Influence of mechanical activation time,annealing, and Fe/O ratio on Fe3O4/Fe composites formation from Fe2O3 and Fe powders mixture

Commercially, iron (α-Fe) and hematite (α-Fe₂O₃) powders were used for the synthesis of composite powders of Fe₂O₃/Fe type by mechanical milling. Several ratios of Fe₂O₃/Fe were chosen for the composite synthesis; the atomic percent of oxygen in the starting mixtures ranged from 21 to 46 %. The Fe₂O₃/Fe composite samples with various Fe/O ratios were milled for different milling times. The milled composite samples were subjected to the heat treatments in argon up to 900 °C. During the heat treatment at temperatures that do not exceed 550 °C, Fe₃O₄/Fe composite particles are formed by the reaction between the Fe₂O₃ and Fe. Further increase of the heat treatment up to 700 °C leads to the reaction of the Fe₃O₄/Fe composite component phases, resulting thus in the formation of FeO/Fe composite. The heat treatment up to 900 °C of the Fe₂O₃/Fe leads to the formation of a composite of FeO/Fe₃O₄/Fe independent of the milling time and Fe₂O₃/Fe ratios. The onset temperatures of the Fe₃O₄ and FeO formations decrease upon increasing the milling time. Another important aspect is that, in the case of the same milling time but with a large amount of iron into the composite powder the formations temperatures of Fe₃O₄ and FeO are also decreasing. The influence of the mechanical activation time, heat treatment temperature, and Fe/O ratio on the formation of the (Fe₃O₄, FeO)/Fe composite from Fe₂O₃+Fe precursor mixtures was studied by differential scanning calorimetry and X-ray diffraction techniques.     

Nano-Architecture of Facetted NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/(Ni,Fe)O Particles Produced by Induction Plasma

Facetted nickel ferrite (NiFe₂O₄) and bunsenite [(Ni,Fe)O] nanocrystals were grown from the decomposition of iron and nickel nitrate precursors using an inductively coupled plasma reactor. The full range of the two-phase region of the Fe₂O₃–NiO pseudo-equilibrium phase diagram was investigated by producing nanopowders with bulk Ni/(Ni + Fe) ratios of 0.33, 0.4, 0.5, 0.75 and 1.0. A Ni-poor [Ni/(Ni + Fe) ≤ 0.5] precursor solution produced truncated octahedron nanocrystals, whereas nanocubes were obtained at higher ratios [Ni/(Ni + Fe) ≈ 1]. In both cases, it is shown that the nanocrystals adopt a morphology close to the Wulff shape of the crystalline system (spinel and NaCl, respectively). As the bulk Ni/(Ni + Fe) ratio increases from 0.33 (the stoechiometric composition of nickel ferrite), bunsenite is epitaxially segregated on the {110} and {111} facets of nickel ferrite, while leaving the NiFe₂O₄ {100} facets exposed. A precursor solution at a Ni/(Ni + Fe) ratio of 0.75 gave an (Ni,Fe)O-rich nanopowder with a random and irregular interconnected morphology. The structure of these nanocrystals can be understood in terms of their thermal history in the plasma reactor. These results highlights the possibility of producing organized multi-phased nanomaterials of binary systems having two phases stable at high temperatures, using a method known to be easily scalable.     

Structural, optical and photocatalytic studies of Fe doped ZnS nanoparticles

Fe doped ZnS nanoparticles (Zn_1?xFe_xS; where x = 0.00, 0.03, 0.05 and 0.10) were synthesized by a chemical precipitation method. The synthesized products were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, ultraviolet–visible and photoluminescence spectrometer. The X-ray diffraction and transmission electron microscope studies show that the size of crystallites is in the range of 2–10 nm. Photocatalytic activities of ZnS and 3, 5 and 10 mol% Fe doped ZnS were evaluated by decolorization of methylene blue in aqueous solution under ultraviolet and visible light irradiation. It was found that the Fe doped ZnS bleaches methylene blue much faster than the undoped ZnS upon its exposure to the visible light as compared to ultraviolet light. The optimal Fe/Zn ratio was observed to be 3 mol% for photocatalytic applications.     

