The Role of Alkali Metal in α‐MnO2 Catalyzed Ammonia‐Selective Catalysis

The unexpected phenomenon and mechanism of the alkali metal involved NH₃ selective catalysis are reported. Incorporation of K⁺ (4.22 wt %) in the tunnels of α‐MnO₂ greatly improved its activity at low temperature (50–200 °C, 100 % conversion of NO_x vs. 50.6 % conversion over pristine α‐MnO₂ at 150 °C). Experiment and theory demonstrated the atomic role of incorporated K⁺ in α‐MnO₂. Results showed that K⁺ in the tunnels could form a stable coordination with eight nearby O atoms. The columbic interaction between the trapped K⁺ and O atoms can rearrange the charge population of nearby Mn and O atoms, thus making the topmost five‐coordinated unsaturated Mn cations (Mn_5c, the Lewis acid sites) more positive. Therefore, the more positively charged Mn_5c can better chemically adsorb and activate the NH₃ molecules compared with its pristine counterpart, which is crucial for subsequent reactions.     

Crossover between Tilt Families and Zero Area Thermal Expansion in Hybrid Prussian Blue Analogues

Materials in the family of Prussian blue analogues (C₃H₅N₂)₂K[ M (CN)₆], where C₃H₅N₂ is the imidazolium ion and M =Fe, Co, undergo two phase transitions with temperature; at low temperatures the imidazolium cations have an ordered configuration (C 2/c ), while in the intermediate‐ and high‐temperature phases (both previously reported as ) they are dynamically disordered. We show from high‐resolution powder neutron diffraction data that the high‐temperature phase has zero area thermal expansion in the ab ‐plane. Supported by Landau theory and single‐crystal X‐ray diffraction data, we re‐evaluate the space group symmetry of the intermediate‐temperature phase to . This reveals that the low‐to‐intermediate temperature transition is due to competition between two different tilt patterns of the [ M (CN)₆]³⁻ ions. Controlling the relative stabilities of these tilt patterns offers a potential means to tune the exploitable electric behaviour that arises from motion of the imidazolium guest.     

Low‐Voltage Gaseous HCl Electrolysis with an Iron Redox‐Mediated Cathode for Chlorine Regeneration

Gaseous HCl as a by‐product is often produced from chlorination processes using Cl₂ gas. Onsite Cl₂ regeneration from HCl is highly desirable as it eliminates the need to buy new Cl₂ and dispose HCl waste. A gaseous HCl electrolysis with Fe³⁺/Fe²⁺ redox‐mediated cathode is demonstrated for Cl₂ regeneration. HCl is oxidized to generate Cl₂ and protons in the anode while Fe³⁺ is reduced to Fe²⁺ in the cathode. Simultaneously Fe³⁺ is regenerated by chemical oxidation of Fe²⁺ by oxygen (air) that also produces water. A low operational voltage and high coulombic efficiency are achieved by using a novel composite porous membrane and hydrophobic anode. Specifically, a cell voltage of only 0.64 V is needed at the typical current density of 4 kA m⁻², leading to a low energy consumption of 483 kWh per ton of Cl₂ (124 kJ mol ⁻¹) which is about 50–55 % of state‐of‐the‐art HCl electrolysis processes.     

A Cationic Unsaturated Platinum(II) Complex that Promotes the Tautomerization of Acetylene to Vinylidene

