In situ — High Temperature Mössbauer Spectroscopy of Iron Nitrides and Nitridoferrates

The stoichiometric iron nitrides γ′‐Fe₄N, ε‐Fe₃N and ζ‐Fe₂N were characterized by Mössbauer spectroscopy. The thermal decomposition of ε‐Fe₃N was studied in‐situ by means of a specially developed Mössbauer furnace. We found ε‐Fe₃N to γ′‐Fe₄N and ε‐Fe₃N_x (x ≥ 1.3) as decomposition products and determined the border of γ′/ε transformation at T ? 930 K. Mössbauer spectroscopy was applied to study in‐situ the thermal decomposition of the nitridometalate Li₃[Fe^IIIN₂] and the formation of Li₂[(Li_1‐xFe^I_x)N], the compound with the largest local magnetic field ever observed in an iron containing material. The kinetics of formation and the stability of Li₂[(Li_1‐xFe^I_x)N] was of particular interest in the present study.     

Surface analysis of nitride layers formed on Fe‐based alloys through plasma nitride process

Nitriding phenomena that occur on the surfaces of pure Fe and Fe? Cr alloy (16 wt% Cr) samples were investigated. An Ar + N₂ mixture‐gas glow‐discharge plasma was used so that surface nitriding could occur on a clean surface etched by Ar⁺ ion sputtering. In addition, the metal substrates were kept at a low temperature to suppress the diffusion of nitrogen. These plasma‐nitriding conditions enabled us to characterize the surface reaction between nitrogen radicals and the metal substrates. The emission characteristics of the band heads of the nitrogen molecule ion (N₂⁺) and nitrogen molecule from the glow‐discharge plasma suggest that the active nitrogen molecule is probably the major nitriding reactant. AES and angle‐resolved XPS were used to characterize the thickness of the nitride layer and the concentration of elements and chemical species in the nitride layer. The thickness of the nitride layer did not depend on the metal substrate type. An oxide layer with a thickness of a few nanometers was formed on the top of the nitride layer during the nitriding process. The oxide layer consisted of several species of N_x‐Fe_y‐O, NO⁺, and NO₂^?. In the Fe? Cr alloy sample, these oxide species could be reduced because chromium is preferentially nitrided. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma

The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow‐discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N₂*) or nitrogen molecule ions (N₂⁺). The optical emission spectra suggested that the formation of N₂*‐rich or N₂⁺‐rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N₂⁺‐rich plasma had a much higher nitrogen concentration than that by a N₂*‐rich plasma, likely due to the larger chemical activity of the N₂⁺ species as well as the N₂⁺ sputtering bombardment to the cathode surface. The strong reactivity of the N₂⁺ species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N₂⁺‐rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N₂*‐rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination. Copyright © 2010 John Wiley & Sons, Ltd.     

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

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

Energetics of binary iron nitrides

High-temperature solution calorimetry in molten sodium molybdate 3Na₂O·4MoO₃ was used to determine the energetics of formation of a series of binary iron nitrides: γ′-Fe₄N, ε-Fe₃N_1+y (y=0, 0.10, 0.22, 0.30, 0.33), ζ-Fe₂N and γ′′-FeN_0.91. The linear relation ΔH°_f (FeN_x)=−65.23x+13.48 kJ mol⁻¹ was found between the enthalpies of formation from the elements at 298 K of iron nitrides FeN_x and their nitrogen content x. Using this linear approximation, the enthalpy of formation of α′′-Fe₁₆N₂ has been estimated to ΔH°_f (Fe₁₆N₂)=85.2±46.8 kJ mol⁻¹.     

