C−H Activation by Iron-Vanadium Bimetallic Oxide Cluster Anions FeV3O10− and FeV5O15−: A Comparison with Scandium-Vanadium Oxide Clusters

Late transition metal-bonded atomic oxygen radicals (LTM−O⋅⁻) have been frequently proposed as important active sites to selectively activate and transform inert alkane molecules. However, it is extremely challenging to characterize the LTM−O⋅⁻-mediated elementary reactions for clarifying the underlying mechanisms limited by the low activity of LTM−O⋅⁻ radicals that is inaccessible by the traditional experimental methods. Herein, benefiting from our newly-designed ship-lock type reactor, the reactivity of iron-vanadium bimetallic oxide cluster anions FeV₃O₁₀⁻ and FeV₅O₁₅⁻ featuring with Fe−O⋅⁻ radicals to abstract a hydrogen atom from C₂−C₄ alkanes has been experimentally characterized at 298 K, and the rate constants are determined in the orders of magnitude of 10⁻¹⁴ to 10⁻¹⁶ cm³ molecule⁻¹ s⁻¹, which are four orders of magnitude slower than the values of counterpart ScV₃O₁₀⁻ and ScV₅O₁₅⁻ clusters bearing Sc−O⋅⁻ radicals. Theoretical results reveal that the rearrangements of the electronic and geometric structures during the reaction process function to modulate the activity of Fe−O⋅⁻. This study not only quantitatively characterizes the elementary reactions of LTM−O⋅⁻ radicals with alkanes, but also provides new insights into structure-activity relationship of M−O⋅⁻ radicals.     

Atomically Dispersed Cobalt/Copper Dual-Metal Catalysts for Synergistically Boosting Hydrogen Generation from Formic Acid

The development of practical materials for (de)hydrogenation reactions is a prerequisite for the launch of a sustainable hydrogen economy. Herein, we present the design and construction of an atomically dispersed dual-metal site Co/Cu−N−C catalyst allowing significantly improved dehydrogenation of formic acid, which is available from carbon dioxide and green hydrogen. The active catalyst centers consist of specific CoCuN₆ moieties with double-N-bridged adjacent metal-N₄ clusters decorated on a nitrogen-doped carbon support. At optimal conditions the dehydrogenation performance of the nanostructured material (mass activity 77.7 L ⋅ g_metal⁻¹ ⋅ h⁻¹) is up to 40 times higher compared to commercial 5 % Pd/C. In situ spectroscopic and kinetic isotope effect experiments indicate that Co/Cu−N−C promoted formic acid dehydrogenation follows the so-called formate pathway with the C−H dissociation of HCOO* as the rate-determining step. Theoretical calculations reveal that Cu in the CoCuN₆ moiety synergistically contributes to the adsorption of intermediate HCOO* and raises the d-band center of Co to favor HCOO* activation and thereby lower the reaction energy barrier.     

Construction of Low-Coordination Cu−C2 Single-Atoms Electrocatalyst Facilitating the Efficient Electrochemical CO2 Reduction to Methane

Constructing Cu single-atoms (SAs) catalysts is considered as one of the most effective strategies to enhance the performance of electrochemical reduction of CO₂ (e-CO₂RR) towards CH₄, however there are challenges with activity, selectivity, and a cumbersome fabrication process. Herein, by virtue of the meta-position structure of alkynyl in 1,3,5-triethynylbenzene and the interaction between Cu and −C≡C−, a Cu SAs electrocatalyst (Cu−SAs/HGDY), containing low-coordination Cu−C₂ active sites, was synthesized through a simple and efficient one-step method. Notably, this represents the first achievement of preparing Cu SAs catalysts with Cu−C₂ coordination structure, which exhibited high CO₂-to-CH₄ selectivity (72.1 %) with a high CH₄ partial current density of 230.7 mA cm⁻², and a turnover frequency as high as 2756 h⁻¹, dramatically outperforming currently reported catalysts. Comprehensive experiments and calculations verified the low-coordination Cu−C₂ structure not only endowed the Cu SAs center more positive electricity but also promoted the formation of H•, which contributed to the outstanding e-CO₂RR to CH₄ electrocatalytic performance of Cu−SAs/HGDY. Our work provides a novel H⋅-transferring mechanism for e-CO₂RR to CH₄ and offers a protocol for the preparation of two-coordinated Cu SAs catalysts.     

