Mössbauer studies of anion-substituted iron chlorophylls

The electronic structure of anion-substituted iron chlorophyll a [Fe(Chl-a)X] and b [Fe(Chl-b)X] (X=Cl^?, NCS^?, Br^?, I^?, CH₃COO^?) has been characterized by Mössbauer spectroscopy. The central iron ion in these complexes is in a ferric high-spin state. The π-donation from the anion plays an important role in the bonding between the iron ion and the anion. The quadrupole splitting reflects the structural difference between iron chlorophylls and iron porphyrins.     

Electric quadrupole interaction of 100Rh in antimony, hafnium and rhenium

The effects of the Mg(II)/Fe(III) ratio on the structure and Fe microenvironments in MgFe LDH substances were investigated. The LDHs were prepared by the co-precipitation method with Mg(II)/Fe(III) ratios from 2:1 to 6:1. The materials were characterized by ⁵⁷Fe Mössbauer spectroscopy and powder X-ray diffractometry. The ⁵⁷Fe Mössbauer spectra exhibited asymmetric doublet corresponding to high-spin Fe(III) microenvironments in all LDH structure. It was found that the quadrupole splitting decreased with increasing Mg(II)/Fe(III)ratio reflecting change in the electric field gradient due to the incorporation of different amounts of iron into the Mg-containing layers.     

Iron speciation of sediments from Kuhai Lake in China by Mössbauer spectroscopy

The vertical distribution of iron species in the sediments collected from Kuhai Lake was investigated in this study. Their Mössbauer spectra were composed of one sextet and four doublets ascribable to one paramagnetic high-spin Fe³⁺, two paramagnetic high-spin Fe²⁺ with different quadrupole splittings, and one diamagnetic low-spin Fe²⁺ that corresponds to pyrite (FeS₂). The distribution of pyrite was considered to reflect the climatic change during the past 2,000 years. Mössbauer spectroscopy was successfully applied to the analysis of the Kuhai Lake sediments so as to reconstruct the history of the past climate.     

Mössbauer Spectroscopic Study on Vertical Distribution of Iron Species in Sediments from Qinghai Lake,China

In this study, ⁵⁷Fe Mössbauer spectroscopy has been applied to sediments collected from Qinghai Lake in Qinghai Province, China, to investigate the vertical distribution of iron species. Their Mössbauer spectra consisted of four doublets ascribable to one paramagnetic high-spin Fe³⁺, two paramagnetic high-spin Fe²⁺ with different quadrupole splittings, and one diamagnetic low-spin Fe²⁺ that corresponds to pyrite (FeS₂). The distribution of pyrite suggested climatic changes during the past nine thousand years. It was demonstrated that the iron speciation in the salt lake sediments by Mössbauer spectroscopy can be used to reconstruct the past environment.

     

Mössbauer and calorimetric studies of portland cement hydration in the presence of black gram pulse

Effect of different concentrations of naturally occurring admixture in the form of fine powder of black gram pulse (BGP) on the hydration of Portland cement was studied by isothermal calorimetry and ⁵⁷Fe Mössbauer spectroscopy. The spectra were recorded for anhydrous cement and the hydration products at room temperature and 77 K. In the presence of BGP, the spectra showed superparamagnetic doublets at room temperature and the sextet at 77 K, due to the presence of fine particles of iron containing component. Mössbauer studies of hydration products confirmed the formation of nanosize hydration products containing Fe^3?+?. The isomer shift (δ) and the quadrupole splitting (ΔE _Q) values of C₄AF in the cement confirmed iron in an octahedral and tetrahedral environment with +3 oxidation state. The high value of quadrupole splitting showed the high asymmetry of the electron environment around the iron atom. The overall mechanism of the hydration of cement in presence of BGP is discussed.     

Spectroscopic and structural investigations of the ferrous and ferric high-spin state of a “picket—fence” porphyrinato acetato iron complex. A refined model for the P460 center of hydroxylamine oxidoreductase

Mössbauer investigations were performed in the ferrous and ferric form of the ‘picket-fence’ porphyrinato acetato iron complex |Fe(CH₃CO₂) (TP_pivP)|^1?,0 at temperatures varying from 1.5–200K and in fields of 0–6.2T. The ferrous complex has an unusually large quadrupole splitting, ΔE_Q=+4.25mms^?1. The quadrupole splitting in the ferric species, ΔE_Q=+1.1mms^?1, is as normally found in ferric high-spin iron porphyrins. Spin-Hamiltonian analysis of the magnetic spectra yields zero-field parameters D=?0.9mms^?1, E/D=0.33 and magnetic hyperfine parameters A_x,y=?17T, A_z=?13.3T in the ferrous high-spin (S=2) complex, and D=7.5cm^?1, E/D≈0 and A_x,y,z=20T in the ferric high-spin (S=5/2) species.     

