In‐situ XAFS Studies of Mn12 Molecular‐Cluster Batteries: Super‐Reduced Mn12 Clusters in Solid‐State Electrochemistry

In situ X‐ray absorption fine structure (XAFS) analyses were performed on rechargeable molecular cluster batteries (MCBs), which were formed by a lithium anode and cathode‐active material, [Mn₁₂O₁₂(CH₃CH₂C(CH₃)₂COO)₁₆(H₂O)₄] with tert‐pentyl carboxylate ligand (abbreviated as Mn12tPe), and with eight Mn³⁺ and four Mn⁴⁺ centers. This mixed valence cluster compound is used in an effort to develop a reusable in situ battery cell that is suitable for such long‐term performance tests. The Mn12tPe MCBs exhibit a large capacity of approximately 210 Ah kg⁻¹ in the voltage range V=4.0–2.0 V. The X‐ray absorption near‐edge structure (XANES) spectra exhibit a systematic change during the charging/discharging with an isosbestic point at 6555 eV, which strongly suggests that only either the Mn³⁺ or Mn⁴⁺ ions in the Mn12 skeleton are involved in this battery reaction. The averaged manganese valence, determined from the absorption‐edge energy, decreased monotonically from 3.3 to 2.5 in the first half of the discharging (4.0>V>2.8 V), but changed little in the second half (2.8>V>2.0 V). The former valence change indicates a reduction of the initial [Mn12]⁰ state by approximately ten electrons, which corresponds well with the half value of the observed capacity. Therefore, the large capacity of the Mn12 MCBs can be understood as being due to a combination of the redox change of the manganese ions and presumably a capacitance effect. The extended X‐ray absorption fine structure (EXAFS) indicates a gradual increase of the Mn²⁺ sites in the first half of the discharging, which is consistent with the XANES spectra. It can be concluded that the Mn12tPe MCBs would include a solid‐state electrochemical reaction, mainly between the neutral state [Mn12]⁰ and the super‐reduced state [Mn12]⁸⁻ that is obtained by a local reduction of the eight Mn³⁺ ions in Mn12 toward Mn²⁺ ions.     

Evolution of Oxygen–Metal Electron Transfer and Metal Electronic States During Manganese Oxide Catalyzed Water Oxidation Revealed with In Situ Soft X‐Ray Spectroscopy

Manganese oxide (MnO_x) electrocatalysts are examined herein by in situ soft X‐ray absorption spectroscopy (XAS) and resonant inelastic X‐ray scattering (RIXS) during the oxidation of water buffered by borate (pH 9.2) at potentials from 0.75 to 2.25 V vs. the reversible hydrogen electrode. Correlation of L‐edge XAS data with previous mechanistic studies indicates Mn^IV is the highest oxidation state involved in the catalytic mechanism. MnO_x is transformed into birnessite at 1.45 V and does not undergo further structural phase changes. At potentials beyond this transformation, RIXS spectra show progressive enhancement of charge transfer transitions from oxygen to manganese. Theoretical analysis of these data indicates increased hybridization of the Mn?O orbitals and withdrawal of electron density from the O ligand shell. In situ XAS experiments at the O K‐edge provide complementary evidence for such a transition. This step is crucial for the formation of O₂ from water.     

Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species

The structure of FeO_x species supported on γ‐Al₂O₃ was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al₂O₃ and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe₂O₃ particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al₂O₃ surface.     

Accelerated Oxygen Atom Transfer and C−H Bond Oxygenation by Remote Redox Changes in Fe3Mn‐Iodosobenzene Adducts

We report the synthesis, characterization, and reactivity of [LFe₃(PhPz)₃OMn(^sPhIO)][OTf]_x ( 3 : x =2; 4 : x =3), where 4 is one of very few examples of iodosobenzene–metal adducts characterized by X‐ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, ⁵⁷Fe Mössbauer and X‐ray absorption spectroscopy provided unique insights into how changes in oxidation state ( Fe^III ₂ Fe^IIMn^II vs. Fe^III ₃ Mn^II ) influence oxygen atom transfer in tetranuclear Fe₃Mn clusters. In particular, a one‐electron redox change at a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude.     