Atomically Dispersed Nickel Anchored on a Nitrogen-Doped Carbon/TiO2 Composite for Efficient and Selective Photocatalytic CH4 Oxidation to Oxygenates

Direct photocatalytic oxidation of methane to liquid oxygenated products is a sustainable strategy for methane valorization at room temperature. However, in this reaction, noble metals are generally needed to function as cocatalysts for obtaining adequate activity and selectivity. Here, we report atomically dispersed nickel anchored on a nitrogen-doped carbon/TiO₂ composite (Ni−NC/TiO₂) as a highly active and selective catalyst for photooxidation of CH₄ to C1 oxygenates with O₂ as the only oxidant. Ni−NC/TiO₂ exhibits a yield of C1 oxygenates of 198 μmol for 4 h with a selectivity of 93 %, exceeding that of most reported high-performance photocatalysts. Experimental and theoretical investigations suggest that the single-atom Ni−NC sites not only enhance the transfer of photogenerated electrons from TiO₂ to isolated Ni atoms but also dominantly facilitate the activation of O₂ to form the key intermediate ⋅OOH radicals, which synergistically lead to a substantial enhancement in both activity and selectivity.     

Understanding Regium Bonds and their Competition with Hydrogen Bonds in Au2:HX Complexes

A theoretical study of the regium and hydrogen bonds (RB and HB, respectively) in Au₂:HX complexes has been carried out by means of CCSD(T) calculations. The theoretical study shows as overall outcome that in all cases the complexes exhibiting RB are more stable that those with HB. The binding energies for RB complexes range between −24 and −180 kJ ⋅ mol^−1, whereas those of the HB complexes are between −6 and −19 kJ ⋅ mol⁻¹. DFT-SAPT also indicated that HB complexes are governed by electrostatics, but RB complexes present larger contribution of the induction term to the total attractive forces. ¹⁹⁷Au chemical shifts have been calculated using the relativistic ZORA Hamiltonian.     

Halocyclopropenium-Halide Halogen-Bonded Ion Pairs and Their Hydrogen-Bonded Halide Solvates

A series of salts with a diaminohalocyclopropenium cation and halide anion [C₃(NⁱPr₂)₂X]X (X=Cl ([ 1 ]Cl) or Br ([ 2 ]Br) were isolated with a variety of solvates and, in one case, as a co-crystal with hydronium chloride. In particular, the initial synthesis of [ 1 ]Cl formed a co-crystal with hydronium and with CH₂Cl₂ solvate ([ 1 ]₂[OH₃Cl₃] ⋅ CH₂Cl₂) upon isolation from acetone/CH₂Cl₂. Recrystallization of this from chloroform gave a dichloroform adduct [ 1 ]Cl ⋅ 2CHCl₃, whereas treatment with ICl formed an octahalide cluster [ 1 ]₂I₄Cl₄. The bromine salt [ 2 ]Br ⋅ C₂H₄Br₂ was prepared by treatment of [ 1 ]Cl with dibromoethane and was isolated as a solvate. The hydronium cation was found as part of a hydronium trichloride cluster [OH₃Cl₃]²⁻ and this, along with a partially-deuterated analogue of [OHD₂Cl₃]²⁻ and [OD₃Cl₃]²⁻, was studied computationally and by mid- and far-infrared spectroscopy. Significant halogen bonds were found between 1 ⁺ or 2 ⁺ and chloride or bromide, respectively. On the other hand, the distance to the octahalide [I₄Cl₄]²⁻ is too long for a halogen bond. Hydrogen bonding from the halides to the halomethane solvates is also significantly stronger than to the cation isopropyl groups. The geometries formed at the halide ions with respect to the halogen bond and strong hydrogen bonds are pyramidal with approximately orthogonal angles.     

