Iron Phenanthroline Complexes Research Articles

Origin of the Second-Order Proton Catalysis of Ferriin Reduction in Belousov-Zhabotinsky Reactions: Density Functional Studies of Ferroin and Ferriin Aggregates with Outer Sphere Ligands Sulfate, Bisulfate, and Sulfuric Acid.

The detailed mechanisms of Belousov-Zhabotinsky oscillating reactions continue to present grand challenges, even after half a century of study. The origin of the pH dependence of the oscillation pattern had never been rigorously identified. In our recent kinetic study of one of the key Belousov-Zhabotinsky reactions, the iron-catalyzed bromate oxidation of malonic acid, compelling agreement between experiments and kinetic simulations was achieved only with the inclusion of second-order proton catalysis of the reduction of the [Fe(phen)3]3+ species. After exhausting all other avenues in search of an explanation of this proton catalysis, we considered the possibility that the parent iron-phenanthroline complexes could aggregate with neutral and anionic outer sphere ligands (OSLs) in the highly concentrated sulfuric acid solution, and we hypothesized that OSL protonation would increase the capacity of the aggregated complex to oxidize the organic fuel. We performed potential energy surface analyses at the SMD(APFD/6-311G*) level of complexes of the types [Fe(phen)3(SO42-)m(HSO4-)n(H2SO4)o](c-2m-n)+ for ferriin (c = 3) and ferroin (c = 2) aggregated with m sulfate, n bisulfate, and o sulfuric acid OSLs. We present structures of the OSL aggregates, develop a nomenclature for their description, and characterize their electronic structure. The structural chemistry provides the foundation to discuss the ferroin/ferriin redox couple with emphasis on the relationship between the vertical electron affinities of ferriin aggregates and their OSL protonation states. For proton catalysis to manifest itself, double-protonation paths that are slightly endergonic should be present, and proton affinities of aggregated OSLs allow the identification of such double-protonation chains. As a first test of our mechanistic proposal for the second-order proton catalysis of the Belousov-Zhabotinsky reaction, the results presented here provide compelling evidence in support of the importance of outer sphere ligation of the iron catalyst.

Structural properties of adsorbent phyllosilicates rule the entrapping ability of intercalated iron-phenanthroline complex towards thiols

Abstract The interaction of volatile organic sulfur derivatives, such as 1-heptanethiol (C7H16S), with clay minerals treated with a μ-oxo Fe3+-phenanthroline 1:1 complex results strongly affected by crystal chemical properties of pristine mineral phases. In particular, two sepiolite clays with different structural features demonstrated significantly different ability to immobilize the Fe3+-phenanthroline complex at two pH values (pH = 5.4 and pH = 2.3). The most effective binding was obtained with sepiolite with higher structural disorder at pH 5.4. Accordingly, the resulting hybrid material showed also the greatest efficiency in removal of thiol in gas phase. A direct correlation can be established between the adsorption of the Fe3+-phenanthroline complex and the gas binding process at room temperature. In fact, 1-heptanethiol entrapping occurs via redox reactions between Fe3+ and a first thiol molecule to give the reduced Fe2+-phenanthroline complex and disulfide, followed by the binding of further thiols to the reduced metal centre. The extremely high amount of thiol immobilized by the hybrid material also suggests the co-presence of a catalytic mechanism that guarantees the reoxidation of Fe+2 to Fe+3 and the restoration of redox reactions with thiol. Investigation and conclusions were supported by the several experimental techniques: elemental analysis, X-ray powder diffraction analyses, UV–Vis measurements, FT-IR and NMR spectroscopies, thermogravimetric analyses.

Heterogeneous Iron-Catalyzed Hydrogenation of Nitroarenes under Water-Gas Shift Reaction Conditions

Reduction of various nitroarenes in the presence of heterogeneous iron oxide-based catalyst Fe2O3/NGr@C under water-gas shift reaction (WGSR) conditions has been demonstrated. The catalytic material is prepared in a straightforward manner via deposition/pyrolysis of iron-phenanthroline complex on carbon support. It shows high chemoselectivity towards the reduction of nitroarenes in the presence of other reducible and/or poisoning-capable functional groups. Hydrogenation is achieved using CO/H2O as a hydrogen source. Furthermore, it is demonstrated that the presence of triethylamine additive has a significant positive effect on the rate of reduction.

Iron-Catalyzed Reductive Cyclization of o-Nitrostyrenes Using Phenylsilane as the Terminal Reductant

Using microscale high-throughput experimentation, an efficient, earth-abundant iron phenanthroline complex was discovered to catalyze the reductive cyclization of ortho-nitrostyrenes into indoles via nitrosoarene reactive intermediates. This method requires only 1 mol % of Fe(OAc)2 and 1 mol % of 4,7-(MeO)2phen and uses phenylsilane as a convenient terminal reductant. The scope and limitations of the method were illustrated with 21 examples, and an investigation into the kinetics of the reaction revealed first-order behavior in catalyst and silane and zero-order behavior with respect to nitrostyrene.

