Hydrogen-Bridged Oligosilanylsilyl Mono- and Oligosilanylsilyl Dications

Hydrogen-bridged oligosilanylsilyl borates 8 [B(C₆F₅)₄], 9 [B(C₆F₅)₄] and diborates 10 [B(C₆F₅)₄]₂ have been prepared by hydride transfer between α-ω-dihydrido- ( 11 ) and branched tetrahydrido-oligosilanes ( 13 ) and trityl cation. The obtained cyclic intramolecularly stabilized silylium ions 8 , 9 and bissilylium ion 10 were characterized by low temperature NMR spectroscopy supported by the results of density functional calculations. The branched Si−H−Si monocation 9 undergoes at low temperatures a fast degenerate rearrangement, which exchanges the Si−H groups with a barrier of 31 kJ mol⁻¹ via an antarafacial transition state. Reaction of the branched monocation 9 with a second equivalent of trityl cation or of the branched oligosilane 13 with two equivalents of trityl cation, gives at −80 °C the corresponding bissilylium ion 10 , an example for a new class of highly reactive poly-Lewis acids.     

New PF3 and Carbonyl Chemistry of Tantalum

Reduction of [TaCl₅] by six equivalents of alkali metal naphthalenide in 1,2-dimethoxyethane at −60°C followed by treatment with gaseous PF₃ provides the first homoleptic phosphane complex containing tantalum in the −1 oxidation state, [Ta(PF₃)₆]⁻. This can be protonated by concentrated sulfuric acid to yield the previously unknown highly acidic and volatile hydride [HTa(PF₃)₆]. An improved normal-pressure synthesis of [Ta(CO)₆]⁻ is described. Reduction of the latter species by sodium in liquid ammonia gives the carbonyl trianion [Ta(CO)₅]³⁻ which undergoes monoprotonation and stannylation to form [HTa(CO)₅]²⁻ and [Ph₃SnTa(CO)₅]²⁻, respectively. The hydride is a useful precursor to [(Ph₃PAu)₃Ta(CO)₅], the only known gold cluster of tantalum.     

Stable Noble Gas Compounds Based on Superelectrophilic Anions [B12(BO)11]− and [B12(OBO)11]−

Superelectrophilic monoanions [B₁₂(BO)₁₁]⁻ and [B₁₂(OBO)₁₁]⁻, generated from stable dianions [B₁₂(BO)₁₂]²⁻ and [B₁₂(OBO)₁₂]²⁻, show great potential for binding with noble gases (Ngs). The binding energies, quantum theory of atoms in molecules (QTAIM), natural population analysis (NPA), energy decomposition analysis (EDA), and electron localization function (ELF) were carried out to understand the B−Ng bond in [B₁₂(BO)₁₁Ng]⁻ and [B₁₂(OBO)₁₁Ng]⁻. The calculated results reveal that heavier noble gases (Ar, Kr, and Xe) bind covalently with both [B₁₂(BO)₁₁]⁻ and [B₁₂(OBO)₁₁]⁻ with large binding energies, making them potentially feasible to be synthesized. Only [B₁₂(OBO)₁₁]⁻ could form a covalent bond with helium or neon but the small binding energy of [B₁₂(OBO)₁₁He]⁻ may pose a challenge for its experimental detection.     

A Structural Diversity of Molecular Alkaline-Earth-Metal Polyphosphides: From Supramolecular Wheel to Zintl Ion

A series of molecular group 2 polyphosphides has been synthesized by using air-stable [Cp*Fe(η⁵-P₅)] (Cp*=C₅Me₅) or white phosphorus as polyphosphorus precursors. Different types of group 2 reagents such as organo-magnesium, mono-valent magnesium, and molecular calcium hydride complexes have been investigated to activate these polyphosphorus sources. The organo-magnesium complex [(^DippBDI−Mg(CH₃))₂] (^DippBDI={[2,6-ⁱPr₂C₆H₃NCMe]₂CH}⁻) reacts with [Cp*Fe(η⁵-P₅)] to give an unprecedented Mg/Fe-supramolecular wheel. Kinetically controlled activation of [Cp*Fe(η⁵-P₅)] by different mono-valent magnesium complexes allowed the isolation of Mg-coordinated formally mono- and di-reduced products of [Cp*Fe(η⁵-P₅)]. To obtain the first examples of molecular calcium-polyphosphides, a molecular calcium hydride complex was used to reduce the aromatic cyclo-P₅ ring of [Cp*Fe(η⁵-P₅)]. The Ca-Fe-polyphosphide is also characterized by quantum chemical calculations and compared with the corresponding Mg complex. Moreover, a calcium coordinated Zintl ion (P₇)³⁻ was obtained by molecular calcium hydride mediated P₄ reduction.     

