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See detailExperimental and Computational Study of the Structural and Electronic Properties of Fe II(2,20-bipyridine)(mes) 2 and [Fe II(2,20-bipyridine)(mes) 2] -, a Complex Containing a 2,20-Bipyridyl Radical Anion
Irwin, Mark; Jenkins, Rhiannon; Denning, Mark et al

in Inorganic Chemistry (2010), 49

Addition of potassium metal and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) to a tetrahydrofuran (THF) solution of Fe(2,20 -bipyridine)(mes)2 (1; mes = 2,4,6-Me3C6H2) yielded ... [more ▼]

Addition of potassium metal and 2,2,2-crypt (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane) to a tetrahydrofuran (THF) solution of Fe(2,20 -bipyridine)(mes)2 (1; mes = 2,4,6-Me3C6H2) yielded the anionic complex [Fe(2,20 -bipyridine)(mes)2] - which was isolated as [K(2,2,2-crypt)][Fe(2,20 -bipyridine)(mes) 2](2) alongside the side-product [K(2,2,2-crypt)][Fe(mes)3] 3 C6H12 (3). A compositionally pure sample of 2 was obtained by dissolving a mixture of 2 and 3 in dry pyridine and layering the resulting solution with toluene. Solid state magnetic susceptibility measurements on 1 reveal Curie-Weiss paramagnetic behavior with a molar magnetic moment of 5.12(1) μB between 20 and 300 K, a value which is in line with the expected iron(II) spin-only value of 4.90 μB. The magnetic measurements carried out on 2 reveal more complex temperature dependent behavior consistent with intramolecular antiferromagnetic coupling (J=-46 cm -1) between the unpaired electrons of the iron(II) ion (S Fe =2) and a π* orbital of the bipyridyl radical (Sbipy = 1/2). Structural data, M€ossbauer and electron paramagnetic resonance (EPR) spectroscopic measurements, and density functional theory (DFT) calculations are all consistent with this model of the electronic structure. To the best of our knowledge, species 2 represents the first crystallographically characterized transition metal complex of the 2,20 -bipyridyl ligand for which magnetic, spectroscopic, and computational data indicate the presence of an unpaired electron in the π* antibonding orbital. [less ▲]

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See detailMagnetic Ordering in Nitrides with the η-Carbide Structure: (Ni,Co,Fe)2(Ga,Ge)Mo3N
Sviridov, A; Battle, Peter D.; Grandjean, Fernande ULg et al

in Inorganic Chemistry (2010), 491

Compositions in the series Ni2-xCoxGeMo3N (0 ex e2),Co2Ge1-xGaxMo3N (0<x e0.7),Co2-xFexGeMo3N (0 e x e 2), and Co2-xFexGe0.5Ga0.5Mo3N (0 e x e 0.8) have been synthesized by the reductive nitridation of ... [more ▼]

Compositions in the series Ni2-xCoxGeMo3N (0 ex e2),Co2Ge1-xGaxMo3N (0<x e0.7),Co2-xFexGeMo3N (0 e x e 2), and Co2-xFexGe0.5Ga0.5Mo3N (0 e x e 0.8) have been synthesized by the reductive nitridation of binary oxides and studied by appropriate combinations of magnetometry, transport measurements, neutron diffraction, and M€ossbauer spectroscopy. All of these compositions adopt the cubic η-carbide structure (a ∼ 11.11 A ̊ ) and show a resistivity of ∼10 -3 Ω cm. No long-range magnetic order was observed in Ni 2-xCoxGeMo3N, although evidence of spin freezing was observed in Co2GeMo3N. The introduction of gallium into this composition leads to the onset of antiferromagnetic ordering at 90 K in Co2Ge0.3Ga0.7Mo3N. The magnetic structure consists of an antiferromagnetic arrangement of ferromagnetic Co4 groups, with an ordered magnetic moment of 0.48(9) μB per cobalt atom. The same magnetic structure is found in Co0.5Fe1.5GeMo3N and Co1.2Fe0.8Ge0.5Ga0.5Mo3N. The former orders above room temperature with an average moment of 1.08(3) μB per transition-metal site, and the latter at 228 K with an average moment of 1.17(4) μB per site. The magnetic behavior of these compounds is discussed in terms of the electron count within each series. [less ▲]