Active Sites in Fe/ZSM-5 Zeolite

Fe/ZSM-5 zeolite has shown great potential in the selective oxidations of hydrocarbons such as methane and benzene. The various competing active sites of Fe/ZSM-5 zeolite are reviewed, including the mono-iron, oxygen-bridged [Fe, X] (X = Fe, Al) and peroxide species; in addition, the influences of H₂ pretreatment are considered. For the mono-iron species, the H₂ molecules are chemisorbed on the Fe(III) sites via the η²-binding mode. Both high- and low-spin Fe(III) ions play an important role during the H₂ reduction process whereas the former predominates in the N₂O decomposition process. As the calculated energy barriers indicate, the Fe(III) ions are facile to be reduced by H₂ pretreatment and therefore the active site of the mono-iron species should be in the FeO(OH) form. Instead, the oxygen-bridged [Fe, X] and peroxide species remain stable by H₂ pretreatment. The suitable oxygen-bridged [Fe, X] structures are screened out by comparisons with the experimental data and energy considerations from computational aspects. The geometries are in good agreement with the experimental data; meanwhile, it provides sound explanations to the distribution of the iron valence states, the thermodynamic facilitation of the “alfa-oxygen” generation by the introduction of extra-lattice Al ions as well as the shift of the Fe–Fe distances from ca. 3.06 to 2.53 Å. The superoxide species exists in Fe/ZSM-5 zeolite but not with the presence of extra-lattice Al ions. As the temperature increases, it gradually converts into the peroxide species and probably is the precursor of the peroxide species, one of the competing active sites in Fe/ZSM-5 zeolite. The clarification of active sites lays a solid foundation on the understanding of the catalytic processes and improvement of the Fe/ZSM-5 catalyst, one of the promising candidates to meet the industry challenges.     

Effective removal of ciprofloxacin from aqueous solutions using magnetic metal–organic framework sorbents: mechanisms,isotherms and kinetics

Metal–organic framework sorbents [MIL-100(Fe), MOF-235(Fe)], Fe₃O₄ nanoparticles and metal–organic framework loaded on iron oxide nanoparticles [Fe₃O₄@MIL-100(Fe) and Fe₃O₄@MOF-235(Fe)] were prepared and examined for ciprofloxacin (CIP) removal. The results showed that sorption kinetics of CIP by Fe₃O₄@MIL-100(Fe) follows the Elovich and pseudo-second-order models indicating that the sorption is both chemisorption and physical adsorption, whereas the sorption to other sorbents occurs mainly by physical sorption. The sorption isotherm studies revealed that Langmuir model provided the best fit to all the experimental data. The thermodynamic studies showed that CIP removal is spontaneous (ΔG° = 2.28 kJ/mol) and endothermic (ΔH° = 18.39 kJ/mol). It was also found that among the sorbents investigated for CIP removal, Fe₃O₄@MIL-100(Fe) has the highest maximum monolayer adsorption capacity of 322.58 mg/g.     

Determination of Fe(II), Fe(III) and Fetotal in thermal water by ion chromatography spectrophotometry (IC-Vis)

Determination of iron speciation in water is one of the major challenges in environmental analytical chemistry. Here, we present and discuss a method for sampling and analysis of dissolved Fe(II), Fe(III), and Fe_total concentrations in natural thermal water covering a wide range of temperature, pH, chemical composition, and redox conditions. Various methods were tried in the collection, preservation, and storage of natural thermal water samples for the Fe(II) and Fe(III) determinations, yet the resultant Fe speciation determined was often found to be significantly affected by the methodology applied. Due to difficulties in preserving accurate Fe speciation in natural samples for later laboratory analysis, a field-deployed on-site method using ion-chromatography and spectrophotometry was developed and tested. The IC-Vis method takes advantage of ion chromatographic separation of Fe(II) and Fe(III), followed by post-column colour reaction and spectrophotometric detection, thus allowing analysis of Fe(II) and Fe(III) in a single 15-minute run. Additionally, Fe_total can be determined after sample oxidation. The analytical detection limits are ~2 µg L^?1 (LOD) using 200–1000 µL injection volumes and depend on the blank and reagent quality. The power of this method relies on the capability to directly determine a wide range of absolute and relative concentrations of Fe(II) and Fe(III) in the field. The field-deployed IC-Vis method was applied for the determination of Fe(II) and Fe(III) concentrations in natural thermal water with discharge temperatures ranging from 12°C to 95°C, pH between 2.46 and 9.75, and Fe_total concentrations ranging from a few μg L^?c up to 8.3 mg L^?1.     

