Electronic Configuration Research Articles

Proton vs Electron: The Dual Role of Redox-Inactive Metal Ions in Permanganate Oxidation Kinetics.

Redox-inactive metal-ion-driven modulation of the oxidation behavior of high-valent metal-oxo complex has garnered significant interest in biological and chemical synthesis; however, their role in permanganate (Mn(VII)) oxidation for the removal of organic pollutants has been largely neglected. Here, we uncover the impact of six metal ions (i.e., Ca2+, Mg2+, Ni2+, Zn2+, Al3+, and Sc3+) presenting in water environments on Mn(VII) activity. These ions uniformly boost the electron and oxygen transfer capabilities of Mn(VII) while impeding proton transfer, as evidenced by electrochemical tests, thioanisole probe analysis, and the kinetic isotope effect. The observed effects are intricately linked to the Lewis acidity of the metal ions. Further mechanistic insights reveal that Mn(VII) can interact with metal ions without direct reduction. Such interactions modify the electronic configuration of Mn(VII) and create an acidic microenvironment, thus increasing its electrophilicity and the energy barrier for the abstraction of proton from organic substrates. More importantly, the efficacy of Mn(VII) in removing phenolic pollutants is regulated by these ions through changing the driving force for proton and electron transfer, i.e., facilitated at pH > 4.5 and inhibited at lower pH. The contribution of active Mn intermediates is also discussed to reveal the oxidative mechanism of the metal ion/Mn(VII) system. These findings not only facilitate the rational design of Mn(VII) oxidation conditions in the presence of metal ions for water decontamination but also offer an alternative paradigm for enhancing electrophilic oxidation.

The structural and electronic configuration of an amorphous silica surface, from its liquid to glassy state

Through classical molecular dynamics computational simulations, the surface of amorphous silica (vitreous silica) was generated for a system comprising 64 SiO2 molecules (192 atoms) via the classical three-body glass potential. Starting from the liquid state of silica at 3400 K, it was cooled in three different ways at intervals of 200, 400, and 2000 K, with a cooling rate of 4.4 K/ps and establishing relaxation at intermediate temperatures, yielding three groups of surfaces from 3400 to 1400 K. Subsequently, these systems underwent sudden cooling from 1400 to 300 K via the Andersen and Nosé‒Hoover thermostats, followed by relaxation at 300 K via a microcanonical ensemble (NVE constant). Each surface that underwent relaxation was analyzed through ab initio molecular dynamics for the following three physical properties, which are temperature dependent. The average electric charges of oxygen and silicon. Microstructures on the outermost part of the surface were observed and comprised nonbridging oxygen atoms, undercoordinated silicon, and N-membered rings (3 ≤ N ≤ 5). The radial distribution functions were analyzed for all surfaces. Below 2000 K, a type of freezing is observed in all the structures because of the glass transition. All analyses were performed at zero pressure.

Weakening O-Intermediates Adsorption Strength Over the Pd Metallene via Lewis-Acidic Site Modulation for Enhanced Oxygen Reduction.

The reasonable design and modulation of the electronic properties of Pd metallene are acknowledged as a promising avenue for enhancing the oxygen reduction reaction (ORR) in anion exchange membrane fuel cells (AEMFCs), yet they remain a formidable challenge. Herein, a thin-sheet structure of Zr-doped Pd metallene (PdZr metallene) with abundant defects is proposed using a facile wet-chemical approach for efficient and highly durable ORR electrocatalysis. Multiple microstructural analyses uncover that orchestrated electronic and oxophilic regulation of PdZr metallene via Lewis-acidic Zr site modulation could concurrently optimize the electronic configuration of Pd, downshift the d-band center of Pd, and, thus, promote the intrinsic activity. Benefiting from the unique two-dimensional morphology and electronic structure optimization facilitated by the Zr coupling effect, the resultant PdZr metallene demonstrates significantly enhanced ORR electrocatalytic performance in basic solutions, with a high half-wave potential (E1/2) of 0.87 V and commendable stability for 30 000 s, surpassing those of Pd metallene and various advanced Pd-based catalysts reported in the literature. Encouragingly, the PdZr metallene-based AEMFC achieves an increased maximum power density (90.4 mW cm-2) and impressive robustness over 12 h in an alkaline environment, manifesting the practical application of PdZr metallene in AEMFCs. This study showcases the applicability of PdZr metallene via Lewis acid site regulation for fabricating highly active electrocatalysts for high-performance AEMFCs.

