Fe Charge Research Articles

Unleashing unprecedented activation of high-valent Ni and Fe charge dynamics in CeF3-NiFe layered double hydroxide heterostructure: Demonstrating oxygen evolution reaction at an extremely high current density

The efficacy of any electrochemical reaction hinges on the extent of interaction achievable between reactive intermediates and the electrocatalytic active site. Any weak adsorption of these intermediates on the metal’s active site results in low oxygen evolution reaction (OER) rates, mainly when catalysed by the Ni-based layered double hydroxide. To tackle this challenge, a heterojunction consisting of nickel-iron layered double hydroxide (NiFe-LDH) and cerium trifluoride (CeF3) is synthesized. Both phases were developed in-situ to have an abundance of heterointerfaces. The charge transfer amid the NiFe-LDH and CeF3 phases is brought about via these heterointerfaces. As a result, the overall charge dynamics associated with nickel (Ni) and iron (Fe) atoms are somewhat increased, and an enhanced positive charge on the metal site makes it more active in grabbing the reactive species, thereby making the entire OER process faster. The CeF3-NiFeLDH catalyst reaches a current density of 1000 mA cm−2 at an overpotential of 340 mV. Such a high current density is highly significant for the industrial-scale production of the products. The catalyst demonstrated impressive durability, maintaining stable performance for 90 h while operating at 500 mA cm−2. The charge dynamics between both phases were thoroughly examined using X-ray photoelectron spectroscopy (XPS).

Unveiling the oxidation mechanism of persistent organic contaminants via visible light-induced dye-sensitized reaction by red mud suspension with peroxymonosulfate

A dye-sensitized photocatalysis system was developed for degrading persistent organic contaminants using solid waste (i.e., red mud, RM) and peroxymonosulfate (PMS) under visible light. Complete degradation of acid orange 7 (AO7) was achieved in RM suspension with PMS, where the co-existence of amorphous FeO(OH)/α-Fe2O3 was the key factor for PMS activation. The experimental results obtained from photochemical and electrochemical observations confirmed the enhanced PMS activation due to the Fe-OH phase in RM. DFT calculations verified the acceleration of PMS activation due to the high adsorption energy of PMS on FeO(OH) and low energy barrier for generating reactive radicals. Compared to the control experiment without AO7 showing almost no degradation of other organic contaminants (phenol, bisphenol A, 4-chlorophenol, 4-nitrophenol, and benzoic acid), photo-sensitized AO7* enhanced electron transfer in the FeIII/FeII cycle, dramatically enhancing the degradation of organic contaminants via radical (•OH, SO4•−, and O2•−) and non-radical (dye*+ and 1O2) pathways. Therefore, the novel finding of this study can provide new insights for unique PMS activation by heterogeneous Fe(III) containing solid wastes and highlight the importance of sensitized dye on the interaction of PMS with Fe charge carrier for the photo-oxidation of organic contaminants under visible light.

The value of charge of Fe single to multiple atoms doped in Ge: Combined experimental and density functional theory study

With the aim to find out the value of an electronic charge that the Fe atoms acquire when they are doped in Ge bulk, a set of experimental and density functional theory (DFT) studies have been carried out of the model systems consisting of intermixed Fe–Ge films. Such films were prepared by electron and thermal evaporation in ultra-high vacuum (UHV) on the surface of Mo(110) substrate by initial formation of the Ge film of a mean thickness of 7.5 nm, onto which the Fe films were subsequently deposited, maintaining certain Fe to Ge concentration ratio, namely, 0.2, 0.4, 0.7 and 1.0. Annealing of such double Fe–Ge films results in notable interdiffusion of the components with quite uniform distribution of the elements throughout the intermixed layer. The details of formation of such layers were in-situ controlled by Auger electron spectroscopy (AES), low-energy ion scattering spectroscopy (LEIS), low-energy electron diffraction (LEED) and work function measurements, in combination with Ar ion depth profiling. By analyzing the Fe Auger LMM-triplet, the absolute values of the charge that Fe atoms acquire when doped in Ge, were estimated for four different Fe–Ge intermixed layers with above-mentioned different Fe to Ge concentration ratio. The corresponding plot of the charge versus Fe to Ge concentration allows to estimate the charge of a single doped Fe atom, which equals to +0.34e (electron charge units) and gradually decreases to 0.07e for high Fe concentration. To verify the experimental values of the Fe charge the calculations were done by periodic DFT as implemented in full-potential FHI-aims code. Among the used algorithms of Mulliken, Hirshfeld, and Bader's atoms-in-molecules, the latter gives good correlation between charges of Fe dopant and its concentration.