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See detailHomoleptic Diphosphacyclobutadiene Complexes [M(4-P2C2R2)2]x- (M=Fe, Co; x=0, 1),
Wolf, Robert; Ehlers, Andreas W; Khusniyarov, Marat M et al

in Chemistry : A European Journal (2010), 16

The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands is reported. Compounds [K([18]crown-6)(thf)2][Fe(h4- P2C2tBu2)2 ... [more ▼]

The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands is reported. Compounds [K([18]crown-6)(thf)2][Fe(h4- P2C2tBu2)2] (K1), [K([18]crown-6)-(thf)2][Co(h4-P2C2tBu2)2] (K2), and [K([18]crown-6)(thf)2][Co(h4- P2C2Ad2)2] (K3, Ad=adamantyl) were obtained from reactions of [K([18]crown-6)(thf)2][M(h4-C14H10)2] (M=Fe, Co) with tBuC P (1, 2), or with AdC P (3). Neutral sandwiches [M(h4-P2C2tBu2)2] (4: M=Fe 5: M= Co) were obtained by oxidizing 1 and 2 with [Cp2Fe]PF6. Cyclic voltammetry and spectro-electrochemistry indicates that the pairs [M(h4-P2C2tBu2)2] / [M(h4-P2C2tBu2)2] can be reversibly interconverted by one electron oxidation and reduction, respectively. Complexes 1–5 were characterized by multinuclear NMR, EPR (1 and 5), UV/Vis, and Mçssbauer spectroscopies (1 and 4), mass spectrometry (4 and 5), and microanalysis (1–3). The molecular structures of 1–5 were determined by usingX-ray crystallography. Essentially D2dsymmetric structures were found for all five complexes, which show the two 1,3-diphosphacyclobutadiene rings in a staggered orientation. Density functional theory calculations revealed the importance of covalent metal–ligand p bonding in 1–5. Possible oxidation state assignments for the metal atoms are discussed. [less ▲]

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See detailCrystal Growth, Transport, and the Structural and Magnetic Properties of Ln4FeGa12 with Ln = Y, Tb, Dy, Ho, and Er
Drake, B. L.; Grandjean, Fernande ULg; Okudzeto, E. K. et al

in Inorganic Chemistry (2010), 49

Ln4FeGa12, where Ln is Y, Tb, Dy, Ho, and Er, prepared by flux growth, crystallize with the cubic Y4PdGa12 structure with the space group and with a = 8.5650(4), 8.5610(4), 8.5350(3), 8.5080(3), and 8 ... [more ▼]

Ln4FeGa12, where Ln is Y, Tb, Dy, Ho, and Er, prepared by flux growth, crystallize with the cubic Y4PdGa12 structure with the space group and with a = 8.5650(4), 8.5610(4), 8.5350(3), 8.5080(3), and 8.4720(4) Å, respectively. The crystal structure consists of an iron-gallium octahedra and face sharing rare-earth cuboctahedra of the Au3Cu type. Y4FeGa12 exhibits weak itinerant ferromagnetism below 36 K. In contrast, Tb4FeGa12, Dy4FeGa12, Ho4FeGa12, and Er4FeGa12 order antiferromagnetically with maxima in the molar magnetic susceptibilities at 26, 18.5, 9, and 6 K. All the compounds exhibit metallic electric resistivity and their iron-57 Mössbauer spectra, obtained between 4.2 and 295 K, exhibit a single-line absorption with a 4.2 K isomer shift of ca. 0.50 mm/s, a shift that is characteristic of iron in an iron-gallium intermetallic compound. A small but significant broadening in the spectral absorption line width is observed for Y4FeGa12 below 40 K and results from the small hyperfine field arising from its spin-polarized itinerant electrons [less ▲]

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See detailCharacterization of modern Prussian blue pigments by Mössbauer spectroscopy and synchrotron radiation
Samain, Louise ULg; Silversmit, Geert; Sougrati, Moulay T. et al