Complex [PtMe₂(PMe₂Ar )] ( 1 ), which contains a tethered terphenyl phosphine (Ar =2,6‐(2,6‐ⁱ Pr₂C₆H₃)₂C₆H₃), reacts with [H(Et₂O)₂]BAr_F (BAr_F⁻=B[3,5‐(CF₃)₂C₆H₃]₄⁻) to give the solvent (S) complex [PtMe(S)(PMe₂Ar )]⁺ ( 2⋅S ). Although the solvent molecule is easily displaced by a Lewis base (e.g., CO or C₂H₄) to afford the corresponding adducts, treatment of 2⋅S with C₂H₂ yielded instead the allyl complex [Pt(η³‐C₃H₅)(PMe₂Ar )]⁺ ( 6 ) via the alkyne intermediate [PtMe(η²‐C₂H₂)(PMe₂Ar )]⁺ ( 5 ). Deuteration experiments with C₂D₂, and kinetic and theoretical investigations demonstrated that the conversion of 5 into 6 involves a Pt^II‐promoted HC≡CH to :C=CH₂ tautomerization in preference over acetylene migratory insertion into the Pt−Me bond.     

A T‐Shaped Nickel(I) Metalloradical Species

A T‐shaped Ni^I complex was synthesized using a rigid acridane‐based pincer ligand to prepare a metalloradical center. Structural data displays a nickel ion is embedded in the plane of a PNP ligand. Having a sterically exposed half‐filled orbital, this three‐coordinate Ni^I species reveals unique open‐shell reactivity including the homolytic cleavage of various σ‐bonds, such as H−H, N−N, and C−C.     

A Low‐Spin Three‐Coordinate Cobalt(I) Complex and Its Reactivity toward H2 and Silane

A three‐coordinate low‐spin cobalt(I) complex generated using a pincer ligand is presented. Since an empty orbital is sterically exposed at the site trans to the N donor of an acridane moiety, the cobalt(I) center accepts the coordination of various donors such as H₂ and PhSiH₃ revealing σ‐complex formation. At this low‐spin cobalt(I) site, homolysis of H–H and Si?H bonds preferentially occurs via bimolecular hydrogen atom transfer instead of two‐electron oxidative addition. When the resulting Co^II–H species was exposed to N₂, H₂ evolution readily occurs at ambient conditions. These results suggest single‐electron processes are favored at the structurally rigidified cobalt center.     

The β‐Agostic Structure in (C5Me5)2Sc(CH2CH3): Solid‐State NMR Studies of (C5Me5)2Sc−R (R=Me,Ph, Et)

Multinuclear solid‐state NMR studies of Cp*₂Sc−R (Cp*=pentamethylcyclopentadienyl; R=Me, Ph, Et) and DFT calculations show that the Sc−Et complex contains a β‐CH agostic interaction. The static central transition ⁴⁵Sc NMR spectra show that the quadrupolar coupling constants (C_q) follow the trend of Ph≈Me>Et, indicating that the Sc−R bond is different in Cp*₂Sc−Et compared to the methyl and phenyl complexes. Analysis of the chemical shift tensor (CST) shows that the deshielding experienced by Cβ in Sc−CH₂CH₃ is related to coupling between the filled σ_C‐C orbital and the vacant orbital.     

An Acyclic Arsenium Cation Stabilised by a Single P–As π‐Interaction and a Cyclic Diphosphinophosphonium Salt

Stable acyclic arsenium cations R₂As⁺, isoelectronic analogues of germylenes, are rare in comparison to the corresponding phosphenium cations. The first example of a diphosphaarsenium salt, [{(Dipp)₂P}₂As][Al{OC(CF₃)₃}₄]?1 PhMe, is described. This salt exhibits remarkable stability due to the delocalisation of a lone pair from a planar phosphorus centre into the vacant p‐orbital at arsenic; the bonding in 2 has been probed by DFT calculations. An attempt to synthesise an analogous diphosphaphosphenium salt unexpectedly generated the cyclic phosphonium salt [cyclo‐{(Mes)P}₂P(Mes)₂][BAr^F₄]?CyMe through the cyclisation of a putative phosphine‐substituted diphosphene cation intermediate.     

