Mossbauer Spectral Parameters Research Articles

Iron(II) Bis-α-Benzyldioximate Complexes with 3- and 4-Pyridine Hemiacetals as Axial Ligands: Synthesis, Structure, and Physicochemical Properties

The coordination compounds [Fe(DfgH)2(HL1)2] and [Fe(DfgH)2(HL2)2], where DfgH = is the α-benzyldioxime monoanion, HL1 = 3-pyridine hemiacetals: methoxy(pyridin-3-yl)methanol (I), ethoxy(pyridin-3-yl)methanol (II); HL2 = 4-pyridine hemiacetal: methoxy(pyridin-4-yl)methanol (III), ethoxy(pyridin-4-yl)methanol (IV), and propoxy(pyridin-4-yl)methanol (V), were synthesized and studied by X-ray diffraction and IR and Mossbayer spectrosopy. According to X-ray diffration data (CIF files CCDC 1578217–1578221 for I–V, respectively), all of these Fe(II) complexes are molecular. The metal coordination polyhedron is an octahedron formed by four equatorial nitrogen atoms of two monodeprotonated α-benzyldioxime residues coordinated in the bidentate chelating fashion and by two axial nitrogen atoms of two neutral 3- or 4-pyridine hemiacetal molecules coordinated in the monodentate fashion. The DfgH– ligands in complexes I–V are joined by intramolecular O–H···O hydrogen bonds to form a pseudomacrocyclic system. The ligands HL1 and HL2 are generated in the reaction of the corresponding alcohols with 3- or 4-pyridinecarboxaldehyde. The IR and Mossbauer spectra of the products were studied. The Mossbauer spectral parameters of compounds I–V correspond to low-spin iron(II) ions.

Iron state in iron nanoparticles with and without zirconium

Mossbauer and X-ray methods are used for investigations of structure, stability and characteristics of pure-iron grain and two iron-zirconium alloys such as Fe + 5 wt.% Zr and Fe + 10 wt.% Zr. The used powder was ground for 24 h in a SPEX Model 8000 mill shaker. Complex nanoparticles are found, which change their properties under milling. Mossbauer spectral parameters are obtained for investigated materials. Milling results in formation of nanosized particles with two states of iron atoms: one main part is pure α-Fe and another part of iron atoms displaced in grain boundaries or defective zones in which hyperfine magnetic splitting decrease to ∼ 30.0 T. In alloys with Zr three iron states are formed in each alloy, main part of iron is in the form of α-Fe and another two states depend on the concentration of Zr and represent iron in grain boundaries with Zr atoms in nearest neighbor. The changing of iron states is discussed.

Structural features of hydrate forms of iron(III) oxalate

The existence of hydrate forms of iron(III) oxalate, which noticeably differ from each other in the Mossbauer spectral parameters (isomer shift and quadrupole splitting), is detected. In the assumption of the formation of phases with different structural characteristics, the samples of compound under study are examined by the powder X-ray diffraction analysis (including the application of synchrotron radiation), Mossbauer and IR spectroscopy. It is shown that the phase characterized by new values of the Mossbauer parameters has its own IR spectrum and it is X-ray amorphous and metastable.

Phenomenological simulation and density functional theory prediction of 57 Fe Mössbauer parameters: application to magnetically coupled diiron proteins

The use of phenomenological spin Hamiltonians and of spin density functional theory for the analysis and interpretation of Mossbauer spectra of antiferromagnetic or ferromagnetic diiron centers is briefly discussed. The spectroscopic parameters of the hydroxylase component of methane monooxygenase (MMOH), an enzyme that catalyzes the conversion of methane to methanol, have been studied. In its reduced diferrous state (MMOHRed) the enzyme displays 57Fe Mossbauer and EPR parameters characteristic of two ferromagnetically coupled high spin ferrous ions. However, Mossbauer spectra recorded for MMOHRed from two different bacteria, Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b, display slightly different electric quadrupole splittings (ΔEQ) in apparent contradiction to their essentially identical active site crystallographic structures and biochemical functions. Herein, the Mossbauer spectral parameters of MMOHRed have been predicted and studied via spin density functional theory. The somewhat different ΔEQ recorded for the two bacteria have been traced to the relative position of an essentially unbound water molecule within their diiron active sites. It is shown that the presence or absence of the unbound water molecule mainly affects the electric field gradient at only one iron ion of the binuclear active sites.