Conference (2009, November 27)

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See detailFading of Modern Prussian Blue Pigments : Preliminary Study
Samain, Louise ULg; Sougrati, Moulay T.; Hatert, Frédéric ULg et al

Poster (2009, June)

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See detailA Structural, Magnetic, and Mössbauer Spectral Study of the TbCo4-xFexB Compounds with x = 0 to 2
Isnard, Olivier; Mayot, Herve; Grandjean, Fernande ULg et al

in Journal of Applied Physics (2009), 105

The TbCo4–xFexB compounds with x = 0, 1, and 2, have been investigated by x-ray and neutron diffraction, magnetic measurements, and iron-57 Mössbauer spectroscopy. The substitution of cobalt by iron ... [more ▼]

The TbCo4–xFexB compounds with x = 0, 1, and 2, have been investigated by x-ray and neutron diffraction, magnetic measurements, and iron-57 Mössbauer spectroscopy. The substitution of cobalt by iron induces both an anisotropic increase in the unit cell volume and a large increase of ca. 250 K in the Curie temperature; the 4.2 K magnetization decreases continuously with increasing iron content. The powder neutron diffraction patterns and the Mössbauer spectra of the TbCo4–xFexB compounds reveal a strong preferential substitution of iron for cobalt on the 2c site, small transition metal magnetic moments of ca. 1.7 µB, and small iron hyperfine fields of ca. 16 T. The compensation temperature of the TbCo4–xFexB compounds decreases continuously from 400 to 350 K between x = 0 and 2 as the result of an iron induced increase in the transition metal magnetization. The magnetic moment and hyperfine field are found to be larger on the 2c site than on the 6i site, a difference that reflects the strong hybridization of the 3d orbitals of the 6i site transition metal with the boron 2p orbitals. [less ▲]

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See detailA study of the high temperature spin reorientation in YCoFe/sub 3/B
Grandjean, Fernande ULg; Sougrati, Moulay Tahar ULg; Mayot, H. et al

in Journal of Physics : Condensed Matter (2009), 21(18), 1860017-1860017

The iron-57 Mossbauer spectra of YCoFe /sub 3/ B have been measured between 4.2 and 480 K and reveal that YCoFe /sub 3/ B exhibits an axial orientation of the iron magnetic moments below 450 K and a basal ... [more ▼]

The iron-57 Mossbauer spectra of YCoFe /sub 3/ B have been measured between 4.2 and 480 K and reveal that YCoFe /sub 3/ B exhibits an axial orientation of the iron magnetic moments below 450 K and a basal orientation above 450 K. This spin reorientation, also observed in the thermomagnetic curves, results from the different signs of the contributions to the magnetic anisotropy of the 2c and 6i sites that are occupied by iron. The neutron diffraction patterns of YCoFe /sub 3/ B have been measured at 2 K and between 290 and 770 K and have been successfully analyzed with a model compatible with the magnetic orientation obtained from the Mossbauer spectra. The hybridization between the cobalt or iron 3d orbitals and the boron 2p orbitals leads to a larger magnetic moment and hyperfine field on the 2c site as compared to the 6i site. [less ▲]

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See detailInfluence of the rare-earth element on the effects of the structural and magnetic phase transitions in CeFeAsO, PrFeAsO and NdFeAsO
McGuire, Michael A; Hermann, Raphaël ULg; Sefat, Athena S et al

in New Journal of Physics (2009), 11

We present results of transport and magnetic properties and heat capacity measurements on polycrystalline CeFeAsO, PrFeAsO and NdFeAsO. These materials undergo structural phase transitions, spin density ... [more ▼]