Confined Lewis Pairs: Investigation of the X−→Si20 Interaction in Halogen-Encapsulating Silafulleranes

A joint theoretical and experimental study on 32 endohedral silafullerane derivatives [X@Si₂₀Y₂₀]⁻ (X=F-I; Y=F-I, H, Me, Et) and -[Cl@Si₂₀H₁₂Y₈]⁻ (Y=F-I) is presented. First, we evaluated the structure-determining template effect of Cl⁻ in a systematic series of concave silapolyquinane model systems. Second, we investigated the X⁻→Si₂₀ interaction energy ( ) as a function of X⁻ and Y and found the largest values for electron-withdrawing exohedral substituents Y. Given that X⁻ ions can be considered as Lewis bases and empty Si₂₀Y₂₀ clusters as Lewis acids, we classify our inseparable host–guest complexes [X@Si₂₀Y₂₀]⁻ as “confined Lewis pairs”. Third, ³⁵Cl NMR spectroscopy proved to be highly diagnostic for an experimental assessment of the Cl⁻→Si₂₀ interaction as the paramagnetic shielding and, in turn, (³⁵Cl) of the endohedral Cl⁻ ion correlate inversely with . Finally, we disclose the synthesis of [PPN][Cl@Si₂₀Y₂₀] (Y=Me, Et, Br) and provide a thorough characterization of these new silafulleranes.     

A Ferroelectric Iron(II) Spin Crossover Material

A dual‐function material in which ferroelectricity and spin crossover coexist in the same temperature range has been obtained. Our synthetic strategy allows the construction of acentric crystal structures in a predictable way and is based on the high directionality of hydrogen bonds. The well‐known iron(II) spin crossover complex [Fe(bpp)₂]²⁺ (bpp=2,6‐bis(pyrazol‐3‐yl)pyridine), a four‐fold noncentrosymmetric H‐bond donor, was combined with a disymmetric H‐bond acceptor such as the isonicotinate (isonic) anion to afford [Fe(bpp)₂](isonic)₂⋅2 H₂O. This low‐spin iron(II) compound crystallizes in the acentric nonpolar I space group and shows piezoelectricity and SHG properties. Upon dehydration, it undergoes a single‐crystal to single‐crystal structural rearrangement to a monoclinic polar Pc phase that is ferroelectric and exhibits spin crossover.     

Oxidative Cleavage of S–S Bond During the Reduction of Tris(pyridine‐2‐carboxylato)manganese(III) by Dithionite in Sodium Picolinate–Picolinic Acid Buffer Medium

The reduction of tris(pyridine‐2‐carboxylato)manganese(III) by dithionite has been investigated within the temperature window 288–303 K and at pH range 5.22–6.10 in sodium picolinate–picolinic acid buffer medium. The reaction obeys the following stoichiometry: The reaction is described in terms of a mechanism that involves an initial complex formation between S₂O₄^2? and [Mn^III(C₅H₄NCO₂)₃] followed by S–S bond cleavage to give 2HSO₃^? and [Mn^II(C₅H₄NCO₂)₂(H₂O)₂] as the products via the formation of SO₂^●? radical anion. Kinetics and spectrophotometric evidences are cited in favor of the suggested mechanism. Thermodynamic parameters associated with the equilibrium step and the activation parameters with the rate‐determining step have been computed.     

Impact of Intramolecular Hydrogen Bonding on the Reactivity of Cupric Superoxide Complexes with O−H and C−H Substrates

The dioxygen reactivity of a series of TMPA‐based copper(I) complexes (TMPA=tris(2‐pyridylmethyl)amine), with and without secondary‐coordination‐sphere hydrogen‐bonding moieties, was studied at ?135 °C in 2‐methyltetrahydrofuran (MeTHF). Kinetic stabilization of the H‐bonded [( TMPA)Cu^II(O₂^.?)]⁺ cupric superoxide species was achieved, and they were characterized by resonance Raman (rR) spectroscopy. The structures and physical properties of [( TMPA)Cu^II(N₃^?)]⁺ azido analogues were compared, and the O₂^.? reactivity of ligand–Cu^I complexes when an H‐bonding moiety is replaced by a methyl group was contrasted. A drastic enhancement in the reactivity of the cupric superoxide towards phenolic substrates as well as oxidation of substrates possessing moderate C?H bond‐dissociation energies is observed, correlating with the number and strength of the H‐bonding groups.     

