolayer behaves stronger physisorption and Rh-PdSe2 monolayer conduct more favorable chemisorption upon two gases. The adsorption characteristic, charge density difference, band structure and density of states of various adsorption configurations are systemically analyzed to understand the gas-surface interactions. Results indicate that Pd-PdSe2 monolayer, rather than the Cu-doped counterpart, is a promising resistive gas sensor with good sensitivity and selectivity for detection of SOF2 and SO2F2. The analysis of work function in gas adsorbed Cu- and Rh-PdSe2 systems reveals their strong potential for the development of Schottky gas sensors upon two gases with high and tunable sensitivity and specificity. These findings in this work hold significant meanings for typical gas detection to evaluate the operational status of SF6-insulated devices. It is hopeful that this work can stimulate more edge-cutting investigations on the PdSe2-based gas sensor for application in some other fields.

Shapeshifting Gabriel Amine Synthesis with Iodo-BCPs

The Gabriel amine synthesis is a textbook method for the preparation of primary amines from alkyl halides. In this work, we demonstrate a Gabriel amine synthesis with iodo-bicyclopentanes to make aminomethyl bicyclobutanes. DFT studies support the concerted rearrangement of a bicyclo[1.1.1]pentyl to a bicyclo[1.1.0]butyl carbocation, initiated by a carbon-halide dissociation. A carboxamide substituent stabilizes the carbocation intermediate with anchimeric assistance.

Synthesis and Catalytic Activity of Thorium Nitride Complex from Dinitrogen Reduction

Metal nitride species are recognized as key intermediates in the conversion of dinitrogen (N2) to ammonia (NH3). In this work, we report the isolation of a multimetallic nitride-bridged thorium complex (2) by completely cleaving the N≡N triple bond of N2. The complex was synthesized through the reduction of a thorium precursor, {N[CH2CH2N-PiPr2]3ThCl}2 (1) and chromium dichloride (CrCl2) using potassium graphite (KC8) under an N2 atmosphere. Isotopic labeling with 15N2 confirms that the nitride in complex 2 originates from N2. Under ambient conditions, complex 2 exhibits remarkable catalytic activity, converting N2 to silylamine with yields of up to 9.9 equiv per thorium molecular catalyst. This work not only represents the first isolation of a thorium nitride complex from N2 reduction but also provides a rare example of N2 functionalization promoted by an actinide catalyst.

Cationic Polyhedral Chalcogenaboranes: Activation without breaking Wade's Rules

Wade's rules are a well-established tool for the description of the geometry of inorganic clusters. Among others, they state that a decrease or increase in charge is always accompanied by a change in the number of skeletal electron pairs (SEPs). This work reports the synthesis of the first cationic chalcogenaboranes closo-[12-X-2-IPr-1-EB11H10]BF4 (IPr=1,3-(2,6-iPr2C6H3)-imidazole-2-ylidene; X=H, I; E=S, Se 3 a/b, 4 a/b) featuring the same SEP count as their neutral precursors, EB11H11, but bearing a positive charge. This ionisation significantly enhances the activity towards the electrophiles. It unlocks reactivity with very weak bases and offers the control of the regioselectivity towards hard/soft bases by the modulation of LUMO. The localisation of the positive charge within the borane cluster has been confirmed experimentally, spectroscopically and theoretically.

A framework for designing main-group single-molecule magnets

Single-molecule magnets (SMMs) are molecular entities with strongly anisotropic magnetic moment. As a result, SMMs display slow relaxation of magnetization at the macroscopic scale. Up to date all experimentally characterized SMMs are based on either d- or f-block metals with lanthanides proving to be the most successful. In the present work, a framework for constructing SMMs consisting purely of main-group elements will be outlined by computational and theoretical means. The proposed main-group SMMs utilize the strong spin-orbit coupling of a single heavy p-block atom or ion that can lead to strong magnetic anisotropy and pronounced SMM properties. A theoretical crystal-field model is developed to describe the magnetic properties of p-block SMMs with a minimal set of parameters related to the chemical structure of the SMMs. The model is used to establish which p-block elements and oxidation states can lead to SMM behavior. A large number of model structures are studied to establish general features of optimal chemical structures. These include one- and two-coordinate structures involving ligands with different coordination modes and all group 13 to 17 elements in periods 4 to 6. The results show that the most viable structures are based on mono-coordinated complexes of bismuth in oxidation state 0 with σ-donor ligands. Structures with bulkier ligands that sterically protect the bismuth atoms are then proposed as a starting point for the practical realization of main-group SMMs. The calculations show that minimizing the anagostic interactions with the bismuth atom is essential in the ligand design, which along with the low oxidation state of bismuth introduces significant synthetic challenges. The results do, however, show that main-group SMMs are plausible from a practical point of view within a limited set of heavier p-block elements in specific oxidation states. Furthermore, the proposed SMMs display much larger energy barriers for the relaxation of magnetization than even the best lanthanide-based SMMs do. This indicates that it is possible that main-group SMMs can supersede even the best currently known SMMs based on d- or f-block elements.

