Replacement Of Fe3 Research Articles

Enhanced catalytic properties of rare-earth substituted cobalt ferrites fabricated by sol-gel auto-combustion route

Abstract Cobalt ferrite has been extensively used in catalysis owing to their remarkable physical and chemical properties. Additionally, further modifications in these properties can be achieved by changing cation distribution. The ionic radii of rare earth (RE3+) ions are larger than the Fe3+ ions. So, on the replacement of Fe3+ ion in cobalt ferrite with even a small amount of RE3+ ion, the physical and chemical properties get greatly affected due to structural distortion and lattice strain. So, in the present work doping of RE element into ferrite crystal lattice has been done via sol-gel auto-combustion route. The synthesized samples were well characterized using various techniques and the change in their structural, magnetic and optical properties was investigated. Further, for studying the effect of RE metal ion substitution on the catalytic properties, the samples were exploited as photo-Fenton catalysts for the removal of cationic and anionic dyes. The RE substituted cobalt ferrite samples exhibited remarkable enhancement in the catalytic activity in comparison to pure cobalt ferrite. The synthesized samples thus can be potentially used for combating the environmental properties.

Phase transformation of Sn in tin-bearing iron concentrates by roasting with FeS2 in CO-CO2 mixed gases and its effects on Sn separation

A novel method to separate Sn and obtain qualified iron concentrates with low sulfur content from tin-bearing iron concentrates is proposed in the present paper. Combining the results of thermodynamic analysis, chemical analysis, and XRD, EPMA and XPS analyses, it can be concluded that the tin volatilization is restricted in the presence of iron-containing phases through the formation of Fe-Sn spinel or Fe-Sn alloy. The Fe-Sn spinel is formed through the replacement of Fe2+ in Fe3O4 by Sn2+, and the formation of Fe-Sn alloy is accelerated at higher CO contents. The pyrrhotite (Fe(1-x)S) and troilite(FeS) which derive from the FeS2 self-decomposition could be oxidized to FeO and SO2 by CO2, causing the sulfur contents in roasted residues to decrease with the increase of the CO2 content in CO-CO2 mixed gases. Under the optimum parameters of roasting temperature of 1473 K, CO content of 28.0 vol%, pyrite-to-cassiterite ratio of 90% and roasting time of 60 min, the tin content in the tin-bearing iron concentrate is decreased from 0.56% to 0.0028%, while the sulfur residual content is only 0.072%.

Structural, magnetic and Mössbauer studies of Nd-doped Mg-Mn ferrite nanoparticles

The present work is focused on the replacement of Fe3+ ions by rare-earth Nd3+ ions and their influence on the cations distribution, structural, magnetic and Mössbauer properties of Mg-Mn nanoferrites. Nanosized Nd-doped Mg-Mn nanoferrites, Mg0.9Mn0.1NdxFe2−xO4, where x=0.1, 0.2 & 0.3, were successfully synthesized for the first time through solution combustion technique. X-ray diffraction studies confirmed the formation of single phase nature of the synthesized nanoferrites. Williamsons-Hall plots were used to obtain the particle size and strain while the lattice parameter was obtained from Nelson-Riley plots. The particle size was observed to decrease (19.2–13.5nm) while lattice parameter was observed to increase (8.373–8.391Å) with the incorporation of Nd3+ ions. Cation distribution between the tetrahedral (A-site) and octahedral (B-site) was estimated by using the X-ray diffraction method & magnetization technique. The estimated cation distribution was used to investigate the detailed structural parameters. Room temperature M−H study revealed a decrease of saturation magnetization (10.15–1.83emu/g) and an increase in coercivity (22.86–27.19Oe) with the increasing substitution of Nd3+ ions. Magnetic results obtained in the present study indicated that the synthesized nanoferrites can be a useful candidate for electromagnet applications.

