Fe Atoms (fe + atom)

Distribution by Scientific Domains


Selected Abstracts


Six-Membered N-Heterocyclic Carbenes with a 1,1,-Ferrocenediyl Backbone: Bulky Ligands with Strong Electron-Donor Capacity and Unusual Non-Innocent Character

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 31 2009
Ulrich Siemeling
Abstract The stable, crystalline N-heterocyclic diaminocarbene fc[N(CH2tBu)-C-N(CH2tBu)] (2d, fc = 1,1,-ferrocenediyl) was prepared by deprotonation of its formamidinium precursor fc[N(CH2tBu)-CH-N(CH2tBu)][BF4] (1d) and used for the preparation of the 16 valence electron complexes [Mo(2d)(CO)4], [RhCl(2d)(cod)] (cod = 1,5-cyclooctadiene) and [RhCl(2d)(CO)2]. 1d, 2d and [RhCl(2d)(cod)] were structurally characterised by single-crystal X-ray diffraction studies. The electrochemical properties of 2d, its 2-adamantyl analogue 2c, its complex [RhCl(2d)(CO)2] and of the precursors 1d and 1,1,-bis(neopentylamino)ferrocene were investigated by electrochemistry. The carbenes are easily oxidised to the corresponding radical cation, whose persistent nature is unprecedented in the chemistry of N-heterocyclic carbenes. The spin density is located at the Fe atom and the carbene C atom according to the results of EPR spectroscopic studies and DFT calculations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


Theory of chemical bonds in metalloenzymes III: Full geometry optimization and vibration analysis of ferredoxin-type [2Fe,2S] cluster

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2007
Mitsuo Shoji
Abstract The nature of chemical bonds in a ferredoxin-type [2Fe,2S] cluster has been investigated on the basis of natural orbitals and several bond indices developed in Parts I and II of this study. The broken-symmetry hybrid density functional theory (BS-HDFT) with spin projection approach has been applied to elucidate the natural orbitals and occupation numbers for a model compound [Fe2S2(SCH3)4] (1), which is used to calculate the indices. The molecular structure, vibration frequencies, electronic structures, and magnetic properties in both oxidized and reduced forms of 1 have been calculated and compared with the experimental values. The optimized molecular structures after approximate spin projection have been in good agreement with experimental data. The structure changes upon one-electron reduction have been slight (<0.1 Å) and only limited around one side of the Fe atom. Raman and infrared (IR) spectra have been calculated, and their vibration modes have been assigned using the bridging 34S isotope substitution. Their magnetic properties have been examined in terms of spin Hamiltonians that contain exchange interactions and double exchange interactions. The BS-HDFT methods have provided the magnetic parameters; i.e., effective exchange integral (J) values and valence delocalization (B) values, which agree with the experimental results. It is found that large charge transfer (CT) from the bridging sulfur to the iron atoms has led to the strong antiferromagnetic interactions between iron atoms. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source]


Density functional study of the heme moiety of cytochrome c,,

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005
Anil Kumar
Abstract A model of cytochrome c (Cyt-c) including the porphyrin ring, a methionine residue (Met), and the imidazole ring of histidine (His), the latter two being situated above and below the iron (Fe) atom of the porphyrin ring, was studied using Density Functional Theory (DFT). The geometries of the model Cyt-c complex with the Fe atom in two different charge states were fully optimized, i.e., in singlet and triplet states for Fe and in doublet and quartet states for Fe3+. The B3LYP method of DFT along with the 3-21G* basis set for C, H, N, and O atoms and the Lanl2dz basis set for the Fe atom was used. We found that with Fe3+, the doublet spin state is the ground state and the quartet state lies slightly above it. The geometry of the singlet spin state is similar to that of the doublet and quartet states. However, methionine has different conformations when Fe has zero charge (singlet, triplet states) relative to the situation when Fe has +3 charges (doublet, quartet states). The Met chain is folded instead of remaining extended in going from the singlet or triplet spin state to the doublet or quartet state and the folding is stabilized by an intramolecular CH..O hydrogen bond. The optimized geometrical parameters of the model of Cyt-c are usually in satisfactory agreement with those observed experimentally. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source]