Room-Temperature Solid-State Transformation of Na4SnS4 ⋅ 14H2O into Na4Sn2S6 ⋅ 5H2O: An Unusual Epitaxial Reaction Including Bond Formation,Mass Transport,and Ionic Conductivity

A highly unusual solid-state epitaxy-induced phase transformation of Na₄SnS₄ ⋅ 14H₂O ( I ) into Na₄Sn₂S₆ ⋅ 5H₂O ( II ) occurs at room temperature. Ab initio molecular dynamics (AIMD) simulations indicate an internal acid-base reaction to form [SnS₃SH]³⁻ which condensates to [Sn₂S₆]⁴⁻. The reaction involves a complex sequence of O−H bond cleavage, S²⁻ protonation, Sn−S bond formation and diffusion of various species while preserving the crystal morphology. In situ Raman and IR spectroscopy evidence the formation of [Sn₂S₆]⁴⁻. DFT calculations allowed assignment of all bands appearing during the transformation. X-ray diffraction and in situ ¹H NMR demonstrate a transformation within several days and yield a reaction turnover of ≈0.38 %/h. AIMD and experimental ionic conductivity data closely follow a Vogel-Fulcher-Tammann type T dependence with D(Na)=6×10⁻¹⁴ m² s⁻¹ at T=300 K with values increasing by three orders of magnitude from −20 to +25 °C.     

Effects of Intra-Base Pair Proton Transfer on Dissociation and Singlet Oxygenation of 9-Methyl-8-Oxoguanine−1-Methyl-Cytosine Base-Pair Radical Cations

8-Oxoguanosine is the most common oxidatively generated base damage and pairs with complementary cytidine within duplex DNA. The 8-oxoguanosine−cytidine lesion, if not recognized and removed, not only leads to G-to-T transversion mutations but renders the base pair being more vulnerable to the ionizing radiation and singlet oxygen (¹O₂) damage. Herein, reaction dynamics of a prototype Watson−Crick base pair [9MOG ⋅ 1MC]⋅⁺, consisting of 9-methyl-8-oxoguanine radical cation (9MOG⋅⁺) and 1-methylcystosine (1MC), was examined using mass spectrometry coupled with electrospray ionization. We first detected base-pair dissociation in collisions with the Xe gas, which provided insight into intra-base pair proton transfer of 9MOG⋅⁺ ⋅ 1MC [9MOG − H_N1]⋅ ⋅ [1MC+H_N3′]⁺ and subsequent non-statistical base-pair separation. We then measured the reaction of [9MOG ⋅ 1MC]⋅⁺ with ¹O₂, revealing the two most probable pathways, C5-O₂ addition and H_N7-abstraction at 9MOG. Reactions were entangled with the two forms of 9MOG radicals and base-pair structures as well as multi-configurations between open-shell radicals and ¹O₂ (that has a mixed singlet/triplet character). These were disentangled by utilizing approximately spin-projected density functional theory, coupled-cluster theory and multi-referential electronic structure modeling. The work delineated base-pair structural context effects and determined relative reactivity toward ¹O₂ as [9MOG − H]⋅>9MOG⋅⁺>[9MOG − H_N1]⋅ ⋅ [1MC+H_N3′]⁺≥9MOG⋅⁺ ⋅ 1MC.     

Tetrabutylammonium Salts of Aluminum(III) and Gallium(III) Phthalocyanine Radical Anions Bonded with Fluoren‐9‐olato− Anions and Indium(III) Phthalocyanine Bromide Radical Anions

Reduction of aluminum(III), gallium(III), and indium(III) phthalocyanine chlorides by sodium fluorenone ketyl in the presence of tetrabutylammonium cations yielded crystalline salts of the type (Bu₄N⁺)₂[M^III(HFl−O⁻)(Pc^.3−)]^.−(Br⁻) ⋅ 1.5 C₆H₄Cl₂ [M=Al ( 1 ), Ga ( 2 ); HFl−O⁻=fluoren‐9‐olato⁻ anion; Pc=phthalocyanine] and (Bu₄N⁺) [In^IIIBr(Pc^.3−)]^.− ⋅ 0.875 C₆H₄Cl₂ ⋅ 0.125 C₆H₁₄ ( 3 ). The salts were found to contain Pc^.3− radical anions with negatively charged phthalocyanine macrocycles, as evidenced by the presence of intense bands of Pc^.3− in the near‐IR region and a noticeable blueshift in both the Q and Soret bands of phthalocyanine. The metal(III) atoms coordinate HFl−O⁻ anions in 1 and 2 with short Al−O and Ga−O bond lengths of 1.749(2) and 1.836(6) Å, respectively. The C−O bonds [1.402(3) and 1.391(11) Å in 1 and 2 , respectively] in the HFl−O⁻ anions are longer than the same bond in the fluorenone ketyl (1.27–1.31 Å). Salts 1 – 3 show effective magnetic moments of 1.72, 1.66, and 1.79 μ_B at 300 K, respectively, owing to the presence of unpaired S= 1/2 spins on Pc^.3−. These spins are coupled antiferromagnetically with Weiss temperatures of −22, −14, and −30 K for 1 – 3 , respectively. Coupling can occur in the corrugated two‐dimensional phthalocyanine layers of 1 and 2 with an exchange interaction of J /k _B=−0.9 and −1.1 K, respectively, and in the π‐stacking {[In^IIIBr(Pc^.3−)]^.−}₂ dimers of 3 with an exchange interaction of J /k _B=−10.8 K. The salts show intense electron paramagnetic resonance (EPR) signals attributed to Pc^.3−. It was found that increasing the size of the central metal atom strongly broadened these EPR signals.     

