A Dinuclear Uranium Complex [{UO2F2(NH3)}2(μ-F)2]2− from Reaction of TlF and UO2F2 in Liquid Anhydrous Ammonia and Fluoride Ion Affinities for Some Uranyl(VI) Species [UO2Fx]2−x and [UO2Fx(NH3)5−x]2−x

UO₂F₂ abstracts F⁻ anions from TlF in liquid ammonia solution and the compound [Tl₂(NH₃)₆][{UO₂F₂(NH₃)}₂(μ-F)₂] is formed. The compound has been characterized by single crystal X-ray diffraction, Raman spectroscopy and quantum-chemical calculations for the solid state. Quantum-chemical investigation of the [{UO₂F₂(NH₃)}₂(μ-F)₂]²⁻ anion showed that the U−(μ-F)−U σ-3c-4e-bond is essentially ionic. The [Tl₂(NH₃)₆]²⁺ cation shows a thallophilic Tl⋅⋅⋅Tl interaction. Fluoride ion affinities (FIAs) were calculated for different UO₂²⁺ species [UO₂F_x]^2−x and [UO₂F_x(NH₃)_5−x]^2−x with x=0 to 4.     

Highly ordered Nb2O5 nanochannel film with rich oxygen vacancies for electrocatalytic N2 reduction: Inactivation and regeneration of electrode

We report the fabrication of highly ordered Nb₂O₅ nanochannel film (Nb₂O₅-NCF) onto niobium foil by an anodization method. After thermal treatment, the obtained Nb₂O₅-NCF with rich oxygen vacancies exhibits electrochemical N₂ reduction reaction (NRR) activity with an NH₃ yield rate of 2.52 × 10⁻¹⁰ mol cm^-2 s^-1 and a faradaic efficiency of 9.81% at −0.4 V (vs. RHE) in 0.1 mol/L Na₂SO₄ electrolyte (pH 3.2). During electrocatalytic NRR, the Nb₂O₅-NCF takes place electrochromism (EC), along with a crystalline phase transformation from pseudo hexagonal phase to hexagonal phase owing to H⁺ insertion. This results in the reduced NRR activity due to the decrease of oxygen vacancies of hexagonal phase Nb₂O₅, which can be readily regenerated by low-temperature thermal treatment or applying an anodic potential, showing superior recycling reproducibility.     

Highly Efficient Electrochemical Nitrate and Nitrogen Reduction to Ammonia under Ambient Conditions on Electrodeposited Cu-Nanosphere Electrode

The electrochemical reduction reaction of nitrogenous species such as NO₃⁻ (NO₃RR) and N₂ (NRR) is a promising strategy for producing ammonia under ambient conditions. However, low activity and poor selectivity of both NO₃RR and NRR remain the biggest problem of all current electrocatalysts. In this work, we fabricated Cu-nanosphere film with a high surface area and dominant with a Cu(200) facet by simple electrodeposition method. The Cu-nanosphere film exhibits high electrocatalytic activity for NO₃RR and NRR to ammonia under ambient conditions. In the nitrate environment, the Cu-nanosphere electrode reduced NO₃⁻ to yield NH₃ at a rate of 5.2 mg/h cm², with a Faradaic efficiency of 85 % at −1.3 V. In the N₂-saturated environment, the Cu-nanosphere electrode reduced N₂ to yield NH₃ with the highest yield rate of 16.2 μg/h cm² at −0.5 V, and the highest NH₃ Faradaic efficiency of 41.6 % at −0.4 V. Furthermore, the Cu-nanosphere exhibits excellent stability with the NH₃ yield rate, and the Faradaic efficiency remains stable after 10 consecutive cycles. Such high levels of NH₃ yield, selectivity, and stability at low applied potential are among the best values currently reported in the literature.     