Pt Ternary Alloy with Rare Earth Metal - Pt5Ce-Co Intermetallic Nanoparticles as Highly Active Catalyst for Oxygen Reduction Reaction in PEMFCs

Alloying with rare earth elements is an important direction of exploring in Pt-based alloy design in oxygen reduction reaction (ORR), due to its special electronic configurations. Here we reported a ternary intermetallic alloy Pt5Ce-Co/C. The electronic valence state of Pt alloys was modified by the unique 4f orbital and the contraction effect of Ce, plus the additional active sites provided by the Co incorporation, optimizing the adsorption energy of the reaction intermediates, and effectively improving the electrocatalytic performance. The Pt5Ce-Co/C achieved 2.8 A∙mgPt -1 of mass activity in ORR catalysis, which can maintain 1.4 A∙mgPt -1 after 30k of accelerated stress test (AST). For membrane electrode assembly test, Pt5Ce-Co/C shows an initial mass activity of 724 mA∙mgPt -1, and a current density of 1876 mA∙cm-2 at 0.7 V under heavy-duty vehicle testing. This work provides an avenue to design advanced PGM ternary alloys by incorporating rare-earth metals to promote the catalyst performance.

Unveiling F-coordination tuning of dense Fe-N4 active sites via nitrogen fixation over advanced electrocatalysts

The manuscript presents a significant advancement in the field of electrocatalytic nitrogen fixation by unveiling the role of fluorine coordination in tuning the activity of atomically dispersed iron-nitrogen (Fe-N4) active sites within porous carbon (PC). The innovative approach employs chemical vapor deposition (CVD) to fabricate F-Fe-NC active sites, which, upon fluorination, modulate the electronic configuration of iron, enhancing nitrogen adsorption and activation. The F-Fe-NC catalyst demonstrated a remarkable enhancement in electrocatalytic nitrogen reduction reaction (NRR) performance, achieving an ammonia yield rate (RNH3) of 125.49 μg h−1 mgcat.−1 and a Faradaic efficiency (FE) of 25.19 %. In-situ electrochemical mass spectrometry and Density Functional Theory (DFT) calculations were utilized to dissect the NRR kinetics and elucidate the underlying reaction mechanism, identifying the potential-determining step. The study introduces a novel, high-performance catalyst for electrocatalytic NRR and provides a practical strategy for optimizing the active-site microenvironment, laying the groundwork for the future commercial application of electrocatalytic NRR processes.

Nitrosation mechanisms, kinetics, and dynamics of the guanine and 9-methylguanine radical cations by nitric oxide-Radical-radical combination at different electron configurations.

As a precursor to various reactive nitrogen species formed in biological systems, nitric oxide (•NO) participates in numerous processes, including enhancing DNA radiosensitivity in ionizing radiation-based radiotherapy. Forming guanine radical cations is another common DNA lesion resulting from ionization and oxidation damage. As such, the interaction of •NO with guanine radical cations (G•+) may contribute to the radiosensitization of •NO. An intriguing aspect of this process is the participation of multiple spin configurations in the reaction, including open-shell singlet 1,OS[G•+(↑)⋯(↓)•NO], closed-shell singlet 1,CS[G(↑↓)⋯NO+], and triplet 3[G•+(↑)⋯(↑)•NO]. In this study, the reactions of •NO with both unsubstituted guanine radical cations (in the 9HG•+ conformation) and 9-methylguanine radical cations (9MG•+, a guanosine-mimicking model compound) were investigated in the absence and presence of monohydration of radical cations. Kinetic-energy dependent reaction product ions and cross sections were measured using an electrospray ionization guided-ion beam tandem mass spectrometer. The reaction mechanisms, kinetics, and dynamics were comprehended by interpreting the reaction potential energy surface using spin-projected density functional theory, coupled cluster theory, and multiconfiguration complete active space second-order perturbation theory, followed by RRKM kinetics modeling. The combined experimental and computational findings revealed closed-shell singlet 1,CS[7-NO-9MG]+ as the major, exothermic product and triplet 3[8-NO-9MG]+ as the minor, endothermic product. Singlet biradical products were not detected due to high reaction endothermicities, activation barriers, and inherent instability.