Deprotonation of a Hydridoborate Anion

The first deprotonation of a borohydride anion was achieved by treatment of [BH(CN)₃]⁻ with strong non‐nucleophilic bases, which resulted in the formation of alkali‐metal salts of the tricyanoborate dianion B(CN)₃²⁻ in up to 97 % yield and 99.5 % purity. [BH(CN)₃]⁻ is less acidic than (Me₃Si)₂NH but a stronger acid than i Pr₂NH. Less sterically hindered, more nucleophilic bases such as PhLi and MeLi mostly attack a CN group under formation of imine dianions [RC(N)B(CN)₃]²⁻, which can be hydrolyzed to ketones of the [RC(O)B(CN)₃]⁻ type. The boron‐centered nucleophile B(CN)₃²⁻ reacts with CO₂ and CN⁺ reagents to give salts of the [B(CN)₃CO₂]²⁻ dianion and the tetracyanoborate anion [B(CN)₄]⁻, respectively, in excellent yields.     

Mechanism for hydrolysis of double six-membered ring tetraborate anion

[B₄O₅(OH)₄²⁻] is a representative borate anion with a double six-membered ring structure, but there is limited knowledge about the hydrolysis mechanisms of [B₄O₅(OH)₄²⁻]. Density functional theory-based calculations show that the tetraborate ion undergoes three-step hydrolysis to form [B(OH)₄⁻] and an ring intermediate, [B₃O₂(OH)₆⁻]. Other new structures, such as linear trimer, branched tetraborate, analogous linear tetraborate, are observed, but they are not stable in neutral systems and change to ring structures. [B₃O₂(OH)₆⁻] hydrolyzes to [B(OH)₄⁻] and [B(OH)₃] in the last two steps. The structure of borate anion and the coordination environment of the bridge oxygen atom control the hydrolysis process. [B₄O₅(OH)₄²⁻] always participates in the hydrolysis reaction, even with a decrease in concentration. [B₃O₃(OH)₄⁻], [B(OH)₄⁻], and [B(OH)₃] have different roles in “water-poor” and “water-rich” zones. Concentration and pH of solution are the key factors that affect the distribution of borate ions.     

Superelectrophilic Behavior of an Anion Demonstrated by the Spontaneous Binding of Noble Gases to [B12Cl11]−

It is common and chemically intuitive to assign cations electrophilic and anions nucleophilic reactivity, respectively. Herein, we demonstrate a striking violation of this concept: The anion [B₁₂Cl₁₁]⁻ spontaneously binds to the noble gases (Ngs) xenon and krypton at room temperature in a reaction that is typical of “superelectrophilic” dications. [B₁₂Cl₁₁Ng]⁻ adducts, with Ng binding energies of 80 to 100 kJ mol⁻¹, contain B−Ng bonds with a substantial degree of covalent interaction. The electrophilic nature of the [B₁₂Cl₁₁]⁻ anion is confirmed spectroscopically by the observation of a blue shift of the CO stretching mode in the IR spectrum of [B₁₂Cl₁₁CO]⁻ and theoretically by investigation of its electronic structure. The orientation of the electric field at the reactive site of [B₁₂Cl₁₁]⁻ results in an energy barrier for the approach of polar molecules and facilitates the formation of Ng adducts that are not detected with reactive cations such as [C₆H₅]⁺. This introduces the new chemical concept of “dipole-discriminating electrophilic anions.”     

Radical Anions,Radical-Anion Salts,and Anionic Complexes of 2,1,3-Benzochalcogenadiazoles