Physicochemical and Redox Characteristics of Fe Ion‐doped CeO2 Nanoparticles

We report the structural, thermal, optical, and redox properties of Fe‐doped cerium oxide (CeO₂) nanoparticles, obtained using the polyol‐co‐precipitation process. X‐ray diffraction data reveal the formation of single‐phase structurally isomorphous CeO₂. The presence of Fe³⁺ may act as electron acceptor and/or hole donor, facilitating longer lived charge carrier separation in Fe‐doped CeO₂ nanoparticles as confirmed by optical band gap energy. The increased content of localized defect states in the ceria gap and corresponding shift of the optical absorption edge towards visible range in Fe‐doped samples can significantly improve the optical activity of nanocrystalline ceria. The better‐quality redox performances of the Fe‐doped CeO₂ nanoparticles, compared with undoped CeO₂ nanoparticles, were ascribed mainly to a decrease in band gap energy and an increase in specific surface area of the material. As observed from TPR studies all Fe ‐doped CeO₂ nanoparticles, particularly the 10 mol % Fe doped CeO₂ nanoproduct, exhibit excellent reduction performance.     

Spinel copper ferrite nanoparticles: Preparation,characterization and catalytic activity

The magnetic CuFe₂O₄ nanoparticles have been synthesized and characterized by various spectroscopic methods, including X‐ray diffraction (XRD), O K, Cu and Fe K ‐edge X‐ray absorption near edge structure (XANES), energy dispersive X‐ray analysis (EDX), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The azide‐alkyne cycloaddition by the reaction of various phenylacetylenes with a mixture of benzyl halides and NaN₃ and also three component (A³) coupling reaction of aldehyde, alkyne and amine catalyzed by CuFe₂O₄ nanoparticles under aerobic conditions led to the formation of the 1,4‐disubstituted‐1,2,3‐triazoles and propargylamines in excellent yields. The catalyst can be recovered by applying an external magnetic field for the subsequent cycloaddition reactions and reused without any tangible loss in catalytic efficiency.     

Crystal‐Field and Covalency Effects in Uranates: An X‐ray Spectroscopic Study

The electronic structure of U^V‐ and U^VI‐containing uranates NaUO₃ and Pb₃UO₆ was studied by using an advanced technique, namely X‐ray absorption spectroscopy (XAS) in high‐energy‐resolution fluorescence‐detection (HERFD) mode. Due to a significant reduction in core–hole lifetime broadening, the crystal‐field splittings of the 5f shell were probed directly in HERFD‐XAS spectra collected at the U 3d edge, which is not possible by using conventional XAS. In addition, the charge‐transfer satellites that result from U 5f–O 2p hybridization were clearly resolved. The crystal‐field parameters, 5f occupancy, and degree of covalency of the chemical bonding in these uranates were estimated by using the Anderson impurity model by calculating the U 3d HERFD‐XAS, conventional XAS, core‐to‐core (U 4f–3d transitions) resonant inelastic X‐ray scattering (RIXS), and U 4f X‐ray photoelectron spectra. The crystal field was found to be strong in these systems and the 5f occupancy was determined to be 1.32 and 0.84 electrons in the ground state for NaUO₃ and Pb₃UO₆, respectively, which indicates a significant covalent character for these compounds.     

Mixed‐Metal MIL‐100(Sc,M) (M=Al,Cr, Fe) for Lewis Acid Catalysis and Tandem CC Bond Formation and Alcohol Oxidation