Investigation of Stability and Magnetic Properties of Ni- and Co-Doped Iron Oxide Nano-particles

The current work is dedicated to investigate the effect of nickel and cobalt doping on the crystallanity, stability, and magnetic and optical properties of magnetite (Fe3O4) nano-particles. Nickel- and cobalt-doped magnetite (NixFe3−xO4 and CoxFe3−xO4 with x = 0, 0.05, 0.1, and 0.15) nano-particles have been prepared by chemical co-precipitation method and are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), themogravimetric analysis (DSC-TGA), scanning electron microscopy (SEM), vibrating sample magnetometry (VSM), and UV-visible spectroscopy to study their structural, thermal, morphological, magnetic, and optical properties, respectively. The structural analysis indicates the formation of a single-phase cubic inverse spinel structure with a decrease in lattice parameters with increasing Ni and Co concentrations. Thermal analysis reveals that the transition temperature increases. The increase in transition temperature is due to the maghemite to hematite phase transition after the replacement of Fe2+ with Co2+ or Ni2+ in the B-site. The increase in transition temperature is attributed to the fact that stability increases with increasing cobalt content. Morphological analysis indicates the spherical shape of nano-particles with least agglomeration at all concentrations. The optical band gap energy increases as the particle size decreases. Magnetic properties reveal that the saturation magnetization decreases in both cases, but coercivity increases in the case of Co. This behavior is ascribed due to the high anisotropic cobalt cation doping in magnetite (Fe3O4) nano-particles, which is the goal to achieve the increase in hyperthermic efficiency.

Magnetic and hyperfine interactions in HoFe1−xCrxO3 (0≤x≤1) compounds

We report on the magnetic and Mössbauer properties of polycrystalline HoFe1-xCrxO3 (0≤x≤1) compounds. Magnetization data reveals the continuous tailoring of magnetic transition due to weakening of Ho3+-Fe3+ and Fe3+-Fe3+ interactions in the entire temperature range by replacing the Fe3+ ions with Cr3+ ions. The observed decrease in Néel temperature (TN) and increase in spin re-orientation transition temperature (TSR) with the replacement of Fe3+ with Cr3+ is ascribed to the weakening of Fe(Cr)-O-Fe(Cr) antiferromagnetic exchange interaction. In addition, we also attribute such a change in TN to the enhancement of ferromagnetic interaction of adjacent Cr3+ moments through t-e hybridization as a result of the structural distortion. The decrease in isomer shift (IS) suggests enhancement of the interaction between nuclear charge with the 3s electrons as a result of decrease in radial part of 3d wave function with Cr addition. In this paper we also discuss about the variation of quadrupole splitting (QS) and hyperfine fields (Hhf) with Cr addition in HoFe1-xCrxO3 (0≤x≤1) compounds.

Controlled cobalt doping in the spinel structure of magnetosome magnetite: new evidences from element- and site-specific X-ray magnetic circular dichroism analyses.

The biomineralization of magnetite nanocrystals (called magnetosomes) by magnetotactic bacteria (MTB) has attracted intense interest in biology, geology and materials science due to the precise morphology of the particles, the chain-like assembly and their unique magnetic properties. Great efforts have been recently made in producing transition metal-doped magnetosomes with modified magnetic properties for a range of applications. Despite some successful outcomes, the coordination chemistry and magnetism of such metal-doped magnetosomes still remain largely unknown. Here, we present new evidences from X-ray magnetic circular dichroism (XMCD) for element- and site-specific magnetic analyses that cobalt is incorporated in the spinel structure of the magnetosomes within Magnetospirillum magneticum AMB-1 through the replacement of Fe(2+) ions by Co(2+) ions in octahedral (Oh) sites of magnetite. Both XMCD at Fe and Co L2,3 edges, and energy-dispersive X-ray spectroscopy on transmission electron microscopy analyses reveal a heterogeneous distribution of cobalt occurring either in different particles or inside individual particles. Compared with non-doped one, cobalt-doped magnetosome sample has lower Verwey transition temperature and larger magnetic coercivity, related to the amount of doped cobalt. This study also demonstrates that the addition of trace cobalt in the growth medium can significantly improve both the cell growth and the magnetosome formation within M. magneticum AMB-1. Together with the cobalt occupancy within the spinel structure of magnetosomes, this study indicates that MTB may provide a promising biomimetic system for producing chains of metal-doped single-domain magnetite with an appropriate tuning of the magnetic properties for technological and biomedical applications.