We present results of transport and magnetic properties and heat capacity measurements on polycrystalline CeFeAsO, PrFeAsO and NdFeAsO. These materials undergo structural phase transitions, spin density wave-like magnetic ordering of small moments on iron and antiferromagnetic ordering of rare-earth moments. The temperature dependence of the electrical resistivity, Seebeck coefficient, thermal conductivity, Hall coefficient and magnetoresistance are reported. The magnetic behavior of the materials have been investigated using Mossbauer spectroscopy and magnetization measurements. Transport and magnetic properties are affected strongly by the structural and magnetic transitions, suggesting significant changes in the band structure and/or carrier mobilities occur, and phonon-phonon scattering is reduced upon transformation to the low-temperature structure. Results are compared with recent reports for LaFeAsO, and systematic variations in properties as the identity of Ln is changed are observed and discussed. As Ln progresses across the rare-earth series from La to Nd, an increase in the hole contributions to the Seebeck coefficient and increases in magnetoresistance and the Hall coefficient are observed in the low-temperature phase. Analysis of hyperfine fields at the iron nuclei determined from Mossbauer spectra indicates that the moment on Fe in the orthorhombic phase is nearly independent of the identity of Ln, in apparent contrast to reports of powder neutron diffraction refinements. [less ▲]

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See detailStructural and magnetic properties of Pr18Li8Fe5-xMxO39 (M = Ru, Mn, Co)
Dutton, Sian E; Battle, Peter D; Grandjean, Fernande ULg et al

in Journal of Solid State Chemistry (2009), 182(7), 1638-1648

A polycrystalline sample of Pr18Li8Fe4RuO39 has been synthesized by a solid state method and characterized by neutron powder diffraction, magnetometry and Mossbauer spectroscopy; samples of Pr18Li8Fe5 ... [more ▼]

A polycrystalline sample of Pr18Li8Fe4RuO39 has been synthesized by a solid state method and characterized by neutron powder diffraction, magnetometry and Mossbauer spectroscopy; samples of Pr18Li8Fe5-xMxO39 and Pr18Li8Fe5-xCoxO39 (x = 1, 2) have been studied by magnetometry. All these Compounds adopt a cubic structure (space group Pm (3) over barn, a(o)similar to 11.97 angstrom) based on intersecting < 111 > chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Pr-O framework. The trigonal-prismatic site in Pr18Li8Fe4RuO39 is occupied by Li+ and high-spin Fe3+. The remaining transition-metal cations occupy the two crystallographically-distinct octahedral sites in a disordered manner. All five compositions adopt a spin-glass-like state at 7 K (Pr18Li8Fe4RuO39) or below. (C) 2009 Elsevier Inc. All rights reserved. [less ▲]

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See detailMonofluoride Bridged, Binuclear Metallacycles of First Row Transition Metals Supported by Third Generation Bis(1-pyrazolyl)methane Ligands: Unusual Magnetic Properties
Reger, Daniel; Watson, R. P.; Foley, E. A. et al

in Inorganic Chemistry (2009), 48

The reaction of M(BF4)2•xH2O, where M is Fe, Co, Cu, and Zn, and the bitopic, bis(pyrazolyl)methane ligand m-[CH(pz)2]2C6H4, Lm, where pz is a pyrazolyl ring, yields the monofluoride bridged, binuclear ... [more ▼]

The reaction of M(BF4)2•xH2O, where M is Fe, Co, Cu, and Zn, and the bitopic, bis(pyrazolyl)methane ligand m-[CH(pz)2]2C6H4, Lm, where pz is a pyrazolyl ring, yields the monofluoride bridged, binuclear [M2(μ-F)(μ-Lm)2](BF4)3 complexes. In contrast, a similar reaction of Lm with Ni(BF4)2•6H2O yields dibridged [Ni2(μ-F)2(μ-Lm)2](BF4)2. The solid state structures of seven [M2(μ-F)(μ-Lm)2](BF4)3 complexes, with M = Fe, Co, Cu, and Zn, indicate that the divalent metal ion is in a five-coordinate, trigonal bipyramidal, coordination environment with either a linear M–F–M bridging arrangement in five of the complexes, or with a slightly bent Cu–F–Cu bridge in two of the complexes. NMR results indicate that [Zn2(μ-F)(μ-Lm)2](BF4)3 retains its dimeric structure in solution. The [Ni2(μ-F)2(μ-Lm)2](BF4)2 complex has a dibridging fluoride structure that has a six-coordination environment about each nickel(II) ion. In the solid state, the [Fe2(μ-F)(μ-Lm)2](BF4)3 and [Co2(μ-F)(μ-Lm)2](BF4)3 complexes show weak intramolecular antiferromagnetic exchange coupling between the two metal(II) ions with J values of –10.4 and –0.67 cm–1, respectively; there is no observed long-range magnetic order. Three different solvates of [Cu2(μ-F)(μ-Lm)2](BF4)3 are diamagnetic between 5 and 400 K, thus showing strong antiferromagnetic exchange interactions of –600 cm–1 or more negative. Mössbauer spectra indicate that [Fe2(μ-F)(μ-Lm)2](BF4)3 exhibits no long-range magnetic order between 4.2 and 295 K and isomer shifts that are consistent with the presence of five-coordinate, high-spin iron(II). [less ▲]