Co-doping a metal (Cr,Mn, Fe,Co, Ni,Cu, and Zn) on Mn/ZSM-5 catalyst and its effect on the catalytic reduction of nitrogen oxides with ammonia

Selective catalytic reduction (SCR) of NO_x by NH₃ over a series of Mn–M/Z catalysts (M = Cr, Mn, Fe, Co, Ni, Cu, Zn, and Z = the ZSM-5 Zeolite) synthesized by wet impregnation method was investigated. Mn–Fe/Z, Mn–Co/Z, and Mn–Cu/Z catalysts exhibited approximately 100 % NO_x conversion over a wide temperature range (200–360 °C) in a defined atmospheric condition, which was noticeably greater than that of Mn–Cr/Z (340–360 °C). Furthermore, the effect of addition of second metal oxide species to the initial Mn/Z catalyst on the structure of catalysts was studied by several characterization techniques. BET measurements revealed high surface area and pore volume of the Mn–Cu/Z catalyst. In addition, the XRD and UV–Vis DR results showed that addition of co-doped metal oxide species improved the dispersion of metal ions and inhibited crystallization of metal oxides. UV–Vis studies also were in good accordance with DTA/TG results confirming the formation of cobalt oxide and copper oxide clusters in Mn–Co/Z and Mn–Cu/Z catalysts, respectively. The FTIR spectra of pyridine adsorption, in addition, suggested the Mn–Cu/Z catalyst contained the most Lewis acid sites leading to more NO_x adsorption capacity.     

Thermal analysis, decomposition kinetics, and molecular modeling of transition metal (Fe, Co) surfactant complexes

A detailed thermal analysis of iron and cobalt surfactant complexes of the type [M(CH₃COO)₄]^2?[C₁₂H₂₅NH₃ ⁺]₂ has been carried out using Thermogravimetric (TG) analysis at different heating rates (i.e., 5, 10, 15, and 20 °C min^?1). It has been observed that iron complex decomposes by a different mechanism compared to other transition metal complexes. Metal is the final product instead of metal oxide. Combining the results from our previous study, first row transition metal complexes exhibit an order of stability in agreement with the famous Irving Williams series, i.e., the apparent activation energy, E for thermal decomposition varies as: E _Fe > E _Co < E _Ni < E _Cu > E _Zn (exception being iron because of different decomposition mechanism). Thermal decomposition parameters have been measured and compared using the multiple heating rate method of Flynn–Wall–Ozawa. Further, molecular modeling calculations have been carried out to compare the experimental TG data with theoretical computations for the synthesized metal surfactant complexes. Minimum energy optimized structures for the complexes have been obtained using Gaussian software.     

Thermal stability of the manganese-nickel mixed ferrite and iron phases in the Mn0.5Ni0.5Fe2O4/Fe composite/nanocomposite powder

The composite/nanocomposite powders of Mn_0.5Ni_0.5Fe₂O₄/Fe type were synthesized starting from nanocrystalline Mn_0.5Ni_0.5Fe₂O₄ (D = 7 nm) (obtained by ceramic method and mechanical milling) and commercial Fe powders. The composites, Mn_0.5Ni_0.5Fe₂O₄/Fe, were milled for up to 120 min and subjected to heat treatment at 600 °C and 800 °C for 2 h. The manganese-nickel ferrite/iron composite samples were subjected to differential scanning calorimetry (DSC) up to 900 °C for thermal stability investigations. The composite component phases evolution during mechanical milling and heat treatments were investigated by X-ray diffraction technique. The present phases in Mn_0.5Ni_0.5Fe₂O₄/Fe composite are stable up to 400–450 °C. In the temperature range of 450-600 °C, the interdiffusion phenomena occurs leading to the formation of Fe_1?xMn_xFe₂O₄/Ni–Fe composite type. The new formed ferrite of Fe_1?xMn_xFe₂O₄ type presents an increased lattice parameter as a result of the substitution of nickel cations into the spinel structure by iron ones. Further increases of the temperature lead to the ferrite phase partial reduction and the formation of wustite-FeO type phase. The spinel structure presents incipient recrystallization phenomena after both heat treatments (600 °C and 800 °C). The mean crystallites size of the ferrite after heat treatment at 800 °C is about 75 nm. After DSC treatment at 900 °C, the composite material consists in Fe_1?xMn_xFe₂O₄, Ni structure, FeO, and (NiO)_0.25(MnO)_0.75 phases.     

