Iron-57 Mossbauer Spectroscopy Research Articles

Redox reactions in Prussian blue containing paint layers as a result of light exposure

Prussian blue, a mixed valence pigment, typically KFeIII[FeII(CN)6]·xH2O, was the most widely used blue artistic pigment from ca. 1720 to the 1970's but, unfortunately, its paint layers, especially when used in conjunction with a white pigment, tend to fade or turn green upon extended exposure to light. In order to identify the mechanism underlying these changes, paint layers have been prepared with differing amounts of these white pigments and subjected to accelerated light exposure fading. The resulting unfaded and faded paint layers as well as both the Berlin white pigment, Fe2II[FeII(CN)6], and the partially oxidized Berlin green pigment, {KFeIII[FeII(CN)6]}x{FeIII[FeIII(CN)6]}1−x, have been characterized by Raman and iron-57 Mossbauer spectroscopy. The results indicate that, upon fading, the Prussian blue pigment painted with a linseed oil binder and (PbCO3)2Pb(OH)2 or ZnO, and to a lesser extent with TiO2, undergoes a reduction at the exposed paint surface and an oxidation in the bulk of the paint layer. This combined reduction and oxidation disrupts, at least in part, the FeIII–N–C–FeII intervalent electron transfer pathways in Prussian blue thus leading to pigment fading through a reduction in the intervalent electron transfer absorbance at about 700 nm.

Spin-Frustrated Complex, [FeIIFeIII(trans-1,4-cyclohexanedicarboxylate)1.5]∞: Interplay between Single-Chain Magnetic Behavior and Magnetic Ordering

A three-dimensional mixed-valent iron(II,III) trans-1,4-cyclohexanedicarboxylate, 1,4-chdc, coordination polymer, [Fe(II)Fe(III)(mu(4)-O)(1,4-chdc)(1.5)](infinity), 1, has been synthesized hydrothermally by mixing iron powder and 1,4-chdcH(2) and investigated by X-ray diffraction, dc and ac magnetic susceptibility, and iron-57 Mossbauer spectroscopy over a wide range of temperatures. Single-crystal X-ray diffraction studies of 1 at 90(2), 293(2), and 473(2) K reveal a tetrahedral [Fe(II)(2)(mu(4)-O)Fe(III)(2)(mu(4)-O)](6+) mixed-spin-chain structure with no change in the P1 space group but with subtle changes in the Fe-O and Fe...Fe distances with increasing temperature. These changes are associated with the electron delocalization observed by Mossbauer spectroscopy above 225 K. Magnetic studies reveal three different magnetic regimes in 1 between 2 and 320 K. Above 36 K 1 is a one-dimensional ferrimagnetic-like complex with frustration arising from competing exchange interactions between the iron(II) and iron(III) ions in the chains. Between 36 and 25 K the interchain interactions are non-negligible and 1 undergoes three-dimensional ordering at 32.16 K but with some residual fluctuations. Below 25 K the residual fluctuations slow and eventually freeze below 15 K; the small net moment of 0.22 mu(B) per mole of 1 observed below 15 K may be attributed to a non-collinear or canted spin structure of the spins of the four iron ions in the [Fe(II)(2)(mu(4)-O)Fe(III)(2)(mu(4)-O)](6+) chains. Below 32 K the Mossbauer spectra of 1 exhibit sharp sextets for both the iron(III) and iron(II) ions and are consistent with either a static long-range or a short-range magnetic ground state or a slow relaxation between two canted magnetic states that are indistinguishable at the observed spectral resolution. The 85 and 155 K spectra reveal no electron delocalization and correspond solely to fixed valence iron(II) and iron(III). Between 225 and 310 K the spectra reveal the onset of electron delocalization such that, at 295 to 310 K, 25, 25, and 50% of the iron in 1 is present as iron(II), iron(III), and iron(II/III) ions, respectively. The absence of any spectral line broadening associated with this electron delocalization and the coexistence of four doublets between 225 and 310 K indicate that the delocalization occurs through electron tunneling via vibronic coupling. The sudden increase in the tunneling rate beginning above about 260 K and the presence of a cusp in the magnetic susceptibility centered at about 275 K strongly suggest the existence of a charge order/disorder transition whose nature and order are discussed.