By means of cyclic voltammetry (CV) and DFT calculations, it was found that the electron-acceptor ability of 2,1,3-benzochalcogenadiazoles 1 – 3 (chalcogen: S, Se, and Te, respectively) increases with increasing atomic number of the chalcogen. This trend is nontrivial, since it contradicts the electronegativity and atomic electron affinity of the chalcogens. In contrast to radical anions (RAs) [ 1 ]^.− and [ 2 ]^.−, RA [ 3 ]^.− was not detected by EPR spectroscopy under CV conditions. Chemical reduction of 1 – 3 was performed and new thermally stable RA salts [K(THF)]⁺[ 2 ]^.− ( 8 ) and [K(18-crown-6)]⁺[ 2 ]^.− ( 9 ) were isolated in addition to known salt [K(THF)]⁺[ 1 ]^.− ( 7 ). On contact with air, RAs [ 1 ]^.− and [ 2 ]^.− underwent fast decomposition in solution with the formation of anions [ECN]⁻, which were isolated in the form of salts [K(18-crown-6)]⁺[ECN]⁻ ( 10 , E=S; 11 , E=Se). In the case of 3 , RA [ 3 ]^.− was detected by EPR spectroscopy as the first representative of tellurium–nitrogen π-heterocyclic RAs but not isolated. Instead, salt [K(18-crown-6)]⁺₂[ 3 -Te₂]²⁻ ( 12 ) featuring a new anionic complex with coordinate Te−Te bond was obtained. On contact with air, salt 12 transformed into salt [K(18-crown-6)]⁺₂[ 3 -Te₄- 3 ]²⁻ ( 13 ) containing an anionic complex with two coordinate Te−Te bonds. The structures of 8 – 13 were confirmed by XRD, and the nature of the Te−Te coordinate bond in [ 3 -Te₂]²⁻ and [ 3 -Te₄- 3 ]²⁻ was studied by DFT calculations and QTAIM analysis.     

Elucidating the Mechanism of Simultaneous Activation of CH4 and CO2 Mediated by Single Group 10 Metal Anions in Gas Phase

Quantum chemistry calculations predict that besides the reported single metal anion Pt⁻, Ni⁻ can also mediate the co-conversion of CO₂ and CH₄ to form [CH₃−M(CO₂)−H]^– complex, followed by transformation to C−C coupling product [H₃CCOO−M−H]⁻ ( A ), hydrogenation products [H₃C−M−OCOH]⁻ ( B ) and [H₃C−M−COOH]⁻. For Pd⁻, a fourth product channel leading to PdCO₂⁻…CH₄ becomes more competitive. For Ni⁻, the feed order must be CO₂ first, as the weaker donor-acceptor interaction between Ni⁻ and CH₄ increases the C−H activation barrier, which is reduced by [Ni−CO₂]⁻. For Ni⁻/Pt⁻, the highly exothermic products A and B are similarly stable with submerged barrier that favors B . The smaller barrier difference between A and B for Ni⁻ suggests the C−C coupling product is more competitive in the presence of Ni⁻ than Pt⁻. The charge redistribution from M⁻ is the driving force for product B channel. This study adds our understanding of single atomic anions to activate CH₄ and CO₂ simultaneously.     

Elucidating the Structures of Intermediate Fragments during Stepwise Dissociation of Monolayer-Protected Silver Clusters

Fragmentation dynamics of ligated coinage metal clusters reflects their structural and bonding properties. So far methodological challenges limited probing structures of the fragments. Herein, we resolve the geometric structures of the primary fragments of [Ag₂₉L₁₂]³⁻, i.e. [Ag₂₄L₉]²⁻, [Ag₁₉L₆]⁻ and [Ag₅L₃]⁻ (L is 1,3-benzene dithiolate). For this, we used trapped ion mobility mass spectrometry to determine collision cross sections of the fragments and compared them to structures calculated by density functional theory. We also report that following two sequential [Ag₅L₃]⁻ elimination steps, further dissociation of [Ag₁₉L₆]⁻ also involves a new channel of Ag₂ loss and Ag−S and C−S bond cleavages. This reflects a competition between retaining the electronic stability of 8 e⁻ superatom cluster cores and increasing steric strain of ligands and staples. These results are also of potential interest for future soft-landing deposition studies aimed at probing catalytic behavior of Ag clusters on supports.     

Double Concave Cesium Encapsulation by Two Charged Sumanenyl Bowls

The controlled reaction of Na and Cs, two alkali metals of different ionic sizes and binding abilities, with sumanene (C₂₁H₁₂) affords a novel type of organometallic sandwich [Cs(C₂₁H₁₁⁻)₂]⁻, which crystallized as a solvent‐separated ion pair with a [Na(18‐crown‐6)(THF)₂]⁺ cation (where THF=tetrahydrofuran). The unprecedented double concave encapsulation of a metal ion by two bowl‐shaped sumanenyl anions in [Cs(C₂₁H₁₁⁻)₂]⁻ was revealed crystallographically. Evaluation of bonding and energetics of the remarkable product was accomplished computationally (B2PLYP‐D/TZVP/ZORA), providing insights into its formation.     