Crystalline Rhodium-Tin Complexes with Radical Trianion and Tetraanion Phthalocyanine Ligands: Observation of Nimine(Pc)−Rh Coordination Bond

Crystalline {Cryptand(Na⁺)}[(COD)Rh^ICl⋅Sn^II(Pc³⁻)]⁻⋅2C₆H₄Cl₂ ( 1 ) and {Cryptand(Cs⁺)}[(COD)Rh^I⋅Sn^II(Pc⁴⁻)]⁻⋅C₆H₅CH₃ ( 2 ) complexes were obtained via the interaction of [Sn^II(Pc³⁻)]⁻ and [Sn^II(Pc⁴⁻)]²⁻, respectively, with organometallic {(COD)RhCl}₂ dimer (COD is 1,5-cyclooctadiene). Dissociation of {(COD)RhCl}₂ followed by the Rh−Sn binding is observed at the formation of 1 . Elimination of the chlorine atom at the rhodium atom is observed in 2 , and rhodium is additionally coordinated to the imine nitrogen atom of Pc⁴⁻. The complexes contain mono- Pc⋅³⁻ and doubly reduced Pc⁴⁻ species, respectively, that is supported by the data of XRD analysis as well as optical and magnetic properties of 1 and 2 . There is an alternation of C-N_imine bonds in the macrocycles, which gradually increases with increasing negative charge on the macrocycle. The difference between shorter and longer bonds increases from 0.051 Å in Pc³⁻ to 0.075 Å in Pc⁴⁻. The formation of 1 is accompanied by an essential blue shift of the Q-band of starting SnPc and the appearance of a new intense band at 1031 nm. The even stronger shift of the Q-band is observed in the spectrum of 2 , but the band in the near-IR range becomes weaker. The value of effective magnetic moment of 1 is 1.76 μ_B at 300 K corresponding the contribution of the Pc³⁻ radical trianions (S=1/2). Only weak magnetic coupling with the Weise temperature of −3 K is observed in 1 due to weak π–π interaction between the macrocycles in the chains. Paramagnetic Pc³⁻ species additionally monitored by EPR spectroscopy show a strong temperature dependence of g-factor and linewidth of the EPR signal. Complex 2 is diamagnetic and EPR silent.     

Back Cover: Illustrating the Fate of Methyl Radical in Photocatalytic Methane Oxidation over Ag−ZnO by in situ Synchrotron Radiation Photoionization Mass Spectrometry (Angew. Chem. Int. Ed. 32/2023)

Photocatalysis has emerged as an ideal method for the direct activation and conversion of methane under mild conditions. In this reaction, methyl radical (⋅CH₃) was deemed a key intermediate that affected the yields and selectivity of the products. However, direct observation of ⋅CH₃ and other intermediates is still challenging. Here, a rectangular photocatalytic reactor coupled with in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) was developed to detect reactive intermediates within several hundred microseconds during photocatalytic methane oxidation over Ag−ZnO. Gas phase ⋅CH₃ generated by photogenerated holes (O⁻) was directly observed, and its formation was demonstrated to be significantly enhanced by coadsorbed oxygen molecules. Methoxy radical (CH₃O⋅) and formaldehyde (HCHO) were confirmed to be key C1 intermediates in photocatalytic methane overoxidation to CO₂. The gas-phase self-coupling reaction of ⋅CH₃ contributes to the formation of ethane, which indicates the key role of ⋅CH₃ desorption in the highly selective synthesis of ethane. Based on the observed intermediates, the reaction network initiated from ⋅CH₃ of photocatalytic methane oxidation could be clearly illustrated, which is helpful for studying the photocatalytic methane conversion processes.     