Mössbauer spectroscopic studies of Al3+ ions substitution effects in superparamagnetic Mg0.2Mn0.5Ni0.3AlyFe2−yO4 compositions

Nanoparticles of Al3+ ions substituted MgMnNi materials with compositions Mg0.2Mn0.5Ni0.3AlyFe2−yO4 (y = 0.15–0.25) were synthesized by citrate precursor technique. Samples were characterized by X-ray diffraction, transmission electron microscopy, vibrating sample magnetometer and room temperature 57Fe Mössbauer spectroscopy. Saturation magnetization decreases with increasing Al3+ ions concentration because replacement of Fe3+ ions by Al3+ ions at octahedral B-site weaken sublattice interaction and lowers magnetic moments. Mössbauer spectral studies show that as-prepared nano-sized samples are superparamagnetic at room temperature. Superparamagnetic relaxation was observed for small crystallite in samples with higher Al content, which is attributed to weakening of A–B exchange interaction. Mössbauer spectra at 300 K show a gradual collapse of magnetic hyperfine splitting typical for superparamagnetic relaxation. An increase in inversion parameter is observed with increasing Al3+ ions substitution, which is attributed to decrease in crystallite size.

Structural and Magnetic Properties of High Coercive Al-Substituted Strontium Hexaferrite Nanoparticles

The aim of this work is to investigate the correlation between replacement of Fe3+ ions by Al3+ and structural and magnetic properties of Sr-hexaferrites. To this regard, a simple sol–gel auto-combustion method followed by subsequent heat treatment in air was employed to synthesize nanocrystalline SrFe12−x Al x O19 (0 ≤ x ≤ 4). X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Fourier-transform infrared (FT-IR), and vibrating sample magnetometer (VSM) methods were used in order to characterize the produced samples. The results show that the formation of the M-type hexaferrite phase is associated with some α-Fe2O3 as a secondary phase at low calcination temperature. By increasing the calcination temperature, high-purity hexaferrite phase without any unwanted phases can be formed. The average particle size of the substituted strontium ferrite gradually became smaller by addition of aluminum. The room temperature saturation magnetization values continuously reduced by increasing Al3+ that is contributed to substitution of Fe3+ by nonmagnetic ions in the lattice. However, the coercivity initially increases and then decreases with increasing the Al3+ content. A high coercivity up to 9.1 kOe was obtained for SrFe10Al2O19 which is much higher than the maximum theoretical value of H C for pure SrFe12O19 (7.5 kOe).

Effect of Mo substitution on structural and magnetic properties of Zinc ferrite nanoparticles

Nano ferrite ZnFe2-xMoxO4 (x = 0.0, 0.1, 0.2, and 0.3) samples were synthesized by using citrate method. The phase purity and the structure parameters were studied using X-ray diffraction, FT-IR spectroscopy, and magnetic measurements. Rietveld analysis of X-ray diffraction data revealed that Mo doping ZnFe2O4 changes the degree of inversion of Zn2+ cations. The oxidation state of Mo was studied by using FTIR analysis. Mo doped ZnFe2O4 has a ferromagnetic properties. The magnetization decreases by the replacement of Fe3+ ions by non-magnetic Mo3+ ions. Mo doped ZnFe2O4 samples have a very small coercive field (Hc), which changes depending on the amount of Mo in the sample and reach its maximum value for ZnFe1.7Mo0.3O4. Cation distribution is proposed in an attempt to explain the experimental results of XRD, IR, and VSM data. The direct proportion between the coercive field and the Fe2+ content in the samples was studied in detailed.