Unraveling the Mechanism of Water Oxidation Catalyzed by Nonheme Iron Complexes

Density functional theory (DFT) is employed to: 1) propose a viable catalytic cycle consistent with our experimental results for the mechanism of chemically driven (Ce^IV) O₂ generation from water, mediated by nonheme iron complexes; and 2) to unravel the role of the ligand on the nonheme iron catalyst in the water oxidation reaction activity. To this end, the key features of the water oxidation catalytic cycle for the highly active complexes [Fe(OTf)₂(Pytacn)] (Pytacn: 1‐(2′‐pyridylmethyl)‐4,7‐dimethyl‐1,4,7‐triazacyclononane; OTf: CF₃SO₃^?) ( 1 ) and [Fe(OTf)₂(mep)] (mep: N,N′‐bis(2‐pyridylmethyl)‐N,N′‐dimethyl ethane‐1,2‐diamine) ( 2 ) as well as for the catalytically inactive [Fe(OTf)₂(tmc)] (tmc: N,N′,N′′,N′′′‐tetramethylcyclam) ( 3 ) and [Fe(NCCH₃)(^MePy₂CH‐tacn)](OTf)₂ (^MePy₂CH‐tacn: N‐(dipyridin‐2‐yl)methyl)‐N′,N′′‐dimethyl‐1,4,7‐triazacyclononane) ( 4 ) were analyzed. The DFT computed catalytic cycle establishes that the resting state under catalytic conditions is a [Fe^IV(O)(OH₂)(LN₄)]²⁺ species (in which LN₄=Pytacn or mep) and the rate‐determining step is the O?O bond‐formation event. This is nicely supported by the remarkable agreement between the experimental (ΔG^≠=17.6±1.6 kcal mol^?1) and theoretical (ΔG^≠=18.9 kcal mol^?1) activation parameters obtained for complex 1 . The O?O bond formation is performed by an iron(V) intermediate [Fe^V(O)(OH)(LN₄)]²⁺ containing a cis‐Fe^V(O)(OH) unit. Under catalytic conditions (Ce^IV, pH 0.8) the high oxidation state Fe^V is only thermodynamically accessible through a proton‐coupled electron‐transfer (PCET) process from the cis‐[Fe^IV(O)(OH₂)(LN₄)]²⁺ resting state. Formation of the [Fe^V(O)(LN₄)]³⁺ species is thermodynamically inaccessible for complexes 3 and 4 . Our results also show that the cis‐labile coordinative sites in iron complexes have a beneficial key role in the O?O bond‐formation process. This is due to the cis‐OH ligand in the cis‐Fe^V(O)(OH) intermediate that can act as internal base, accepting a proton concomitant to the O?O bond‐formation reaction. Interplay between redox potentials to achieve the high oxidation state (Fe^V?O) and the activation energy barrier for the following O?O bond formation appears to be feasible through manipulation of the coordination environment of the iron site. This control may have a crucial role in the future development of water oxidation catalysts based on iron.     

Catalytic Properties of Nanoscale Iron‐Doped Zirconia Solid‐Solution Aerogels

Nanoscale iron‐doped zirconia solid‐solution aerogels are prepared via a simple ethanol thermal route using zirconyl nitrate and iron nitrate as starting materials, followed by a supercritical fluid drying process. Structural characteristics are investigated by means of powder X‐ray diffraction (XRD), thermal analyses (TG/DTA), N₂ adsorption measurements and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results show that the resulting iron‐doped solid solutions are metastable tetragonal zirconia which exhibit excellent dispersibility and high solubility of iron oxide. Further, when the Fe:(Fe+Zr) ratio x is lower than 0.10, all of the Fe³⁺ ions can be incorporated into ZrO₂ by substituting Zr⁴⁺ to form Zr_1?xFe_xO_y solid solutions. Moreover, for the first time, an additional hydroxyl group band that is not present in pure ZrO₂ is observed by DRIFTS for the Zr(Fe)O₂ solid solution. This is direct evidence of Fe³⁺ ions incorporated into ZrO₂. These Zr_1?xFe_xO_y solid solutions are excellent catalysts for the solvent‐free aerobic oxidation of n‐hexadecane using air as the oxidant under ambient conditions. The Zr_0.8Fe_0.2O_y solid‐solution catalyst demonstrates the best catalytic properties, with the conversion of n‐hexadecane reaching 36.2 % with 48 % selectivity for ketones and 24 % selectivity for alcohols and it can be recycled five times without significant loss of activity.     

Structural Interconversion of Bimetallic Carbonyl Clusters ­Induced by a NHC Ligand and Its Selectivity on Fragments

The reactions of IMes‐HCl with bimetallic iron‐copper clusters were investigated and it showed that interconversions among bimetallic Fe_xCu_y(CO)_z^n– clusters were induced by IMes‐HCl. The reaction priority of IMes‐HCl with fragments in Fe_xCu_y(CO)_z^n– was also investigated and the reaction behaviors of zero valent Fe(CO)₄ and divalent Fe(CO)₄ with IMes‐HCl were discussed.     