Outer‐Sphere 2 e−/2 H+ Transfer Reactions of Ruthenium(II)‐Amine and Ruthenium(IV)‐Amido Complexes

A diverse set of 2 e⁻/2 H⁺ reactions are described that interconvert [Ru^II(bpy)(en*)₂]²⁺ and [Ru^IV(bpy)(en‐H*)₂]²⁺ (bpy=2,2′‐bipyridine, en*=H₂NCMe₂CMe₂NH₂, en*‐H=H₂NCMe₂CMe₂NH⁻), forming or cleaving different O−H, N−H, S−H, and C−H bonds. The reactions involve quinones, hydrazines, thiols, and 1,3‐cyclohexadiene. These proton‐coupled electron transfer reactions occur without substrate binding to the ruthenium center, but instead with precursor complex formation by hydrogen bonding. The free energies of the reactions vary over more than 90 kcal mol⁻¹, but the rates are more dependent on the type of X−H bond involved than the associated ΔG °. There is a kinetic preference for substrates that have the transferring hydrogen atoms in close proximity, such as ortho ‐tetrachlorobenzoquinone over its para ‐isomer and 1,3‐cyclohexadiene over its 1,4‐isomer, perhaps hinting at the potential for concerted 2 e⁻/2 H⁺ transfers.     

Comparison of Characteristic Structural Features among the Triade of Tris(cyclopentadienyl)(Group-4 Metal) Complex Cations: a Combined Theoretical and Experimental Study

A density functional theory computational chemistry study has revealed a fundamental structural difference between [Ti(Cp)₃]⁺ and its congeners [Zr(Cp)₃]⁺ and [Hf(Cp)₃]⁺/(Cp=cyclopentadienyl). Whereas the latter two are found to contain three uniformely η⁵-coordinated Cp ligands (3η⁵-structural type), [Ti(Cp)₃]⁺ is shown to prefer a 2η⁵η² structure. [Ti(Cp)₃]⁺[B(C₆F₅)₃(Me)]⁻ ( 10 ⋅[B(C₆F₅)₃(Me)]⁻) was experimentally generated by treatment of [Ti(Cp)₃(Me)] ( 7a ) with B(C₆F₅)₃ (Scheme 3). Low-temperature ¹H-NMR spectroscopy in CDFCl₂ (143 K, 600 MHz; Fig. 8) showed a splitting of the Cp resonance into five lines in a 2 : 5 : 2 : 5 : 1 ratio which would be in accord with the theoretically predicted 2η⁵η²-type structure of [Ti(Cp)₃]⁺. The precursor [Ti(Cp)₃(Me)] ( 7a ) exhibits two ¹H-NMR Cp resonances in a 10 : 5 ratio in CD₂Cl₂ at 223 K. Treatment of [HfCl(Cp)₂(Me)] ( 6c ) with sodium cyclopentadienide gave [Hf(Cp)₃(Me)] ( 7c ) (Scheme 1). Its reaction with B(C₆F₅)₃ furnished the salt [Hf(Cp)₃]⁺[B(C₆F₅)₃(Me)]⁻ ( 8 ⋅[B(C₆F₅)₃(Me)]⁻), which reacted with tert-butyl isocyanide to give the cationic complex [Hf(Cp)₃(C=N−CMe₃)]⁺ ( 9a ; with counterion [B(C₆F₅)₃(Me)]⁻ (Scheme 2). Complex cation 9a was characterized by X-ray diffraction (Fig. 7). Its Hf(Cp₃) moiety is of the 3η⁵-type. The structure is distorted trigonal-pyramidal with an average D−Hf−D angle of 118.8° and an average D−Hf−C(1) angle of 96.5° (D denotes the centroids of the Cp rings; Table 6). Cation 9a is a typical d⁰-isocyanide complex exhibiting structural parameters of the C≡N−CMe₃ group (d(C(1)−N(2))=1.146 (5) Å; IR: v˜(C≡N) 2211 cm⁻¹) very similar to free uncomplexed isonitrile. Analogous treatment of 8 with carbon monoxide yielded the carbonyl (d⁰-group-4-metal) complex [Hf(Cp)₃(CO)]⁺ ( 9b ; with counterion [B(C₆F₅)₃(Me)]⁻) (Scheme 2) that was also characterized by X-ray crystal-structure analysis (Fig. 6). Complex 9b is also of the 3η⁵-structural type, similar to the peviously described cationic complex [Zr(Cp)₃(CO)]⁺, and exhibits properties of the CO ligand (d(C−O)=1.11 (2) Å; IR: v˜(C≡O) 2137 cm⁻¹) very similar to the free carbon monoxide molecule.     