Determination of Structural Factors Contributing to Protection of Zinc Fingers in Estrogen Receptor α through Molecular Dynamic Simulations

The ERα transcription factor that induces tumor growth is a potential target for breast cancer treatment. Each monomer of the ERα DNA-binding domain (ERαDBD) homodimer has two conserved (Cys)4-type zinc fingers, ZF1 (N-terminal) and ZF2 (C-terminal). Electrophilic agents release Zn2+ by oxidizing the coordinating Cys of the more labile ZF2 to inhibit dimerization and DNA binding. Microsecond-length molecular dynamics (MD) simulations show that greater flexibility of ZF2 in the ERαDBD monomer leaves its Cys more solvent accessible and less shielded from electrophilic attack by sulfur-centered hydrogen bonds than ZF1 which is buried in the protein. In the unreactive DNA-bound dimer, the formation of the dimer interface between the highly flexible D-box motif of ZF2 decreases the solvent accessibility of its Cys toward electrophiles and increases the populations of sulfur-containing hydrogen bonds that reduce their nucleophilicity. Examination of these factors in ERαDBD and other proteins with labile ZF motifs may reveal new targets to treat viral infections and cancer.

Lithium Anionic Dicarbenes or Acetylides: What is in the Name?

The two-fold deprotonation of the C2-arylated 1,3-imidazolium salts (IPr-Ar)X (1-Ar)X (IPr-Ar = ArC{N(Dipp)CH}2; Ar = Ph, 4-Me2NC6H4 (DMP) or 4-PhC6H4 (Bp); Dipp = 2,6-iPr2C6H3) with nBuLi affords the so-called anionic dicarbenes Li(ADC) (2-Ar) (ADC = ArC{N(Dipp)C}2). 2-Ar can be used to prepare a variety of main group heterocycles, however their structures in the solid-state remained hitherto unknown. Herein reported single-crystal X-ray diffraction studies reveal an acetylide type [ArC{N(Dipp)}(Dipp)NC≡CLi)]n (3-Ar) dimeric (n = 2) or trimeric (n = 3) molecular structure for 2-Ar. Treatment of 3-Ph with Et3B cleanly yields the monoanionic carbene Li[(ADC)(BEt3)] (4-Ph) featuring a weakly coordinating anion embedded in the same molecular entity. 3-Ar readily undergo reactions with CO2 and N2O to form the ring-closing products Li[(ADC)(CO2)2] (5-Ar) and Li[(ADC)N2O] (6-Ar), respectively.

Side-on phosphinoboryl platinum(II) complexes

The oxidative addition of bromo(phosphino)boranes to platinum(0) compounds enabled the formation of platinum(II) complexes with unprecedented side-on coordination of the boryl ligand. The resulting complex underwent a reaction with carbon dioxide, leading to the insertion of a CO2 molecule into the B-P bond of the phosphinoboryl ligand.

Structural Snapshots on Stepwise Anionic Oxoborane Formation: Access to an Acyclic BO Ketone Analogue and Its Metathesis Chemistry with CO2 and CS2

In this work, we disclose the synthesis and characterization of non-acid/base-stabilized anionic oxoboranes [MesTer2BO][K(L)] (MesTer = -C6H3-2,6-(2,4,6-Me3-C6H2)2, L = [2.2.2]-cryptand or 18-crown-6), which are isoelectronic and isostructural with aryl-substituted ketones. The stepwise synthetic formation of these ion-separated oxoboranes is demonstrated on the one hand by the treatment of the parent borinic acid MesTer2BOH with N-heterocyclic carbenes (NHCs) to give [MesTer2BO][HNHC] derivatives, and on the other hand by a deprotonation-sequestration sequence. Bearing polarized boron-oxygen moieties, their inherent reactivity toward both carbon disulfide and carbon dioxide reveals a unique π-bond metathesis reactivity to yield [(MesTer)2B-μ-E2C=E][K(L)] (E = O, S) derivatives.

Observation of the Smallest Three-Dimensional Neutral Boron Cluster

Despite major progress in the investigation of boron cluster anions, direct experimental study of neutral boron clusters remains a significant challenge because of the difficulty in size selection. Here we report a size-specific study of the neutral B9 cluster using threshold photoionization with a tunable vacuum ultraviolet free electron laser. The ionization potential of B9 is measured to be 8.45±0.02 eV and it is found to have a heptagonal bipyramid D7h structure, quite different from the planar molecular wheel of the B9 - anionic cluster. Chemical bonding analyses reveal superior stability of the bipyramidal structure arising from delocalized σ and π bonding interactions within the B7 ring and between the B7 ring and the capping atoms. Photoionization of B9 breaks the single-electron B-B bond of the capping atoms, which undergo off-axis distortion to enhance interactions with the B7 ring in the singlet ground state of B9 +. The single-electron B-B bond of the capping atoms appears to be crucial in stabilizing the D7h structure of B9. This work opens avenues for direct size-dependent experimental studies of a large variety of neutral boron clusters to explore the stepwise development of network structures.