Synthesis of Two New Polyferrocenylsilanes and Magnetic Properties of Their Charge Transfer Complexes

Two polyferrocenylsilanes (PFSs) 1 and 2 with aniline and carbazolyl as side chains have been prepared by treating silyl-chloride functionalized PFS (PFS-Cl) with hydroxyl-ended aniline and carbazole compounds, respectively, and characterized by NMR, FT-IR, elemental analysis (EA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cyclic voltammetry (CV). Both of them could be oxidized by iodine and 2,3-dichloro-5,6-dicyanoquinone (DDQ) to form complexes. PFS 1 could be oxidized by tetracyanoethylene (TCNE) too. The complexes are characterized by FT-IR, EA, Iron-57 Mossbauer spectroscopy. All of them are partially oxidized by the oxidants and both FeII and FeIII coexist in the complexes. Magnetic property measurement by superconducting quantum interference device (SQUID) shows their paramagnetic properties with somewhat antiferromagnetic interaction. Results show that the joint type between PFS backbone and the electron-rich side groups has less direct effect on the exhibition of ferromagnetic interaction in their complexes.

Evolution of electronic state, magnetism, and magnetotransport properties in Sr3Fe2 – xCoxO7 – y (x ≤ 1)Electronic supplementary information (ESI) available: additional characterisation data. See http://www.rsc.org/suppdata/jm/b1/b107981f/

Iron-rich Ruddlesden–Popper phases Sr3Fe2 − xCoxO7 − y (x ≤ 1) have been synthesized by two citrate precursor techniques and investigated in order to explore the correlation between electron transport properties, electronic state, magnetism, and magnetoresistance effects in iron(IV) based oxides. The materials were characterized by X-ray powder diffraction, temperature and field dependent magnetization measurements, magnetotransport studies, and iron-57 Mossbauer spectroscopy. With increasing cobalt content there is a smooth development of electronic properties: a gradual increase in the low-temperature conductivity of the semiconducting materials, a successive reduction and finally suppression of the charge ordering of Fe(4 − Δq)+ and Fe(4 + Δq)+ sites resulting from a charge disproportionation of the Fe4+ ions, and an evolution from antiferromagnetic to ferromagnetic behaviour via a spin glass regime. Large magnetoresistance (MR) effects at low temperatures were apparent for all the samples (up to −47% at 5 K and 7 T). Maximization of the MR effects in the title system appears to involve an optimized balance between ferro- and antiferromagnetic interactions.

Charge Ordering, Competing Magnetic Interactions, and Magneto-Resistance Effects in Layered Iron(IV)-Based Oxides

Iron(IV)-based Ruddlesden-Popper-type oxides Sr3Fe2−x Co x O7−y (0≤x≤1) have been synthesized and studied by various techniques. It is shown that iron-57 Mossbauer spectroscopy is a powerful tool for elucidating the intimate correlations between chemical composition, electron-transport properties, electronic state, magnetism, and the large magneto-resistance effects in this system.

Physical and chemical characterization of therapeutic iron containing materials: A study of several superparamagnetic drug formulations with the β-FeOOH or ferrihydrite structure

The effectiveness of therapeutically used iron compounds is related to their physical and chemical properties. Four different iron compounds used in oral, intravenous, and intramuscular therapy have been examined by X-ray powder diffraction, iron-57 Mossbauer spectroscopy, transmission electron microscopy, BET surface area measurement, potentiometric titration and studied through dissolution kinetics determinations using acid, reducing and chelating agents. All compounds are nanosized with particle diameters, as determined by X-ray diffraction, ranging from 1 to 4.1 nm. The superparamagnetic blocking temperatures, as determined by Mossbauer spectroscopy, indicate that the relative diameters of the aggregates range from 2.5 to 4.1 nm. Three of the iron compounds have an akaganeite-like structure, whereas one has a ferrihydrite-like structure. As powders the particles form large and dense aggregates which have a very low surface area on the order of 1 m2 g−1. There is evidence, however, that in a colloidal solution the surface area is increased by two to three orders of magnitude, presumably as a result of the break up of the aggregates. Iron release kinetics by acid, chelating and reducing agents reflect the high surface area, the size and crystallinity of the particles, and the presence of the protective carbohydrate layer coating the iron compound. Within a physiologically relevant time period, the iron release produced by acid or large chelating ligands is small. In contrast, iron is rapidly mobilized by small organic chelating agents, such as oxalate, or by chelate-forming reductants, such as thioglycolate.