Photochemistry with Chlorine Trifluoride: Syntheses and Characterization of Difluorooxychloronium(V) Hexafluorido(non)metallates(V), [ClOF2][MF6] (M=V,Nb, Ta,Ru, Os,Ir, P,Sb)

A photochemical route to salts consisting of difluorooxychloronium(V) cations, [ClOF₂]⁺, and hexafluorido(non)metallate(V) anions, [MF₆]⁻ (M=V, Nb, Ta, Ru, Os, Ir, P, Sb) is presented. As starting materials, either metals, oxygen and ClF₃ or oxides and ClF₃ are used. The prepared compounds were characterized by single-crystal X-ray diffraction and Raman spectroscopy. The crystal structures of [ClOF₂][MF₆] (M=V, Ru, Os, Ir, P, Sb) are layer structures that are isotypic with the previously reported compound [ClOF₂][AsF₆], whereas for M=Nb and Ta, similar crystal structures with a different stacking variant of the layers are observed. Additionally, partial or full O/F disorder within the [ClOF₂]⁺ cations of the Nb and Ta compounds occurs. In all compounds reported here, a trigonal pyramidal [ClOF₂]⁺ cation with three additional Cl⋅⋅⋅F contacts to neighboring [MF₆]⁻ anions is observed, resulting in a pseudo-octahedral coordination sphere around the Cl atom. The Cl−F and Cl−O bond lengths of the [ClOF₂]⁺ cations seem to correlate with the effective ionic radii of the M^V ions. Quantum-chemical, solid-state calculations well reproduce the experimental Raman spectra and show, as do quantum-chemical gas phase calculations, that the secondary Cl⋅⋅⋅F interactions are ionic in nature. However, both solid-state and gas-phase quantum-chemical calculations fail to reproduce the increases in the Cl−O bond lengths with increasing effective ionic radius of M in [MF₆]⁻ and the Cl−O Raman shifts also do not generally follow this trend.     

Molybdenum(VI) Bis(imido) Complexes: From Frustrated Lewis Pairs to Weakly Coordinating Cations

Molybdenum(VI) bis(imido) complexes [Mo(NtBu)₂(L^R)₂] (R=H 1 a ; R=CF₃ 1 b ) combined with B(C₆F₅)₃ ( 1 a /B(C₆F₅)₃, 1 b /B(C₆F₅)₃) exhibit a frustrated Lewis pair (FLP) character that can heterolytically split H−H, Si−H and O−H bonds. Cleavage of H₂ and Et₃SiH affords ion pairs [Mo(NtBu)(NHtBu)(L^R)₂][HB(C₆F₅)₃] (R=H 2 a ; R=CF₃ 2 b ) composed of a Mo(VI) amido imido cation and a hydridoborate anion, while reaction with H₂O leads to [Mo(NtBu)(NHtBu)(L^R)₂][(HO)B(C₆F₅)₃] (R=H 3 a ; R=CF₃ 3 b ). Ion pairs 2 a and 2 b are catalysts for the hydrosilylation of aldehydes with triethylsilane, with 2 b being more active than 2 a . Mechanistic elucidation revealed insertion of the aldehyde into the B−H bond of [HB(C₆F₅)₃]⁻. We were able to isolate and fully characterize, including by single-crystal X-ray diffraction analysis, the inserted products Mo(NtBu)(NHtBu)(L^R)₂][{PhCH₂O}B(C₆F₅)₃] (R=H 4 a ; R=CF₃ 4 b ). Catalysis occurs at [HB(C₆F₅)₃]⁻ while [Mo(NtBu)(NHtBu)(L^R)₂]⁺ (R=H or CF₃) act as the cationic counterions. However, the striking difference in reactivity gives ample evidence that molybdenum cations behave as weakly coordinating cations (WCC).     