Structure of Bromotrinitrosyl Iron, [Fe(NO)3Br], and DFT Calculations of the Structures of [Fe(NO)3X] (X = Cl,Br, I)

Bromotrinitrosyl iron was prepared by passing a stream of nitrogen monoxide over a mixture of iron dibromide and iron powder at elevated temperatures. It readily loses NO to give [(ON)₂Fe(μ‐Br)Fe(CO)₂]. The structure of freshly obtained [Fe(NO)₃Br] was determined by X‐ray diffraction at 200 K and shows (distorted) tetrahedral coordination with N–Fe–N and N–Fe–Br angles of 107.9(2)° and 111.0(2)° and bent Fe–N–O groups (162.5(6)°). The DFT calculations in the series [Fe(NO)₃X] (X = Cl, Br, I) reproduce well the experimental structural parameters and vibrational frequencies.     

Mass Spectrometric Identification of [4Fe–4S](NO)x Intermediates of Nitric Oxide Sensing by Regulatory Iron–Sulfur Cluster Proteins

Nitric oxide (NO) can function as both a cytotoxin and a signalling molecule. In both cases, reaction with iron–sulfur (Fe–S) cluster proteins plays an important role because Fe–S clusters are reactive towards NO and so are a primary site of general NO-induced damage (toxicity). This sensitivity to nitrosylation is harnessed in the growing group of regulatory proteins that function in sensing of NO via an Fe–S cluster. Although information about the products of cluster nitrosylation is now emerging, detection and identification of intermediates remains a major challenge, due to their transient nature and the difficulty in distinguishing spectroscopically similar iron-NO species. Here we report studies of the NO-sensing Fe–S cluster regulators NsrR and WhiD using non-denaturing mass spectrometry, in which non-covalent interactions between the protein and Fe/S/NO species are preserved. The data provide remarkable insight into the nitrosylation reactions, permitting identification, for the first time, of protein-bound mono-, di- and tetranitrosyl [4Fe–4S] cluster complexes ([4Fe–4S](NO), [4Fe–4S])(NO)₂ and [4Fe–4S](NO)₄) as intermediates along pathways to formation of product Roussin's red ester (RRE) and Roussin's black salt (RBS)-like species. The data allow the nitrosylation mechanisms of NsrR and WhiD to be elucidated and clearly distinguished.     

Structures and energies of coadsorbed CO and H2 on Fe5C2(001), Fe5C2(110), and Fe5C2(100)

Density functional theory calculations have been carried out on the CO/H2 coadsorption on the (001), (110), and (100) surfaces of Fe5C2 for the understanding of the Fischer-Tropsch synthesis (FTS) mechanism. The stable surface species changes with the variation of the H2 and CO coverage. Along with dissociated hydrogen and adsorbed CO in 2-, 3-, and 4-fold configurations, methylidyne (C(s)H) (C(s), surface carbon), ketenylidene (C(s)CO), ketenyl (C(s)HCO), ketene (C(s)H2CO), and carbon suboxide (C(s)C2O2) are computed as thermodynamically stable surface species on Fe5C2(001) and Fe5C2(110) containing both surface iron and carbon atoms. These surface carbon species can be considered as the preliminary stages for FTS. On Fe5C2(100) with only iron atoms on the surface layer, the stable surface species is dissociated hydrogen and CO with top and 2-fold configurations. The bonding nature of these adsorbed carbon species has been analyzed.     

Bacterial sensitivity and SOD behavior of N-pyrone glucosamine Schiff base Fe(III) complex: conjoint experimental-DFT evaluation

Iron and sugar are essential components of life processes. In the evident interest toward Fe(III) compounds to explore the ability of sugars toward metallotherapy, a systematic hyphenated DFT-experimental study of a novel sugar Schiff base Fe(III) complex of general composition [Fe(L)(OH)], where L = N-dehydroacetic acid-glucosamine (dha-glsH₂), is presented. Based on various experimental spectrometric and spectroscopic characterization techniques in combination with theoretical data, a suitable distorted tetragonal structure is suggested for the complex. In addition to the formulation of the synthesized complex, superoxide dismutase (SOD) mimetic, and antimicrobial actions have also been the active goal of the work. A promising superoxide dismutazing potential with IC₅₀ = 69 μM was found. But on the other hand antibacterial action of the complex has shown less sensitivity to be called as efficient bactericidal agent.     