3D MHD Time-dependent Charge State Ionization and Recombination Modeling of the Bastille Day Coronal Mass Ejection

Heavy ion signatures of coronal mass ejections (CMEs) indicate that rapid and strong heating takes place during the eruption and early stages of propagation. However, the nature of the heating that produces the highly ionized charge states often observed in situ is not fully constrained. An MHD simulation of the Bastille Day CME serves as a test bed to examine the origin and conditions of the formation of heavy ions evolving within the CME in connection with those observed during its passage at L1. In particular, we investigate the bimodal nature of the Fe charge state distribution, which is a quintessential heavy ion signature of CME substructure, as well as the source of the highly ionized plasma. We find that the main heating experienced by the tracked plasma structures linked to the ion signatures examined is due to field-aligned thermal conduction via shocked plasma at the CME front. Moreover, the bimodal Fe distributions can be generated through significant heating and rapid cooling of prominence material. However, although significant heating was achieved, the highest ionization stages of Fe ions observed in situ were not reproduced. In addition, the carbon and oxygen charge state distributions were not well replicated owing to anomalous heavy ion dropouts observed throughout the ejecta. Overall, the results indicate that additional ionization is needed to match observation. An important driver of ionization could come from suprathermal electrons, such as those produced via Fermi acceleration during reconnection, suggesting that the process is critical to the development and extended heating of extreme CME eruptions, like the Bastille Day CME.

The impact of small organic molecules on Fe(II) coagulation: Facilitating vs. shielding mechanisms on charge transfer

During the Fe(II) coagulation process, organics can significantly alter the structure of formed flocs, thereby influencing their efficacy in water treatment. However, the underlying mechanisms are not fully understood. This study investigates the impact of small organic molecules (SOM) on Fe(II) coagulation using serine, cysteine, histidine, and citric acid as examples. Results demonstrate that different SOM can significantly change the coagulation behavior by forming particles with distinct nanostructures, including flake-shaped γ-FeOOH, spherical γ-FeOOH, and ferrihydrite globules. The detection of Fe2+ in solution partially explains these phenomena, as Fe2+ can catalyze lattice rearrangement through charge transfer. By controlling the oxidation rate of Fe2+, SOM can influence the structure of flocs: cysteine and serine prolong the existence time of Fe2+ and promote the formation of highly crystalline γ-FeOOH, while citric acid accelerates Fe2+ oxidation, resulting in the opposite effect. However, histidine, despite delaying the oxidation of Fe2+, inhibits the formation of crystalline minerals, leading to the presence of flocs containing spherical γ-FeOOH. Mediated electrochemical analyses indicate that this is due to the adsorption of SOM on flocs, which hinders the effective entry of Fe2+ into the solid phase and disrupts the charge transfer. This study demonstrates that SOM can affect the interaction between Fe2+ and the nanostructure of flocs in two ways: directly influencing the oxidation rate of Fe2+ and indirectly interfering with the charge transfer between flocs and free Fe2+, which highlights the critical role of Fe(II)-Fe(III) charge transfer in coagulation and provides new possibilities for analyzing more complex organics-coagulation systems.