Heterobimetallic Dinitrogen Complexes That Contain the {[N3N]Mo−NN}-Ligand

{[N3N]Mo−NN}2Mg(THF)2 reacts with FeCl2 at −20 °C in a mixture of ether, THF, and toluene to yield paramagnetic {[N3N]Mo−NN}3Fe (1), an X-ray study of which shows it to contain iron in a trigonal planar environment. X-band ESR, iron-57 Mossbauer spectroscopy, and magnetic susceptibility studies of 1 confirm that it contains high-spin Fe(III) in an anisotropic magnetic environment. Addition of DMPE to toluene solutions of 1 results in loss of [N3N]MoN2 from the coordination sphere to give {[N3N]Mo−NN}2Fe(DMPE) (2). SQUID magnetic susceptibility and Mossbauer data are in accord with formulation of 2 as a high-spin Fe(II) complex. {[N3N]Mo−NN}2Mg(THF)2 reacts with VCl4(DME) and VCl3(THF)3 in THF to give paramagnetic {[N3N]Mo−NN}3VCl (3) in 28−42% yield. A second paramagnetic complex is also produced in these reactions and has been identified by X-ray crystallography as {[N3N]Mo−NN}2VCl(THF) (4). Several zirconium/molybdenum dinitrogen complexes have been prepared by the reaction between {[N3N]Mo−NN}2Mg(THF)2...

Identification of newly generated iron phases in recent anoxic sediments: 57Fe Mössbauer and microRaman spectroscopic studies

Both biota (primarily bacteria) and conditions of low natural redox potential and pH involved in surface sediments from the Seine estuary (in Northern France) are responsible for the reduction of sedimentary oxidized forms of iron into iron(II). Such processes generate insoluble inorganic compounds. Iron-57 Mossbauer spectroscopy has been used to characterize newly generated iron(II) carbonates [solid solution Fe x Ca 1−x CO 3 and ‘green rusts’, Fe III Fe II (CO 3 )(OH)] in these recent anoxic sediments. It is also demonstrated that sedimentary iron reductions occurring in these sediments play an important role in the biogeochemical cycles of sulfur. Thus, using X-ray diffraction, pyrite was detected in sulfide-rich sediments (1.5–1.8 wt.%). Furthermore, laser Raman microprobe spectroscopy has helped us to establish the existence of small quantities of pyrite and amorphous iron sulfide(s), scarcely detectable by conventional macroanalysis techniques, and to visualize/discriminate them on the anoxic sediment surface.

First Examples of Long Range Magnetic Ordering of Structurally Characterized Pentachloroferrate III Di-Anions: FeCl5 2-, and Its Methanol and Aquo Adducts

Abstract A. C. susceptibility and iron-57 Mossbauer spectroscopy measurements are used to investigate the first examples of cooperative magnetic ordering phenomena for FeCl3 2- anions and the related methanol and aquo adducts. Depending on the counter cation and/or solvate identity examples of uncanted antiferromagnetic and canted (weakly ferromagnetic) three dimensional order are observed with critical temperatures - 7K.

Observation of independent cation and anion sublattice long- range magnetic orderings in complex ferricenium salts: Layered magnetic composites

The low temperature magnetism of some magnets based on ferricenium cations and tetrahedral tetraholaferrate anions is discussed. Some of these materials behave as layered magnetic composites with distinctly different ordering temperatures for their respective anion and cation sublattices based on iron-57 Mossbauer spectroscopy and low-field DC magnetic susceptibility studies. Exemplary results are presented for the specific case of [Cp2Fe]+[FeBr4]− and indicateTcritical (anion) ∼ 14 K, while Tcritical (cation) ∼ 2.5 K whereχM versusT suggests canted 3D-AF (likely Heisenberg) behavior for the former and 2D-Ising AF behavior for the latter.

Synthesis, structure and properties of [Hpy]2[{M(mnt)2}2](M = Co or Fe, Hpy = pyridinium, mnt = maleonitriledithiolate)

The compounds [Hpy]2[{M(mnt)2}2][M = Fe or Co, Hpy = pyridinium, mnt = maleonitriledithiolate (2,3-disulfanylmaleonitrile)] have been prepared by electrocrystallization and characterized by single-crystal X-ray diffraction, magnetic susceptibility measurements and IR and 57Fe Mossbauer spectroscopies. The compounds are isostructural, monoclinic, space group P21/n with Z= 2. They both consist in alternate packing of [{M(mnt)2}2]2– units, with the metal in a square-pyramidal environment co-ordinated by sulfur atoms, and pyridinium cations bridged by three-centred hydrogen bonds to the mnt ligands. Iron-57 Mossbauer spectroscopy confirmed the presence of five-co-ordinate FeIII atoms. Magnetic susceptibility measurements on the cobalt compound showed a small (≈ 1.5 × 10–4 emu mol–1 at room temperature) paramagnetism, almost temperature independent below 150 K (≈ 0.7 × 10–4 emu mol –1), while the iron analogue had a strong paramagnetic contribution of antiferromagnetically coupled pairs of S= 3/2; in the [{Fe(mnt)2}2]2– units, with –2J/kB= 515 K. These properties are correlated to the crystal structure and compared with other [{M(mnt)2}2]2– compounds with M = Fe or Co.