Antiferromagnetic-to-ferromagnetic transition induced by aluminum in the Ti(Fe1,xAlx)2 intermetallic compounds: a 57Fe Mössbauer spectroscopy study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2007
N. N. Delyagin
Abstract Mössbauer spectroscopy has been used to investigate the hyperfine field distributions and the local spin configurations of Fe atoms in the magnetically ordered Ti(Fe1,xAlx)2 compounds. The evolution of the spin arrangement of the Fe atoms was observed over the concentration range 0 , x , 0.25 at 5 K. The Al impurity suppresses the ferromagnetic exchange in the Fe(6h) layers and simultaneously provides the conditions for a transition of the Fe(2a) atoms, which are nonmagnetic in the TiFe2 compound, to the states with nonzero magnetic moment. The magnetic behavior of the Fe(2a) atoms is the key factor governing the anti- to ferromagnetic transition in the Ti(Fe1,xAlx)2 compounds. The magnetic ordering temperatures of the Ti(Fe1,xAlx)2 compounds were determined. In addition, the parameters of the electric-field gradient in TiFe2 as well as the relationship between the value of the magnetic moment of the Fe atom and the type of atomic configuration were discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Soft X-ray absorption spectroscopy and magnetic circular dichroism study of electroless-deposited CoNiFe ternary alloy soft magnetic films

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2006
Masahito Tanaka
Abstract We studied microscopic magnetic properties of each consistent atom in boron added CoNiFe electroless-deposited soft magnetic films, which is a promising candidate for the soft magnetic underlayer of the perpendicular magnetic recording medium, by X-ray absorption spectra (XAS) and magnetic circular dichroism (MCD) measurement. It was found that various monoxides and Fe sesquioxide coexisted with the metals at the upper part of the films. The results of MCD sum rule showed the expected values of orbital angular moment ,Lz, for the film with macroscopic magnetic domain boundaries were larger than those of without domains at Co and Ni atoms and smaller at Fe atom. The appearance of macroscopic magnetic domain boundaries probably originated from the increase in ,Lz, of Co and/or Ni atoms. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Tris{bis­[hydro­tris(1-pyrazolyl)­borato-,3N2,N2,,N2,,]iron(III)} hexaiso­thio­cyanato­iron(III)

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2004
Shi Wang
The title compound, [Fe(C9H10BN6)2]3[Fe(NCS)6] or [FeIII(Tp)2]3[FeIII(NCS)6] [Tp is hydro­tris(1-pyrazolyl)­borate], crystallizes in space group ; the asymmetric unit comprises one-half of an [Fe(Tp)2]+ cation, with its Fe atom on a crystallographic inversion centre, and one-sixth of an [Fe(NCS)6]3, anion, on a site of symmetry. The anions and cations are stacked into a three-dimensional supramolecular aggregate via two distinct types of weak C,H,, interactions. [source]


5- n -Butylpyridine-2-carboxylate,copper(II) and ,iron(III) complexes

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2002
Yoshio Wada
In trans -bis(5- n -butyl­pyridine-2-carboxyl­ato-,2N,O)­bis­(methanol-,O)copper(II), [Cu(C10H12NO2)2(CH4O)2], the Cu atom lies on a centre of symmetry and has a distorted octahedral coordination. The Cu,O(methanol) bond length in the axial direction is 2.596,(3),Å, which is much longer than the Cu,­O(carboxylate) and Cu,N distances in the equatorial plane [1.952,(2) and 1.977,(2),Å, respectively]. In mer -tris(5- n -bu­tyl­pyridine-2-carboxyl­ato-,2N,O)­iron(III), [Fe(C10H12NO2)3], the Fe atom also has a distorted octahedral geometry, with Fe,O and Fe,N bond-length ranges of 1.949,(4),1.970,(4) and 2.116,(5),2.161,(5),Å, respectively. Both crystals are stabilized by stacking interactions of the 5- n -butyl­pyridine-2-carboxyl­ate ligand, although hydrogen bonds also contribute to the stabilization of the copper(II) complex. [source]


X-ray structure of azide-bound fully oxidized cytochrome c oxidase from bovine heart at 2.9,Å resolution