Probing the structural transformation and bonding of metal-boride clusters MB3 (M = La, Ta, Re, Ir)

Theoretical investigations using density functional theory (DFT) and ab initio wavefunction theory (WFT) have been performed to understand the geometric and electronic structures, chemical bonding, and structural transformation of 5dx6s2-metal doped triboron clusters MB3 (M = La, Ta, Re, Ir; x = 1, 3, 5, 7). Global-minimum structural searches find that early-metal doped MB3 (M = La, Ta) clusters adopt a two-dimensional (2D) planar structure, with σ- and π-type delocalized molecular orbitals (MOs) consisting of M-5d and B-2p atomic orbitals (AOs) identified by chemical bonding analysis. In contrast, late-metal doped MB3 (M = Re, Ir) clusters prefer three-dimensional (3D) structures of near-pyramidal and triangular pyramid geometries, respectively, which exhibit enhanced stability involving σ- and δ-type M(5d)-B(2p) interactions. The M-B bonding in the Re and Ir borides is more covalent than the La and Ta ones due to less charge transfer and similar orbital energies of late 5d-metals and boron. Moreover, the Jahn-Teller effect leads to MO mixing and electron redistribution, thus enlarging the HOMO-LUMO gaps. This work provides insights into the nature of the structural stability in triboron clusters induced by metal doping.

Annulated carbocyclic gallylene and bis-gallylene with two-coordinated Ga(i) atoms

The first carbocyclic gallylene [(ADC)2Ga(GaI2)] and bis-gallylene [(ADC)Ga]2 (ADC = PhC{N(Dipp)C}2; Dipp = 2,6-iPr2C6H3) featuring a central C4Ga2 ring annulated between two 1,3-imidazole rings are prepared by KC8 reductions of [(ADC)GaI2]2. Treatment of [(ADC)Ga]2 with Fe2(CO)9 affords complex [(ADC)GaFe(CO)4]2 in which each Ga(i) atom serves as a two-electron donor. [(ADC)Ga]2 activates white phosphorus (P4) and the Csp2 -F bond of aryl fluorides (ArF) to yield compounds [(ADC)Ga(P4)]2 and cis-/trans-[(ADC)GaF(Ar)]2, respectively. [(ADC)Ga]2 undergoes oxidation with (Me2S)AuCl to give [(ADC)GaCl2]2, while with PhN[double bond, length as m-dash]NPh it forms [1 + 4]-cycloaddition product [(ADC)GaN(Ph)N[double bond, length as m-dash]C6H5]2 by the dearomatization of one of the phenyl rings.

Synthesis, characterization and functionalization of titanium κ1N amidinato complexes from carbodiimides

A series of titanium amidinato complexes were synthesized by stoichiometric insertion reactions of carbodiimides into bis(π-η5:σ-η1-pentafulvene)titanium complexes. NMR studies and single-crystal X-ray diffraction showed κ1N coordination of the former carbodiimides to the metal center. DFT calculations were performed, confirming the clear preference for a single nitrogen atom coordinating to the metal center with a high energy transition state for the formation of a chelating heteroallyl ligand. Depending on the pentafulvene ligand, additional insertion reactions of carbodiimides into the remaining Ti-Cexo bond were observed. This allows for a stepwise insertion of the corresponding carbodiimides and offers the possibility to further functionalize the complexes. The reactivity of the remaining pentafulvene ligand is further demonstrated in reactions with H-acidic and multiple bond substrates.

Nucleophilicity at copper(-I) in a compound with a Cu-Mg bond

Copper is ubiquitous as a structural material, and as a reagent in (bio)chemical transformations. A vast number of chemical reactions rely on the near-inevitable preference of copper for positive oxidation states to make useful compounds. Here we show this electronic paradigm can be subverted in a stable compound with a copper-magnesium bond, which conforms to the formal oxidation state of Cu(-I). The Cu-Mg bond is synthesized by the reaction of an N-heterocyclic carbene (NHC) ligated copper alkoxide with a dimeric magnesium(I) compound. Its identity is confirmed by single-crystal X-ray structural analysis and NMR spectroscopy, and computational investigations provide data consistent with a high charge density at copper. The Cu-Mg bond acts as a source of the cupride anion, transferring the NHC-copper fragment to electrophilic s-, p-, and d-block atoms to make known and new copper-containing compounds.

Accurate QM/MM Molecular Dynamics for Periodic Systems in GPU4PySCF with Applications to Enzyme Catalysis

We present an implementation of the quantum mechanics/molecular mechanics (QM/MM) method for periodic systems using GPU accelerated QM methods, a distributed multipole formulation of the electrostatics, and a pseudobond treatment of the QM/MM boundary. We demonstrate that our method has well-controlled errors, stable self-consistent QM convergence, and energy-conserving dynamics. We further describe an application to the catalytic kinetics of chorismate mutase. Using an accurate hybrid functional reparametrized to coupled cluster energetics, our QM/MM simulations highlight the sensitivity in the calculated rate to the choice of quantum method, quantum region selection, and local protein conformation. Our work is provided through the open-source PySCF package using acceleration from the GPU4PySCF module.