Steering intermediates coverage of W-doped Fe3N for efficient kinetic promotion in water splitting by lattice and electronic configuration engineering

The development of catalysts that promote kinetic processes represents a significant frontier in the field of catalyst design. Here, a facile strategy is employed to fabricate W-Fe3N@NC. The incorporation of W results in effective lattice and electronic configuration engineering, providing a favorable environment for the in-situ formation of high-valent Fe4+ and the lattice contraction. The kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are fully improved by steering the intermediate coverages and binding energies. W-Fe3N@NC exhibits superior HER performance at universal pH range and a significantly enhanced alkaline OER performance. Density functional theory (DFT) analysis verifies the lattice and electronic engineering and indicates that the higher valence state and weakened adsorption of the intermediates boost the activity of OER and HER. This study offers new insights into effective electrocatalyst design through lattice and electronic engineering, and provides a basis for further exploration of the kinetic promotion mechanism of catalysts.

Constructing hollow cobalt sulfide nanocages strung by manganese molybdate nanorods for high-efficiency supercapacitors and electrocatalytic methanol oxidation

Constructing core-shell heterostuctures with rationally designed nanoarchitectures and components is a promising strategy to pursuit high-efficiency energy storage and conversion in supercapacitors (SCs) and direct methanol fuel cells (DMFCs). Herein, a multi-dimensional MnMoO4@CoS core-shell heterostructure is designed and synthesized by stringing metal-organic framework-derived hollow CoS nanocages with MnMoO4 nanorods. Such heterostructure provides more electroactive sites and enhanced structural stability. Theory calculations unveil that the work function difference between MnMoO4 and CoS induces the charge redistribution and modulate interfacial electronic configuration in the MnMoO4/CoS heterojunction. Meanwhile, a interfacial built-in electrical field is established, enhancing interfacial charge transfer efficiency and promoting the surface adsorption of electrolyte ions. By integrating all these advantages, the MnMoO4@CoS electrode demonstrates enhanced rate capacities (933 C g−1 at 1 A g−1 and 623 C g−1 at 10 A g−1) and cycling durability (90.3 % capacity retention after 10,000 cycles) compared to bare MnMoO4 and CoS electrodes. Moreover, the MnMoO4@CoS electrode exhibits an appreciable electrocatalytic performance for methanol oxidation, with a current density of 294.8 mA cm−2 at 10 mV s−1 and 96.6 % current retention after 10,000 s. Our work offers a fundamental guideline for designing and engineering core-shell heterostructures with desirable electrochemical performance for SCs and DMFCs.

Investigating the optoelectronic properties of Mn and Fe doped CuAlS₂ for intermediate band solar cell applications

Chalcopyrites demonstrate compelling features for optoelectronic and photovoltaic devices, attributed to their valuable properties. Their remarkable light-absorption capabilities and well-suited band gap render them so attractive for applications in these fields. By allowing low-energy sub-bandgap photons to pass through and reducing the thermalisation loss from high-energy photons, intermediate-band materials address the primary problems in solar cells. This approach allows for more efficient use of the solar spectrum, helping solar cells exceed the traditional efficiency limits defined by the Shockley-Queisser limit. The objective of this study was to evaluate the electronic and optical characteristics of CuAlS2 systems doped with transition metals (TM = Mn, Fe) using the Full Potential Linearized Augmented Plane Wave approach within the framework of Density Functional Theory. A stable phase within the systems was observed upon replacing the Al atom with TM. The functionality of the intermediate band was governed by the 3d electronic characteristics of the TM3+ ion and its electronic configuration. The optical properties of CuAlS2 doped with Mn and Fe were analysed by calculating the dielectric function, refractive index, reflectivity, and absorption coefficient. Furthermore, the introduction of Mn and Fe through doping led to the creation of an intermediate band, enhancing visible light absorption and power conversion efficiency. Consequently, the optical spectrum of Mn-doped CuAlS2 and Fe-doped CuAlS2 compounds exhibits additional absorption peaks, accompanied by a significant improvement in absorption intensity. Our findings highlighted the need for continued and futuristic research into the scalability of these materials for practical applications in solar cells, optoelectronics, and spintronic devices. This investigation suggests that Mn-doped CuAlS2 holds the highest potential due to its high charge carriers and low recombination rate, indicating enhanced performance in CuAlS2-based intermediate band solar cells.