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2000
Ming Jie Fei
Two azide ions were identified, one between the Fe and Cu atoms in the O2 -reduction site and the other at the transmembrane surface of the enzyme, in the crystal structure of the azide-bound form of bovine heart cytochrome c oxidase at 2.9,Å resolution. Two geometries, a ,-1,3 type geometry between the Fe and Cu atoms and a terminal geometry on the Fe atom, are equally possible for an azide ion in the O2 -­reduction site. The other azide molecule was hydrogen bonded to an amide group of an asparagine and a hydroxyl group of tyrosine in a ,-1,1 type geometry. The antisymmetric infrared bands arising from these azide ions, which show essentially identical intensity [Yoshikawa & Caughey (1992), J. Biol. Chem.267, 9757,9766], strongly suggest terminal binding of the azide to Fe. The electron density of all three imidazole ligands to CuB was clearly seen in the electron-density map of the azide-bound form of bovine heart enzyme, in contrast to the crystal structure of the azide-bound form of the bacterial enzyme [Iwata et al. (1995), Nature (London), 376, 660,669], which lacks one of the three imidazole ligands to CuB. [source]


The magnetic moments and their long-range ordering for Fe atoms in a wide variety of metallic environments

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010
A. Ayuela
Abstract The magnitudes of Fe magnetic moments, together with their long-range ordering when appropriate, are compared and contrasted in a variety of metallic environments. Thus, Fe, in its stable body-centered-cubic (bcc) phase under ambient conditions, is considered under pressures p, which can yield different crystal structures at high p, including fcc. The modification of the ferromagnetism in bcc Fe is surveyed as one passes through a bc-tetragonal lattice to the fcc form. In the latter, evidence is presented, both from theory and experiment, that the ordering is antiferromagnetic in character. Then, binary metallic alloys with Fe atoms as the majority component are considered, Fe,Co and Fe,Ga being focal points in both ordered and disordered materials. Finally, some discussion is given, involving again both experiment and theory, of the possible spin polarization of neighboring Cs atoms when Fe impurity atoms are inserted into the low conduction electron density characterizing this heavy alkali metal under ambient conditions. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source]


The electronic structure and magnetism of a rocksalt FeN(001) surface: A density functional study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2007
J. I. Lee
Abstract We investigated the electronic structure and magnetism of the rocksalt FeN(001) surface. We considered both the ferromagnetic and antiferromagnetic configurations. We calculated the electronic structure using the full-potential linearized augmented plane wave method within generalized gradient approximation. We found that the antiferromagnetic phase is more stable than the ferromagnetic one, as in bulk, with an energy difference of 0.14 eV per the considered slab. The magnetic moments of the Fe atoms in the antiferromagnetic phase slab are 2.90 ,B, ,2.26 ,B and 2.37 ,B for the surface, subsurface, and center layers, respectively, while the values for the ferromagnetic one are 2.85 ,B, 1.81 ,B, and 2.37 ,B, respectively. The detailed electronic structures for ferromagnetic and antiferromagnetic phases are compared and discussed with the calculated spin-densities and density of states. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Antiferromagnetic-to-ferromagnetic transition induced by aluminum in the Ti(Fe1,xAlx)2 intermetallic compounds: a 57Fe Mössbauer spectroscopy study

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2007
N. N. Delyagin
Abstract Mössbauer spectroscopy has been used to investigate the hyperfine field distributions and the local spin configurations of Fe atoms in the magnetically ordered Ti(Fe1,xAlx)2 compounds. The evolution of the spin arrangement of the Fe atoms was observed over the concentration range 0 , x , 0.25 at 5 K. The Al impurity suppresses the ferromagnetic exchange in the Fe(6h) layers and simultaneously provides the conditions for a transition of the Fe(2a) atoms, which are nonmagnetic in the TiFe2 compound, to the states with nonzero magnetic moment. The magnetic behavior of the Fe(2a) atoms is the key factor governing the anti- to ferromagnetic transition in the Ti(Fe1,xAlx)2 compounds. The magnetic ordering temperatures of the Ti(Fe1,xAlx)2 compounds were determined. In addition, the parameters of the electric-field gradient in TiFe2 as well as the relationship between the value of the magnetic moment of the Fe atom and the type of atomic configuration were discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Electronic structure and magnetic properties of Fe3C with 3d and 4d impurities