Redox Cycling with Tellurium. Si-H Bond Activation by a Lewis Superacidic Tellurenyl Cation

The C,N-chelated aryltellurenyl triflate [2-(tBuNCH)C6H4Te][OTf] (1) activates the Si-H bonds in the tertiary silanes R3SiH via umpolung of H- to H+ to give rise to the iminium salts (tBuN(H)CH)C6H4TeSiR3][OTf] (2R, R=Et, Ph (elusive) and R=Si(CH3)3 isolated; OTf=O3SCF3) comprising Te-Si bonds, which are capable of generating silyl triflates, R3SiOTf, under attack of a second equivalent of 1. The unprecedented Si-H activation was utilized in main group redox catalysis using p-quinones, which were converted into (silylated) hydroquinones.

Spectroscopy and Bonding Analysis of ArnBO+ (n = 1-3) Cations That Possess Argon-Boron Multiple Bonds

ArnBO+ (n = 1-3) complexes have been prepared and subjected to spectroscopic characterization in the gas phase. Mass-selected infrared photodissociation spectroscopy, in combination with theoretical calculations, reveals the coexistence of two nearly isoenergetic structural isomers in Ar2BO+. One isomer entails two equivalent Ar atoms chemically bound to BO+, while the other features an ArBO+ core ion accompanied by a weakly tagging argon atom. However, only the structure with an ArBO+ core ion was observed for the Ar3BO+ complex. Quantum chemical calculations using density functional theory and ab initio methods complement the experimental work. The calculations help to identify the spectroscopically observed cations whose equilibrium structures and bond dissociation energies are given. The electronic structure and bonding situation are analyzed with a variety of theoretical methods. The ArBO+ core ion is characterized as having an exceptionally strong Ar-B covalent bond with some multiple bonding character.

Open Sn Framework Structure Hosting Bi Guest atoms-Synthesis, Crystal and Electronic Structure of Na13Sn26Bi

The large variety of structures of Zintl phases are generally well understood since their anionic substructures follow bonding rules according to the valence concept. But there are also exceptions, which make the semiconductors especially interesting in terms of structure-property relationships. Although several Na-Sn-Pnictides with a variety of structural motives are known, up to this point no ternary compound in the Na-Sn-Bi system has been described. In this paper we present the Zintl-phase Na13Sn25.73Bi1.27 comprising a complex, open-framework structure of Sn atoms, with one mixed Sn/Bi site, hosting Na atoms. An additional Bi atom is loosely connected with only weak contacts to the framework filling a larger cavity within the network. According to band structure calculations of the two ordered variants with either full occupation of the mixed site with Sn or Bi, resulting in Na13Sn26Bi and Na13Sn24Bi3, respectively, both compounds are semiconductors with band gaps of 0.5 eV. A comparison of the band structures with the structurally related binary compounds Na5Sn13 and Na7Sn12 shows that only the perfectly charge balanced Na7Sn12 is a semiconductor whereas Na5Sn13 is metallic. The rather specific electronic situation in the ternary compound is traced back to the loosely bound Bi atom, which acts as a guest atom according to Bix@Na13Sn26-yBiy, with x=1 and y=0.27, capable to change its oxidation state and thus to uptake additional electrons allowing the system to be a semiconductor. Therefore, Na13Sn25.73Bi1.27 can be understood as a rare example of an open framework structure of Sn atoms comprising Bi atoms in the cavities.

Planar Pentacoordinate Halogens

Planar hypercoordinate motifs represent an intriguing frontier in chemistry, challenging traditional bonding norms. As electronegativity of the central atom increases, achieving planar hypercoordination becomes more difficult due to restricted delocalization, making the design of planar hypercoordinate halogens particularly puzzling. Here, we conduct an extensive computational survey of LinXn+1 - (n=4, 5, 6; X=F, Cl, Br, I) clusters, revealing a starlike D5h-symmetry global minimum in Li5X6 - (X=F, Cl, Br) with a planar pentacoordinate halogen (ppX), where X- is located at the center of Li5X5 crown. The clusters are stabilized predominantly through electrostatic interactions between X- and Li5X5, complemented by weak covalent bonding from dative interaction. Due to the weak orbital overlap, ppX clusters exhibit localized diatropic ring currents around X and Li.

Planar Tetracoordinate Silicon in Si3Cu3 - Cluster

Photoelectron spectroscopy and theoretical calculations have identified the global minimum structure of the 16-valence electron Si3Cu3 - cluster, which features a planar tetracoordinate silicon (ptSi) in a rhombic arrangement. The Si3 and Cu3 triangles are interconnected by a Si2/Cu2 edge, forming an ordered chain-like structure. Besides the conventional 2c-2e σ-bond connecting Si3 and Cu3, the stability of this cluster is reinforced by a delocalized 3c-2e σ-bond in Cu3 and a π-bond in Si3. Our study provides experimental confirmation of a planar hypercoordinate heavier Group 14 element, opening possibilities for exploring similar structures in two-dimensional materials.