Cu-N-bridged Fe-3d electron state regulations for boosted oxygen reduction in flexible battery and PEMFC

Rational design of hetero-diatomic catalysts (DACs) with tunable electronic structures is an effective approach to accelerate the sluggish kinetics of oxygen reduction reaction (ORR) in metal-air batteries and proton-exchange membrane fuel cells (PEMFCs), which, however, still remains a great challenge to date. Herein, we propose a novel multi-step collaborative synthesis strategy to fabricate the N-bridged Fe and Cu diatomic electrocatalysts (Fe, Cu DAs-NC). Benefitting from the inter-atomic electron transfer and robust graphitized structure, the optimized Fe, Cu DAs-NC catalyst exhibits significantly enhanced ORR performances in both alkaline and acidic media, featuring the half-wave potentials of 0.94 V and 0.80 V, respectively. The established solid-state flexible Zn-air battery and H2-O2 single fuel cell using Fe, Cu DAs-NC as cathode deliver an extra-high power density of 83 mW cm−2 and a maximum power output of 875 mW cm−2, respectively. In-situ Raman spectroscopy and density functional theory calculations reveal that the strong synergistic interactions between FeN4 and CuN4 moieties are responsible for the d-orbital shift of the atomic Fe and Cu sites and charge polarization between them in the N-bridged coordination environment, which results in the well-defined and favorable adsorption free energy regulations and consequent much enhanced catalytic activity of the diatomic catalysts.

FeSe/FeSe2 Heterostructure as a Low‐Cost and High‐Performance Electrocatalyst for Oxygen Evolution Reaction

AbstractA key consensus of implementing large‐scale water splitting is developing highly efficient, durable, and earth‐abundant electrocatalysts for oxygen evolution reaction (OER). In recent years, the Fe‐based materials used in OER have attracted researchers’ great attention around the globe, and Fe has been identified as the OER active sites. In this study, we firstly synthesized the coral‐like FeSe/FeSe2 heterostructure catalyst via a one‐pot solvothermal method. We demonstrated that different components of FeSe/FeSe2 heterostructure can facilitate the electron transfer process of the system, where a high Fe charge state promotes OER performance, rendering the coral‐like FeSe/FeSe2 heterostructure to be more promising Fe‐based electrocatalyst for oxygen evolution reaction in alkaline. As expected, the as‐prepared FeSe/FeSe2 heterostructure with highly charged iron and negatively charged selenium species exhibited better OER performance and needed only an overpotential of 309 mV to achieve an anodic current density of 10 mA cm−2. In addition, the catalyst had quick kinetics and good durability in alkaline medium. The present study would open up a potential avenue for the development of highly active non‐noble‐metal electrocatalysts.

Manifestation of Gravitational Settling in Coronal Mass Ejections Measured in the Heliosphere

Elemental composition in the solar wind reflects the fractionation processes at the Sun. In coronal mass ejections (CMEs) measured in the heliosphere, the elemental composition can vary between plasma of high and low ionization states as indicated by the average Fe charge state, 〈QFe〉. It is found that CMEs with higher ionized plasma, 〈QFe〉 greater than 12, are significantly more enriched in low first ionization potential (FIP) elements compared to their less ionized, 〈QFe〉 less than 12, counterparts. In addition, the CME elemental composition has been shown to vary along the solar cycle. However, the processes driving changes in elemental composition in the plasma are not well understood. To gain insight into this variation, this work investigates the effects of gravitational settling in the ejecta to examine how that process can modify signatures of the FIP effect found in CMEs. We examine the absolute abundances of C, N, O, Ne, Mg, Si, S, and Fe in CMEs between 1998 and 2011. Results show that the ejecta exhibits some gravitational settling effects in approximately 33% of all CME periods in plasma where the Fe abundance of the ejecta compared to the solar wind (Fe/HCME:Fe/HSW) is depleted compared to the C abundance (C/HCME:C/HSW). We also find gravitational settling is most prominent in CMEs during solar minimum; however, it occurs throughout the solar cycle. This study indicates that gravitational settling, along with the FIP effect, can become important in governing the compositional makeup of CME source regions.