The trivalent metal cations Al³⁺, Cr³⁺, and Fe³⁺ were each introduced, together with Sc³⁺, into MIL‐100(Sc,M) solid solutions (M=Al, Cr, Fe) by direct synthesis. The substitution has been confirmed by powder X‐ray diffraction (PXRD) and solid‐state NMR, UV/Vis, and X‐ray absorption (XAS) spectroscopy. Mixed Sc/Fe MIL‐100 samples were prepared in which part of the Fe is present as α‐Fe₂O₃ nanoparticles within the mesoporous cages of the MOF, as shown by XAS, TGA, and PXRD. The catalytic activity of the mixed‐metal catalysts in Lewis acid catalysed Friedel–Crafts additions increases with the amount of Sc present, with the attenuating effect of the second metal decreasing in the order Al>Fe>Cr. Mixed‐metal Sc,Fe materials give acceptable activity: 40 % Fe incorporation only results in a 20 % decrease in activity over the same reaction time and pure product can still be obtained and filtered off after extended reaction times. Supported α‐Fe₂O₃ nanoparticles were also active Lewis acid species, although less active than Sc³⁺ in trimer sites. The incorporation of Fe³⁺ into MIL‐100(Sc) imparts activity for oxidation catalysis and tandem catalytic processes (Lewis acid+oxidation) that make use of both catalytically active framework Sc³⁺ and Fe³⁺. A procedure for using these mixed‐metal heterogeneous catalysts has been developed for making ketones from (hetero)aromatics and a hemiacetal.     

Chemoselective Hydrogenation of Nitroaromatics at the Nanoscale Iron(III)–OH–Platinum Interface

Catalytic hydrogenation of nitroaromatics is an environment‐benign strategy to produce industrially important aniline intermediates. Herein, we report that Fe(OH)_x deposition on Pt nanocrystals to give Fe(OH)_x/Pt, enables the selective hydrogenation of nitro groups into amino groups without hydrogenating other functional groups on the aromatic ring. The unique catalytic behavior is identified to be associated with the Fe^III‐OH‐Pt interfaces. While H₂ activation occurs on exposed Pt atoms to ensure the high activity, the high selectivity towards the production of substituted aniline originates from the Fe^III‐OH‐Pt interfaces. In situ IR, X‐ray photoelectron spectroscopy (XPS), and isotope effect studies reveal that the Fe³⁺/Fe²⁺ redox couple facilitates the hydrodeoxygenation of the ‐NO₂ group during hydrogenation catalysis. Benefitting from Fe^III‐OH‐Pt interfaces, the Fe(OH)_x/Pt catalysts exhibit high catalytic performance towards a broad range of substituted nitroarenes.     

The Proportion of Fe‐NX,N Doping Species and Fe3C to Oxygen Catalytic Activity in Core‐Shell Fe‐N/C Electrocatalyst

A bifunctional oxygen electrocatalyst composed of iron carbide (Fe₃C) nanoparticles encapsulated by nitrogen doped carbon sheets is reported. X‐ray photoelectron spectroscopy and X‐ray absorption near edge structure revealed the presence of several kinds of active sites (Fe?N_x sites, N doping sites) and the modulated electron structure of nitrogen doped carbon sheets. Fe₃C@N‐CSs shows excellent oxygen evolution and oxygen reduction catalytic activity owing to the modulated electron structure by encapsulated Fe₃C core via biphasic interfaces electron interaction, which can lower the free energy of intermediate, strengthen the bonding strength and enhance conductivity. Meanwhile, the contribution of the Fe?N_x sites, N doping sites and the effect of Fe₃C core for the electrocatalytic oxygen reaction is originally revealed. The Fe₃C@N‐CSs air electrode‐based zinc‐air battery demonstrates a high open circuit potential of 1.47 V, superior charge‐discharge performance and long lifetime, which outperforms the noble metal‐based zinc‐air battery.     

d–d Dative Bonding Between Iron and the Alkaline‐Earth Metals Calcium,Strontium, and Barium