Structural and vibrational studies of NiAlxFe2−xO4 ferrites (0≤x≤1)

Nickel–Aluminium ferrites with the general formula NiAlxFe2−xO4 (0≤x≤1) were synthesized using the solid-state reaction technique and characterized using X-ray diffraction, FT-Infra Red and Raman spectroscopy. XRD diffraction patterns show that all samples have a pure single-phase cubic spinel structure over the whole composition range. From these patterns, the lattice parameter, bonds length, crystallite size, density and porosity have been calculated. Infra Red spectra showed two significant absorption bands, the high band corresponds to tetrahedral (A) sites and the lower band to octahedral [B] sites, thus confirming the single phase spinel structure. The force constants Kt and Ko for the two sites have been deduced from IR band frequencies and compared with the trend of bond lengths. For all compositions, Raman spectra show the five active modes A1g+E1g+3 T2g of the motion of O2− ions and both the A-site and B-site ions. The Raman frequencies trend with aluminium content show a blue shift for all modes consistent with the replacement of Fe3+ by lower mass Al3+.

High-frequency millimeter wave absorption of indium-substituted ε-Fe2O3 spherical nanoparticles (invited)

In this work, we prepared indium-substituted ε-iron oxide (ε-InxFe2−xO3) spherical nanoparticles by a combination method of reverse-micelle and sol-gel techniques. The powder X-ray diffraction pattern with Rietveld analysis shows that ε-InxFe2−xO3 has an orthorhombic crystal structure (space group: Pna21), and the In3+ ions mainly replace the Fe3+ ions at B site among the four nonequivalent Fe3+ sites (A–D sites). The magnetic measurements show that the coercive field (Hc) at 300 K decreases with increasing x, i.e., Hc = 21.9 kOe (x = 0), 12.2 kOe (x = 0.04), 11.6 kOe (x = 0.09), 7.8 kOe (x = 0.13), and 5.9 kOe (x = 0.18). Millimeter wave absorption was measured by terahertz time-domain spectroscopy, and the decrease of resonance frequency (fr) is observed, i.e., fr = 182 GHz (x = 0), 160 GHz (x = 0.04), 143 GHz (x = 0.09), 123 GHz (x = 0.13), and 110 GHz (x = 0.18). This decrease in the fr value is understood by the decrease of magnetic anisotropy, which is caused by the replacement of Fe3+ (S = 5/2) with nonmagnetic In3+ (S = 0) at B site contributing to the magnetic anisotropy.

Aluminum substituted low loss Z-type hexaferrites for antenna applications

Z-type hexaferrites in series (Ba0.5Sr0.5)3Co2Fe22−xAlxO38+1.0wt% H3BO3 (where x=0.0, 0.4, 0.8, 1.2, 1.6, 2.0, and 2.4) were prepared by a conventional ceramic technique. Aluminum substitution iron has been used to enhance sintering density and direct current (DC) resistivity, and decrease magneto-dielectric losses of the ferrites. Meanwhile H3BO3 addition has been used to lower sintering temperature, reduce permeability and enhance resonance frequency. A second phase of Al4B2O9 was found in the XRD patterns (where x=2.0, 2.4). The replacement of Fe3+ ions by Al3+ ions promoted sintering and increased density of the ferrites, which resulted in the increase of real permittivity. Comparatively, a ferrite sample with x=1.6 presented the best performances in terms of densification, microstructure, magneto-dielectric property, and loss tangent. Since loss tangent was kept low with the frequency ranging from 10MHz to 1.2GHz, such magneto-dielectric material could be used in this frequency range for antenna miniaturization.