The Interplay of Oxygen Reduction Reaction and Iron Dissolution from Fe-N-C Electrocatalysts

Fe-N-C catalysts are regularly proposed as promising earth-abundant and cheap catalysts replacing platinum group metal catalysts for fuel cells (FCs). Besides the activity, especially the stability of those materials remains challenging. It was found that the electrochemical activity and durability of Fe-N-C catalysts are superior in alkaline compared to acidic media, [1-3] yet most of their degradation studies are done in acidic media. [4-9] Moreover, although these are systematic works, discrepancies in these results from aqueous model systems (AMS) [5,6] and FC testing [7-9] remain puzzling. For example, the origin of the dissolved Fe species was found to be from poorly active sites in AMS [5] yet from highly active sites in operating FCs. [7,8] Additionally, the harmful effects of reactive oxygen species (ROS) on Fe-N-C catalysts are proven in AMS [6] but not directly correlated to the durability in FCs. [9] To bridge this gap, a gas diffusion electrode (GDE) half-cell coupled with inductively coupled plasma mass spectrometry (ICP-MS) has been developed to study on-line dissolution in realistic catalyst layers. [10] In this work, using a GDE-ICP-MS, we investigate the impacts of oxygen reduction reaction (ORR) on Fe leaching from realistic Fe-N-C alkaline catalyst layers. [11] For the first time, Fe dissolution is measured online at current densities above -100 mA·cm-2. The novel results show that compared to the model Ar-saturated environment, the Fe dissolution is dramatically higher during ORR. Furthermore, between 0.6 and 1.0 VRHE, we unveil an interesting correlation between Fe dissolution and charge transfer events. This subsequently leads to our hypothesis that the instability of the coordinated Fe during Fe3+/Fe2+ redox transitions is responsible for Fe leaching from Fe-N-C catalysts in alkaline media in this potential region. The novel insights into Fe-N-C catalyst degradation in realistic conditions can lead to rational design of this promising platinum group metal free catalyst for efficient, durable, and affordable FCs.

Tailoring the microenvironment in Fe–N–C electrocatalysts for optimal oxygen reduction reaction performance

Fe–N–C electrocatalysts, comprising FeN4 single atom sites immobilized on N-doped carbon supports, offer excellent activity in the oxygen reduction reaction (ORR), especially in alkaline solution. Herein, we report a simple synthetic strategy for improving the accessibility of FeN4 sites during ORR and simultaneously fine-tuning the microenvironment of FeN4 sites, thus enhancing the ORR activity. Our approach involved a simple one-step pyrolysis of a Fe-containing zeolitic imidazolate framework in the presence of NaCl, yielding a hierarchically porous Fe–N–C electrocatalyst containing tailored FeN4 sites with slightly elongated Fe–N bond distances and reduced Fe charge. The porous carbon structure improved mass transport during ORR, whilst the microenvironment optimized FeN4 sites benefitted the adsorption/desorption of ORR intermediates. Accordingly, the developed electrocatalyst, possessing a high FeN4 site density (9.9 × 1019 sites g−1) and turnover frequency (2.26 s−1), delivered remarkable ORR performance with a low overpotential (a half-wave potential of 0.90 V vs. reversible hydrogen electrode) in 0.1 mol L−1 KOH.

Systematically theoretical investigation the effect of nitrogen and iron-doped graphdiyne on the oxygen reduction reaction mechanism in proton exchange membrane fuel cells

Developing economical electrocatalysts as alternatives to platinum for oxygen reduction reaction (ORR) to develop the applications of green energy devices like proton exchange membrane fuel cells (PEMFCs) is of paramount importance. In the current study, a different ratio of nitrogen-doped graphdiyne (GDY) with Fe single-site is reported to be more cost-effective and efficient for PEMFCs. The current study also demonstrates the design principle to improve the ORR activity associated with catalysts using Fe single-site with a greater Fe charge, which is controlled through the coordinated structure of the active center. Based on the simulation results, the formation of N2-doped GDY and N2-doepd Fe-GDY are more lucrative compared to the formation of Nx-doped GDY (x > 2) in terms of energy. O2 molecules have a direct dissociation on the N2-doepd Fe-GDY via Eley-Rideal (ER) mechanism, which involves the formation of H2O by reacting with H+ from the electrolyte. Moreover, N2-doepd Fe-GDY exhibits better performance as an ORR catalyst in an acidic medium because of its low overpotential of 0.488 V. However, N2-doped GDY follows the OOH∗ formation pathway, showing a higher overpotential for ORR. Furthermore, in the structure under study, the thermodynamic favorability of ORR is observed since the reaction energies calculated at each reaction step are exothermic and the energy profile of all reaction steps are downhill. The results of the current work provide new insights into the construction of extremely efficient heterogeneous catalysts in electrochemical energy technologies.