Double deprotonation of the diamine 1,1′‐(tBuCH₂NH)‐ferrocene ( 1 ‐H₂) by alkaline‐earth (Ae) or Eu^II metal reagents gave the complexes 1 ‐Ae (Ae=Mg, Ca, Sr, Ba) and 1 ‐Eu. 1 ‐Mg crystallized as a monomer while the heavier complexes crystallized as dimers. The Fe???Mg distance in 1 ‐Mg is too long for a bonding interaction, but short Fe???Ae distances in 1 ‐Ca, 1 ‐Sr, and 1 ‐Ba clearly support intramolecular Fe???Ae bonding. Further evidence for interactions is provided by a tilting of the Cp rings and the related ¹H NMR chemical‐shift difference between the Cp α and β protons. While electrochemical studies are complicated by complex decomposition, UV/Vis spectral features of the complexes support Fe→Ae dative bonding. A comprehensive bonding analysis of all 1 ‐Ae complexes shows that the heavier species 1 ‐Ca, 1 ‐Sr, and 1 ‐Ba possess genuine Fe→Ae bonds which involve vacant d‐orbitals of the alkaline‐earth atoms and partially filled d‐orbitals on Fe. In 1 ‐Mg, a weak Fe→Mg donation into vacant p‐orbitals of the Mg atom is observed.     

The Role of Reduced Graphite Oxide in Transition Metal Oxide Nanocomposites Used as Li Anode Material: An Operando Study on CoFe2O4/rGO

A composite consisting of CoFe₂O₄ spinel nanoparticles and reduced graphite oxide (rGO) is studied as an anode material during Li uptake and release by applying synchrotron operando X‐ray diffraction (XRD) and operando X‐ray absorption spectroscopy (XAS), yielding a comprehensive picture of the reaction mechanisms. In the early stages of Li uptake, a monoxide is formed as an intermediate phase containing Fe²⁺ and Co²⁺ ions; this observation is in contrast to reaction pathways proposed in the literature. In the fully discharged state, metallic Co and Fe nanoparticles are embedded in an amorphous Li₂O matrix. During charge, metallic Co and Fe are oxidized simultaneously to Co²⁺ and Fe³⁺, respectively, thus enabling a high and stable capacity to be achieved. Here, evidence is presented that the rGO acts as a support for the nanoparticles and prevents the particles from contact loss. The operando investigations are complemented by TEM, Raman spectroscopy, galvanostatic cycling, and cyclic voltammetry.     

Synthesis,crystal structure and magnetic properties of a new tri‐nuclear iron (II,III) complex,a precursor for the preparation of superparamagnetic Fe3O4 nanoparticles applicable in the removal of Cd2+

This study reports the structural and spectroscopic characterization of a novel metal organic compound formulated as [Fe (bpy)₃] [Fe (dipic)₂]₂.7H₂O ( 1 ) (dipic = pyridine‐2,6‐dicarboxylate and bpy = 2,2^′‐bipyridine). 1 was investigated by elemental analysis, FT‐IR spectroscopy, powder X‐ray diffraction and single crystal X‐ray diffraction (SC‐XRD), which revealed a triclinic structure of expected composition. Thermal degradation of 1 was also investigated. Complex 1 was used as a precursor to prepare superparamagnetic nanoparticles of Fe₃O₄ by thermal analysis. The obtained Fe₃O₄ was characterized by Fourier transformed infrared spectroscopy (FT‐IR), powder X‐ray diffraction (XRD) and scanning electron microscopy (SEM). Fe₃O₄ nanoparticles were used as a nano‐adsorbent to remove Cd²⁺ from water at room temperature. The results showed that this nano‐adsorbent is effective in removing Cd²⁺ from contaminated water sources, and that the maximal effectivity of adsorption occurs at pH = 6. Magnetic measurements of complex 1 and Fe₃O₄ nanoparticles at room temperature revealed paramagnetic and superparamagnetic behavior, respectively.     

Cube‐like 12‐MC‐4 and Offset Stacked 10‐MC‐3 Metallacrowns: Synthesis,Structure, and Magnetic Properties

Two complexes [Mn^III₄(naphthsao)₄(naphthsaoH)₄] ( 1 ) and [Fe^III₆O₂(naphthsao)₄(O₂CPh)₆] ( 2 ) [naphthsao = 1‐(1‐hydroxy‐naphthalen‐2‐yl)ethanone oxime] were obtained through the reactions of naphthsao ligand and MnCl₂ · 4H₂O or FeCl₃ · 6H₂O in the presence of triethylamine (Et₃N). Their structures were determined by X‐ray single crystal diffraction, elemental analysis, and IR spectra. Complex 1 displays 12‐MC‐4 metallacrown structural type with cube‐like configuration and 2 shows an offset stacked 10‐MC‐3 structural type with the ring connectivity containing Fe–O–C–O–Fe–O–N–Fe–O–N. Magnetic susceptibility measurement reveals the ferromagnetic interactions and field‐induced slow relaxation of the magnetization for 1 , whereas out‐of‐phase signal is not observed for 2 .     