The relaxation dynamics, iron valence state, and Mössbauer effect in PFN ceramics

The dielectric properties, X-ray emission spectra, and Mossbauer effect in ceramics made of PbFe1/2Nb1/2O3 (PFN) compound were studied. The relaxation dynamics revealed above Curie temperature TC at a frequency of 3 × 10−2–105 Hz is described in detail. Analysis of the X-ray emission and Mossbauer spectra showed that at room temperature (T = 300 K), the iron ions in PFN are mainly in the high-spin valence state Fe3+. The Mossbauer spectral parameters obtained at T = (300, 353, and 393 K) indicate an octahedral environment for Fe3+ in both the ferroelectric and paraelectric phases.

A Second-Generation Janus Scorpionate Ligand: Controlling Coordination Modes in Iron(II) Complexes by Steric Modulation

The second-generation Janus scorpionate ligand [HB(mtda (Me)) 3] (-) (mtda (Me) = 2-mercapto-5-methyl-1,3,4-thiadiazolyl) with conjoined ( N, N, N-) and ( S, S, S-) donor faces has been prepared. This second-generation Janus scorpionate ligand [HB(mtda (Me)) 3] (-) differs from the first-generation [HB(mtda) 3] (-) ligand by the replacement of hydrogens on the heterocyclic rings proximal to the nitrogenous face with methyl groups. This study probed whether steric interactions introduced by such methyl group substitution could modulate the reactivity and coordination preferences of these ambidentate ligands. The crystal structures of a sodium complex Na[HB(mtda (Me)) 3].3(MeOH), the potassium complexes K[HB(mtda) 3].MeOH, and K 2[HB(mtda (Me)) 3] 2.3MeOH, and several iron complexes were obtained. The difference between first- and second-generation Janus scorpionate ligands is most obvious from the discrepancy between the properties and structures of the two iron(II) compounds with the formula Fe[HB(mtda (R)) 3] 2.4DMF (R = H or Me). The complex with the first-generation ligand (R = H) is pink and diamagnetic. An X-ray structural study revealed two facially coordinated kappa (3)N-scorpionates with no bound solvent molecules. The average Fe-N bond distance of 1.97 A is indicative of the low-spin t 2g (6)e g* (0) electron configuration. In contrast, the iron(II) complex of the second-generation ligand (R = Me) is yellow and paramagnetic. This structure shows two trans-kappa (1)S-scorpionates and four equatorial-bound DMF where the average Fe-O and Fe-S distances of 2.12 and 2.51 A, respectively, are indicative of the high-spin t 2g (4)e g* (2) electron configuration. The discrepancy in binding modes and spin-states of iron(II) is carried over to the solvent-free Fe[HB(mtda (R)) 3] 2 (R = H, Me) complexes, as determined from Mossbauer spectral studies. The Mossbauer spectral parameters for Fe[HB(mtda) 3] 2 are fully consistent with low-spin iron(II) in a FeN 6 environment, whereas those for Fe[HB(mtda (Me)) 3] 2 are most consistent with high-spin iron(II) in a FeS 6 environment. Interestingly, when either complex is dissolved in highly polar solvents (DMF, DMSO, or H 2O), the ligand completely dissociates forming [Fe(solvent) 6][HB(mtda (R)) 3] 2 (R = H, Me).

Use of Mössbauer spectroscopy to determine the effect of salinity on the speciation of triorganotins in Anacostia River sediments

The speciation of several tributyltin and triphenyltin compounds under varying salinity conditions (0, 20, 40 and 60%) was studied by Mossbauer spectroscopy in both anaerobic and aerobic Anacostia River sediments. The Mossbauer spectral parameters of the spiked sediments indicated that changes in the salinity did not affect the speciation of the tin compounds in either aerobic or anaerobic sediments.