Synthesis and reactivity of a six-membered heterocyclic 1,3-diphosphaallene

1,3-Diphosphaallenes are a new class of heavier heteroallenes and show a fascinating chemical behavior and reactivity. Herein we report on the room temperature transformation of gallaphosphene LGa(OCP)PGaL 1 (L = HC[C(Me)N(Ar)]2, Ar = 2,6-i-Pr2C6H3) to the six-membered metallaheterocycle LGa(PCP)OGaL 2 featuring a LGa-substituted 1,3-diphosphaallene unit. The possible mechanism of formation of 2 is supported by quantum chemical calculations, which revealed that the formation of 2 is energetically more favorable (ca. 2 kcal mol-1) than the formation of 1 at ambient temperature. Remarkably, 2 reacts with singlet carbenes selectively to new five-membered metallaheterocycles LGa(PC)OGaL(P)NHC (NHC = [CMeN(R)]2C; R = Me 3, iPr 4; C{(NAr)CMe2CH2CMe2 = cAAC (5) featuring a 1,3-diphospha-1,3-butadiene unit. In stark contrast, its reaction with trimethylsilyldiazomethane yields (LGa)2O(P2C2H)SiMe36 featuring a 1,3-diphosphacyclobutene unit. Compounds 2-6 were characterized by heteronuclear NMR (1H, 13C, 31P), UV-vis, and IR spectroscopy. Compounds 2-4 and 6 were also characterized by single crystal X-ray diffraction (sc-XRD) and their bonding nature was investigated by quantum chemical calculations.

Synthesis and Redox Chemistry of Co3E4 (E=P, As) Clusters

The synthesis of the cluster complexes [(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)] (E=P (3), As (4)) starting from the anionic triple-decker complexes [K(18cr6)(dme)2][(Cp'''Co)2(μ,η4:η4-E4)] (E=P (1), As (2)) by electrophilic quenching with the Co dimer [(Cp'''CoCl)2] is reported. Both complexes show a distinct redox chemistry, which was first investigated by cyclic voltammetry. Subsequently, the monoanions [K(L)(sol)n][(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)] (E=P, L=18cr6, sol=dme, n=2 (5), E=As, L=2,2,2-crypt, n=0 (6)), the monocations [(Cp'''Co)3(μ3,η2:η2:η2-E3)(μ3-E)][FAl] (E=P (7), As (8)) and the dications [(Cp'''Co)3(μ3,η3:η3:η3-E4)][TEF]2 (E=P (9), As (10)) could be realized experimentally and isolated in moderate to good yields. All compounds were characterized by single crystal X-ray structure analysis, NMR and EPR spectroscopy, mass spectrometry and elemental analysis.

A Crystalline Unsupported Phosphagallene and Phosphaindene

The synthesis and isolation of TerP═GaTer and TerP═InTer (Ter = 2,6-Dipp2-C6H3; Dipp = 2,6-diisopropylphenyl) is reported. These compounds feature unsupported P═Ga and P═In double bonds and two-coordinate triel element centers. Key to the stabilization of such compounds is the steric bulk of the terphenyl substituents, which serve to shield the highly reactive P═E bonds (E = Ga, In) and prevent further aggregation. When smaller aromatic substituents are employed on the phosphorus-containing precursor, the cyclic compounds Mes*P(ETer)2 (Mes* = 2,4,6-tBu3-C6H2) are isolated instead. These species contain weakly aromatic three-membered rings. The presence of an external base (PMe3) is required in order to stabilize a phosphagallene when the smaller Mes* substituent is used, allowing for the isolation of Mes*P═GaTer(PMe3).

Nucleophilic Functionalization of a Cationic Pentaphosphole Complex-A Systematic Study of Reactivity

The systematic nucleophilic functionalization of the cationic pentaphosphole ligand complex [Cp*Fe(η4-P5Me)][OTf] (A) with group 16/17 nucleophiles is reported. This method represents a highly reliable and versatile strategy for the design of novel transition-metal complexes featuring twofold substituted end-deck cyclo-P5 ligands, bearing unprecedented hetero-element substituents. By the reaction of A with classical group 16 nucleophiles, complexes of the type [Cp*Fe(η4-P5MeE)] (E=OEt (1), OtBu (2), SPh (3), SePh (4)) are obtained. By transferring this protocol to group 17 nucleophiles, the highly sensitive complexes [Cp*FeP5(η4-P5MeX)] (X=F (5), Cl (6), Br (7), I (8)) could be isolated. All products show exclusively 1,1'-substitution at the cyclo-P5 ring. Interestingly, further studies on the reactivity of the halogenated species revealed their ability to undergo ring-opening reactions with cyclic ethers such as THF and ethylene oxide yielding [Cp*FeP5(η4-P5MeOC4H8X)] (X=Br (9), I (10)) or [Cp*FeP5(η4-P5MeOC2H4X)] (X=Br (11), I (12)), respectively. Furthermore, the use of acyclic ethers such as dimethoxyethane led to the formation of [Cp*FeP5(η4-P5MeOC2H4OCH3)] (13) mediated by C-O bond cleavage, followed by subsequent P-O bond formation, as further enlightened by DFT calculations.