In situ iron-57 Mössbauer spectroscopic investigations of the effect of titania surface area on the reducibility of titania-supported iron oxide

Iron-57 Mossbauer spectroscopy has been used to monitor the reducibility in hydrogen of iron oxides supported on titania of differing surface areas. The results show that although Fe3+ in the iron oxide supported on low surface area titania (11 m2g−1) is not amenable to facile reduction at low temperatures, complete reduction to metallic iron is achieved by treatment at 600°C. The data also show that the extent of reduction at elevated temperatures exceeds that which is obtained on similar silica- and alumina-supported systems. Fe3+ in iron oxide supported on higher surface area titania (50 m2g−1 and 240 m2g−1) is partially reduced in hydrogen at 235°C to Fe2+ but fails to attain complete reduction to the metallic state following treatment at 600°C. The results are related to the different dispersions of iron oxide which can be attained on titania of differing surface area and the consequent interactions between the support and the supported phases.

Iron-57, tin-119, and antimony-121 mössbauer spectroscopic investigations of metal atom incorporation into the oxide NbTiP3O12

Tin-119 and iron-57 Mossbauer spectroscopy show that the incorporation of tin and iron into the white oxide NbTiP3O12 to form black compounds of composition Sn0.5NTiP3O12 and Fe0.33NbTiP3O12 involves the accomodation of Sn2+ and Fe2+ in two types of sites in the NbTiP3O12 host lattice. The change in colour is associated which charge transfer arising from the transfer of electrons from the incorporated metal to the host lattice and the partial reduction of Nb5+ to a lower oxidation state. The compound SbTiP3O12 has been synthesised and shown by antimony-121 Mossbauer spectroscopy to contain Sb5+. The resistance of the SbTiP3O12 structure to the incorporation of tin and iron is associated with the reluctance of Sb3+ to adopt octahedral coordination.

Applications of Mössbauer spectroscopy to the coals of Central Queensland

The importance of mineral deposits in coal has been appreciated for some time especially in the subsequent processing of coal after it has been mined. In this paper use has been made of iron-57 Mossbauer spectroscopy at room temperature to analyse black coals from the Central Queensland area. The key components of these spectra are the sulphates and sulphides of iron. The components of these spectra are modified upon heat treatment up to 150°C.

Slow paramagnetic relaxation versus magnetic ordering of high-spin iron III in trigonal bipyramidal environments: Hyperfine splitting of the low temperature Mössbauer spectra of some high symmetry chloroferrate anion salts, [FeCl 5 2− ] and [FeCl5(CH3OH)2−

A combination of Iron-57 Mossbauer spectroscopy and magnetic susceptibility measurements are used to show that the [FeCl5 2−] and [FeCl5-(CH3OH)−2] anions (stabilized in the solid state by large quaternary cations) undergo ferromagnetic order, Tcritical∿6 K.

An in situ Mössbauer investigation of the influence of metal–support and metal–metal interactions on the activity and selectivity of iron–ruthenium catalysts

The hydrogen reduction of a series of alumina- and silica-supported iron–ruthenium catalysts has been studied in situ by iron-57 Mossbauer spectroscopy. The data, complemented by results from temperature-programmed reduction experiments, show that ruthenium enhances the reducibility of iron and that the metal–support interaction in the silica-supported samples is weaker than in those supported on alumina.The performance of the iron–ruthenium catalysts for carbon monoxide hydrogenation has been evaluated in a fixed-bed microreactor, and the activity of the alumina-supported catalysts was found to be higher than those supported on silica. However, alumina-supported catalysts in which the iron content exceeded ca. 27 atom % showed a gradual decrease in activity. At ca. 65 atom % this began to approach the activities of the silica-supported materials, which were generally less dependent on the iron content of the bimetallic phase. Catalysts with low metal loadings were more active than their counterparts with high metal loadings. These variations in catalytic activity have been interpreted in terms of the stronger interactions between the metallic phase and alumina, as compared with silica, supports and the smaller metallic particle sizes which are obtained on alumina.Metal–support interactions and particle dispersions have also been found to influence selectivity. Hence ruthenium, which interacts strongly with alumina, showed high activity and tended to form higher-molecular-weight hydrocarbons, whilst silica-supported ruthenium was less active and favoured the formation of lower hydrocarbons. The addition of iron to alumina-supported ruthenium shifted the product distribution towards lower hydrocarbons but had little influence on the selectivity of catalysts supported on silica.The variations in metal–support interaction which result from changes in the iron concentration and which are reflected in the catalytic properties of the solids have been correlated with the Mossbauer data, which showed the capacity of iron to donate electrons to ruthenium.