Dual-Templating Approaches to Soybeans Milk-Derived Hierarchically Porous Heteroatom-Doped Carbon Materials for Lithium-Ion Batteries

Biomass derived carbon materials are widely available, cheap and abundant resources. The application of these materials as electrodes for rechargeable batteries shows great promise. To further explore their applications in energy storage fields, the structural design of these materials has been investigated. Hierarchical porous heteroatom-doped carbon materials (HPHCs) with open three-dimensional (3D) nanostructure have been considered as highly efficient energy storage materials. In this work, biomass soybean milk is chosen as the precursor to construct N, O co-doped interconnected 3D porous carbon framework via two approaches by using soluble salts (NaCl/Na₂CO₃ and ZnCl₂/Mg₅(OH)₂(CO₃)₄, respectively) as hard templates. The electrochemical results reveal that these structures were able to provide a stable cycling performance (710 mAh ⋅ g⁻¹ at 0.1 A ⋅ g⁻¹ after 300 cycles for HPHC-a, and 610 mAh ⋅ g⁻¹ at 0.1 A ⋅ g⁻¹ after 200 cycles for HPHC-b) in Li-ion battery and Na-ion storage (210 mAh ⋅ g⁻¹ at 0.1 A ⋅ g⁻¹ after 900 cycles for HPHC-a) as anodes materials, respectively. Further comparative studies showed that these improvements in HPHC-a performance were mainly due to the honeycomb-like structure containing graphene-like nanosheets and high nitrogen content in the porous structures. This work provides new approaches for the preparation of hierarchically structured heteroatom-doped carbon materials by pyrolysis of other biomass precursors and promotes the applications of carbon materials in energy storage fields.     

Weak Antiferromagnetic Exchange and Ferromagnetic Alignment of FeII (S=2) Spins in Differently Charged {HAT ⋅ (FeIICl2)3}n (n=2- and 3-) Assemblies of Hexaazatriphenylenes (HAT)

Hexaazatrianthracene (HATA) and hexaazatriphenylenehexacarbonitrile {HAT(CN)₆} are reduced by metallic iron in the presence of crystal violet (CV⁺)(Cl⁻). Anionic ligands are produced, which simultaneously coordinate three Fe^IICl₂ to form (CV⁺)₂{HATA ⋅ (Fe^IICl₂)₃}²⁻ ⋅ 3 C₆H₄Cl₂ ( 1 ) and (CV⁺)₃{HAT(CN)_6. (Fe^IICl₂)₃}³⁻ ⋅ 0.5CVCl ⋅ 2.5 C₆H₄Cl₂ ( 2 ). High-spin (S=2) Fe^II atoms in both structures are arranged in equilateral triangles at a distance of 7 Å. An antiferromagnetic exchange is observed between Fe^II in {HATA ⋅ (Fe^IICl₂)₃}²⁻ ( 1 ) with a Weiss temperature (Θ) of −80 K, the PHI estimated exchange interaction (J) is −4.7 cm⁻¹. The {HAT(CN)₆ ⋅ (Fe^IICl₂)₃}³⁻ assembly is obtained in 2 . The formation of HAT(CN)₆^.3− is supported by the appearance of an intense EPR signal with g=2.0037. The magnetic behavior of 2 is described by a strong antiferromagnetic coupling between the Fe^II and HAT(CN)₆^.3− spins with J₁=−164 cm⁻¹ (−2 J formalism) and by a weaker antiferromagnetic coupling between the Fe^II spins with J₂=−15.4 cm⁻¹. The stronger coupling results in the spins of the three Fe^IICl₂ units to be aligned parallel to each other in the assembly. As a result, an increase of the χ_MT values is observed with the decrease of temperature from 9.82 at 300 K up to 15.06 emu ⋅ K/mol at 6 K, and the Weiss temperature is also positive being at +23 K. Thus, a change in the charge and spin state of the HAT-type ligand to ⋅3⁻ results in ferromagnetic alignment of the Fe^II spins, yielding a high-spin (S=11/2) system. DFT calculations showed that, due to the high symmetry and nearly degenerated LUMO of both HATA and HAT(CN)₆, their complexes with Fe^IICl₂ have a variety of closely lying excited high-spin states with multiplicity up to S=15/2.     