57Fe Mössbauer study under high pressure; ε-Fe and Fe2O3

Using diamond anvil cell, the⁵⁷Fe Mössbauer spectra of pure iron foil and α-Fe₂O₃ powder under high pressure have been measured at room temperature.⁵⁷Fe Mössbauer spectra of α-Fe were measured from 15 GPa to 45 GPa. Isomer shift value decreased and the quadrupole splitting slightly increased as the pressure increased.⁵⁷Fe Mössbauer spectra of Fe₂O₃ under high pressure up to 72 GPa were observed. Above 52 GPa, the new lines appeared at the center portion of the spectrum corresponding to the new high pressure phase. The spectrum of new high pressure phase consisted of 6-line splitting and doublet, suggesting the existence of the two different kinds of iron states in it.     

Synthesis and properties of NaFeGe<Subscript>2</Subscript>O<Subscript>6</Subscript> polycrystals

NaFeGe₂O₆ polycrystals were synthesized and their x-ray diffraction, magnetic, electrical, and Mössbauer characteristics were measured. It is established that this monoclinic compound is a dielectric with a temperature of antiferromagnetic ordering of 15 K. The Mössbauer spectrum at 300 K is a quadrupole doublet. The isomer shift is 0.40 mm/s, which is characteristic of the high-spin Fe³⁺ ion in the octahedral coordination. The quadrupole splitting is 0.34 mm/s, which indicates that the oxygen octahedron around the iron cation is distorted. The exchange interactions are estimated, and the crystal magnetic structure is discussed.     

On the structure and Mössbauer spectra of ferrous nitroprusside

Monoclinic ferrous nitroprusside trihydrate and its dehydration products have Mössbauer spectra composed of two quadrupole doublets. The quadrupole splitting of the high-spin ferrous cation decreases stepwise as the compound loses water up to the anhydrous state. Cubic ferrous nitroprusside has a complex Mössbauer spectrum with three quadrupole doublets for high-spin ferrous cations, which are determined by the number of water molecules in its environment. The Mössbauer parameters of low-spin ferrous cations in ferrous nitroprusside are practically independent of its hydration degree and crystalline structure.     

Complexes based on ethylene- and propylene-bridged-pentadentate-Fe(III)-units allow interplay between magnetic centers and multistability investigated by Mössbauer spectroscopy

The propylene-based ⁵3,3-L?=?[N,N′-Bis(1-hydroxy-2-benzylidene)-1,7-diamino-4-azaheptane] and ethylene-based pentadentate ligand ⁵2,2-L?=?[N,N′-Bis(1-hydroxy-2-benzylidene)-1,5-diamino-3-azapentane] has been prepared. Complexation with Fe(III) yields high-spin (S?=?5/2) complexes of [Fe^III(⁵2,2-L)Cl] and [Fe^III(⁵3,3-L)Cl]. Such precursors were combined with [M(CN) _x ] ^y? (M?=?W(IV), Mo(IV), Ru(II), Co(III)) and heptanuclear and nonanuclear clusters of [M{(CN-Fe^III(⁵2,2-L)} _x ]Cl _y and [M{(CN-Fe^III(⁵3,3-L)} _x ]Cl _y resulted. Such starshaped hepta- and nonanuclear compounds are high-spin systems at room temperature. On cooling to 20 K in all presented ethylene compounds the iron(III) centers switch to a second high-spin state as proven by Mössbauer spectra with a yield of about 30%, i.e., multiple electronic transitions. The propylene compounds, however, perform a high-spin to low-spin transition. Mössbauer spectra taken during green light irradiation indicate changes in the population of the different electronic states, i.e. concerted inorganic reaction.     

Quadrupole Splitting Distributions in Grandidierite and Kornerupine from Antarctica

The Mössbauer spectra of grandidierite and kornerupine at 298 and 90 K were measured. The quadrupole splitting distributions from the Mössbauer spectra were obtained by using the Voigt-based method, and the assignments for QSDs in the Mössbauer spectra of both minerals are presented. Site occupancies of iron in the crystal structures of two minerals were determined, and the chemical formulas of grandidierite and kornerupine were rewritten based on the relative absorption areas and Mössbauer fraction f for Fe³⁺ and Fe²⁺.     

Low temperature 151Eu and 57Fe Mössbauer study of mechanically alloyed EuFeO3

Low temperature ⁵⁷Fe Mössbauer spectra of mechanically alloyed EuFeO₃ prepared by mechanical alloying depicts an interesting transformation in its hyperfine magnetic state, from a triple phase magnetic system at room temperature to a single phase ferromagnetic state at 20 K. The hyperfine magnetic field increased by 12% at 20 K from its room temperature. The isomer shift and quadrupole splitting values exhibit a peak around 200 K. Low temperature ¹⁵¹Eu Mössbauer measurements show that the line-width increased to its maximum value at 80 K which is 45% compared to its room temperature value not enough to suggest splitting.     

Variable temperature Mössbauer spectroscopic studies of oxo-centered trinuclear mixed-valence iron succinate, mesaconate and isophthalate complexes

Three new oxo-centered trinuclear mixed-valence iron complexes, iron succinate, iron mesaconate and iron isophthalate have been prepared. Temperature dependent valence delocalization processes were observed for all the complexes on variable temperature Mössbauer spectroscopic studies. Two clear quadrupole split doublets attributed to high-spin Fe(III) and high-spin Fe(II) states were existed for the complexes at liquid nitrogen temperature. At room temperature a nearly averaged singlet peak was observed for mesaconate complex and averaged doublet peaks were observed for succinate and isophthalate complexes with IS values 0.68 and 0.68 mms^?1 and QS values 0.44 and 0.48 mms^?1 respectively.     

