John D. Cashion

Mössbauer Spectroscopy of Environmental Materials and Their Industrial Utilization

-Introduction. List of Contents. Symbols and Abbreviations. Foreword. Acknowledgments. -1: Theory and Characteristics of the Mossbauer Effect. Theory of the Mossbauer Effect. Magnetism. Hyperfine Interactions. Relaxation Effects. Line Intensities. Diffusional Broadening. Mossbauer Spectroscopy in Mineralogy and Minerals Processing. Summary. -2: Mossbauer Instrumentation. General Considerations. Source and Reference Absorber. Conventional Spectrometers. Other Spectrometers. Sample Environment. Sample preparation. Summary. -3: Data Analysis and Interpretation. Fitting using Simple Lorentzians. Tests of Goodness of Fit. Convolution and Deconvolution. Thickness Effects and Recoilless Fraction. Fitting of Thickness Broadened Lines. Fitting of Lines Broadened by a Hyperfine Parameter Distribution. Magnetic Relaxation and Superparamagnetism. The Non Uniqueness Problem. Problems in Fitting and Interpretation. Presentation of Results. Summary. -4: Bulk and Clay Sized Phyllosilicates. 1:1 Minerals: Kaolinite. 2:1 Minerals: Illite. Montmorillonite. Nontronite. Summary. - 5: Iron Oxides and Oxyhydroxides. Anhydrous Oxides: Hematite. Magnetite. Maghemite. Oxyhydroxides: Goethite. Ferrihydrite. Summary. -6: Sediments. Terrestrial Sediments. Freshwater Sediments. Marine Sediments. Airborne Particles. Summary. -7: Soils and Clays. Soils. Clays. Summary. -8: Weathering. Silicate Weathering. Sulfide Weathering and Acid Mine Drainage. Summary. -9: Metastable Materials. Green Rusts. Fine Particle Magnetite. Anoxic Sediments. Fe2+ Sulfates Produced by Acid Mine Drainage. Summary. -10: Coal. Coal Characterization. Heat and Chemical Treatment. Hydroliquefaction. Summary. -11: ClayFiring. Individual Minerals: Kaolinite. Illite. Montmorillonite. Nontronite. Samples of Complex Mineralogy. Summary. -12: Mineral processing. Introduction. Iron Ores. Titanium Ores. Other Processing Operations Involving Iron. Gold. Summary. References. Index.

Chemically Induced Permanent Magnetism in Au, Ag, and Cu Nanoparticles: Localization of the Magnetism by Element Selective Techniques

We report a direct observation of the intrinsic magnetization behavior of Au in thiol-capped gold nanoparticles with permanent magnetism at room temperature. Two element specific techniques have been used for this purpose: X-ray magnetic circular dichroism on the L edges of the Au and 197Au Mössbauer spectroscopy. Besides, we show that silver and copper nanoparticles synthesized by the same chemical procedure also present room-temperature permanent magnetism. The observed permanent magnetism at room temperature in Ag and Cu dodecanethiol-capped nanoparticles proves that the physical mechanisms associated to this magnetization process can be extended to more elements, opening the way to new and still not-discovered applications and to new possibilities to research basic questions of magnetism.

The first X-ray crystal structure determination of a dinuclear complex trapped in the [low spin–high spin] state: [FeII2(PMAT)2](BF4)4·DMF

The two metal centres in the doubly 1,2,4-triazole-bridged spin crossover complex [Fe(II)2(PMAT)2](BF4)4.DMF (1.DMF) are trapped in different spin states below ca. 200 K, with no evidence that this particular [LS-HS] species can be converted into the [LS-LS] form at ambient pressure.

Structure and magnetism of a new pyrazolate bridged iron(II) spin crossover complex displaying a single HS–HS to LS–LS transition

The dinuclear iron(II) complex [(pypzH)(NCSe)Fe([micro sign]-pypz)(2)Fe(NCSe)(pypzH)].2H(2)O displays a single, sharp spin crossover transition between the [HS-HS] and [LS-LS] states and is structurally characterised above and below the T(1/2)= 225 K value

Low‐Coordinate Iron(I) and Manganese(I) Dimers: Kinetic Stabilization of an Exceptionally Short FeFe Multiple Bond

The fundamental and applied chemistry of metal–metal bonded complexes has rapidly expanded since Cotton s landmark report of metal–metal quadruple bonding in the dianion, [Re2Cl8] 2 , nearly 50 years ago. Many of the recent advances in the field have centered on the stabilization of reactive low oxidation state/low coordination number M– M bonded complexes using sterically imposing ligand systems. Representative examples include the singly bonded zinc(I) and magnesium(I) dimers, [Cp*ZnZnCp*] (Cp* = C5Me5) [3]

Unprecedented encapsulation of a [FeIIICl4]− anion in a cationic [FeII4L6]8+ tetrahedral cage derived from 5,5′′′-dimethyl-2,2′:5′,5′′:2′′,2′′′-quaterpyridine

A unique example of incorporation of a tetrahalometalate anion in a small supramolecular cage is described in which a tetrahedral cage of type [Fe4L6]8+ selectively encapsulates a [FeIIICl4]− anion over a [FeIICl4]2− anion in its central cavity to yield a discrete, mixed oxidation state, Fe(II)/Fe(III) supramolecular assembly. This unusual outcome has been achieved using two alternative synthetic strategies.