Iron-catalyzed synthesis of secondary amines: on the way to green reductive aminations.

Amines represent important intermediates in chemical and biological processes. Herein, we describe the use of a nanostructured iron-based catalyst for the tandem reductive amination between nitroarenes and aldehydes using hydrogen as reductant. The nanostructured iron-catalyst is prepared by immobilization of an iron-phenanthroline complex onto a commercially available carbon support. In the reaction sequence a primary amine is formed in situ from the corresponding nitro compound. Reversible condensation with aldehydes forms the respective imines, which are finally reduced to the desired secondary amine. This synthesis of secondary amines is atom-economical and environmentally attractive using cheap and readily available organic compounds as starting materials.

An efficient oxygen reduction electrocatalyst from graphene by simultaneously generating pores and nitrogen doped active sites

A simple way to simultaneously create pores and nitrogen doped active sites on graphene for the electrochemical oxygen reduction reaction (ORR) is developed. The key aspect of the process is the in-situ generation of Fe2O3 nanoparticles and their concomitant dispersion on graphene by pyrolyzing graphene oxide (GO) with the iron phenanthroline complex. Thus the deposited Fe2O3 nanoparticles act as the seeds for pore generation by etching the carbon layer along the graphene–Fe2O3 interface. Detection of the presence of Fe3C along with Fe2O3 confirms carbon spill-over from graphene as a plausible step involved in the pore engraving process. Since the process offers a good control on the size and dispersion of the Fe2O3 nanoparticles, the pore size and distribution also could be managed very effectively in this process. As the phenanthroline complex decomposes and gives Fe2O3 nanoparticles and subsequently the pores on graphene, the unsaturated carbons along the pore openings simultaneously capture nitrogen of the phenanthroline complex and provide very efficient active sites for ORR under alkaline conditions. The degree of nitrogen doping and hence the ORR activity could be further improved by subjecting the porous material for a second round of nitrogen doping using iron-free phenanthroline. This porous graphene enriched with the N-doped active sites effectively reduces oxygen molecule through a 3e− pathway, suggesting a preferential shift towards the more favourable 4e− route compared to the 2e− reaction as reported for many N-doped carbon nano-morphologies. The 90 mV onset potential difference for oxygen reduction as compared to the state-of-the art 20 wt% Pt/C catalyst is significantly low compared to the overpotentials in the range of 120–200 mV reported in the literature for few N-doped graphenes.

Efficient and highly selective iron-catalyzed reduction of nitroarenes

Pyrolysis of iron-phenanthroline complexes supported on carbon leads to highly selective catalysts for the reduction of structurally diverse nitroarenes to anilines in 90-99% yields. Excellent chemoselectivity for the nitro group reduction is demonstrated.

Ferrous ion-induced strand breaks in the DNA plasmid pBR322 are not mediated by hydrogen peroxide

Ferrous ion-induced generation of single and multiple strand breaks in the DNA plasmid pBR322 induces the formation of two new plasmid forms with altered electrophoretic mobility. The yield of these plasmid forms, the circular relaxed and the linear forms, depended on the applied Fe(2+) concentration. This property was independent of the presence of hydrogen peroxide in the incubation mixture indicating the lack of Fenton chemistry to explain the DNA degradation. The removal of dioxygen or the presence of superoxide dismutase diminished partially the yield of ferrous ion-induced DNA plasmid degradation, while catalase was without any effect. Autoxidation of divalent iron as followed by the formation of a coloured iron-phenanthroline complex was enhanced in a concentration-dependent manner by phosphate and bicarbonate and very efficiently using a mixture of 0.15 M NaCl, 1.2 mM phosphate, 23.8 mM bicarbonate, pH 7.4, that concentrations correspond closely to the intracellular values of buffer components. Thus, the formation of a yet unknown reactive species from Fe(2+), and dioxygen, that is complexed to buffer components especially phosphate and its contribution in DNA plasmid degradation is more likely than the often cited formation of hydroxyl radicals in result of the Fenton reaction from Fe(2+) and hydrogen peroxide.

Perturbations of the Briggs–Rauscher oscillating system by iron–phenanthroline complexes

Perturbations of the oscillatory regime of the Briggs–Rauscher (BR) reaction by the iron(II)–phenanthroline (ferroin) complex were observed in batch conditions. The path of the perturbation (immediate quenching of oscillations – inhibition time – resumption of oscillations) is similar to that provoked by antioxidant free-radical scavengers; however, perturbations occur in a ferroin concentration range much lower than that in which antioxidants act. To investigate this effect, reactions between the iron(II)–or iron(III)–phenanthroline (ferriin) and reagents or intermediates of the BR system were studied in detail. Results of these studies showed that the interaction of the ferroin/ferriin couple with iodine production is responsible for the observed perturbation. A mechanistic interpretation involving HOO radical is proposed.