Study in Aqueous Solutions of Bioactive 2-Pyridineformamide-Derived Thiosemicarbazones and Their Iron(II) and Iron(III) Complexes

The binary systems of iron(II) and iron(III) with 2-pyridineformamide thiosemicarbazone (H2Am4DH) and its N(4)-methyl (H2Am4Me), N(4)-ethyl (H2Am4Et) and N(4)-phenyl (H2Am4Ph) derivatives were studied in aqueous solution by pH-potentiometry, ultraviolet–visible spectroscopy and EPR spectra. The formation constants of the iron(II) and iron(III) complexes were calculated from potentiometric and electronic absorption data at 25 °C and ionic strength μ = 0.1 mol·L^?1 using the HYPERQUAD program. The values of the formation constant of the FeL species decrease in the order Fe:H2Am4DH > Fe:H2Am4Me ≈ Fe:H2Am4Et > Fe:H2Am4Ph in the same way as the basicity of the ligands. The species distribution diagrams show that the species FeL₂ predominates at physiological pH in the Fe:H2Am4DH, Fe:H2Am4Me and Fe:H2Am4Et systems. The similar EPR spectra of these iron(III) binary systems indicate the same coordination spheres around the metallic center and the EPR g values suggests that the unpaired electron is in the d_xy orbital, indicating a d _xz ² d _yz ² d _xy ¹ ground state configuration for the complexes. For the Fe(III):H2Am4Ph system the EPR results indicated dimerization and antiferromagnetic interaction due to the presence of only one thiosemicarbazone ligand around the metallic center.     

Spectroscopic validation and biological screening of new iron(III) complexes with N,O donor ligands

Monometallic trivalent complexes of iron were synthesized by reaction between N, O type donor ligands (L) or (L′) and metal salt in a 1:2 (metal:ligand) molar ratio. Structure and composition of metal complexes were evaluated by elemental analysis, conductance measurements, magnetic moment measurements, and various spectroscopic studies viz. FTIR, UV–visible, and ESI–MS. Analytical and molar conductance data are consistent with the formulation of complexes as [Fe(L)₂X₂]·X and [Fe(L′)₂X₂]·X (where; L = Hydrazine carboxylic acid ethyl ester, L′ = Hydrazine carboxylic acid tert-butyl ester and X = Cl^?, Br^? or NO₃ ^?) due to their 1:1 electrolytic nature. IR spectral data revealed bi-dentate coordination behavior of ligands. An octahedral geometry may be assigned for metal complexes on the basis of electronic absorption data and magnetic moment parameters. The compounds were evaluated for their biological activity by in vitro antimicrobial screening against bacteria Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Salmonella typhi and fungi Candida parapsilosis and Saccharomyces cerevisiae. The results indicate that metal complexes exhibit more activity than free ligands against studied microbes.     

Thermal decomposition mechanism of iron(III) nitrate and characterization of intermediate products by the technique of computerized modeling

The nonahydrate of iron(III) nitrate shows no phase transitions in the range of ?40 to 0 °C. Both hexahydrate Fe(NO₃)₃·6H₂O and nonahydrate Fe(NO₃)₃·9H₂O have practically the same thermal behavior. Thermal decomposition of iron nitrate is a complex process which has a different mechanism than those described for other trivalent elements. Thermolysis begins with the successive condensation of 4 mol of the initial monomer accompanied by the loss of 4 mol of nitric acid. At higher temperature, hydrolytic processes continue with the gradual elimination of nitric acid from resulting tetramer and dimeric iron oxyhydroxide Fe₄O₄(OH)₄ is formed. After complete dehydration, oxyhydroxide is destroyed leaving behind 2 mol of Fe₂O₃. The molecular mechanics method provides a helpful insight into the structural arrangement of intermediate compounds.     

Microstructure and Magnetic Properties of Ag/Fe/Ag Pseudo-Sandwich Nanogranular Films

"Nanogranular Ag/Fe/Ag films were prepared by magnetron sputtering from a silver and an iron target onto glass substrates at room temperature and subsequent in situ annealing. The structural and magnetic properties of the films were investigated as a function of silver layer thickness and annealing temperature. X-ray diffraction shows the Fe(110) peak is formed in all the samples. Vibrating sample magnetometer measurements indicate that the magnetic moments lie well perpendicular to the film plane. Coercivityreaches the maximum in the sample annealed at 500 oC for 30 min with 3 nm Ag layer. A scanning probemicroscope was used to scan surface morphology and magnetic domain structures. In as-deposited samplesthe average grain size and the average roughness is smaller than that the annealing samples. After annealing,the grain size is larger and the contrast of domains increases, but the domain size becomes smaller."     