Magnesium complexes incorporated by sulfonate phenoxide ligands as efficient catalysts for ring‐opening polymerization of ε‐caprolactone and trimethylene carbonate

Two novel sulfonate phenol ligands—3,3′‐di‐tert‐butyl‐2′‐hydroxy‐5,5′,6,6′‐tetramethyl‐biphenyl‐2‐yl 4‐X‐benzenesulfonate (X?CF₃, L^CF3 ‐H, and X?OCH₃, L^OMe ‐H)—were prepared through the sulfonylation of 3,3′‐di‐tert‐butyl‐5,5′,6,6′‐tetramethylbiphenyl‐2,2′‐diol with the corresponding 4‐substituted benzenesulfonyl chloride (1 equiv.) in the presence of excess triethylamine. Magnesium (Mg) complexes supported by sulfonate phenoxide ligands were synthesized and characterized structurally. The reaction of MgⁿBu₂ with L‐H (2 equiv.) produces the four‐coordinated monomeric complexes ( L^CF3 )₂Mg ( 1 ) and ( L^OMe )₂Mg ( 2 ). Complexes 1 and 2 are efficient catalysts for the ring‐opening polymerization of ε‐caprolactone (ε‐CL) and trimethylene carbonate (TMC) in the presence of 9‐anthracenemethanol; complex 1 catalyzes the polymerization of ε‐CL and TMC in a controlled manner, yielding polymers with the expected molecular weights and narrow polydispersity indices (PDIs). In ε‐CL polymerization, the activity of complex 1 is greater than that of complex 2 , likely because of the greater Lewis acidity of Mg²⁺ metal caused by the electron‐withdrawing substitute trifluoromethyl (? CF₃) at the 4‐position of the benzenesulfonate group. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3564–3572, 2010     

A cyanide‐bridged FeII–NdIII bimetallic assembly with a one‐dimensional ladder‐like chain structure

The title complex, catena‐poly[[[(2,2′‐bipyridine‐1κ²N,N′)tris(methanol‐2κO)(nitrato‐2κ²O,O′)‐μ‐cyanido‐1:2C:N‐cyanido‐1κC‐iron(II)neodymium(III)]‐di‐μ‐cyanido‐1:2′C:N;2:1′N:C] methanol solvate], {[Fe^IINd^III(CN)₄(NO₃)(C₁₀H₈N₂)(CH₃OH)₃]·CH₃OH}_n, is made up of ladder‐like one‐dimensional chains oriented along the c axis. Each ladder consists of two strands based on alternating Fe^II and Nd^III centers connected by cyanide bridges. Furthermore, two such parallel chains are connected by additional cyanide cross‐pieces (the `rungs' of the ladder), which likewise connect Fe^II and Nd^III centers, such that each [Fe(CN)₄(bipy)]²⁻ unit (bipy is 2,2′‐bipyridine) coordinates with three Nd^III centers and each Nd^III center connects with three different [Fe(CN)₄(bipy)]²⁻ units. In the complex, the iron(II) cation is six‐coordinated with a distorted octahedral geometry and the neodymium(III) cation is eight‐coordinated with a distorted dodecahedral environment.     

Effect of Substitution of Cobalt for Iron in Sr4Fe6O13-δon the Catalytic Activity for Methane Combustion

A series of mixed oxides Sr₄Fe_6?xCo_xO_13?δ (x=0, 1, 2, 3, or 4) were prepared by sol‐gel method and used for catalytic combustion of methane. The structural properties of oxides were characterized by XRD, TGA, and XPS. The layered intergrowth perovskite‐like oxide Sr₄Fe₅CoO_13?δ exhibits the highest catalytic activity for methane combustion under the experimental conditions. The enhanced catalytic activity of Sr₄Fe₅CoO_13?δ for methane combustion could be attributed to the increased amount of oxygen vacancy caused by the partial substitution of cobalt for iron in the Sr₄Fe₆O₁₃, which was confirmed by TGA and XPS.     