V-doped, divacancy-containing β-FeOOH electrocatalyst for high performance oxygen evolution reaction

Improving the oxygen evolution reaction (OER) performance of Fe-based (oxy)hydroxides is vital for the development of cost-effective electrocatalysts. In this work, for the first time, we demonstrate that the OER activity of β-FeOOH is enhanced via V-doping and the generation of both iron and oxygen vacancies. The novel V-doped, divacancy-containing β-FeOOH is obtained in-situ through a pre-OER cyclic voltammetry activation of hydrated layered Fe5V15O39(OH)9·9H2O Various analyses reveal that the vanadium dissolution in basic electrolyte accounts for the in-situ formation of V-doping and divacancy β-FeOOH. The experiment shows that V-doping regulates the formation of oxygen vacancies, subsequently resulting in the modulation of Fe oxidation state and charge transfer characteristics. Metallic Fe in the β-FeOOH also contributes to the enhanced charge transfer. Density functional theory calculation reveals that V-doping and iron vacancy balance the adsorption and desorption of oxygen intermediate species, giving a reduced energy barrier of the rate determining step during OER. As a result, the V-doped, divacancy-containing β-FeOOH exhibits an excellent OER overpotential of 232 mV at 10 mA cm−2, high current density > 450 mA cm−2, no potential decay after 2,000 cycles, and 72 h stability, outperforming the benchmark RuO2 and the other Fe-based catalysts. A water splitting cell consisting of the β-FeOOH anode F(V)OOH and a Pt/C cathode demonstrates an excellent cell voltage of 1.51 V at 10 mA cm−2. This facile method to obtain metal doping and divacancy simultaneously leads to a new approach for further development of electrocatalysts.

Effect of vitamins and metal ions on productivity and charge heterogeneity of IgG1 expressed in CHO cells.

Recombinant monoclonal antibodies have emerged as the most successful modality of biotherapeutics. They are primarily expressed in Chinese Hamster Ovary (CHO) cells. It is well known that post-translational modifications (PTM) contribute significantly to heterogeneity with respect to charge, glycosylation, and size. These attributes in turn impact stability, pharmacokinetics, and pharmacodynamics of the biotherapeutic product. Cell culture media components are known to significantly contribute to both cellular productivity as well as post-translational modifications. Thus, it is highly desirable to understand how media components affect product quality. This study aims to explore the impact of vitamins and metal ions on protein expression and post-translational modifications specifically charge heterogeneity. Biotin, choline chloride, D-calcium pantothenate, folic acid, pyridoxine hydrochloride, thiamine hydrochloride vitamins and Fe, Cu, Mg, Co, Zn, Mn, Ni metal ions were examined in this study. The results indicate that pyridoxine enhances productivity while Zn, Cu, Fe, Mn, and biotin impact charge heterogeneity. While, Fe, Mn and Ni enhance production of the acidic variants, Cu and biotin inhibit it. Zn reduces formation of basic variants while biotin enhances it. The results from this investigation could be used for process control so as to get consistent charge variant profile, in particular for biosimilars.

Os Doping Suppressed Cu-Fe Charge Transfer and Induced Structural and Magnetic Phase Transitions in LaCu3Fe4-xOsxO12 (x = 1 and 2).