A new high-spin iron(III) bis(aqua) complex with the <Emphasis Type="Italic">meso</Emphasis>-tetra(para-chlorophenyl)porphyrin: X-ray crystallography,Hirshfeld surface analysis,magnetic, EPR and electrochemical properties

Chemical preparation of the bis(aqua) iron(III) metalloporphyrin [Fe^III(TClPP)(H₂O)₂](SO₃CF₃)·2(Pnz)·3/4(C₆H₁₂)·2H₂O (TClPP?=?TClPP?=?5,10,15,20-tetra(para-chlorophenyl)porphyrinato and Pnz?=?phenazine) coordination complex (I) was made. The crystal structure of (I) was determined by X-ray single-crystal diffraction and elucidated by Hirshfeld surface approach. Magnetic, spectroscopic and electrochemical properties were also reported and discussed. The mean equatorial distance (Fe–Np) between the iron(III) atom and porphyrin nitrogen atoms is appropriate to a high-spin (S?=?5/2) iron(III) complex. The high-spin state is also confirmed by both magnetic and electron paramagnetic resonance (EPR) spectroscopy data. The repetitive building unit of the crystal structure provides [Fe^III(TClPP)(H₂O)₂]⁺ ion complexes, two non-coordinated Pnz molecules and two water molecules which are interconnected by O–H···O/N/Cl, C–H···O/F/Cl hydrogen bonds, and by C–X···π, C–H···π and π–π stacking intermolecular contacts, forming a 3D supramolecular network. The role and nature of these intermolecular interactions were quantitatively analysed by 3D Hirshfeld surface analysis and associated 2D fingerprint plots. Cyclic voltammetry measurements indicate a one-electron reversible reduction wave with an E_1/2 (Fe(III)/Fe(II) half-potential value of ?0.24 V, which confirms the high-spin S?=?5/2 state of the studied complex.     

Effect of nitrate on the determination of iron concentration in phytoplankton culture medium by liquid scintillation counting (LSC) method using 55Fe as radioisotope tracer

Liquid scintillation counting (LSC) method using a radioisotope tracer has several advantages such as simple procedure, high sensitivity and low detection limit, and has been used for the determination Fe concentrations in water samples. Several factors such as nitrate concentration, pH, chelating ligand affect the efficiency of this method in the determination of iron (Fe) in waters. In this study, the effect of nitrate in phytoplankton culture medium on the determination of Fe concentration by LSC method using ⁵⁵Fe radioisotope tracer was evaluated. The measured Fe concentrations in the medium were lower than its added concentration (1.5 μM) when liquid samples contain nitrate. Fe concentrations decreased exponentially as nitrate concentrations increased up to 2.64 mM, reaching a constant value of 1.31 μM Fe at nitrate concentrations higher than 2.64 mM. A correction factor (f = 1.14) was calculated from the decrease rate of Fe concentrations at different nitrate concentrations in the phytoplankton culture medium. This correction factor can be used to correct the measurement values of Fe concentrations in phytoplankton culture medium obtained from LSC method. Our results showed that up to 94 % of the added Fe can be determined by LSC using ⁵⁵Fe radioisotope tracer. The remaining 6 % was probably bound to the walls of the culturing vessel. This method is also applicable for the measurement of Fe size-fractionation in phytoplankton culture medium.     

A density functional study of Fe(SINGLE BOND)N2, Fe(SINGLE BOND)N+2, and Fe(SINGLE BOND)N−2

The interaction of an iron atom with molecular nitrogen was studied using density functional theory. Calculations were of the all-electron type and both conventional local and gradient-dependent models were used. A ground state of linear structure was found for Fe(SINGLE BOND)N₂, with 2S + 1 = 3, whereas the triangular Fe(SINGLE BOND)N₂ geometry, of C_2v symmetry, was located 2.1 kcal/mol higher in energy, at least for the gradient-dependent model. The reversed order was found using the conventional local approximation. In Fe(SINGLE BOND)N₂, the N(SINGLE BOND)N bond is strongly perturbed by the iron atom: It has a bond order of 2.4, a vibrational frequency of 1886 cm⁻¹, and an equilibrium bond length of 1.16 Å: These values are 3.0, 2359 cm⁻¹, and 1.095 Å, respectively, for the free N₂ molecule. With the gradient-dependent model and corrections for nonsphericity of the Fe atom, a very small binding energy, 8.8 kcal/mol, was calculated for Fe(SINGLE BOND)N₂. Quartet ground states were found for both Fe(SINGLE BOND)N⁺₂ and Fe(SINGLE BOND)N⁻₂. The adiabatic ionization potential, electron affinity, and electronegativity were also computed; the predicted values are 7.2, 1.22, and 4.2 eV, respectively. © 1997 John Wiley & Sons, Inc.