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 6 2007
I. R. Shein
Abstract We study the electronic structure, formation energies, and magnetic properties of cementite Fe3C doped by 3d and 4d transition metals (TM) by means of first-principles calculations. All TM elements demonstrate a preference for the substitution of the general iron position in Fe3C. We predict that early elements (Sc, Ti, V, Cr, Zr, and Nb) stabilize the cementite, while the end elements (Ni, Cu, Pd, and Ag) in the TM series sharply destabilize it. The magnetic properties of impurity atoms are found to depend strongly on their atomic numbers and the trends to ferromagnetic or antiferromagnetic coupling of impurities with Fe atoms in Fe3C coincide with the magnetic behavior of these impurities in Fe. The physical reason is a similar location of the Fermi level in the pseudogap of spin-down and almost filled spin-up Fed states in both Fe3C and Fe. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


The C,C pair in the vicinity of a bcc Fe bulk vacancy: electronic structure and bonding

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2007
S. Simonetti
Abstract C,Fe and C,C interactions near a bcc Fe vacancy were analysed using DFT calculations. A cell containing 14 atoms was used to simulate the local environment of the Fe vacancy. Carbon atoms were positioned in their local energy minimum configurations. The most stable positions for the C atoms in the vacancy region were found at about 1.23 Å from the vacancy centre and near the first nearest-neighbour octahedral sites. Changes in the electronic structure of Fe atoms near a vacancy were analysed. Fe,Fe bonds surrounding the vacancy weaken their bond when the C atoms are present. This bond weakening is a consequence of C,Fe bond formation. The Fe,C interactions occur mainly via Fe 4s orbitals with a lesser participation of Fe 3p orbitals. There is an electron transfer to the C atoms from their Fe nearest neighbours. The C,C interaction was also analysed. For the C,C distance of 1.462 Å, there is a bonding between the C atoms. The C,C interaction is stronger than the C,Fe interactions. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Properties of the UFe5Sn compound: electronic structureand X-ray photoemission

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003
A. Szajek
Abstract The UFe5Sn compound crystallizes in the orthorhombic CeCu5Au-type structure having the Pnma space group with iron atoms located in four inequivalent sites. The electronic structure UFe5Sn compound has been studied using spin-polarized tight binding version of the linear muffin-tin orbital method in the atomic sphere approximation (TB LMTO ASA). The calculations showed that the magnetic moments on uranium atoms are antiparallel to the moments formed on Fe atoms, whose values depend on local environments. The X-ray photoemission spectra were calculated. [source]


Structural and spectroscopic study of the Fe doped TiO2 thin films for applications in photocatalysis

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2009
N. R. Mathews
Abstract In this work we are presenting the results of structural and optical investigations of TiO2 and Fe doped TiO2 films using XRD, XPS, UV-VIS transmittance spectroscopy, and the application of these films in photocatalysis is demonstrated. Fe-doped TiO2 films were prepared by sol-gel method. The concentration of Fe utilized for doping ranged from 0.5 to 4% by atomic weight. For lower concentrations of Fe the transformation from amorphous-to-polycrystalline occurred at 400 °C. However, as the Fe concentration was increased to 4% this transformation occurred only after annealing at 600 °C. The average grain size for 4% Fe doped sample was in the range of 13 nm. In the case of pure TiO2 the XPS analysis showed only the presence of Ti 4+, where the 4% Fe doped film showed the presence of two species of Ti atoms; one of unperturbed Ti atoms and another of negatively charged surface of Ti atoms due to the interaction with Fe atoms in the anatase lattice of TiO2. The optical band gap was found to decrease with Fe concentration. The resistivity was found to decrease by one order after doping. The 4% Fe doped TiO2 films showed an increased photocatalytic activity. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Revision of pyrrhotite structures within a common superspace model