Valence Distributions of Iron and Manganese in Pure,Manganese‐doped and Calcium‐doped Yttrium Orthoferrite

The valence distributions of Fe and Mn in yttrium orthoferrite (YFeO,), YFe_0.6Mn0.4O3 and Y_0.9Ca_0.1Fe_0.6Mn_0.4O_3.8 were studied by the measurement of thermal power. Pure YFeO₃ shows the n‐type electrical conductivity associated with small polaron hopping between Fe²⁺ and Fe³⁺. Both YFe_0.4Mn_0.4‐O₃ and Y_0–9Ca_0–1.Fe_0–6Mn_0–4O_3–8 show n‐type and p‐type conductivities at high and low temperatures respectively associated with small polaron hopping between Mn³⁺ and Mn⁴⁺, iron has only oxidation state of Fe³⁺ and does not have contribution to the electrical conductivity.     

A Redox‐Induced Spin‐State Cascade in a Mixed‐Valent Fe3(μ3‐O) Triangle

One‐electron reduction of a pyrazolate‐bridged triangular Fe₃(μ₃‐O) core induces a cascade wherein all three metal centers switch from high‐spin Fe³⁺ to low‐spin Fe^2.66+. This hypothesis is supported by spectroscopic data (¹H‐NMR, UV‐vis‐NIR, infra‐red, ⁵⁷Fe‐Mössbauer, EPR), X‐ray crystallographic characterization of the cluster in both oxidation states and also density functional theory. The reduction induces substantial contraction in all bond lengths around the metal centers, along with diagnostic shifts in the spectroscopic parameters. This is, to the best of our knowledge, the first example of a one‐electron redox event causing concerted change in multiple iron centers.     

Syntheses,Structures and Magnetic Properties of Two Mixed‐Valent Disc‐like Hepta‐nuclear Compounds of [FeIIFeIII6(tea)6](ClO4)2 and [MnII3MnIII4(nmdea)6(N3)6]·CH3OH (tea = N(CH2CH2O)33−, nmdea = CH3N(CH2CH2O)22−)

Two mixed‐valent disc‐like hepta‐nuclear compounds of [Fe^IIFe^III₆(tea)₆](ClO₄)₂ ( 1Fe , tea = N(CH₂CH₂O)₃^3?) and [Mn^II₃Mn^III₄(nmdea)₆(N₃)₆]·CH₃OH ( 2Mn , nmdea = CH₃N(CH₂CH₂O)₂^2?) have been synthesized by the reaction of Fe(ClO₄)₂·6H₂O with triethanolamine (H₃tea) for the former and reaction of Mn(ClO₄)₂·6H₂O with diethanolamine (H₂nmdea) and NaN₃ for the later, respectively. 1Fe has the cationic cluster with a planar [Fe^IIFe^III₆] core consisting of one central Fe^II and six rim Fe^III atoms in hexagonal arrangement. The Fe ions are linked by the oxo‐bridges from the alcohol arms in the manner of edge‐sharing of their coordination octahedra. 2Mn is a neutral cluster with a [Mn^II₃Mn^III₄] core possessing one central Mn^II atom surrounded by six rim Mn ions, two Mn^II and four Mn^III. The structure is similar to 1Fe but involves six terminal azido ligands, each coordinate one rim Mn ion. 1Fe showed dominant antiferromagnetic interaction within the cluster and long‐range ordering at 2.7 K. The cluster probably has a ground state of low spin of S = 5/2 or 4/2. The long‐range ordering is weak ferromagnetic, showing small hysteresis with a remnant magnetization of 0.3 Nβ and a coercive field of 40 Oe. Moreover, the isofield of lines 1Fe are far from superposition, indicating the presence of significant zero–field splitting. Ferromagnetic interactions are dominant in 2Mn . An intermediate spin ground state 25/2 is observed at low field. In high field of 50 kOe, the energetically lowest state is given by the m_s = 31/2 component of the S = 31/2 multiplet due to the Zeeman effect. Despite of the large ground state, no single‐molecule magnet behavior was found above 2 K.     