Evolution of aluminum aminophenolate complexes in the ring-opening polymerization of ε-caprolactone: electronic and amino-chelating effects

A series of aluminum complexes bearing phenolate (O-Al and O2-Al), biphenolate (OO-Al type), aminophenolate (ON-Al), aminobiphenolate (ONO-Al), bis(phenolato)bis(amine) (NNOO-Al), and Salan (ONNO-Al) type ligands were synthesized. ε-Caprolactone (CL) polymerization using these aluminum complexes as catalysts was investigated. The overall polymerization rates of Al catalysts with different ligands were found to be in the following order (kobs values): ONBr-Al (0.124 min-1) ≥ OBr2-Al (0.121 min-1) > ONNOBr-Al (0.054 min-1) > NNOBr-Al (0.044 min-1) ≥ ONOBr-Al (0.043 min-1) > OBr-Al (0.033 min-1) > NNOOBr-Al (0.015 min-1) ≥ BuONNOBu-Al (0.001 min-1) = OOBr-Al (0.001 min-1). In addition, Al complexes with electron-donating substituents on ligands exhibited higher catalytic activity than those with bromo substituents. Density functional theory (DFT) calculations revealed that a dinuclear Al complex with two bridging methoxides had to rearrange to a phenolate bridged dinuclear Al complex with terminal methoxides. This is due to the low initiating ability of two bridging benzyl alkoxides. Combining the polymerization data and DFT results, it was concluded that the electron-donating substituents on the phenolate ring and chelating amino group enhance the electron density of the Al center. This may prevent the formation of a less active dinuclear Al complex with two bridging alkoxides (initiators) or facilitate its structural rearrangement. OOMe-Al has been established as a powerful candidate with a high polymerization rate and it exhibits well-controlled polymerization for synthesizing the mPEG-b-PCL copolymer.

Influence of Pnictogen and Ligand Framework on the Lewis Acidity and Steric Environment in Pnictogen Pincer Complexes

Pnictogen pincer complexes are a fascinating class of compounds due to their dynamic molecular and electronic structures, and valuable stoichiometric or catalytic reactivity. As recognition of their unique chemistry has grown, so too has the library of pincer ligands employed and pnictogen centres engaged to prepare them. Here we computationally study how the choice of pincer ligand framework and pnictogen influence the electronic and steric outcomes within the complexes obtained. The most relevant electronic parameter is the pnictogen-centred electrophilicity, which has been quantified by fluoride ion affinities and LUMO energies, while the most relevant steric parameter is the crowding around the central pnictogen, which has been quantified by the %Vbur values and visualized using steric maps. The resulting trends are analyzed with reference to binding pocket size, acceptor orbital type, electronic delocalization, π-donor strengths, and heteroatom incorporation. Thus, considering 16 ligand frameworks and 4 heavy pnictogen centres, this study provides a broad-spectrum view of stereo-electronic variation in pnictogen pincer complexes, which, together with a recent study on geometric variation in the same family, provides a substantial dataset to guide future molecular design and reactivity studies.

Neutral 4π-electron tetrasilacyclobutadiene contains unusual features of a Möbius-type aromatic ring

The search for stable compounds containing an antiaromatic cyclic 4π system is a challenge for inventive chemists that can look back on a long history. Here we report the isolation and characterization of the novel 4π-electron tetrasilacyclobutadiene, an analogue of a 4π neutral cyclobutadiene that exhibits surprising features of a Möbius-type aromatic ring. Reduction of RSiCl3 (R = (iPr)2PC6H4) with KC8 in the presence of cycloalkyl amino-carbene (cAAC) led to the formation of corresponding silylene 1. Compound 1 shows further reactivity when treated with RSiCl3 under reducing conditions resulting in the formation of unsymmetrical bis-silylene 2, which was isolated as a dark red crystalline solid. Compound 3 was obtained when chlorosilylene was reduced with potassium graphite in the presence of 2. Although 3 is, according to Hückel's rule an antiaromatic system it possesses significant aromatic character due to the unusual delocalization of the HOMO-1 and the loss of degeneracy of the higher-lying π MOs. The aromatic character of 3 is indicated by the structural stability of the compound by the very similar Si-Si bond lengths and by the NICS values. There is an unusual π conjugation between the 4 π electrons in the nearly square-planar Si4 ring where the delocalization of the HOMO-1 occurs at two opposite sides of the ring. The reversal of the π conjugation resembles the twisting of the π conjugation in Möbius aromatic systems and it contributes to the stability of the compound.

Activation of small molecules by ambiphilic NHC-stabilized phosphinoborenium cation: formation of boreniums with B-O-C, B-O-B, and B-O-P structural motifs

The reactivity of the phosphinoborenium cation supported by a 1,3,4,5-tetramethylimidazolin-2-ylidene ligand toward small molecules was explored. The phosphinoborenium cation exhibited dual Lewis acid-base properties due to the presence of the Lewis acidic boron center and the Lewis basic phosphido ligand connected by a covalent bond. The reaction of the title cation with CO2 led to the insertion of a CO2 molecule into the P-B bond. The obtained borenium CO2-adduct underwent hydrolysis, forming an N-heterocyclic carbene stabilized diborenium dication bearing a B-O-B functionality. The activation of N2O proceeded via the insertion of an oxygen atom into the B-P bond of the parent cation, yielding a borenium cation with a phosphinite moiety. An alternative synthetic pathway to borenium cations with a B-O-P skeleton was achieved via the activation of secondary phosphine oxides by the phosphinoborenium cation. Furthermore, borenium cations and diborenium dications with B-O-C structural motifs were obtained from the reaction of the title compound with perfluorinated tert-butyl alcohol and hydroquinone, respectively. The structure of the obtained borenium cations is discussed based on multinuclear NMR spectroscopy, X-ray diffraction, and density functional theory calculations.