Vacancy Engineering of Iron-Doped W18O49 Nanoreactors for Low-Barrier Electrochemical Nitrogen Reduction

The electrochemical nitrogen reduction reaction (NRR) is a promising energy-efficient and low-emission alternative to the traditional Haber–Bosch process. Usually, the competing hydrogen evolution reaction (HER) and the reaction barrier of ambient electrochemical NRR are significant challenges, making a simultaneous high NH₃ formation rate and high Faradic efficiency (FE) difficult. To give effective NRR electrocatalysis and suppressed HER, the surface atomic structure of W₁₈O₄₉, which has exposed active W sites and weak binding for H₂, is doped with Fe. A high NH₃ formation rate of 24.7 μg h⁻¹ mg_cat⁻¹ and a high FE of 20.0 % are achieved at an overpotential of only −0.15 V versus the reversible hydrogen electrode. Ab initio calculations reveal an intercalation-type doping of Fe atoms in the tunnels of the W₁₈O₄₉ crystal structure, which increases the oxygen vacancies and exposes more W active sites, optimizes the nitrogen adsorption energy, and facilitates the electrocatalytic NRR.     

Selective Four-Electron Reduction of Oxygen by a Nonheme Heterobimetallic CuFe Complex

We report herein the first nonheme CuFe oxygen reduction catalyst ([Cu^II(bpbp)(μ-OAc)₂Fe^III]²⁺, CuFe−OAc ), which serves as a functional model of cytochrome c oxidase and can catalyze oxygen reduction to water with a turnover frequency of 2.4×10³ s⁻¹ and selectivity of 96.0 % in the presence of Et₃NH⁺. This performance significantly outcompetes its homobimetallic analogues (2.7 s⁻¹ of CuCu−OAc with %H₂O₂ selectivity of 98.9 %, and inactive of FeFe−OAc ) under the same conditions. Structure-activity relationship studies, in combination with density functional theory calculation, show that the CuFe center efficiently mediates O−O bond cleavage via a Cu^II(μ-η¹ : η²-O₂)Fe^III peroxo intermediate in which the peroxo ligand possesses distinctive coordinating and electronic character. Our work sheds light on the nature of Cu/Fe heterobimetallic cooperation in oxygen reduction catalysis and demonstrates the potential of this synergistic effect in the design of nonheme oxygen reduction catalysts.     

Influence of the chloride counterion on the redox reactivity of tetraammineplatinum(II) cation with octacyanotungstate(V) anion: Crystal structure of [Pt(NH3)4]2[W(CN)8]

The redox reaction between [Pt(NH₃)₄]²⁺ and [W(CN)₈]³⁻ in the presence of Cl⁻ anions in aqueous solution affords single crystals of [Pt^II(NH₃)₄]₂[W^IV(CN)₈] and [Pt^IV(NH₃)₄Cl₂]Cl₂. Trapped cyano ligands of [W(CN)₈]⁴⁻ rectangular antiprisms of D₂ point symmetry between parallel Pt(II) square planes show that the inner-sphere redox pathway is prohibited. The presence of Cl⁻ counterions enables the formation of [Pt(NH₃)₄Cl₂]Cl₂ as the product of the rare outer-sphere pathway of the oxidation of Pt(II) by [W(CN)₈]³⁻.     

Fluorine-Stabilized Defective Black Phosphorene as a Lithium-Like Catalyst for Boosting Nitrogen Electroreduction to Ammonia

Electrocatalytic N₂ reduction reaction (NRR) is recognized as a zero-carbon emission method for NH₃ synthesis. However, to date, this technology still suffers from low yield and low selectivity associated with the catalyst. Herein, inspired by the activation of N₂ by lithium metal, a highly reactive defective black phosphorene (D−BP_ene) is proposed as a lithium-like catalyst for boosting electrochemical N₂ activation. Correspondingly, we also report a strategy for producing environmentally stable D−BP_ene by simultaneously constructing defects and fluorination protection based on topochemical reactions. Reliable performance evaluations show that the fluorine-stabilized D−BP_ene can induce a high NH₃ yield rate of ≈70 μg h⁻¹ mg_cat.⁻¹ and a high Faradaic efficiency of ≈26 % at −0.5 V vs. RHE in an aqueous electrolyte. This work not only exemplifies the first stable preparation and practical application of D−BP_ene, but also brings a new design idea for NRR catalysts.     