Mössbauer, Crystallographic, and Density Functional Theoretical Investigation of the Electronic Structure of Bis-Ligated Low-Spin Iron(II) Phthalocyanines

We present the crystal structure of pcFe(4-methylpiperidine)2 as a first example of a low-spin iron(II) phthalocyanine (pc) complex bis-axially coordinated by aliphatic amines. It is shown that electronic rather than steric effects are responsible for the elongation of the Fe−N(axial) bond in pcFeL2 complexes. Using density functional theory, the electronic structures as well as Mossbauer isomer shifts and quadrupole splittings have been investigated for a large number of pcFeL2 and pcFeL1L2 complexes, in which the axial ligands have varying electronic and steric properties. The electron charge densities and electric field gradients at the iron ion were evaluated using a locally dense basis approach with Wachters’ all-electron basis set for the iron ion, the 6-311++G(2d) basis set for atoms directly bonded to the iron ion, the 6-31G(d) basis set for atoms two bonds away from the iron ion, and the 3-21G* basis set for all other atoms. A good correlation between the theoretical and experimental isomer shifts and quadrupole splittings has been observed for all the complexes tested. It has also been shown that the proposed model for the calculation of Mossbauer spectral parameters is adequate for the evaluation of the axial ligand conformation in cases of conformational flexibility in pcFeL2 complexes.

Synthesis, crystal structures, Mössbauer spectra, and redox properties of binuclear and tetranuclear iron-sulfur nitrosyl clusters

The iron-sulfur nitrosyl complexes A[Fe4S3(NO)7], where A=Na+, NH4 +, or N(Bu n )4 +, and B2[Fe2S2(NO)4], where B=Na+, Cs+, or N(Bun)4 +, were synthesized. Their structures and properties were studied by X-ray diffraction analysis, Mossbauer spectroscopy, and cyclic voltammetry. The effect of the crystal packing on the geometry of the tetranuclear NH4[Fe4S3(NO)7]·H2O and binuclear Cs2[Fe2S2(NO)4]·2H2O complexes was analyzed. The changes in the Fe57 Mossbauer spectral parameters of the anion in the B2[Fe2S2(NO)4] series depend on the size of the B cation and agree with variations in the structural parameters of the Fe[S2(NO)2] chromophores as well as in the stretching vibrations of the NO groups caused by changes in intermolecular contacts. The presence of electronic states delocalized through the Fe−Fe bonds explains the fact that the electronic states of the Fea(S3NO) and Feb(S2(NO)2) chromophores in the [Fe4S3(NO)7]− anion are nearly identical. The binuclear clusters are unstable upon storage in the solid phase and decompose in solutions to form the tetranuclear [Fe4S3(NO)7]− complexes, sulfur, and nitrogen oxides. The redox properties of the [Fe4S3(NO)7]− and [Fe2S2(NO4)]2− anions in CH3CN and THF solutions were studied. The mechanism of reduction of the anion in the tetranuclear cluster is proposed.

Molecular and crystal structure of the clathrochelate complex FeDm3(BF)2⋅C6H6 and parameters of its 57Fe Mossbauer spectra

The molecular and crystal structure of the macrobicyclic complex FeDm3(BF)2⋅C6H6 was established by X-ray diffraction analysis at 138, 208, and 291 K. The X-ray diffraction data were compared with the 57Fe Mossbauer spectral parameters of this complex in the temperature range of 135-290 K. A substantial disagreement between the experimental values of quadrupole splitting and the corresponding values calculated based on the concept of partial quadrupole splitting was attributed to the displacement of the Fe atom from the center of the cavity of the macrobicyclic ligand and to the distortion of the axial symmetry of the electron density distribution about the metal atom.