The application of Co3S4@NCNT/NCHS with excellent bifunctional catalytic activity in aqueous and flexible Zn-air batteries

In this work, we prepared a hybrid structure Co3S4@NCNT/NCHS using SiO2 nanospheres as a template. The structure is supported by hollow carbon spheres (NCHS), which are coated by Co3S4 nanoparticles and cross-linked N-doped carbon nanotubes. The combination of Co3S4 with N-doped carbon material significantly improves the electrocatalytic activity. In addition, the presence of N-doped carbon nanotubes induces more defects, which can regulate the electronic configuration of the material and improve its electrical conductivity. Therefore, Co3S4@NCNT/NCHS has good catalytic performance. At 10 mA cm−2, the OER overpotential of Co3S4@NCNT/NCHS is only 230 mV, which is lower than that of the commercial catalyst RuO2, and the ORR half-wave potential can reach 0.80 V. In the battery discharge test, Co3S4@NCNT/NCHS based ZABs can discharge continuously for 71.5 h, the specific capacity of 790.12 mA h g−1, power density of 113.09 m W cm−2, better than Pt/C+RuO2 battery. When the current density is 3 mA cm−2, ZABs assembled with Co3S4@NCNT/NCHS as catalyst can maintain a voltage gap of 0.62 V to 0.63 V within 300 h without significant change. When the current density is increased to 5 mA cm−2, ZABs based on Co3S4@NCNT/NCHS can be stably cycled for 300 h at a voltage gap between 0.80 V and 0.82 V.

Zero‐Bias Anti‐Ohmic Behaviour in Diradicaloid Molecular Wires

AbstractOpen‐shell materials bearing multiple spin centres provide a key route to efficient charge transport in single‐molecule electronic devices. They have narrow energy gaps, and their molecular orbitals align closely to the Fermi level of the metallic electrodes, thus allowing efficient electronic transport and higher conductance. Maintaining and stabilising multiple open‐shell states—especially in contact with metallic electrodes—is however very challenging, generally requiring a continuous chemical or electrochemical potential to avoid self‐immolation of the open‐shell character. To overcome this issue, we designed, synthesised, and measured the conductance of a series of bis(indeno) fused acenes, where stability is imparted by a close‐shell quinoidal conformation in resonance with the diradical electronic configuration. We show here that these compounds have anti‐ohmic behaviour, with conductance increasing with increasing molecular length, at an unprecedented rate and across the entire bias window ( ). Density Functional Theory (DFT) calculations support our findings, showing the rapidly narrowing HOMO–LUMO gap, unique to these diradicaloid structures, is responsible for the observed behaviour. Our results provide a framework for achieving efficient transport in neutral compounds and demonstrate the promise that diradicaloid materials have in single‐molecule electronics, owing to their great stability and unique electronic structure.

Fluorine-Tuned Carbon-Based Nickel Single-Atom Catalysts for Scalable and Highly Efficient CO2 Electrocatalytic Reduction.

Electrocatalytic CO2 reduction is garnering significant interest due to its potential applications in mitigating CO2 and producing fuel. However, the scaling up of related catalysis is still hindered by several challenges, including the cost of the catalytic materials, low selectivity, small current densities to maintain desirable selectivity. In this study, Fluorine (F) atoms were introduced into an N-doped carbon-supported single nickel (Ni) atom catalyst via facile polymer-assisted pyrolysis. This method not only maintains the high atom utilization efficiency of Ni in a cost-effective and sustainable manner but also effectively manipulates the electronic structure of the active Ni-N4 site through F doping. The catalyst has also been further optimized by controlling the F states, including convalent and semi-ionic states, by adjusting the fluorine sources involved. Consequently, this catalyst with unique structure exhibited comparable electrocatalytic performance for CO2-to-CO conversion, achieving a Faradaic efficiency (FE) of over 99% across a wide potential range and an exceptional CO evolution rate of 9.5 × 104 h-1 at -1.16 V vs reversible hydrogen electrode (RHE). It also delivered a practical current of 400 mA cm-2 while maintaining more than 95% CO FE. Experimental analysis combined with density functional theory (DFT) calculations have also shown that F-doping modifies the electron configuration at the central Ni-N4 sites. This modification lowers the energy barrier for CO2 activation, thereby facilitating the production of the crucial *COOH intermediate.