A facile approach to enhance the high temperature stability of magnetite nanoparticles with improved magnetic property

We study the effect of Zn2+ doping on crystal structure, magnetic properties, blocking and Curie temperatures, and the high temperature phase stability of magnetite nanoparticles under air and vacuum annealing. The Zn2+ doped nanoparticles (ZnxFe3−xO4 with x = 0, 0.2, 0.4, and 0.6) are prepared by simple co-precipitation technique and are characterized by high temperature X-ray powder diffraction (HTXRD), vibrating sample magnetometer, small angle X-ray scattering, thermogravimetry, differential scanning calorimetry (DSC), and transmission electron microscopy. Our HTXRD studies show that the decomposition temperature of pure magnetite (Fe3O4) in vacuum is increased by 300 °C (from 700 to 1000 °C), with 0.2 fraction of Zn2+ doping. The DSC studies under air environment also show that the γ-Fe2O3 to α-Fe2O3 phase transition temperature increases with the zinc fraction. The increase in transition temperature is attributed to the increase in the activation energy of the maghemite to hematite phase transition after the replacement of Fe3+ with larger diameter Zn2+ in the A site. Interestingly, the saturation magnetization increases from 61 to 69 emu/g upon 0.2 fraction of Zn2+, which augments the utility of the doped compound for practical applications. While the Curie temperature is found to increase with doping concentration, the blocking temperature shows an opposite trend. The blocking temperature values were found to be 262, 196, 144, and 153 K for 0, 0.2, 0.4, and 0.6 fraction of zinc, respectively. The reduction in TB is attributed to weak dipole–dipole interactions and local exchange coupling between nanoparticles. All the Zn2+ doped samples show superparamagnetic nature. These findings are extremely useful in producing superparamagnetic nanoparticles with enhanced magnetic properties for high temperature applications.

Exploring the dielectric behaviour of nano-structured Al3+ doped BiFeO3 ceramics synthesized by auto ignition process

Dielectric relaxation and electrical properties of Al doped polycrystalline bismuth ferrite (BAFO) nano-structured ceramics (13–20nm having composition Bi1−xAl2xFe1−xO3 (0.0≤x≤0.3) were investigated over a wide range of frequency and temperature. Relaxation peaks were obtained in low as well as high frequency regions for all samples which are explained on the basis of Debye-type relaxation model. The replacement of Fe3+ and Bi3+ by Al3+ ions in the BFO system creates oxygen vacancies and hence Schottky barriers, which are responsible for the anomalous behaviour in the dielectric properties. Debye relaxation model and Maxwell–Wagner charge carriers hopping were utilized in overall estimation of the dielectric behaviour of the system. The values of dielectric constant and loss tangent were found to decrease with the increase in frequency, while these parameters increase with the increase in temperature as well as dopant concentration. The a.c. conductivity has a general decreasing trend as a function of composition while it increases with the increase in frequency. The temperature dependence of a.c. conductivity and relaxation time follow well-defined Arrhenius behaviour. The calculated values of activation energies are in the order of 0.54eV–0.73eV (<1.0eV) which are indicative of the conduction by means of space charge carriers and O2− vacancies.

Infrared and Visible Spectrum Study on Yellowish Green Peridot from Jinlin

10 pieces of yellowish green peridot from Jilin province with fine and pure texture were selected to analyze the relationship between frequency drift in middle-infrared band and color appearance, through the replacement of Fe2+. The actual crystal chemical formula of the samples calculated by Oxygen atom method is: (Mg1.84,Fe0.19)2.04[(Si0.982,Al0.001)0.983O4], so prove that it is chrysolite [1] and the replacement of Fe2+ and Mg2+ in the position M, which led to the yellowish green appearance. With the help of Fourier infrared spectrometer TENSOR27 and One Way ANOVA analysis study the infrared spectra of 10 samples and analyze the impact Fe2+ had on frequency drift, getting the Correlation coefficient r between Fe2+ and the wave-number near 1040cm-1, 622cm-1, 522cm-1, and the value of r are -0.896,-0.884,-0.903, therefore, with Fe2+ increasing ,three reflection peaks drift to the lower frequency. Compare the reflectivity in the visible area (360nm ~ 750nm) tested by colorimeter Color i5 with the mafic peridot end of forsterite solid solution, finding that with the reflectance peaks drift to low frequency, reflection of blue and purple light decrease, blue and purple tone in peridot decreasing; reflection of the red and orange light increases, red and orange tone increasing. It is concluded that in the transformation of mafic Peridot end to chrysolite peridot end, reflection peaks in infrared band drift to lower frequency, causing the increase of red and orange tone, decrease of blue and purple tone in Peridot.