Rapid Polyolefin Hydrogenolysis by a Single-Site Organo-Tantalum Catalyst on a Super-Acidic Support: Structure and Mechanism

The novel electrophilic organo-tantalum catalyst AlS/TaNp_x ( 1 ) (Np=neopentyl) is prepared by chemisorption of the alkylidene Np₃Ta=CH^tBu onto highly Brønsted acidic sulfated alumina (AlS). The proposed catalyst structure is supported by EXAFS, XANES, ICP, DRIFTS, elemental analysis, and SSNMR measurements and is in good agreement with DFT analysis. Catalyst 1 is highly effective for the hydrogenolysis of diverse linear and branched hydrocarbons, ranging from C2 to polyolefins. To the best of our knowledge, 1 exhibits one of the highest polyolefin hydrogenolysis activities (9,800 (CH₂ units) ⋅ mol(Ta)⁻¹ ⋅ h⁻¹ at 200 °C/17 atm H₂) reported to date in the peer-reviewed literature. Unlike the AlS/ZrNp₂ analog, the Ta catalyst is more thermally stable and offers multiple potential C−C bond activation pathways. For hydrogenolysis, AlS/TaNp_x is effective for a wide variety of pre- and post-consumer polyolefin plastics and is not significantly deactivated by standard polyolefin additives at typical industrial concentrations.     

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.     

Deuteron Solid-State NMR Relaxation Measurements Reveal Two Distinct Conformational Exchange Processes in the Disordered N-Terminal Domain of Amyloid-β Fibrils

We employed deuterium solid-state NMR techniques under static conditions to discern the details of the μs–ms timescale motions in the flexible N-terminal subdomain of Aβ_1–40 amyloid fibrils, which spans residues 1–16. In particular, we utilized a rotating frame (R_1ρ) and the newly developed time domain quadrupolar Carr-Purcell-Meiboom-Gill (QCPMG) relaxation measurements at the selectively deuterated side chains of A2, H6, and G9. The two experiments are complementary in terms of probing somewhat different timescales of motions, governed by the tensor parameters and the sampling window of the magnetization decay curves. The results indicated two mobile “free” states of the N-terminal domain undergoing global diffusive motions, with isotropic diffusion coefficients of 0.7−1 ⋅ 10⁸ and 0.3−3 ⋅ 10⁶ad² s⁻¹. The free states are also involved in the conformational exchange with a single bound state, in which the diffusive motions are quenched, likely due to transient interactions with the structured hydrophobic core. The conformational exchange rate constants are 2−3 ⋅ 10⁵ s⁻¹ and 2−3 ⋅ 10⁴ s⁻¹ for the fast and slow diffusion free states, respectively.     

Self-Assembly of a Redox Active,Metallosupramolecular [Pd3L6]6+ Complex Using a Rotationally Flexible Ferrocene Ligand

A new ferrocene-containing [Pd₃( L_4EFc )₆]⁶⁺(X⁻)₆ ( C ⋅ BF₄ and C ⋅ SbF₆ where X=BF₄⁻ or SbF₆⁻) self-assembled double-walled triangle has been synthesized from the known, rotationally flexible, 1,1′-bis(4-pyridylethynyl)ferrocene ligand ( L_4EFc ), and characterized by ¹H, ¹³C and diffusion ordered (DOSY) NMR spectroscopies, high-resolution electrospray ionization mass spectrometry (HR−ESI−MS), X-ray crystallography and cyclic voltammetry (CV). The molecular structures confirmed that double-walled triangle cage systems ( C ⋅ BF₄ and C ⋅ SbF₆ ) were generated. C ⋅ BF₄ was shown to interact with the anionic guest, p-toluenesulfonate. CV experiments revealed that the triangles were redox active, however addition of the guest did not influence the redox potentials.     