B-site Os-doped quadruple perovskite oxides LaCu3Fe4-xOsxO12 (x = 1 and 2) were prepared under high-pressure and high-temperature conditions. Although parent compound LaCu3Fe4O12 experiences Cu-Fe intermetallic charge transfer that changes the Cu3+/Fe3+ charge combination to Cu2+/Fe3.75+ at 393 K, in the Os-doped samples, the Cu and Fe charge states are found to be constant 2+ and 3+, respectively, indicating the complete suppression of charge transfer. Correspondingly, Os6+ and mixed Os4.5+ valence states are determined by X-ray absorption spectroscopy for x = 1 and x = 2 compositions, respectively. The x = 1 sample crystallizes in an Fe/Os disordered structure with the Im3̅ space group. It experiences a spin-glass transition around 480 K. With further Os substitution up to x = 2, the crystal symmetry changes to Pn3̅, where Fe and Os are orderly distributed in a rocksalt-type fashion at the B site. Moreover, this composition shows a long-range Cu2+(↑)Fe3+(↑)Os4.5+(↓) ferrimagnetic ordering near 520 K. This work provides a rare example for 5d substitution-suppressed intermetallic charge transfer as well as induced structural and magnetic phase transitions with high spin ordering temperature.

Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending over a Solar Cycle

Abstract This letter capitalizes on a unique set of total solar eclipse observations acquired between 2006 and 2020 in white light, Fe xi 789.2 nm (T fexi = 1.2 ± 0.1 MK), and Fe xiv 530.3 nm (T fexiv = 1.8 ± 0.1 MK) emission complemented by in situ Fe charge state and proton speed measurements from Advanced Composition Explorer/SWEPAM-SWICS to identify the source regions of different solar wind streams. The eclipse observations reveal the ubiquity of open structures invariably associated with Fe xi emission from Fe10+ and hence a constant electron temperature, T c = T fexi, in the expanding corona. The in situ Fe charge states are found to cluster around Fe10+, independently of the 300–700 km s−1 stream speeds, referred to as the continual solar wind. Thus, Fe10+ yields the fiducial link between the continual solar wind and its T fexi sources at the Sun. While the spatial distribution of Fe xiv emission from Fe13+ associated with streamers changes throughout the solar cycle, the sporadic appearance of charge states >Fe11+ in situ exhibits no cycle dependence regardless of speed. These latter streams are conjectured to be released from hot coronal plasmas at temperatures ≥T fexiv within the bulge of streamers and from active regions, driven by the dynamic behavior of prominences magnetically linked to them. The discovery of continual streams of slow, intermediate, and fast solar wind characterized by the same T fexi in the expanding corona places new constraints on the physical processes shaping the solar wind.

Mössbauer studies on magnetism in FeSe

Iron selenide (FeSe) was used to investigate magnetic properties by using Mössbauer spectroscopy. The crystalline structure of the sample was found to be tetragonal and hexagonal with a 3c structure. The temperature-dependent magnetic susceptibility curve under 100 Oe confirmed the spin rotation temperature TS = 150 K. Based on the applied field dependent magnetization measurements up to 15 kOe at 295 K, the saturation magnetization and coercivity were found to be 8.03 emu/g and 357.40 Oe, respectively. The spin rotation process of the sample from the dependence temperature ZFC-FC curves occurs at approximately TS. The Mössbauer spectra below the Néel temperature (TN) were fitted with a doublet for the tetragonal phase and three sextets (A, B, and C sites) for the hexagonal phase. The spectrum was fitted to a single line at TN = 500 K. We also observed abrupt changes in Hhf and ΔEQ at the spin rotation temperature. The Fe charge states in the tetragonal and hexagonal phases are found to be ferric and highly covalent ferrous ion (or high-spin ferric), respectively.