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2007
Zunbeltz Izaola
The structure of pyrrhotite (Fe1,,,xS with 0.05 ,x, 0.125) has been reinvestigated in the framework of the superspace formalism. A common model with a centrosymmetric superspace group is proposed for the whole family. The atomic domains in the internal space representing the Fe atoms are parametrized as crenel functions that fulfil the closeness condition. The proposed model explains the x -dependent space groups observed and the basic features of the structures reported up to now. Our model yields for any x value a well defined ordered distribution of Fe vacancies in contrast to some of the structural models proposed in the literature. A new (3,+,1)-dimensional refinement of Fe0.91S using the deposited dataset [Yamamoto & Nakazawa (1982). Acta Cryst. A38, 79,86] has been performed as a benchmark of the model. The consistency of the proposed superspace symmetry and its validity for other compositions has been further checked by means of ab initio calculations of both atomic forces and equilibrium atomic positions in non-relaxed and relaxed structures, respectively. [source]


One-dimensional structure of catena -poly[tetra­ethyl­ammonium [tetra­cyano­iron(III)-,-cyano-[bis­(ethyl­ene­diamine)­cadmium(II)]-,-cyano] tetra­hydrate]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2006
Werner Massa
The title compound, {(C8H20N)[CdFe(CN)6(C2H8N2)2]·4H2O}n, was isolated from the aqueous system Cd2+/ethyl­ene­diamine (en)/[Fe(CN)6]3, in the presence of [Et4N]Br. The crystal structure is dominated by a one-dimensional motif, viz. a negatively charged 2,2-CT (cis,trans) [,Cd(en)2,NC,Fe(CN)4,CN,]nn, chain. The Cd and Fe atoms of the anion and the N atom of the cation all lie on twofold axes. The ethyl groups of the cation are equally disordered over two orientations. The cationic building block of the chain consists of a CdII atom coordinated by two chelating en ligands, and the distorted octa­hedral coordination is completed by two bridging cyano ligands in cis positions. The anionic building block is an [Fe(CN)6]3, anion in which the FeIII atom is octa­hedrally coordinated by six cyano ligands; two of the cyano ligands, in trans positions, are bridging. The uncoordinated water mol­ecules link neighbouring chains through O,H,N and N,H,O hydrogen bonds. [source]


Mixed-chalcogenide double-butterfly complex [{(CO)6Fe2SSe}2{,-­C(H),C(H)}]

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2000
Kaliyamoorthy Panneerselvam
Bubbling acetyl­ene gas slowly through a methanol solution of [(CO)6Fe2{,-SSe}] containing sodium acetate for 48,h at room temperature yields the double-butterfly complex ,-[ethane-1,1,2,2-tetra(selenido/sulfido)]bis[hexacarbonyldiiron(Fe,Fe)], [Fe4(C2H2S2Se2)(CO)12]. The molecular structure was established by single-crystal X-ray diffraction techniques. The structure consists of two Fe2SSe butterfly units linked to each other through a bridging HC,CH group. The mol­ecule has twofold symmetry and the two Fe atoms have distorted octahedral geometries. [source]


Hyperstability and crystal structure of cytochrome c555 from hyperthermophilic Aquifex aeolicus

ACTA CRYSTALLOGRAPHICA SECTION D, Issue 8 2009
Marii Obuchi
In order to elucidate the relationship between the stability and the structure of the monohaem cytochrome c555 (AA c555) from the hyperthermophilic bacterium Aquifex aeolicus, chemical denaturation and crystal structure determination were carried out. AA c555 exhibited higher stability than the thermophilic Hydrogenobacter thermophilus cytochrome c552 (HT c552), which is one of the most stable cytochromes c. The three-dimensional crystal structure of AA c555, which was determined using the multiple anomalous dispersion technique at 1.15,Å resolution, included a unique 14-residue extra helix, while the side-chain interactions of several amino-acid residues responsible for the stability of HT c552 were conserved in AA c555. The side chain of the Met61 residue in the extra helix was aligned towards the haem, forming a coordination bond between the Met S and haem Fe atoms. In other cytochromes c the corresponding regions always form , loops which also include the haem-liganding Met residue and are known to be involved in the initial step in cytochrome c denaturation. The formation of the extra helix in AA c555 results in the highest helix content, 59.8%, among the monohaem cytochromes c. The extra helix should mainly contribute to the hyperstability of AA c555 and is presumed to be a novel strategy of cytochromes c for adaptation to a hyperthermophilic environment. [source]