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See detailStructural, Magnetic and Mössbauer Spectral Study of the Electronic Spin-state Transition in {Fe[HC(3-Mepz)2(5-Mepz)]2}(BF4)2
Reger, Daniel; Elgin, J.; Foley, E. et al

in Inorganic Chemistry (2009), 48

The complex {Fe[HC(3-Mepz)2(5-Mepz)]2}(BF4)2 (pz = pyrazolyl ring) has been prepared by the reaction of HC(3-Mepz)2(5-Mepz) with Fe(BF4)2·6H2O. The solid state structures obtained at 294 and 150 K show a ... [more ▼]

The complex {Fe[HC(3-Mepz)2(5-Mepz)]2}(BF4)2 (pz = pyrazolyl ring) has been prepared by the reaction of HC(3-Mepz)2(5-Mepz) with Fe(BF4)2·6H2O. The solid state structures obtained at 294 and 150 K show a distorted iron(II) octahedral N6 coordination environment with the largest deviations arising from the restrictions imposed by the chelate rings. At 294 K the complex is predominately high-spin with Fe–N bond distances averaging 2.14 Å, distances that are somewhat shorter than expected for a purely high-spin iron(II) complex because of the presence of an admixture of ca. 70 (I get 80 from both mag and X-ray, 3/15, where 3 is the subtraction of 2.14 and 2.17 and 15 1.99 and 2.14 and from Figure 3b) percent high-spin and 30 (20) percent low-spin iron(II). At 294 K the twisting of the pyrazolyl rings from the ideal C3v symmetry averages only 2.2o, a much smaller twist than has been observed previously in similar complexes. At 150 K the Fe–N bond distances average 1.99 Å, indicative of an almost fully low-spin iron(II) complex; the twist angle is only 1.3o, as expected for a complex with these Fe–N bond distances. The magnetic properties show that the complex undergoes a gradual change from low-spin iron(II) below 85 K to high-spin iron(II) at 400 K. The 4.2 to 60 K Mössbauer spectra correspond to a fully low-spin iron(II) complex but, upon further warming, the iron(II) begins to undergo spin-state relaxation on the Mössbauer time scale such that, at 155 and 315 K, the complex is 7.5 and 65 percent high-spin in the absence of any adjustment for the differing low-spin and high-spin recoil-free fractions. I would replace the previous sentence with the red. I see no reason to give the % from the Mössbauer in the abstract as it is likely a bit low as discussed in detail – neither the mag data nor X-ray data have the recoil issue. The last sentence in the abstract is the key information. OK The 4.2 to 60 K Mössbauer spectra correspond to a fully low-spin-iron(II) complex but, upon further warming above 85 K the iron(II) begins to undergo spin-state relaxation between the low- and high-spin forms on the Mössbauer time scale. At 155 and 315 K the complex exhibits spin-state relaxation rates of 0.36 and 7.38 MHz, respectively, and an Arrhenius plot of the logarithm of the relaxation rate yields an activation energy of 670 ± 40 cm–1 for the spin-state relaxation. [less ▲]