Enhancement of oxygen electroreduction activity via surface modification of carbon supported ruthenium nanoparticles: A new class of electrocatalysts

Oxygen reduction catalysts have been prepared by modifying Ru/C catalysts (either commercial or self-made) using iron phenanthroline complexes adsorbed at the surface of the catalysts and heat treated at elevated temperatures. This new type of catalyst shows an oxygen reduction activity which is 3–5 times higher than the activity of an unmodified Ru/C catalyst. Furthermore, it is higher than that of catalysts based on Ru/C modified with Se, however, the activity of Pt/C is still not yet matched. Structural characterisation indicates that the catalysts consist of ruthenium nanoparticles. These nanoparticles most likely are covered by centres of type FeN x C y also found in carbon supported iron catalyst for oxygen reduction prepared by pyrolysis of iron, nitrogen and carbon via heat treatment steps.

Thermogravimetry/Mass Spectrometry Investigations on the Formation of Oxygen Reduction Catalysts for PEM Fuel Cells on the Basis of Heat‐Treated Iron Phenanthroline Complexes

AbstractOxygen reduction catalysts for PEM fuel cells on the basis of carbon supported, heat‐treated iron phenanthroline complexes have been investigated with rotating disc‐electrode (RDE) measurements and with thermogravimetry/mass spectrometry (TG/MS). It has been found, that the slope of the Koutecky–Levich plot from RDE measurements changes with electrode potential and with catalyst loading of the electrode. The results can be understood in terms of a two times 2‐electron reduction of oxygen at the iron‐based catalysts. TG/MS indicate, that during the heat‐treatment step the phenathroline molecule of the catalyst precursor is completely embedded into the carbon. The results are discussed in terms of the structure of the active centre of these catalysts.

EXAFS, XPS and electrochemical studies on oxygen reduction catalysts obtained by heat treatment of iron phenanthroline complexes supported on high surface area carbon black

Oxygen reduction catalysts have been prepared on the basis of heat-treated, carbon supported iron phenanthroline complexes. The activity of the catalyst towards oxygen reduction depends on the surface area of the carbon used in the synthesis. It is higher than the activity of other alternative oxygen reduction catalysts based on ruthenium. Related to the amount of metal, the activity is comparable to that of the state-of-the-art oxygen reduction catalyst, platinum supported onto carbon. EXAFS measurements indicate that the structure of the active centre of the catalyst consists of an iron ion, which is coordinated to four nitrogen atoms. No crystalline particles can be found in the catalyst using TEM.

Spectrophotometric determination of iron(III) dimethyldithiocarbamate (ferbam)

A spectrophotometric method was developed for the determination of ferbam (iron(III) dimethyldithiocarbamate) by converting it into an iron-phenanthroline complex, which was then absorbed on microcystalline naphthalene in the presence of tetraphenylborate, and the absorbance was measured at 515 nm against a reagent blank. The molar absorptivity of the complex was 1.2 × 10 4l mol −1cm −1. Ten replicate analyses of a sample solution containing 150 μg of ferbam gave a relative standard deviation of 0.84%. Beer's law was obeyed over the concentration range 22.4–372.9 μg of ferbam. The effects of various factors such as reagent concentration and naphthalene, shaking time and diverse ions were studied in detail. The method is sensitive and selective and can be applied to the direct determination of ferbam in commercial samples and in mixtures containing various other dithiocarbamates (e.g. ziram, zineb and maneb) in foodstuffs.

Structural and electronic responses of coordination compounds to changes in the molecule and molecular environment

A. Introduction B. The first bond length variation rule and the “pile up” and “spill over” effects C. The second bond length variation rule D. Variations in bond angles (i) Bond angle variation in trimethylchlorostannane (ii) Bond angle variation in tetranuclear Cu(II) complexes E. Effects at the terminal positions F. Solvent and substituent effects on iron-phenanthroline complexes ....... G. Spin transition systems H. Solvatochromism of coordination compounds (i) Bis-cyano-bis-phenanthroline-iron complexes (ii) Mixed-ligand copper and nickel complexes (iii) Solvent effects on hexathiocyanatochromate(Il1) I. Molecular system organization: chemical functionality (i) System organization in ironphenanthroline complexes (ii) Molecular system organization of haemoglobin (iii) Conclusion Acknowledgement References 159 160 163 I64 I65 168 169 169 171 172 172 173 176 177 179 180 181 I81 I81

ChemInform Abstract: Questions of Molecular System Organization. Part l. Iron‐Phenanthroline Complexes.

Chemischer InformationsdienstVolume 17, Issue 3 Physical Organic Chemistry ChemInform Abstract: Questions of Molecular System Organization. Part l. Iron-Phenanthroline Complexes. V. GUTMANN, V. GUTMANNSearch for more papers by this authorG. RESCH, G. RESCHSearch for more papers by this author V. GUTMANN, V. GUTMANNSearch for more papers by this authorG. RESCH, G. RESCHSearch for more papers by this author First published: January 21, 1986 https://doi.org/10.1002/chin.198603063AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume17, Issue3January 21, 1986 RelatedInformation