Electrocatalytically Active Fe‐(O‐C2)4 Single‐Atom Sites for Efficient Reduction of Nitrogen to Ammonia

Single‐atom catalysts have demonstrated their superiority over other types of catalysts for various reactions. However, the reported nitrogen reduction reaction single‐atom electrocatalysts for the nitrogen reduction reaction exclusively utilize metal–nitrogen or metal–carbon coordination configurations as catalytic active sites. Here, we report a Fe single‐atom electrocatalyst supported on low‐cost, nitrogen‐free lignocellulose‐derived carbon. The extended X‐ray absorption fine structure spectra confirm that Fe atoms are anchored to the support via the Fe‐(O‐C₂)₄ coordination configuration. Density functional theory calculations identify Fe‐(O‐C₂)₄ as the active site for the nitrogen reduction reaction. An electrode consisting of the electrocatalyst loaded on carbon cloth can afford a NH₃ yield rate and faradaic efficiency of 32.1 μg h^?1 mg_cat.^?1 (5350 μg h^?1 mg_Fe^?1) and 29.3 %, respectively. An exceptional NH₃ yield rate of 307.7 μg h^?1 mg_cat.^?1 (51 283 μg h^?1 mg_Fe^?1) with a near record faradaic efficiency of 51.0 % can be achieved with the electrocatalyst immobilized on a glassy carbon electrode.     

X‐Ray Emission Spectroscopy: A Spectroscopic Measure for the Determination of NO Oxidation States in Fe–NO Complexes

Extensive study of the electronic structure of Fe‐NO complexes using a variety of spectroscopic methods was attempted to understand how iron controls the binding and release of nitric oxide. The comparable energy levels of NO π* orbitals and Fe 3d orbitals complicate the bonding interaction within Fe? NO complexes and puzzle the quantitative assignment of NO oxidation state. Enemark–Feltham notation, {Fe(NO)_x}ⁿ, was devised to circumvent this puzzle. This 40‐year puzzle is revisited using valence‐to‐core X‐ray emission spectroscopy (V2C XES) in combination with computational study. DFT calculation establishes a linear relationship between ΔE_σ2s*‐σ2p of NO and its oxidation state. V2C Fe XES study of Fe? NO complexes reveals the ΔE_σ2s*‐σ2p of NO derived from NO σ_2s*/σ_2p→Fe_1s transitions and determines NO oxidation state in Fe? NO complexes. Quantitative assignment of NO oxidation state will correlate the feasible redox process of nitric oxide and Fe‐nitrosylation biology.     

Introducing Fe2+ into Nickel–Iron Layered Double Hydroxide: Local Structure Modulated Water Oxidation Activity

Exploring materials with regulated local structures and understanding how the atomic motifs govern the reactivity and durability of catalysts are a critical challenge for designing advanced catalysts. Herein we report the tuning of the local atomic structure of nickel–iron layered double hydroxides (NiFe‐LDHs) by partially substituting Ni²⁺ with Fe²⁺ to introduce Fe‐O‐Fe moieties. These Fe²⁺‐containing NiFe‐LDHs exhibit enhanced oxygen evolution reaction (OER) activity with an ultralow overpotential of 195 mV at the current density of 10 mA cm^?2, which is among the best OER catalytic performance to date. In‐situ X‐ray absorption, Raman, and electrochemical analysis jointly reveal that the Fe‐O‐Fe motifs could stabilize high‐valent metal sites at low overpotentials, thereby enhancing the OER activity. These results reveal the importance of tuning the local atomic structure for designing high efficiency electrocatalysts.