Using Ylide Functionalization to Stabilize Boron Cations

The metalated ylide YNa [Y=(Ph₃PCSO₂Tol)⁻] was employed as X,L‐donor ligand for the preparation of a series of boron cations. Treatment of the bis‐ylide functionalized borane Y₂BH with different trityl salts or B(C₆F₅)₃ for hydride abstraction readily results in the formation of the bis‐ylide functionalized boron cation [Y−B−Y]⁺ ( 2 ). The high donor capacity of the ylide ligands allowed the isolation of the cationic species and its characterization in solution as well as in solid state. DFT calculations demonstrate that the cation is efficiently stabilized through electrostatic effects as well as π‐donation from the ylide ligands, which results in its high stability. Despite the high stability of 2 [Y−B−Y]⁺ serves as viable source for the preparation of further borenium cations of type Y₂B⁺←LB by addition of Lewis bases such as amines and amides. Primary and secondary amines react to tris(amino)boranes via N−H activation across the B−C bond.     

Dinitramidoborates: A Fascinating Case of Competing Oxygen and Nitrogen Donors and Tautomerism

Reactions of the BH₄⁻ anion with equimolar amounts of HN(NO₂)₂ or of BH₃⋅THF with K[N(NO₂)₂]⁻ produced a mono‐substituted [BH₃N(NO₂)₂]⁻ anion, which contains a B−N connected dinitramido ligand. The reaction of BH₄⁻ with two equivalents of HN(NO₂)₂ afforded the di‐substituted borate anion consisting of two isomers, one with both nitramido ligands attached to B through N and the other one with one ligand attached through N and the other one through O. The disubstituted dinitramidoborates are marginally stable under ambient conditions, and the isomer with two N‐connected ligands was characterized by its crystal structure. A tri‐substituted borate was tentatively identified by NMR in the reaction of BH₄⁻ with a large excess of HN(NO₂)₂. All of the anions are highly energetic. Theoretical calculations show that the energy differences between the B−N and B−O tautomers are small, explaining the formation of both.     

Calculation of force constants and vibrational frequencies of octahedral MX6 molecules

The vibrational frequencies of some octahedral species ([SbX₆]⁻, [SbX₆]³⁻, [NbX₆]⁻, [NbX₆]²⁻, [TaX₆]⁻, [TaX₆]²⁻; X = F, Cl, Br, I) have been calculated by means of six extrapolated molecular force constants using some linear relations between the force constants and the reciprocal radii of the ligands. A statistical treatment of these correlations allowed the calculation of error limits for a probability of 90%. The computations of the force constants and vibrational frequencies were based on the GF-matrix method.     

The Hexacyanodiborane(6) Dianion [B2(CN)6]2−

Diborane(6) dianions with substituents that are bonded to boron via carbon are very reactive and therefore only a few examples are known. Diborane(6) derivatives are the simplest catenated boron compounds with an electron‐precise B–B σ‐bond that are of fundamental interest and of relevance for material applications. The homoleptic hexacyanodiborane(6) dianion [B₂(CN)₆]²⁻ that is chemically very robust is reported. The dianion is air‐stable and resistant against boiling water and anhydrous hydrogen fluoride. Its salts are thermally highly stable, for example, decomposition of (H₃O)₂[B₂(CN)₆] starts at 200 °C. The [B₂(CN)₆]²⁻ dianion is readily accessible starting from 1) B(CN)₃²⁻ and an oxidant, 2) [BF(CN)₃]⁻ and a reductant, or 3) by the reaction of B(CN)₃²⁻ with [BHal(CN)₃]⁻ (Hal=F, Br). The latter reaction was found to proceed via a triply negatively charged transition state according to an S_N2 mechanism.     