Computational Insights into the Effect of Ligands and Transition-Metal Centers on the Mechanism and Regioselectivity of Hydrosilylation of Alkenes

Development of sustainable synthetic methods for the hydrosilylation of alkenes, catalyzed by 3d transition metals, offers a promising alternative to traditional noble metal catalysts. This study presents a computational mechanistic investigation into the hydrosilylation of alkenes, focusing on the role of ligands and metal centers in modulating the reaction's mechanism and regioselectivity. The ligand's electronic and steric properties were found to modulate the regioselectivity for cobalt catalysts, with phosphine ligand (xantphos) promoting higher linear selectivity compared to nitrogen-based ligand (mesPDI). The energy decomposition analysis reveals that the xantphos ligand favors linear products due to stronger electrostatic and orbital interactions despite increased steric repulsion. The metal center also plays a crucial role, with cobalt catalysts favoring the modified Chalk-Harrod mechanism for branched product formation in the presence of PNN ligand (iPrPCNNMe), due to lower activation barriers in alkene insertion. Beneficial electrostatic and orbital interactions predominate, rendering the alkene insertion transition state for cobalt more favorable compared to that for iron. This work provides a comprehensive understanding of how ligand and metal center effects can be harnessed to control regioselectivity in hydrosilylation reactions.

Improvement of Electrochemical Performance with Cetylpyridinium Chloride for the Al Anode of Alkaline Al-Air Batteries

Aluminum-air batteries (AABs) are considered among high-power battery systems with various potential applications. However, the strong self-corrosion of Al in alkaline electrolytes negatively affects its Coulombic efficiency and significantly limits their large-scale application. This work presents the use of cetylpyridinium chloride (CPC) as an inexpensive and environmentally benign electrolyte additive in alkaline AABs. Hydrogen evolution test, electrochemical measurement, and surface analysis techniques were used to investigate the inhibition effects of CPC additive for the Al anode. The potentiodynamic polarization data indicated that the effectiveness of the CPC in inhibiting corrosion increased proportionally with higher CPC concentration. The maximum inhibition efficiency of 53.6% was achieved at a CPC dosage of 5 mM. The hydrogen evolution experiment revealed that the rate of hydrogen evolution decreased from 0.789 mL cm-2 min-1 for the pristine NaOH solution to 0.415 mL cm-2 min-1. The combination of X-ray photoelectron spectroscopy (XPS) and ab initio molecular dynamics (AIMD) provides conclusive evidence that CPC may adhere to the surface of Al and create a protective film. These findings indicate that CPC is successful in preventing the self-corrosion of the Al anode. Additionally, the Al anode has improved electrochemical characteristics, including a high specific capacity of 2041 mAh g-1 and a high energy density of 2874 Wh kg-1. This work focuses on the inhibition of self-corrosion of Al and provides novel insights for the design and development of effective additives for AABs.

Theoretical Prediction of Divalent Actinide Borozene Complexes

The aromatic boron cluster B82- (D7h) has similar π bonding to C6H6, which is named "borozene". The B82- ligand has been observed to stabilize monovalent Ln(+I) in C7v-LnB8- (Ln = La, Pr, Tb, Tm, and Yb) borozene complexes. Low-valency actinide complexes have been reported more rarely, and B82- may be one of the potential ligands. Here, we report a theoretical study on a series of actinide metal-doping octa-boron clusters AnB8 (An = Pa, U, Np, and Pu). It was found that each species has both half-sandwich and chair-like structures. Except for PaB8, the half-sandwich structures of UB8, NpB8, and PuB8 are more energetically stable than the chair-like structures, and the half-sandwich clusters of AnB8 are found to be actinide(II) borozene complexes with the MII[B82-] type. For each of the half-sandwich clusters, the B82- ligand has σ and π double aromaticity. Various bonding analyses of AnB8 confirm the covalent interactions between the doped actinide metals and the octa-boron clusters, which further stabilize the complexes and determine the relative stability of AnB8. As expected, these complexes show high bond dissociation energies, especially PaB8 with stronger Pa-B covalent bonds. These results demonstrate that the B82- doubly aromatic ligand is able to stabilize divalent actinides.

Isolation of a NHC-stabilized heavier nitrile and its conversion into an isonitrile analogue

Nitriles (R-C≡N) have been investigated since the late eighteenth century and are ubiquitous encounters in organic and inorganic syntheses. In contrast, heavier nitriles, which contain the heavier analogues of carbon and nitrogen, are sparsely investigated species. Here we report the synthesis and isolation of a phosphino-silylene featuring an N-heterocyclic carbene-phosphinidene and a highly sterically demanding silyl group as substituents. Due to its unique structural motif, it can be regarded as a Lewis base-stabilized heavier nitrile. The Si-P bond displays multiple bond character and a bent R-Si-P geometry, the latter indicating fundamental differences between heavier and classical nitriles. In solution, a quantitative unusual rearrangement to a phosphasilenylidene occurs. This rearrangement is consistent with theoretical predictions of rearrangements from heavier nitriles to heavier isonitriles. Our preliminary reactivity studies revealed that both isomers exhibit highly nucleophilic silicon centres capable of oxidative addition and coordination to iron tetracarbonyl.