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.     

Structural and Oxidation State Alternatives in Platinum and Palladium Complexes of a Redox-Active Amidinato Ligand

Reaction of [Pt(DMSO)₂Cl₂] or [Pd(MeCN)₂Cl₂] with the electron-rich LH=N,N’-bis(4-dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL₂] ( 1 ) but dinuclear [Pd₂L₄] ( 2 ), a paddle-wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV-vis-NIR spectroscopy, magnetic resonance) and TD-DFT calculations as metal(II) species with noninnocent ligands L⁻. The reversibly accessible cations [PtL₂]⁺ and [Pd₂L₄]⁺ were also studied, the latter as [Pd₂L₄][B{3,5-(CF₃)₂C₆H₃}₄] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [Pt^II(L⁻)₂] or [Pt^.(L )₂], [Pt^II(L^0.5−)₂]⁺ or [Pt^III(L⁻)₂]⁺, [(Pd^II)₂(μ-L⁻)₄] or [(Pd^1.5)₂(μ-L^0.75−)₄], and [(Pd^2.5)₂(μ-L⁻)₄]⁺ or [(Pd^II)₂(μ-L^0.75−)₄]⁺. In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL₂] with an N-Pt-N bite angle of 62.8(2)° in contrast to [Pd₂L₄], and the dimetal (Pd₂⁴⁺→Pd₂⁵⁺) instead of ligand (L⁻→L ) oxidation of the dinuclear palladium compound.     

Dopant-Induced Electronic States Regulation Boosting Electroreduction of Dilute Nitrate to Ammonium

Electrochemically converting NO₃⁻ into NH₃ offers a promising route for water treatment. Nevertheless, electroreduction of dilute NO₃⁻ is still suffering from low activity and/or selectivity. Herein, B as a modifier was introduced to tune electronic states of Cu and further regulate the performance of electrochemical NO₃⁻ reduction reaction (NO₃RR) with dilute NO₃⁻ concentration (≤100 ppm NO₃⁻−N). Notably, a linear relationship was established by plotting NH₃ yield vs. the oxidation state of Cu, indicating that the increase of Cu⁺ content leads to an enhanced NO₃⁻-to-NH₃ conversion activity. Under a low NO₃⁻−N concentration of 100 ppm, the optimal Cu(B) catalyst displays a 100 % NO₃⁻-to-NH₃ conversion at −0.55 to −0.6 V vs. RHE, and a record-high NH₃ yield of 309 mmol h⁻¹ g_cat⁻¹, which is more than 25 times compared with the pristine Cu nanoparticles (12 mmol h⁻¹ g_cat⁻¹). This research provides an effective method for conversion of dilute NO₃⁻ to NH₃, which has certain guiding significance for the efficient and green conversion of wastewater in the future.     

Metal complexes of anionic 3-borane-1-alkylimidazol-2-ylidene derivatives

Addition of BH₃·thf to 1-alkylimidazoles (alkyl=methyl, butyl) and 1-methylbenzimidazole leads to BH₃ adducts, which are deprotonated by BuLi to yield the organolithium compounds (L)Li⁺(1b–d)⁻. In the solid state (thf)Li⁺1b⁻ is dimeric. The acyl–iron complexes (thf)₃Li⁺(3b,d)⁻ are formed from (thf)Li⁺(1b,d)⁻ and Fe(CO)₅. (L)Li⁺(1a–c)⁻ react with [CpFe(CO)₂X], however, the only complex obtained is [CpFe(CO)₂1a] (5a). The analogous reaction of (L)Li⁺1a⁻ with the pentadienyl complex [(C₇H₁₁)Fe(CO)₂Br] yields the corresponding iron compound 6a. Their compositions follow from spectroscopic data. Treatment of Cp₂TiCl with (L)Li⁺1a⁻ leads to [Cp₂Ti1a] (7a), which could not be oxidized with PbCl₂ to give the corresponding Ti(IV) complex. The compounds [Li(py)₄]⁺9a⁻ and [Li(L)₄]⁺(10b–d)⁻ are obtained when (L)Li⁺1⁻ are reacted with VCl₃ and ScCl₃. The X-ray structure analysis of the vanadium complex reveals a distorted tetrahedron of the anion [V(1a)₄]⁻ with two smaller and four larger CVC angles. The scandium compound [Li(dme)₂⁺10c⁻] has a different structure: the distorted tetrahedron of the anion [Sc(1c)₄]⁻ contains two larger (140.2 and 142.9°) and four smaller CScC angles (93.9–98.7°). This arrangement allows the formation of four bridging BHSc 3c,2e bonds to give an eight-fold coordination. The anion 10c⁻ is formally a 16e complex.     