Cation-Radius-Controlled Sn−O Bond Length Boosting CO2 Electroreduction over Sn-Based Perovskite Oxides

Despite the intriguing potential shown by Sn-based perovskite oxides in CO₂ electroreduction (CO₂RR), the rational optimization of their CO₂RR properties is still lacking. Here we report an effective strategy to promote CO₂-to-HCOOH conversion of Sn-based perovskite oxides by A-site-radius-controlled Sn−O bond lengths. For the proof-of-concept examples of Ba_1−xSr_xSnO₃, as the A-site cation average radii decrease from 1.61 to 1.44 Å, their Sn−O bonds are precisely shortened from 2.06 to 2.02 Å. Our CO₂RR measurements show that the activity and selectivity of these samples for HCOOH production exhibit volcano-type trends with the Sn−O bond lengths. Among these samples, the Ba_0.5Sr_0.5SnO₃ features the optimal activity (753.6 mA ⋅ cm⁻²) and selectivity (90.9 %) for HCOOH, better than those of the reported Sn-based oxides. Such optimized CO₂RR properties could be attributed to favorable merits conferred by the precisely controlled Sn−O bond lengths, e.g., the regulated band center, modulated adsorption/activation of intermediates, and reduced energy barrier for *OCHO formation. This work brings a new avenue for rational design of advanced Sn-based perovskite oxides toward CO₂RR.     

Study on Cd2+ Determination Using Bud-like Poly-L-Tyrosine/Bi Composite Film Modified Glassy Carbon Electrode Combined with Eliminating of Cu2+ Interference by Electrodeposition

A bud-like poly-L-tyrosine/Bi modified glassy carbon electrode (p-Tyr/Bi/GC) was prepared by CV and in situ Bi plating, whose conductivity and membrane morphology were characterized by CV, EIS and SEM, respectively. The p-Tyr membrane can effectively promote the enrichment of Cd²⁺. The optimal Tyr concentration and scanning number for p-Tyr/GC preparation were 2.0 mmol ⋅ L⁻¹ and 35, while the optimal Bi³⁺ concentration, pH and Cd²⁺ accumulation potential in test medium were 3.0 μmol ⋅ L⁻¹, 6.5 and −1.3 V, respectively. The linear equation of p-Tyr/Bi/GC's response to Cd²⁺ (1.0 nmol ⋅ L⁻¹ to 2.0 μmol ⋅ L⁻¹) was i_p (μA) = −0.6809 + 100.2c (μmol ⋅ L⁻¹) (R² = 0.9985) with a detection limit of 0.11 nmol ⋅ L⁻¹ (3S/N). The elimination of interference caused by Cu²⁺ in sample was studied by electrodeposition. The p-Tyr/Bi/GC electrode was successfully used for detecting Cd in rice samples with good reliability and accuracy. The developed Cd²⁺ sensor exhibits high sensitivity, wide linear range and low detection limit, especially the designed method of eliminating Cu²⁺ interference has the characteristics of high selectivity, simple operation and wide application range.     

Direct Conversion of Benzothiadiazole to Benzimidazole: New Benzimidazole-Derived Metal–Organic Frameworks with Adjustable Honeycomb-Like Cavities

Up to now, the direct conversion of the thiadiazole ring to other heterocyclic rings has been a very challenging task. Herein, a Cd^II-mediated alcohol-substitution strategy for direct conversion from benzothiadiazole to benzimidazole is reported. Experimental and molecular modeling studies on the role of the chelated metal ion in this in situ alcohol-substitution reaction revealed that it serves as an all-rounder that is involved in the insertion of alcohol, activation of the thiadiazole ring by coordinative interaction, and the sulfur-extrusion process. Interestingly, the insertion of alcohol occurs much earlier than the sulfur-extrusion process, supported by a water-mediated proton-transfer process. This strategy also is suitable for constructing new benzimidazole-derived MOFs [Cd₂(HMBIDC²⁻)₂] ⋅ 4 H₂O ( Cd-BID-MOF-1 , HMBIDC²⁻=2-methyl-1H-benzimidazole-4,7-dicarboxylate) and [Cd₂(HPBIDC²⁻)₂] ⋅ 1/3 H₂O ( Cd-BID-MOF-2 , HPBIDC²⁻=2-(3-hydroxypropyl)-2H-benzimidazole-4,7-dicarboxylate). Because the terminal hydroxyl group on the imidazole ring protrudes into the circular channel in rhombohedral Cd-BID-MOF-2 , the cavity is closer to hydrophilic than the honeycomb-like cavity in Cd-BID-MOF-1 with similar 3D structure. This rare observation will provide a new strategy to develop in situ ligand-reaction synthesis of functional MOFs and useful chelation-assisted catalytic reactions in heteroaromatic chemistry.