Terminal Iron Carbyne Complexes Derived from Arrested CO2 Reductive Disproportionation

The encumbered tetraisocyanide dianion Na₂[Fe(CNAr )₄] reacts with two molecules of CO₂ to effect reductive disproportionation to CO and carbonate ([CO₃]²⁻). When the reaction is performed in the presence of silyl triflates, reductive disproportionation is arrested by silylative esterification of a mono‐CO₂ adduct. This results in the formation of four‐coordinate terminal iron carbynes possessing an aryl carbamate substituent owing to the direct attachment of an C(O)OSiR₃ group to an isocyanide nitrogen atom. Crystallographic, spectroscopic, and computational analyses of these iron–carbon multiply bonded species reveal electronic structure properties indicative of a conformationally locked iron carbyne unit.     

Atomically Dispersed Molybdenum Catalysts for Efficient Ambient Nitrogen Fixation

NH₃ synthesis by the electrocatalytic N₂ reduction reaction (NRR) under ambient conditions is an appealing alternative to the currently employed industrial method—the Haber–Bosch process—that requires high temperature and pressure. We report single Mo atoms anchored to nitrogen‐doped porous carbon as a cost‐effective catalyst for the NRR. Benefiting from the optimally high density of active sites and hierarchically porous carbon frameworks, this catalyst achieves a high NH₃ yield rate (34.0±3.6 μg h^?1 mg_cat.^?1) and a high Faradaic efficiency (14.6±1.6 %) in 0.1 m KOH at room temperature. These values are considerably higher compared to previously reported non‐precious‐metal electrocatalysts. Moreover, this catalyst displays no obvious current drop during a 50 000 s NRR, and high activity and durability are achieved in 0.1 m HCl. The findings provide a promising lead for the design of efficient and robust single‐atom non‐precious‐metal catalysts for the electrocatalytic NRR.     

Electrocatalytic Synthesis of Ammonia at Room Temperature and Atmospheric Pressure from Water and Nitrogen on a Carbon‐Nanotube‐Based Electrocatalyst

Ammonia is synthesized directly from water and N₂ at room temperature and atmospheric pressure in a flow electrochemical cell operating in gas phase (half‐cell for the NH₃ synthesis). Iron supported on carbon nanotubes (CNTs) was used as the electrocatalyst in this half‐cell. A rate of ammonia formation of 2.2×10⁻³ g m⁻² h⁻¹ was obtained at room temperature and atmospheric pressure in a flow of N₂, with stable behavior for at least 60 h of reaction, under an applied potential of −2.0 V. This value is higher than the rate of ammonia formation obtained using noble metals (Ru/C) under comparable reaction conditions. Furthermore, hydrogen gas with a total Faraday efficiency as high as 95.1 % was obtained. Data also indicate that the active sites in NH₃ electrocatalytic synthesis may be associated to specific carbon sites formed at the interface between iron particles and CNT and able to activate N₂, making it more reactive towards hydrogenation.     

Large Magnetoelectric Coupling Near Room Temperature in Synthetic Melanostibite Mn2FeSbO6

Multiferroic materials exhibit two or more ferroic orders and have potential applications as multifunctional materials in the electronics industry. A coupling of ferroelectricity and ferromagnetism is hereby particularly promising. We show that the synthetic melanostibite mineral Mn₂FeSbO₆ (R space group) with ilmenite‐type structure exhibits cation off‐centering that results in alternating modulated displacements, thus allowing antiferroelectricity to occur. Massive magnetoelectric coupling (MEC) and magnetocapacitance effect of up to 4000 % was detected at a record high temperature of 260 K. The multiferroic behavior is based on the imbalance of cationic displacements caused by a magnetostrictive mechanism, which sets up an unprecedented example to pave the way for the development of highly effective MEC devices operational at or near room temperature.     