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See detailStructural Chemistry and Magnetic Properties of Nd18Li8Fe5-xMxO39 (M = Mn, Co),
Dutton, S. E.; Battle, Peter D.; Grandjean, Fernande ULg et al

in Inorganic Chemistry (2009), 48

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See detailSpin-frustrated Complex, [FeIIFeIII(trans-1,4-cyclohexanedicarboxylate)1.5]∞: Interplay between Single-Chain Magnet Behavior and Magnetic Ordering
Zheng, Y. Z.; Xue, W.; Zhang, W. X. et al

in Inorganic Chemistry (2009), 48

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See detailA structural, magnetic and Mössbauer spectral study of the magnetocaloric Mn1.1Fe0.9P1-xGex compounds
Sougrati, Moulay Tahar ULg; Hermann, Raphaël ULg; Grandjean, Fernande ULg et al

in Journal of Physics : Condensed Matter (2008), 20

The structural, magnetic and Mössbauer spectral properties of the magnetocaloric Mn1.1Fe0.9P1−xGex compounds, with 0.19 < x < 0.26, have been measured between 4.2 and 295 K. The 295 K unit-cell volume ... [more ▼]

The structural, magnetic and Mössbauer spectral properties of the magnetocaloric Mn1.1Fe0.9P1−xGex compounds, with 0.19 < x < 0.26, have been measured between 4.2 and 295 K. The 295 K unit-cell volume increases from x = 0.19 to 0.22 and is substantially smaller in the ferromagnetic Mn1.1Fe0.9P0.74Ge0.26. The temperature dependence of the magnetization reveals a ferromagnetic to paramagnetic transition with a Curie temperature between approximately 250 and 330 K and hysteresis width of 10 to 4 K, for 0.19 < x < 0.25. The composition Mn1.1Fe0.9P0.78Ge0.22 shows the largest isothermal entropy change of approximately 10 J/(kgKT) at 290 K. The M¨ossbauer spectra have been analysed with a binomial distribution of hyperfine fields correlated with a change in isomer shift and quadrupole shift, a distribution that results from the distribution of phosphorus and germanium among the near neighbours of the iron. The coexistence of paramagnetic and magnetically ordered phases in ranges of temperature of up to 50 K around the Curie temperature is observed in the Mössbauer spectra and is associated with the first-order character of the ferromagnetic to paramagnetic transition. The temperature dependence of the weighted average hyperfine field is well fitted within the magnetostrictive model of Bean and Rodbell. Good fits of the Mössbauer spectra could only be achieved by introducing a difference between the isomer shifts in the paramagnetic and ferromagnetic phases, a difference that is related to the magnetostriction and electronic structure change. [less ▲]

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See detailIron(III) species dispersed in porous silica through sol-gel chemistry
Heinrichs, Benoît ULg; Rebbouh, Leila; Geus, John W et al

in Journal of Non-Crystalline Solids (2008), 354(2-9), 665-672

Fe/SiO2 catalysts have been prepared by two different sol-gel methods, cogelation and dissolution. The cogelation and dissolution preparative methods lead to xerogels with fundamentally different pore ... [more ▼]

Fe/SiO2 catalysts have been prepared by two different sol-gel methods, cogelation and dissolution. The cogelation and dissolution preparative methods lead to xerogels with fundamentally different pore width distributions. The nature of the iron species obtained has been examined in detail by UN-visible and Mossbauer spectroscopy, and magnetic, transmission electron microscopy, and X-ray diffraction studies. There is no evidence for the presence of any ordered iron(III) oxides in the samples but all three contain two types of iron species, specifically paramagnetic high-spin iron(III) ions isolated in silica and iron(III) containing nanoparticles with a broad width distribution centered on 1.5 nm, nanoparticles that contain antiferromagnetically coupled clusters of a few ligated bridged iron(III) ions. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailSyntheses, structure, and a Mossbauer and magnetic study of Ba4Fe2I5S4
Gray, Danielle L; Long, Gary J; Grandjean, Fernande ULg et al

in Inorganic Chemistry (2008), 47(1), 94-100

The compound Ba4Fe2I5S4 has been prepared at 1223-1123 K by the "U-assisted" reaction of FeS, BaS, S, and U with BaI2 as a flux. A more rational synthesis was also found; however, the presence of U ... [more ▼]