Micas from the Khaluta carbonatite deposit, western Transbaikal region

The Khaluta carbonatite deposit located in the western Transbaikal region was formed during the Late Mesozoic rifting in the southern framework of the Siberian Craton. Carbonatite is associated with shonkinite and syenite and is accompanied by fenitization. The composition of mica in more than 160 samples of country rocks, carbonatites, silicate rocks, and fenites was studied. The Fe3+ and Fe2+ contents, as well as oxygen isotopic composition, were determined. The Mg and Fe contents increase, whereas the Ti and Al contents decrease in micas when passing from silicate rocks and fenites to carbonatites. Micas from carbonatites are depleted in Al, enriched in Fe3+, and distinguished by high Si and F contents. According to our calculations, in some cases Al replaces Si in the tetrahedral site instead of replacement of Fe3+ as is characteristic of tetraferriphlogopite. Formally, the mica from carbonatites falls within the tetraferriphlogopite field, but typical inverse pleochroism is not always observable. The δ18O values of micas from carbonatite, shonkinite, syenite, and fenite are similar to those of mantle-derived silicate minerals. The δ18O values in the minerals coexisting with phlogopite testify to their isotopic equilibrium and make it possible to calculate the crystallization temperature of carbonatite.

The effect of Mg doping on the structural and physical properties ofLuFe2O4 and Lu2Fe3O7

The structural and physical properties of the recently discovered electronic ferroelectric materialsLuFe2O4 and Lu2Fe3O7 have been investigated for Mg substitution of Fe. X-ray diffraction datademonstrate that the lattice parameters in both systems change progressivelywith increasing Mg content, with a smaller unit cell volume on replacingFe2+ by Mg2+. X-ray absorption near-edge spectroscopy experiments at the Fe K-edge showthat the average Fe oxidation state is slightly increased along with Mg doping inLu2Fe3O7 materials, consistent with isomorphous replacement ofFe2+ by Mg2+. Measurements of dielectric properties demonstrate that Mg dopingcould have an effect on the electron hopping energy betweenFe2+ and Fe3+ ions. Transmission electron microscopy and magnetization analysis reveal that Mg doping inLuFe2O4 has a much greaterinfluence than in Lu2Fe3O7 on both the charge ordering and the low-temperature magnetic properties.

An investigation of low-field magnetoresistance in the double perovskitesSr2Fe1−xZnxMoO6,x = 0, 0.05, 0.15 and 0.25

The electrical, magnetic and transport properties of Zn doped polycrystalline samples ofSr2Fe1−xZnxMoO6 (x = 0,0.05,0.15 and 0.25) with the double perovskite structure have been investigated. The subtle replacement ofFe3+ ionsby Zn2+ ions facilitates the formation of a more ordered structure, while further substitution leadsto disordered structure because of the presence of a striped phase. Analysis of the x-raypowder diffraction patterns based on Rietveld analysis indicates that the replacement ofFe3+ byZn2+ ions favoursthe formation of Mo6+ ions. The spin-glass behaviour can be explained on the basis of the competitionbetween the antiferromagnetic superexchange and the ferromagnetic double-exchangeinteraction. The low-field magnetoresistance was moderately enhanced atx = 0.05, and its origin was found to be the competition between the decrease of the concentrationof the itinerant electrons and the weaker antiferromagnetic superexchange in the antiphaseboundaries. An almost linear negative magnetoresistance in moderate field has been observed forx = 0.25. A possibledouble-exchange mechanism is proposed for elucidating the observations; it also suggests a coexistenceof (Fe3+,Mo5+)and (Zn2+,Mo6+) valence pairs.