Tuning Magnetic Properties of CeO2 by Fe Doping via an Electrochemical Deposition Route

Herein Ce_1?xFe_xO_2?δ nanocomposites were investigated for dilute magnetic semiconductor (DMS) properties. Ce_1?xFe_xO_2?δ nanospheres and porous nanostructures with high surface areas have been successfully prepared by electrochemical deposition at room temperature and atmospheric pressure. The structures and morphologies of Ce_1?xFe_xO_2?δ deposits were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N₂ adsorption–desorption techniques. The magnetic properties of the prepared Ce_1?xFe_xO_2?δ nanospheres and porous nanostructures were studied, and they showed room‐temperature ferromagnetism and giant magnetic moments. In addition, the effects of morphologies and compositions on the magnetic properties of Ce_1?xFe_xO_2?δ deposits were studied.     

In-situ observation of the nitrogenation of Sm2Fe17 by means of high temperature x-ray diffraction

The mechanism of nitrogenation of Sm₂Fe₁₇ was investigated with in-situ high temperature x-ray diffraction with Debye-Scherrer optic using a quartz capillary equipped with an additional buffer volume to supply sufficient nitrogen for the expected phase reaction. The formation of Sm₂Fe₁₇N_x with x ≈ 3 was observed at temperatures between 325?°C and 450?°C. During the phase transition period, taking 30–90 min at 450?°C and up to 300 min at 350?°C, two phases were observed simultaneously, a non-nitrided Sm₂Fe₁₇ phase and the already fully nitrided Sm₂Fe₁₇N₃ phase. At 325?°C no single-phase material could be obtained during 300 min. The resulting lattice parameters measured after the complete nitrogenation are the same as those, obtained from the externally nitrogenized samples.     

Humidity effects in Fe16N2 fine powder preparation by low-temperature nitridation

Low-temperature nitridation has been reported to produce ferromagnetic α″-Fe₁₆N₂ by ammonia nitridation of α-Fe fine powder, which was obtained from the reduction of vapor-grown γ-Fe₂O₃. The effects of humidity during this preparation were investigated in the present study. α″-Fe₁₆N₂ was inconsistently obtained, and at low yield, from Fe₃O₄ fine powder (MT-40) prepared from aqueous solution. Reducing the adsorbed water content in the iron oxide starting powder resulted in improved reproducibility of the α″-Fe₁₆N₂ yield of the nitridation. The use of a smaller-diameter reaction tube, less than 25 mm in diameter, enabled more reproducible preparation from vapor-grown γ-Fe₂O₃ powder (CI-30). The reaction yield was further improved by using high-quality ammonia with a water content of ≤0.05 ppm. Minimizing the humidity made it possible to obtain a fine powder with a high α″-Fe₁₆N₂ content. Enhancement of the magnetization to 210 emu g⁻¹ at room temperature was observed from a nitrided mixture of α″-Fe₁₆N₂ with residual α-Fe, compared to 199 emu g⁻¹ for an α-Fe fine powder reduced from γ-Fe₂O₃. However, excess nitrogen and residual oxygen in the nitrided products reduced the magnetization below the value of α-Fe powder after nitridation. The magnetization was enhanced in nitrided products with a nitrogen content slightly below the stoichiometric amount for α″-Fe₁₆N₂.     

Understanding the Activity of Co‐N4−xCx in Atomic Metal Catalysts for Oxygen Reduction Catalysis

Atomic metal catalysis (AMC) provides an effective way to enhance activity for the oxygen reduction reaction (ORR). Cobalt anchored on nitrogen‐doped carbon materials have been extensively reported. The carbon‐hosted Co‐N₄ structure was widely considered as the active site; however, it is very rare to investigate the activity of Co partially coordinated with N, for example, Co‐N_4?xC_x. Herein, the activity of Co‐N_4?xC_x with tunable coordination environment is investigated as the active sites for ORR catalysis. The defect (di‐vacancies) on carbon is essential for the formation of Co‐N_4?xC_x. N species play two important roles in promoting the intrinsic activity of atomic metal catalyst: N coordinated with Co to manipulate the reactivity by modification of electronic distribution and N helped to trap more Co to increase the number of active sites.     