Identification of Hot Plasma Anomalies in Solar Wind Using Fe Ion Charge Distributions

Abstract A presence of high Fe charge states in the ionic charge state distributions of the solar wind (SW) plasma, commonly characterized by the mean charge Q Fe, provides valuable information on heating processes in the SW sources. We study the relationship between the parameter Q Fe and the charge state distributions of Fe ions using the Solar TErrestrial RElations Observatory/PLAsma and SupraThermal Ion Composition data on the beginning of the 24th Cycle (2010 January–2011 July). We find that the Fe charge state distributions related to SW with Q Fe ≈ 8–10 have an uni-modal shape peaked around Fe8+–Fe9+. When the Q Fe value increases, the distributions change: at first, the profile extends to higher charge states and then transforms into a bi-modal shape with a second maximum around Fe16+ and a minimum around Fe12+. We discuss possible reasons for such bi-modality through the example of the interplanetary coronal mass ejection (ICME) event on 2011 February 24–26, where it was related to the heating of an eruptive prominence. For such an analysis, it is informative to have a special measure of the fraction of highly charged ions for the Fe ion charge distribution in SW. In addition to Q Fe, we introduce a parameter q12 equal to a fraction of Fe ions with charges Q ≥ 12 and show that this parameter can be applied for identifying both the large-scale hot plasma enhancements associated with ICMEs and small hot fragments of SW plasma, which may be associated with small-scale solar activity in various coronal structures.

Element Abundances in the Unshocked Ejecta of Cassiopeia A

Abstract We analyze and model the infrared spectrum of the Cassiopeia A supernova remnant with the aim of determining the masses of various elements in the unshocked ejecta. In this way, we complement the survey of the X-ray-emitting ejecta to provide a complete census of the elemental composition of the Cas A ejecta. We calculate photoionization–recombination equilibria to determine the ionization balance of various elements in the ejecta as a function of density using the X-ray and UV emission from the forward and reverse shocks as the ionizing radiation. With the assumption that all emission lines are principally excited at the ejecta density that maximizes their emission, we can convert observed line intensities into element masses. We find that the majority of the ∼3 M ⊙ ejecta have already been through the reverse shock and are seen today in X-rays. A minority, ∼0.47 ± 0.05 M ⊙, with uncertainties quoted here coming from the data fitting procedure only, are still expanding inside the reverse shock and emitting in the infrared. This component is comprised mainly of O, Si, and S, with no Fe readily detectable. Incorporating uncertainties estimated to come from our modeling, we quote M ⊙. We speculate that up to a further 0.07 M ⊙ of Fe may be present in diffuse gas in the inner ejecta, depending on the Fe charge state.

Cyclic voltammograms and electrochemical data of FeII polypyridine complexes.

Data in this article is associated with our research article, Electronic Properties of Fe Charge Transfer Complexes – a Combined Experimental and Theoretical Approach [1].The oxidation and reduction potentials of fourteen FeII complexes are presented here, as extracted from the redox data obtained from its associated cyclic voltammograms, which were measured at scan rates varying from 0.05 V.s−1 to 5.00 V.s−1, under similar experimental conditions. Acetonitrile was used as solvent, and tetrabutylammonium hexafluorophosphate as supporting electrolyte. All data are reported versus the FeII redox couple in ferrocene.

Electronic Structure of the Hieber Anion [Fe(CO)3(NO)]− Revisited by X-ray Emission and Absorption Spectroscopy

While the Hieber anion [Fe(CO)3(NO)]- has been reincarnated in the last years as an active catalyst in organic synthesis, there is still a debate about the oxidation state of the central Fe atom and the resulting charge of the NO ligand. To shed new light on this question and to understand the Fe-NO interaction in the Hieber anion, it is investigated in comparison to the formal 3d8 reference Fe(CO)5 and the formal 3d10 reference [Fe(CO)4]2- by the combination of valence-to-core X-ray emission spectroscopy (VtC-XES), X-ray absorption near-edge structure spectroscopy (XANES), and high-energy-resolution fluorescence-detected XANES. In order to extract information about the electronic structure, time-dependent density functional theory and ground-state density functional theory calculations are applied. This combination of experimental and computational methods reveals that the electron density at the Fe center of the Hieber resembles that of the isoelectronic [Fe(CO)4]2-. These observations challenge recent descriptions of the Hieber anion and reopen the debate about the experimentally and computationally determined Fe oxidation state and charge on the NO ligand.