Abrupt spin crossover in an iron(III) quinolylsalicylaldimine complex: structural insights and solvent effects

The first Fe(III) qsal-X complex exhibiting abrupt complete spin crossover at 228 K with a hysteresis of 8 K, [Fe(qsal-I)2]OTf is reported. Structural studies of the MeOH solvate in the LS and HS state and at the spin transition are described.

μ-Carbido Diporphyrinates and Diphthalocyaninates of Iron and Ruthenium

μ-Carbido diporphyrinates and diphthalocyaninates of general formula [{Mp2−}2(μ-C)] (p2− = tpp (M = Fe), oep (Fe), pc (Fe, Ru); H2tpp: 21H,23H-5,10,15,20-tetraphenylporphine; H2oep: 21H,23H-2,3,4,8,12,13,17,18-octaethylporphine; H2pc: 29H,31H-phthalocyanine) of formally FeIV and RuIV are prepared by a new and improved ‘one-pot’ synthesis. The corresponding chloro complexes of the tervalent metal ions react successively with potassium hydroxide in boiling 2-propanol and then with trichloromethane. Potassium hydroxide is proven to be a very versatile and powerful reductant in tetrapyrrolic chemistry. As evidenced from electron spin resonance and UV vis spectral measurements, the precursor is reduced primarily to an ate-complex of type [MIp2−]− of a formally monovalent metal ion. This active species is assumed to react with trichloromethane via a dichlorocarbene complex of type [MII(CCl2)p2−] to yield the actual -carbido complex. [{Feoep2−}2(μ-C)] is crystallographically characterized. It is monoclinic, space group C12/c1 (15), with a = 18.279(3) A, b = 15.005(2) A, c = 23.392(7) A, β = 107.12(2)°, Z = 4, R1 = 0.0773. The iron atom is displaced by 0.192(3) A out of the centre (Ct) of the (Np)4 plane toward the (μ-C) atom. Average d(Fe-Np) is 1.986(5) A; d(Fe-(μ-C)) is 1.6638(9) A. The Fe-C-Fe skeleton is linear (179.5(3)°). The two slightly waving porphyrinato cores are in a staggered conformation, the (Np-Fe-Fe″-Np″) torsion angle being 21.0(3)°. Solutions of each μ-carbido complex in pyridine/dichloromethane show four distinct quasi-reversible redox processes in their differential-pulse voltammograms and these are assigned to the successive one-electron reduction and oxidation of the macrocyclic ligands. 13C CP MAS NMR spectra indicate effective four-fold symmetry within the series of the μ-carbido complexes with isotropic shifts occurring at similar fields to those of the corresponding macrocyclic complex of a closed-shell metal ion. Resonances of the bridging carbon atom are not detected. A characteristic increase of line broadening within the series tpp2− > oep2− > pc2− may be due to Fermi contact interactions with the strongly coupled low-spin MIV centres. The magnetic susceptibility studies show that the complexes all display non-zero μ values at 295 K increasing from pc2− to tpp2−. Mossbauer spectra confirm the low-spin FeIV oxidation state for the iron centres. Isomer shift, δ, and quadrupole splitting, ΔEQ, for [{Fepc2−}2(μ-C)] and [{Fetpp2−}2(μ-C)] are identical to those previously reported. Data for [{Feoep2−}2(μ-C)] are essentially the same as for the pc and tpp complex. Thus the order of δ is tpp ≈ oep > pc whilst that of ΔEQ is pc >> oep > tpp. Small impurity lines are observed which help explain the magnetic data. UV vis/NIR spectra of the μ-carbido complexes show the characteristic π-π* transitions. These are shifted with respect to the corresponding mononuclear complexes to higher energy because of excitonic interactions. Vibrational spectra are discussed in detail νas(M-C-M) (in cm−1) is at 937 (M = Fe; tpp) ν > 25 000 cm−1.

Some triphenyltin(IV) complexes containing potentially bidentate, biologically active anionic groups

Abstract Triphenyltin(IV) derivatives have been synthesized which contain anions from various biologically active acids. The coordination about the tin atom was investigated by infrared, 119 Sn NMR and Mossbauer spectroscopic methods. The triphenyltin cation with S-bonding groups generally acquires a four-coordinated structure. On the other hand, combination with O-bonding groups can produce several structural possibilities: four-coordinate, five-coordinate cis- and trans -trigonal bipyramidal and bridging carboxylate examples being obtained. Some of the higher coordination number species appear to dissociate in solution.

Mössbauer study of iron exchanged into Victorian brown coal

Abstract Mossbauer spectroscopy was used to characterize iron species introduced by an ion exchange method into Victorian brown coal to promote its hydroliquefaction. The iron speciation does not depend on the nature of the treatment solution (iron(II) sulphate, chloride or acetate). The two principal phases identified are divalent iron bound to dissolved humic material and a precipitate of microparticulate ferric oxyhydroxide; lesser amounts of both are also present before exchange. There is no evidence of association between iron and tin when introduced simultaneously into the coal.