First-principles investigation of the metal-insulator transition in the high-temperature phase of VO2 (A) at 473 K

The structure, electronic and magnetic properties of the high-temperature phase of VO2 (A) [HT-VO2 (A)] are extensively investigated by employing first-principles electronic structure calculations. Structural distortion is observed due to the alternative formation of V-V square wells and V-V rectangular four-chain columns in the ab plane and extending along the c-direction. The system is found to be a ferrimagnetic metal due to sharing of the available single V-3d electron by the V-dxy, dyz, dxz states in the spin majority channel and exclusively by the V-dxy states in the spin minority channel. This material encounters metal-to-half-metal transition for an effective Coulomb interaction of Ueff = 2 eV, exhibiting ferromagnetism. The sharing of the single V-3d electron by the V-dxy, dyz and dxz states in the spin majority channel results in the half-metallic behaviour of HT-VO2 (A). The system eventually encounters metal-insulator transition (MIT) upon the application of Ueff = 2.5 eV. Strong electron correlation triggered by U completely breaks both the V-dxy and dyz states into occupied and unoccupied components and hence sets up complete orbital ordering that is responsible for the observed MIT in HT-VO2 (A). The cooperative effect of p-d hybridization and V-O antiferromagnetic coupling gives rise to ferromagnetism in both the half-metallic and insulating phases of HT-VO2 (A).

Exploring rare-earth Kitaev magnets by massive-scale computational analysis

The Kitaev honeycomb model plays a pivotal role in the quest for quantum spin liquids, in which fractional quasiparticles would provide applications in decoherence-free topological quantum computing. The key ingredient is the bond-dependent Ising-type interactions, dubbed the Kitaev interactions, which require strong entanglement between spin and orbital degrees of freedom. Here we investigate the identification and design of rare-earth materials displaying robust Kitaev interactions. We scrutinize all possible 4f electron configurations, which require up to 6+ million intermediate states in the perturbation processes, by developing a parallel computational program designed for massive-scale calculations. Our analysis reveals a predominant interplay between the isotropic Heisenberg J and anisotropic Kitaev K interactions across all realizations of the Kramers doublets. Remarkably, instances featuring 4f3 and 4f11 configurations showcase the prevalence of K over J, presenting unexpected prospects for exploring the Kitaev quantum spin liquids in compounds, including Nd3+ and Er3+, respectively.

Optical and electrochemical performance of NdVO4 nanorods

Tetragonal structured NdVO4 nanorods were prepared by simple solvothermal route with various temperatures. An optimized NdVO4 sample was characterized through XRD, FTIR, RAMAN, UV–Visible, PL, SEM, HRTEM and EDX techniques. Electrochemical performance of NdVO4 electrodes were analyzed by CV instrument. From XRD, it is confirmed that the prepared samples were perfectly formed in pure tetragonal structured NdVO4 nanoparticles with the crystallite size of 41.08 nm, 44.92 nm and 54.78 nm for the temperature of 240 °C, 260 °C, and 280 °C, respectively. In UV–Visible absorption spectrum, there are seven peaks raised for NdVO4. The XPS shows the three elements that are Nd, V and O with the corresponding electronic configuration states of 3d, 2p and 1 s, respectively. SEM and HRTEM picture the nanorod morphology of the prepared NdVO4 nanoparticles. The electrochemical performance of the NV1 electrode showed pseudocapacitive existence with the current density of 10 mV/s (362F/g) and it will act as well behaved electrode in supercapacitors.

A Click Chemistry Strategy Toward Spin-Polarized Transition-Metal Single Site Catalysts for Dynamic Probing of Sulfur Redox Electrocatalysis.

Catalytic conversion of lithium polysulfides (LiPSs) is a crucial approach to enhance the redox kinetics and suppress the shuttle effect in lithium-sulfur (Li-S) batteries. However, the roles of a typical heterogenous catalyst cannot be easily identified due to its structural complexity. Compared with the distinct sites of single atom catalysts (SACs), each active site of single site catalysts (SSCs) is identical and uniform in their spatial energy, binding mode, and coordination sphere, etc. Benefiting from the well-defined structure, iron phthalocyanine (FePc) is covalently clicked onto CuO nanosheet to prepare low spin-state Fe SSCs as the model catalyst for Li-S electrochemistry. The periodic polarizability evolution of Fe-N bonding is probed during sulfur redox reaction by in situ Raman spectra. Theoretical analysis shows the decreased d-band center gap of Fe (Δd) and delocalization of dxz/dyz after the axial click confinement. Consequently, Li-S batteries with Fe SSCs exhibit a capacity decay rate of 0.029% per cycle at 2 C. The universality of this methodological approach is demonstrated by a series of M SSCs (M = Mn, Co, and Ni) with similar variation of electronic configuration. This work provides guidance for the design of efficient electrocatalysis in Li-S batteries.