The compound Ba4Fe2I5S4 has been prepared at 1223-1123 K by the "U-assisted" reaction of FeS, BaS, S, and U with BaI2 as a flux. A more rational synthesis was also found; however, the presence of U appears to be essential for the formation of single crystals suitable for X-ray diffraction studies. Ba4Fe2I5S4 crystallizes in a new structure type with two formula units in space group 14/m of the tetragonal system. The structure consists of a Ba-I network penetrated by (1)(infinity) [Fe2S4] chains. Each Fe atom, which is located on a site with 4 symmetry, is tetrahedrally coordinated to four S atoms. The FeS4 tetrahedra edge-share to form linear (1)(infinity)[Fe2S4] chains in the [001] direction. The Fe-Fe interatomic distance in these chains is 2.5630(4) angstrom, only about 3 % longer than the shortest Fe-Fe distance in alpha-Fe metal. Charge balance dictates that the average formal oxidation state of Fe in these chains is +2.5. The Mossbauer spectra obtained at 85 and 270 K comprise a single quadrupole doublet that has hyperfine parameters consistent with an average Fe oxidation state of +2.5. The Mossbauer spectrum obtained at 4.2 K consists of a single magnetic sextet with a small hyperfine field of -15.5 T. This spectrum is also consistent with rapid electron delocalization and an average Fe oxidation state of +2.5. The molar magnetic susceptibility of Ba4Fe2I5S4, obtained between 3.4 and 300 K, qualitatively indicates the presence of weak pseudo-one-dimensional ferromagnetic exchange within a linear chain above 100 K and weak three-dimensional ordering between the chains at lower temperatures. [less ▲]

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See detailColossal positive magnetoresistance in a doped nearly magnetic semiconductor
Hu, Rongwei; Thomas, K. J.; Lee, Y. et al

in Physical Review B (2008), 77(8),

We report on a positive colossal magnetoresistance (MR) induced by metallization of FeSb2, a nearly magnetic or "Kondo" semiconductor with 3d ions. We discuss the contribution of orbital MR and quantum ... [more ▼]

We report on a positive colossal magnetoresistance (MR) induced by metallization of FeSb2, a nearly magnetic or "Kondo" semiconductor with 3d ions. We discuss the contribution of orbital MR and quantum interference to the enhanced magnetic field response of electrical resistivity. [less ▲]

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See detailA density functional theory calculation of the electronic properties of several high-spin and low-spin iron(II) pyrazolylborate complexes
Remacle, Françoise ULg; Long, G. J.; Grandjean, Fernande ULg

in Inorganic Chemistry (2008), 47(10), 4005-4014

Density functional theory has been used to study the electronic spin-state properties of low-spin Fe[HB(PZ)(3)](2), lhigh-spin Fe[HB(3-MePZ)(3)](2), high-spin Fe[HB(3,5-Me(2)PZ)(3)](2), and high-spin Fe ... [more ▼]

Density functional theory has been used to study the electronic spin-state properties of low-spin Fe[HB(PZ)(3)](2), lhigh-spin Fe[HB(3-MePZ)(3)](2), high-spin Fe[HB(3,5-Me(2)PZ)(3)](2), and high-spin Fe[HB(3,4,5-Me(3)PZ)(3)](2) complexes that exhibit very different iron(II) electronic spin-sate crossover behaviors with changing temperature and pressure. Excellent agreement is obtained between the experimentally,observed Mossbauer-effect quadrupole splittings and isomer shifts of these complexes and those calculated with the B3LYP functional and various different basis sets for both the high-spin and low-spin states of iron(II). The calculations for Fe[HB(PZ)(3)](2) that use the LANL2DZ, 6-31++G(d,p), and 6-311++G(d,p) basis sets for iron all lead to very similar electric field gradients and thus quadrupole splittings. The initial calculations, which were based upon the known X-ray structures, were followed by structural optimization, an optimization that led to small increases in the Fe-N bond distances. Optimization led to at most trivial changes in the intraligand bond distances and angles. The importance of the 3-methy I-H center dot center dot center dot H-3-methyl nonbonded intramolecular interligand interactions in controlling the minimum Fe-N bond distances and determining the iron(II) spin state both in Fe[HB(3-Mepz)(3)](2) and in the related methyl-substituted complexes has been identified. [less ▲]

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