Competitive Coordination of Chloride and Fluoride Anions Towards Trivalent Lanthanide Cations (La3+ and Nd3+) in Molten Salts

Molten salt electrolysis is a vital technique to produce high-purity lanthanide metals and alloys. However, the coordination environments of lanthanides in molten salts, which heavily affect the related redox potential and electrochemical properties, have not been well elucidated. Here, the competitive coordination of chloride and fluoride anions towards lanthanide cations (La³⁺ and Nd³⁺) is explored in molten LiCl-KCl-LiF-LnCl₃ salts using electrochemical, spectroscopic, and computational approaches. Electrochemical analyses show that significant negative shifts in the reduction potential of Ln³⁺ occur when F⁻ concentration increases, indicating that the F⁻ anions interact with Ln³⁺ via substituting the coordinated Cl⁻ anions, and confirm [LnCl_xF_y]^3−x−y (y_max=3) complexes are prevailing in molten salts. Spectroscopic and computational results on solution structures further reveal the competition between Cl⁻ and F⁻ anions, which leads to the formation of four distinct Ln(III) species: [LnCl₆]³⁻, [LnCl₅F]³⁻, [LnCl₄F₂]³⁻ and [LnCl₄F₃]⁴⁻. Among them, the seven-coordinated [LnCl₄F₃]⁴⁻ complex possesses a low-symmetry structure evidenced by the pattern change of Raman spectra. After comparing the polarizing power (Z/r) among different metal cations, it was concluded that Ln−F interaction is weaker than that between transition metal and F⁻ ions.     

A three‐dimensional framework of bis­[tris­(ethyl­enediamine)zinc] tetra­iodo­cadmate diiodide assisted by N—H⋯I hydrogen bonds

The title salt, [Zn(C₂N₂H₈)₃]₂[CdI₄]I₂, conventionally abbreviated [Zn(en)₃]₂[CdI₄]I₂, where en is ethyl­enediamine, contains discrete [Zn(en)₃]²⁺ cations and [CdI₄]²⁻ anions with distorted octa­hedral and nearly tetra­hedral geometries, respectively, as well as uncoordinated I⁻ ions. The cation and the free I⁻ anion lie on twofold rotation axes and the [CdI₄]²⁻ anion lies on a axis in the space group I2d. The structure exhibits numerous weak inter‐ionic hydrogen bonds of two types, viz. N—H⋯I⁻(free ion) and N—H⋯I([CdI₄]²⁻), which support the resulting three‐dimensional framework.     

Construction of Ternary Iodine–Bromine–Chlorine Octahalides

A series of five ternary octanuclear iodine-bromine-chlorine interhalides, [I₂Br₂Cl₄]²⁻ ( 1 ), [I₃BrCl₄]²⁻ ( 2 ), [I₄Br₂Cl₂]²⁻ ( 3 ), [I₂Br₄Cl₂]²⁻ ( 4 ) and [I₃Br₃Cl₂]²⁻ ( 5 ), have been rationally constructed in two steps. Firstly, addition of a dihalogen (ICl or IBr) to the triaminocyclopropenium chloride salt [C₃(NEt₂)₃]Cl forms the corresponding trihalide salt with [ICl₂]⁻ or [BrICl]⁻ anions, respectively. Secondly, addition of a half-equivalent of a second dihalogen, followed by crystallization at low temperature, gives the corresponding octahalide: addition of Br₂ and IBr to [ICl₂]⁻ gives 1 and 2 , respectively, whereas addition of I₂, Br₂ and IBr to [BrICl]⁻ gives 3 , 4 and 5 , respectively. The five octahalides were characterized by X-ray crystallography and far–IR spectroscopy.     

Hydrogen-Release Reaction of a Complex Transition Metal Hydride with Covalently Bound Hydrogen and Hydride Ions

The hydrogen-release reaction of a complex transition metal hydride, LaMg₂NiH₇, composed of La³⁺, 2×Mg²⁺, [NiH₄]⁴⁻ and 3×H⁻, was studied by thermal analyses, powder X-ray, and neutron diffraction and inelastic neutron scattering. Upon heating, LaMg₂NiH₇ released hydrogen at approximately 567 K and decomposed into LaH₂₋₃ and Mg₂Ni. Before the reaction, covalently bound hydrogen (H^c°^v.) in [NiH₄]⁴⁻ exhibited a larger atomic displacement than H⁻, although a weakening of the chemical bonds around [NiH₄]⁴⁻ and H⁻ was observed. These results indicate the precursor phenomenon of a hydrogen-release reaction, wherein there is a large atomic displacement of H^c°^v. that induces the hydrogen-release reaction rather than H⁻. As an isothermal reaction, LaMg₂NiH₇ formed LaMg₂NiH_2.4 at 503 K in vacuum for 48 h, and LaMg₂NiH_2.4 reacted with hydrogen to reform LaMg₂NiH₇ at 473 K under 1 MPa of H₂ gas pressure for 10 h. These results revealed that LaMg₂NiH₇ exhibited partially reversible hydrogen-release and uptake reactions.