Boosting Electroreduction Kinetics of Nitrogen to Ammonia via Atomically Dispersed Sn Protuberance

Atomically dispersed metal catalysts show potential advantages in N₂ reduction reaction (NRR) due to their excellent activity and efficient metal utilization. Unfortunately, the reported catalysts usually exhibit unsatisfactory NRR activity due to their poor N₂ adsorption and activation. Herein, we report a novel Sn atomically dispersed protuberance (ADP) by coordination with substrate C and O to induce positive charge accumulation on Sn site for improving its N₂ adsorption, activation and NRR performance. The extended X-ray absorption fine structure (EXAFS) spectra confirmed the local coordination structure of the Sn ADPs. NRR activity was significantly promoted via Sn ADPs, exhibiting a remarkable NH₃ yield (R_NH3) of 28.3 μg h⁻¹ mg_cat⁻¹ (7447 μg h⁻¹ mg_Sn⁻¹) at −0.3 V. Furthermore, the enhanced N₂H_x intermediates was verified by in situ experiments, yielding consistent results with DFT calculation. This work opens a new avenue to regulate the activity and selectivity of N₂ fixation.     

Synthesis and Characterization of a Stable Nickelocenium Dication Salt

We report the synthesis and characterization of the nickelocenium cations [NiCp₂]⋅⁺ and [NiCp₂]²⁺ as their [F-{Al(OR^F)₃}₂]⁻ (Cp = C₅H₅; R^F=C(CF₃)₃) salts. Diamagnetic [NiCp₂]²⁺ represents the first example for the isolation of an unsubstituted parent metallocene dication. Both salts were generated by reacting neutral NiCp₂ with [NO]⁺[F-{Al(OR^F)₃}₂]⁻ in 1,2,3,4-tetrafluorobenzene (4FB). The salts were characterized by single crystal X-ray diffraction (XRD), indicating shorter metal-ligand bond lengths for the higher charged salt. Powder XRD shows the salts to be phase pure, cyclic voltammetry in 4FB gave quasi reversible redox waves at −0.44 (0→1) and +1.17 V (1→2) vs Fc/Fc⁺. The ¹H NMR of [NiCp₂]²⁺ is a singlet at 8.6 ppm, whereas paramagnetic [NiCp₂]⋅⁺ is significantly shifted upfield to −103.1 ppm.     

Group 6 Hexacarbonyls as Ligands for the Silver Cation: Syntheses,Characterization, and Analysis of the Bonding Compared with the Isoelectronic Group 5 Hexacarbonylates

The syntheses of the two novel complexes [Ag{Mo/W(CO)₆}₂]⁺[F-{Al(OR^F)₃}₂]⁻ (R^F=C(CF₃)₃) are reported along with their structural and spectroscopic characterization. The X-ray structure shows that three carbonyl ligands from each M(CO)₆ fragment bend towards the silver atom within binding Ag−C distance range. DFT calculations of the free cations [Ag{M(CO)₆}₂]⁺ (M=Cr, Mo, W) in the electronic singlet state give equilibrium structures with C₂ symmetry with two bridging carbonyl groups from each hexacarbonyl ligand. Similar structures with C₂ symmetry (M=Nb) and D₂ symmetry (M=V, Ta) are calculated for the isoelectronic group 5 anions [Ag{M(CO)₆}₂]⁻ (M=V, Nb, Ta). The electronic structure of the cations is analyzed with the QTAIM and EDA-NOCV methods, which provide detailed information about the nature of the chemical bonds between Ag⁺ and the {M(CO)₆}₂^q (q = −2, M = V, Nb, Ta; q = 0, M = Cr, Mo, W) ligands.     