Mechanistic Insight into Peroxo‐Shunt Formation of Biomimetic Models for Compound II,Their Reactivity toward Organic Substrates,and the Influence of N‐Methylimidazole Axial Ligation

High‐valent iron‐oxo species have been invoked as reactive intermediates in catalytic cycles of heme and nonheme enzymes. The studies presented herein are devoted to the formation of compound II model complexes, with the application of a water soluble (TMPS)Fe^III(OH) porphyrin ([meso‐tetrakis(2,4,6‐trimethyl‐3‐sulfonatophenyl)porphinato]iron(III) hydroxide) and hydrogen peroxide as oxidant, and their reactivity toward selected organic substrates. The kinetics of the reaction of H₂O₂ with (TMPS)Fe^III(OH) was studied as a function of temperature and pressure. The negative values of the activation entropy and activation volume for the formation of (TMPS)Fe^IV?O(OH) point to the overall associative nature of the process. A pH‐dependence study on the formation of (TMPS)Fe^IV?O(OH) revealed a very high reactivity of OOH^? toward (TMPS)Fe^III(OH) in comparison to H₂O₂. The influence of N‐methylimidazole (N‐MeIm) ligation on both the formation of iron(IV)‐oxo species and their oxidising properties in the reactions with 4‐methoxybenzyl alcohol or 4‐methoxybenzaldehyde, was investigated in detail. Combined experimental and theoretical studies revealed that among the studied complexes, (TMPS)Fe^III(H₂O)(N‐MeIm) is highly reactive toward H₂O₂ to form the iron(IV)‐oxo species, (TMPS)Fe^IV?O(N‐MeIm). The latter species can also be formed in the reaction of (TMPS)Fe^III(N‐MeIm)₂ with H₂O₂ or in the direct reaction of (TMPS)Fe^IV?O(OH) with N‐MeIm. Interestingly, the kinetic studies involving substrate oxidation by (TMPS)Fe^IV?O(OH) and (TMPS)Fe^IV?O(N‐MeIm) do not display a pronounced effect of the N‐MeIm axial ligand on the reactivity of the compound II mimic in comparison to the OH^? substituted analogue. Similarly, DFT computations revealed that the presence of an axial ligand (OH^? or N‐MeIm) in the trans position to the oxo group in the iron(IV)‐oxo species does not significantly affect the activation barriers calculated for C?H dehydrogenation of the selected organic substrates.     

A cyanide‐bridged FeIII–MnII heterobimetallic one‐dimensional coordination polymer: synthesis,crystal structure,experimental and theoretical magnetism investigation

A new cyanide‐bridged Fe^III–Mn^II heterobimetallic coordination polymer (CP), namely catena‐poly[[[N,N′‐(1,2‐phenylene)bis(pyridine‐2‐carboxamidato)‐κ⁴N,N′,N′′,N′′′]iron(III)]‐μ‐cyanido‐κ²C:N‐[bis(4,4′‐bipyridine‐κN)bis(methanol‐κO)manganese(II)]‐μ‐cyanido‐κ²N:C], {[FeMn(C₁₈H₁₂N₄O₂)(CN)₂(C₁₀H₈N₂)₂(CH₃OH)₂]ClO₄}_n, ( 1 ), was prepared by the self‐assembly of the trans‐dicyanidoiron(III)‐containing building block [Fe(bpb)(CN)₂]^? [bpb^2? = N,N′‐(1,2‐phenylene)bis(pyridine‐2‐carboxamidate)], [Mn(ClO₄)₂]·6H₂O and 4,4′‐bipyridine, and was structurally characterized by elemental analysis, IR spectroscopy, single‐crystal X‐ray crystallography and powder X‐ray diffraction (PXRD). Single‐crystal X‐ray diffraction analysis shows that CP 1 possesses a cationic linear chain structure consisting of alternating cyanide‐bridged Fe–Mn units, with free perchlorate as the charge‐balancing anion, which can be further extended into a two‐dimensional supramolecular sheet structure via inter‐chain π–π interactions between the 4,4′‐bipyridine ligands. Within the chain, each Mn^II ion is six‐coordinated by an N₆ unit and is involved in a slightly distorted octahedral coordination geometry. Investigation of the magnetic properties of 1 reveals an antiferromagnetic coupling between the cyanide‐bridged Fe^III and Mn^II ions. A best fit of the magnetic susceptibility based on the one‐dimensional alternating chain model leads to the magnetic coupling constants J₁ = ?1.35 and J₂ = ?1.05 cm^?1, and the antiferromagnetic coupling was further confirmed by spin Hamiltonian‐based density functional theoretical (DFT) calculations.     