Trigonal Planar Heteroleptic Lanthanide(III) Bis(silyl)amide Complexes Containing Aminoxyl Radicals and Anions

Modulation of the crystal field (CF) in lanthanide (Ln) complexes can enhance optical and magnetic properties, and large CF splitting can be achieved with low coordination numbers in specific geometries. We previously reported that the homoleptic near-linear Sm2+ complex [SmII{N(SiiPr3)2}2] (1-Sm) is oxidized by the 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO•) radical to give the heteroleptic, approximately trigonal planar Sm3+ complex, [SmIII{N(SiiPr3)2}2(TEMPO-)] (2-Sm). Here, we report the synthesis of homologous [LnIII{N(SiiPr3)2}2(TEMPO-)] (2-Ln; Ln = Tm, Yb) complexes by the oxidation of the parent [Ln{N(SiiPr3)2}2] (1-Ln; Ln = Tm, Yb) with TEMPO•; complexes 2-Ln all contain TEMPO- anions. The homoleptic bent Ln3+ complexes [LnIII{N(SiiPr3)2}2][B(C6F5)4] (3-Ln; Ln = Sm, Tm, Yb) were also treated with TEMPO• to yield the heteroleptic, approximately trigonal planar Ln3+ complexes [LnIII{N(SiiPr3)2}2(TEMPO•)][B(C6F5)4] (4-Ln; Ln = Sm, Tm, Yb); the cations of 4-Ln all contain TEMPO• radicals. We have compared the electronic structures of the two geometrically similar families of Ln3+ complexes with the TEMPO- anion (2-Ln) or TEMPO• radical (4-Ln) using a combination of UV-vis-NIR and EPR spectroscopy, magnetic measurements, and ab initio calculations. These studies revealed no single-molecule magnet behavior for 2-Yb despite evidence for sizable CF splitting and a high degree of purity of the ground stabilized mJ = |±7/2⟩ state, while the radical TEMPO• in 4-Yb did not significantly improve performance.

Regiospecific Methylalumination of Silacyclopropenes: The Access to Z-1-Silyl-2-Aluminyl-Disubstituted Olefins

A methodology to access Z-1-silyl-2-aluminyl-disubstituted olefins is developed. It relies on the uncatalyzed ring opening of silacyclopropenes in the presence of a stoichiometric amount of trimethylaluminum. The resulting heterosubstituted alkenes exhibit a particular interaction between the electron-rich [Si-CH3] moiety and the electron-deficient diorganoaluminyl group, resulting in similar geometrical features due to the proximity of these two centers. This interaction is rationalized using experimental and theoretical descriptors. The regioselectivity and functional tolerance of the methylalumination were also studied in the case of unsymmetrical silacyclopropenes, and the methodology ultimately transposed to the synthesis of a polymeric organoalane incorporating tricoordinated aluminum centers.

Smoother Semiclassical Dispersion for Density Functional Theory via D3S: Understanding and Addressing Unphysical Minima in the D3 Dispersion Correction Model

One of the most widely used and computationally efficient models that accounts for London dispersion interactions within density functional theory (DFT) is the D3 dispersion correction model. In this work, we demonstrate that this model can induce the appearance of unphysical minima on the potential energy surface (PES) when the coordination number of atoms changes. Optimizing to these artifactual structures can lead to significant errors in determining the interaction energy between two molecules and in estimating the thermodynamic properties of the system. In several specific examples, such as Kuratowski-type H2-NiKur and H2-PdKur clusters, these local minima exhibited extremely high PES curvature, resulting in incorrect estimations of harmonic frequencies and significant overestimations of zero-point energy and enthalpy values. Although such erroneous behavior of the D3 model is relatively rare, it can occur across a wide range of chemical species, including molecules like the [Li(C6H6)]+ complex and the dispiro(acridan)-substituted pyracene (DSAP) molecule. Our analysis reveals that the root of the problem lies in the definition of the AB atomic-pair dependent C6AB coefficients in the D3 model. To address this issue, we propose a reparameterization of the D3 model by introducing a modified C6AB functional form that now depends on the specific pair of considered atoms. This new model, termed D3-Smooth (or D3S for short), is designed to smooth out the PES associated with the dispersion correction. By doing so, we demonstrate that D3S eliminates unphysical local minima while maintaining the quite satisfactory accuracy of the parent D3 method in interaction energy benchmark sets. For example, the RMS difference between using the D3(BJ) correction to B3LYP and the D3S(BJ) correction across the large MGCDB84 data set of nearly 5000 data points is only 0.12 kJ/mol. Similar results are obtained for every other D3-corrected functional tested. Consistent with this result, no significant improvement could be obtained for the B3LYP-D3S(0) correction by reoptimizing the damping function.