Magnetic properties of a quasi-one-dimensional NaFeGe<Subscript>2</Subscript>O<Subscript>6</Subscript> polycrystal

The magnetic properties of a synthesized dielectric NaFeGe₂O₆. polycrystal have been studied. The antiferromagnetic ordering of this compound below 15 K has been established. The Mössbauer spectrum at 300 K is a quadrupole doublet; it is characterized by an isomeric shift typical of the high-spin Fe³⁺ ion in the octahedral coordination and quadrupole splitting, which indicates distortion of the oxygen octahedron around the iron cation. Quasi-one-dimensionality of the sample magnetic structure is proved.     

Mössbauer spectroscopic study on (Eu1−x Gd x )FeO3

Europium gadolinium ferrites (Eu_1?xGd_x)FeO₃ (X=0, 0.2, 0.4, 0.6, 0.8) are synthesized. The results of the X-ray diffraction show that all the compounds possess a perovskite structure. Both the¹⁵¹Eu Mössbauer spectra and the⁵⁷Fe Mössbauer spectra are measured. The¹⁵¹Eu Mössbauer spectra are considered to be the pure quadrupole spectra. The results show that the isomer shift and the quadrupole splitting of the¹⁵¹Eu spectra vary with x. The hyperfine filed of the⁵⁷Fe Mössbauer spectrum depends on the unit-cell volume. The⁵⁷Fe spectra of the samples synthesised by the high-pressure and high-temperature mothod show a part of paramagnetic structure.     

Relaxation as seen by nuclei: Comparison between conventional Mössbauer spectra and nuclear resonant scattering of synchrotron radiation

The mechanism of spin‐lattice relaxation has been investigated in the “picket‐fence” porphyrin [Fe(CH₃COO)(TP_pivP)]^-, a high‐spin iron(II) complex with unusual large quadrupole splitting of 4.25 mm s^-1, by conventional Mössbauer spectroscopy as well as by nuclear resonant forward scattering (NFS). Superparamagnetism with a blocking temperature of about 8 K is observable by both methods in the spectra of bacterioferritin from S. olivaceus. From these two examples general conclusions about the merits of both methods can be drawn.     

Mössbauer study of cobalt and iron in the cyanobacterium (blue green alga)

Mössbauer emission and absorption studies have been performed on cobalt and iron in the cyanobacterium (blue-green alga). The Mössbauer spectrum of the cyanobacterium cultivated with⁵⁷Co is decomposed into two doublets. The parameters of the major doublet are in good agreement with those of cyanocobalamin (vitamin B₁₂) labeled with⁵⁷Co. The other minor doublet has parameters close to those of Fe(II) coordinated with six nitrogen atoms. These suggest that cobalt is used for the biosynthesis of vitamin B₁₂ or its analogs in the cyanobacterium. The spectra of the cyanobacterium grown with⁵⁷Fe show that iron is in the high-spin trivalent state and possibly in the form of ferritin, iron storage protein.     

Multiplet splittings and other properties from density functional theory: an assessment in iron–porphyrin systems

In transition metal compounds with spin states close in energy, the magnitude and sign of the energy splitting calculated with density functional theory depends strongly on the functional used. Therefore we must turn to additional criteria to assess the level of accuracy and reliability of predictions based on this level of theory. We report optimized geometries, total energies, and Mössbauer quadrupole splitting values for low-spin and high-spin, ferric and ferrous model hemes using a variety of gradient-corrected and hybrid functionals. In one model, the iron–porphyrin is axially ligated by two strong-field imidazole ligands [FeP(Im)₂] and has a low-spin ground state. In the other model complex the axial ligands are two weak-field, water molecules [FeP(H₂O)₂], and have a high-spin ground state. Among all the functionals used (UHF, B3LYP, B3LYP*, BLYP, half-and-half, LSDA), the B3LYP hybrid functional most consistently reproduced the experimental geometry, Mössbauer, and spin state data for the two model hemes. Simply gradient-corrected functionals exhibit strong biases towards low spin states, while Hartree–Fock favours strongly high spin states. These findings suggest that for systems with similar characteristics of several accessible electronic spin configurations, it is imperative to include properties other than just the energy in the assessment of the DFT predictions.     

Distribution of hyperfine fields of57Fe2+ in amorphous LiNbO3: Mössbauer study at low temperatures in high magnetic fields

Mössbauer spectra of amorphous LiNbO₃ doped with⁵⁷Fe²⁺ ions were measured atT≥4.2 K in external magnetic fields up toH=5.5 T. It was found that the oxygen octahedra around the high-spin Fe²⁺ ions are randomly distorted obeying no symmetry at all. The correlation of isomer shift and quadrupole splitting is probably due to T_2g distortions.