Cyclopentadienyl Complexes of IrIII for Attempted C−D Bond Activation

The complexes Cp(MeIm)IrI₂ and Cp^Me4(MeIm)IrCl₂ have been prepared and subsequently methylated to form Cp(MeIm)IrMe₂ and Cp^Me4(MeIm)IrMe₂ (Cp=η⁵-C₅H₅, Cp^Me4=η⁵-C₅HMe₄, MeIm=1,3-dimethylimidazol-2-ylidene). We attempted unsuccessfully to use the dimethyl complexes to study C−D bond activation via methyl-group abstraction. Protonation with one equivalent of a weak acid, such as 2,6-dimethylpyridinium chloride, affords methane and Ir^III methyl chloride complexes. ¹H-NMR experiments show addition of pyridinium [BArF₂₀]⁻ (BArF₂₀=[B(C₆F₅)₄]⁻) to the dimethyl species forms [Cp(MeIm)IrMe(py)]⁺[BArF₂₀]⁻ (py=pyridine) or [Cp^Me4(MeIm)IrMe(py)]⁺[BArF₂₀]⁻ respectively, alongside methane, while use of the [BArF₂₀]⁻ salts of more bulky 2,6-dimethylpyridinium and 2,6-di-tert-butylpyridinium gave an intractable mixture. Likewise, the generation of 16 e⁻ species [Cp^Me4(MeIm)IrMe]⁺[BArF₂₀]⁻ or [Cp(MeIm)IrMe]⁺[BarF₂₀]⁻ at low temperature using 2,6-dimethylpyridinium or 2,6-di-tert-butylpyridinium in thawing C₆D₆ or toluene-d₈ formed an intractable mixture and did not lead to C−D bond activation. X-ray structures of several Ir^III complexes show similar sterics as that found for the previously reported Cp* analogue.     

Syntheses,Structures, and Bonding of NgF2⋅CrOF4, NgF2⋅2CrOF4 (Ng=Kr,Xe), and (CrOF4)∞

The noble-gas difluoride adducts, NgF₂ ⋅ CrOF₄ and NgF₂ ⋅ 2CrOF₄ (Ng=Kr and Xe), have been synthesized and structurally characterized at low temperatures by Raman spectroscopy and single-crystal X-ray diffraction. The low fluoride ion affinity of CrOF₄ renders it incapable of inducing fluoride ion transfer from NgF₂ (Ng=Kr and Xe) to form ion-paired salts of the [NgF]⁺ cations having either the [CrOF₅]⁻ or [Cr₂O₂F₉]⁻ anions. The crystal structures show the NgF₂ ⋅ CrOF₄ adducts are comprised of F_t−Ng−F_b- - -Cr(O)F₄ structural units in which NgF₂ is weakly coordinated to CrOF₄ by means of a fluorine bridge, F_b, in which Ng−F_b is elongated relative to the terminal Ng−F_t bond. In contrast with XeF₂ ⋅ 2MOF₄ (M=Mo or W) and KrF₂ ⋅ 2MoOF₄, in which the Lewis acidic, F₄(O)M- - -F_b- - -M(O)F₃ moiety coordinates to Ng through a single M- - -F_b−Ng bridge, both fluorine ligands of NgF₂ coordinate to CrOF₄ molecules to form F₄(O)Cr- - -F_b−Ng−F_b- - -Cr(O)F₄ adducts in which both Ng−F_b bonds are only marginally elongated relative to the Ng−F bonds of free NgF₂. Quantum-chemical calculations show that the Cr−F_b bonds of NgF₂ ⋅ CrOF₄ and NgF₂ ⋅ 2CrOF₄ are predominantly electrostatic with a small degree of covalent character that accounts for their nonlinear Cr- - -F_b−Ng bridge angles and staggered O−Cr- - -F_b−Ng−F_t dihedral angles. The crystal structures and Raman spectra of two CrOF₄ polymorphs have also been obtained. Both are comprised of fluorine-bridged chains that are cis- and trans-fluorine-bridged with respect to oxygen.