Crystal Structure of Pyrococcus furiosus Phosphoglucose Isomerase: IMPLICATIONS FOR SUBSTRATE BINDING AND CATALYSIS

Phosphoglucose isomerase (PGI) catalyzes the reversible isomerization between d-fructose 6-phosphate and d-glucose 6-phosphate as part of the glycolytic pathway. PGI from the Archaea Pyrococcus furiosus (Pfu) was crystallized, and its structure was determined by x-ray diffraction to a 2-A resolution. Structural comparison of this archaeal PGI with the previously solved structures of bacterial and eukaryotic PGIs reveals a completely different structure. Each subunit of the homodimeric Pfu PGI consists of a cupin domain, for which the overall structure is similar to other cupin domain-containing proteins, and includes a conserved transition metal-binding site. Biochemical data on the recombinant enzyme suggests that Fe2+ is bound to Pfu PGI. However, as catalytic activity is not strongly influenced either by the replacement of Fe2+ by a range of transition metals or by the presence or absence of the bound metal ion, we suggest that the metal may not be directly involved in catalysis but rather may be implicated in substrate recognition.

The primary and secondary acceptors in bacterial photosynthesis: II. The structure of the Fe2+-Q− complex

The primary processes of bacterial photosynthesis take place in a membrane-bound protein called the reaction center (RC). The process involves light-induced electron transfer from a primary electron donor to a sequence of electron acceptors. The terminal acceptors, operating sequentially, are two ubiquinones, QA and QB, that couple magnetically to a high-spin (S = 2) Fe2+ forming an Fe2+-Q− complex. We have used a variety of techniques to investigate the electronic as well as some features of the spatial structure of the Fe2+-Q− complex in RCs fromRb. sphaeroides. These include: (a) static magnetization measurements in the temperature range of 0.7 to 190 K and magnetic fields up to 8 kG, (b) EPR spectroscopy at helium temperatures at 1.2, 9, and 35 GHz, (c) Mossbauer spectroscopy and (d) extended X-ray fine structure (EXAFS) determinations. The results of these measurements showed that Fe2+ resides in an asymmetric ligand field environment forming 6 ligands with a combination of oxygens and nitrogens. From the EXAFS results the distances of the Fe2+ to the first and third coordination shells were determined. These spatial features were subsequently corroborated by the X-ray structure of the RC, which showed the environment of the Fe to be a distorted octahedron, the base plane of which is formed by three Nɛ’s of histidines and one carbonyl oxygen; the apex is formed by a fourth Nɛ and a second carbonyl oxygen. The distances from the Fe2+ to the first and third shell were in good agreement with the values obtained from EXAFS. The most detailed information of the electronic structure of the Fe2+-Q− complex was obtained from the EPR spectra using the spin Hamiltonian formalism. The following spin-Hamiltonian parameters were obtained: for the crystalline field parameters,D = 7.60 K,E/D = 0.25; for the electronicg-values, gFe, x = 2.16, gFe, y = 2.27, gFe, z = 2.04 and for the antiferromagnetic exchange interaction,J x = −0.13 K,J y = −0.58 K,J z = −0.58 K. The use of the spin Hamiltonian was validated by comparing the results obtained from it with those obtained from an exact numerical solution of the 25 lowest energy levels of the orbital Hamiltonian. Possible roles that Fe2+ may play in the function of the RC are discussed. They include a structural role in which Fe2+ liganded to four histidine nitrogens imparts a rigid structure to a four α-helix bundle and a role in the electron transfer kinetics, most notably from the intermediate acceptor I− (bacteriopheophytin) to QA. Replacement of Fe2+ by diamagnetic Zn2+ retained all observed native characteristics of the RC.