Fe-doped phosphide nanosheet array derived from prussian blue analogues for high-efficient electrocatalytic water splitting

Doping heterogeneous atoms can modulate electronic structure, which matters for creating efficient bifunctional electrocatalysts in realizing conversion of hydrogen and electricity. This study demonstrates that Fe-doped Ni5P4 nanosheet arrays on nickel foam (Fe–Ni5P4/NF) using Prussian blue analogues as precursors are successfully synthesized by straightforward hydrothermal reactions and phosphating. Fe–Ni5P4/NF exhibits great efficiency in creating hydrogen from water under alkaline conditions. The Fe–Ni5P4/NF dual electrode just need a minimal cell voltage of 1.54 V at 10 mA cm−2 and maintain operational stability for a minimum of 50 h, demonstrating outstanding bifunctional properties. The introduction of Fe modifies the electronic configuration for Ni5P4, substantially boosting the activity of the electrocatalyst. This study offers a framework for designing splendid bifunctional electrocatalysts through synergistic doping strategies in electrochemical applications.

Avoided metallicity in a hole-doped Mott insulator on a triangular lattice

Doping of a Mott insulator gives rise to a wide variety of exotic emergent states, from high-temperature superconductivity to charge, spin, and orbital orders. The physics underpinning their evolution is, however, poorly understood. A major challenge is the chemical complexity associated with traditional routes to doping. Here, we study the Mott insulating CrO2 layer of the delafossite PdCrO2, where an intrinsic polar catastrophe provides a clean route to doping of the surface. From scanning tunnelling microscopy and angle-resolved photoemission, we find that the surface stays insulating accompanied by a short-range ordered state. From density functional theory, we demonstrate how the formation of charge disproportionation results in an insulating ground state of the surface that is disparate from the hidden Mott insulator in the bulk. We demonstrate that voltage pulses induce local modifications to this state which relax over tens of minutes, pointing to a glassy nature of the charge order.

Insights on the hydrogenation of furfural and its derivatives to 1,5-Pentanediol over Ni/La-substituted CeO2 catalysts

The discerning activation of specific bonds in furfural and its derivatives presents a formidable task in the realm of biomass refinement, necessitating the provision of a precisely tailored catalyst. In this work, 1,5-pentanediol was realized by direct hydrogenation of furfural over Ni/La-substituted CeO2 catalysts. The doping of La species significantly increased the oxygen vacancies, as well as leaded to expose more interfacial Niδ+-OV-LaxCe sites and optimize the metallic Ni electronic configuration. The Ni/3.0La2O3-CeO2 catalyst showcased a remarkable catalytic activity and high yield of 1,5-pentanediol (70 %), effectively reducing the activation energy required for the hydrogenation of furfural to 1,5-pentanediol (57.5 kJ mol−1). These findings surpassed the performances of Ni/La2O3, Ni/CeO2, and non-precious metal catalysts documented in existing literature. This outcome serves as a valuable reference for the controllable optimization of furfural directed hydrogenation catalysts, as well as provides theoretical support for the efficient and environmentally-friendly synthesis of 1,5-pentanediol.

Crystal Structure and Electron Configuration of {MNO}8 Heme Complexes.

Although research on nitrosyl (NO) heme complexes and their one-electron reduced form, nitroxyl (or nitroxyl anion, NO-) derivatives, has been going on for decades, there are still disagreements about the electrical configuration of nitroxyl complexes, and the majority of the work on this topic is based on theoretical calculations. Following the initial nitroxyl iron porphyrin crystal structure, we present two further polymorphic forms of [CoCp2][Fe(TFPPBr8)(NO)]. Using the same completely halogenated porphyrin ligand, we also present two polymorphic forms of nitrosyl cobalt(II) complexes, which are another sort of {MNO}8 structure. In addition to the EXANES and EPR studies of these {FeNO}7 and {CoNO}8 complexes, the {FeNO}8 [CoCp2][Fe(TFPPBr8)(NO)] complex is also investigated by temperature-dependent Mössbauer experiments for the first time with the {FeNO}7 precursor as a control sample. The analysis of the Mössbauer and crystal structural parameters between these two types of {MNO}8 (M = Fe or Co) species and previously reported analogous ones allow us to conclude that the electronic configuration of [Fe(TFPPBr8)(NO)]- is best described as an intermediate between low-spin Fe(II)-NO- and Fe(I)-NO•.