Aromatic Hydroxylation at a Non‐Heme Iron Center: Observed Intermediates and Insights into the Nature of the Active Species

Mechanism of substrate oxidations with hydrogen peroxide in the presence of a highly reactive, biomimetic, iron aminopyridine complex, [Fe^II(bpmen)(CH₃CN)₂][ClO₄]₂ ( 1 ; bpmen=N,N'‐dimethyl‐N,N'‐bis(2‐pyridylmethyl)ethane‐1,2‐diamine), is elucidated. Complex 1 has been shown to be an excellent catalyst for epoxidation and functional‐group‐directed aromatic hydroxylation using H₂O₂, although its mechanism of action remains largely unknown. 1 , 2 Efficient intermolecular hydroxylation of unfunctionalized benzene and substituted benzenes with H₂O₂ in the presence of 1 is found in the present work. Detailed mechanistic studies of the formation of iron(III)–phenolate products are reported. We have identified, generated in high yield, and experimentally characterized the key Fe^III(OOH) intermediate (λ_max=560 nm, rhombic EPR signal with g=2.21, 2.14, 1.96) formed by 1 and H₂O₂. Stopped‐flow kinetic studies showed that Fe^III(OOH) does not directly hydroxylate the aromatic rings, but undergoes rate‐limiting self‐decomposition producing transient reactive oxidant. The formation of the reactive species is facilitated by acid‐assisted cleavage of the O? O bond in the iron–hydroperoxide intermediate. Acid‐assisted benzene hydroxylation with 1 and a mechanistic probe, 2‐Methyl‐1‐phenyl‐2‐propyl hydroperoxide (MPPH), correlates with O? O bond heterolysis. Independently generated Fe^IV?O species, which may originate from O? O bond homolysis in Fe^III(OOH), proved to be inactive toward aromatic substrates. The reactive oxidant derived from 1 exchanges its oxygen atom with water and electrophilically attacks the aromatic ring (giving rise to an inverse H/D kinetic isotope effect of 0.8). These results have revealed a detailed experimental mechanistic picture of the oxidation reactions catalyzed by 1 , based on direct characterization of the intermediates and products, and kinetic analysis of the individual reaction steps. Our detailed understanding of the mechanism of this reaction revealed both similarities and differences between synthetic and enzymatic aromatic hydroxylation reactions.     

New ferromagnetic materials for magnetic recording: The iron carbonitrides

New ferromagnetic materials derived from iron nitride Fe₄N by partial substitution of nitrogen by carbon have been prepared by nitriding the iron oxalate whose thermal decomposition gives a carburating atmosphere. The morphology of the carbonitride crystallites depends on the elaboration conditions of the precursor. The particle shapes have been examined by electron microscopy. The coercive field can be improved by partially replacing iron by tin. For a composition close to Fe₃Fe_0.6Sn_0.4N_0.7C_0.3 the coercive field reaches 600 Oe. The average size of the microcrystallites was determined by X-ray diffractometry. An investigation of the aging of the material has been also carried out.     

Iron(III) Catecholates for Cellular Imaging and Photocytotoxicity in Red Light

Iron(III) complexes [Fe( L )( L′ )(NO₃)]—in which L is phenyl‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 1 ), (anthracen‐9‐yl)‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 2 ), (pyreny‐1‐yl)‐N,N‐bis[(pyridin‐2‐yl)methyl]methanamine ( 3 – 5 ), and L′ is catecholate ( 1 – 3 ), 4‐tert‐butyl catecholate ( 4 ), and 4‐(2‐aminoethyl)‐benzene‐1,2‐diolate ( 5 )—were synthesized and their photocytotoxic properties examined. The five electron‐paramagnetic complexes displayed a Fe^III/Fe^II redox couple near ?0.4 V versus a saturated calomel electrode (SCE) in DMF/0.1 m tetrabutylammonium perchlorate (TBAP). They showed unprecedented photocytotoxicity in red light (600–720 nm) to give IC₅₀≈15 μM in various cell lines by means of apoptosis to generate reactive oxygen species. They were ingested in the nucleus of HeLa and HaCaT cells in 4 h, thereby interacting favorably with calf thymus (ct)‐DNA and photocleaving pUC19 DNA in red light of 785 nm to form hydroxyl radicals.