Reordering d Orbital Energies of Single‐Site Catalysts for CO2 Electroreduction

The single‐site catalyst (SSC) characteristic of atomically dispersed active centers will not only maximize the catalytic activity, but also provide a promising platform for establishing the structure–activity relationship. However, arbitrary arrangements of active sites in the existed SSCs make it difficult for mechanism understanding and performance optimization. Now, a well‐defined ultrathin SSC is fabricated by assembly of metal‐porphyrin molecules, which enables the precise identification of the active sites for d‐orbital energy engineering. The activity of as‐assembled products for electrocatalytic CO₂ reduction is significantly promoted via lifting up the energy level of metal d orbitals, exhibiting a remarkable Faradaic efficiency of 96 % at the overpotential of 500 mV. Furthermore, a turnover frequency of 4.21 s^?1 is achieved with negligible decay over 48 h.     

Transition metal complexes of a hydrazone–oxime ligand containing the isonicotinoyl moiety: Synthesis,characterization and microbicide activities

Complexes of VO²⁺, Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Ru³⁺ and UO₂²⁺ with (3‐(hydroxyimino)butan‐2‐ylidene)isonicotinohydrazide were synthesized and characterized using physical and spectral methods. Analytical data revealed that the complexes formed in 1:1 or 1:2 metal–ligand ratios. Spectral studies showed that the ligand bonded to the metal ion in neutral tridentate, monobasic tridentate or monobasic bidentate fashion through azomethine nitrogen atom, protonated/deprotonated imine oxime group and/or ketonic/enolic carbonyl group. From the electronic spectral data together with magnetic susceptibility values a square planar, tetrahedral or distorted octahedral structure can be proposed for all complexes. Electron spin resonance spectra for Cu²⁺ complexes ( 2 – 4 ) revealed axial symmetry with g_|| > g_⊥ > g_e, indicating distorted octahedral or square planar structures and the unpaired electron exists in a orbital with marked covalent bond feature. The prepared complexes showed good to excellent biological activity, and the most active complexes against Aspergillus niger were 4 and 9 with zone of inhibition of 25 and 23 mm, respectively. Complexes 10 and 11 showed interesting activity against Escherichia coli with zone of inhibition of 44 and 32 mm, respectively.     

An Experimental Study of the Kinetics of the Reactions of Isopropyl,sec‐Butyl,and tert‐Butyl Radicals with Molecular Chlorine at Low Pressures (0.5–7.0 Torr) in the Temperature Range 190–480 K

In this work, we have measured the rate coefficients of the reactions of isopropyl (propan‐2‐yl), sec‐butyl (butan‐2‐yl), and tert‐butyl (2‐methylpropan‐2‐yl) radicals with molecular chlorine as a function of temperature (190–480 K). The experiments were done in a tubular laminar flow reactor coupled to a photoionization quadrupole mass spectrometer employing a gas‐discharge lamp for ionization. The radicals were homogeneously produced in the reactor by photolyzing suitable precursor molecules with 193‐nm pulsed exciplex laser radiation. The bimolecular rate coefficients were obtained by monitoring the radical decay signals in real time under pseudo–first‐order conditions. The rate coefficients of all three reactions showed negative temperature dependence. The bath gas used in the experiments was helium, and the rate coefficients appeared to be independent of the helium concentrations employed ([2.4–14] × 10¹⁶ cm^?3) for all three reactions. The rate coefficients of the reactions can be approximated in the studied temperature range by the following parameterizations: We estimate that the overall uncertainties of the measured rate coefficients are ±20%. We were able to observe 2‐chloropropane (i‐C₃H₇Cl) product for the i‐C₃H₇^● + Cl₂ reaction. No products were observed for the other two reactions, and the reasons for this are briefly discussed in the text.