Solid State Dynamics of Fe3(CO)12 Revisited

An analysis of the temperature dependence of the Mössbauer spectral hyperfine parameters of Fe3(CO)12, in conjunction with recently reported temperature-dependent X-ray structural results, indicates different temperature dependences for the recoil-free fractions of the two iron sites, completely supports the presence of Goldanskii−Karyagin asymmetry in the Mössbauer spectra of this compound, and eliminates the possibility of 60° rotational disorder for the iron sites, at least on the Mössbauer time scale.

Identification of crystalline structures using Mössbauer parameters and artificial neural network

Mossbauer spectroscopy is a useful technique for characterizing the valencies, electronic and magnetic states, coordination symmetries and site occupancies of Fe cations. The Mossbauer parameters of Isomer Shift (I.S.) and Quadrupole Splitting (Q.S.) are useful to distinguish paramagnetic ferrous and ferric ions in several substances, while the internal magnetic field provides information on the crystallinity. A correlation is being sought between Mossbauer parameters and several structure properties of some iron-containing minerals using Artificial Neural Networks (ANN). Distinct regions of crystalline structures are defined when any two parameters are plotted, but in several cases superposition of these regions leads to erroneous conclusions. We have tried to eliminate this difficulty by using convenient axes. These axes form n-dimensional vectors as input to our ANN. In recent years ANN has shown to be a powerful technique to solve problems as pattern recognition, optimization, preview ups and downs in stock market, automatic control and identification of a mineral from a Mossbauer spectrum or Mossbauer data bank. Using ANN we have been successful in identification of crystalline structures from plots of Mossbauer spectral parameters of I.S., Q.S., and structure properties of mean metal-oxygen distance in coordination site. Results using ANN in identification of crystalline structures using Mossbauer parameters of I.S., Q.S., and polyhedral volume of a coordination site are presented.

Influence of heme periphery on the electronic structure and M�ssbauer parameters of hemoglobin

For the five-coordinated complexes of ferroprotoporphynynn with imidazole, a quantum-chemical analysis of the electronic structure and Mossbauer spectral parameters has been canied out. Peripheral substituents (―CH3, ―Cf13, ―C2H4COOH) were introduced into the porphynin macrocycle to model the real chemical structure of protopo'phynynn in the heme group of desoxyhemoglobin. The calculations have shown that near the occupation border in the complaes there are MO which are due to the π-systems of the ―CH= CM2 and ―CH2―CH2COOH substituents. The orientalion of the vinyl fragments has a considerable effect on the populations of the Fe d-orbitals and the quadrupole splitting ΔEQ for the5B1 and5B2 terns.

Mossbauer spectroscopic evidence of a IVFe3+ intermediate in the oxidation of Fe(Oh)2 to α-FeOOH

Mossbauer spectroscopy was used to study the oxidation of Fe(OH)2 under high pH conditions with the aim of detecting the formation of Fe(OH)3. The Mossbauer spectral parameters indicated that a small IVFe3+ component was initially present in the Fe(OH)2. The Mossbauer spectra were recorded at 77 K, thus any Fe species in solution would also be observed in the frozen state. The small IVFe3+ component increased progressively with the oxidation of the Fe(OH)2, maximizing with the onset of �-FeOOH formation. As �-FeOOH formation increased, the IVFe3+ component decreased, with �-FeOOH being the final sole phase. It is suggested that the Mossbauer spectral parameters indicate that a component such as Fe(OH)2 may form at high pH values as used in this study. Furthermore, any Fe3+ produced by the initial oxidation of Fe(OH)2 is exsolved from the solid and at the high pH of the surrounding liquid produces Fe(OH)-4 until the formation of the more stable �-FeOOH begins. This suggests Fe(OH)2 could be the building blocks for �-FeOOH in alkaline solution. No apparent Fe(OH)3 phase was observed as anticipated.

Mössbauer effect investigation of amorphous FeZr interlayers formed by solid state reaction

Recent investigations claimed the complete amorphization of elemental FeZr multilayer films by solid state reaction during vacuum annealing. In the present study it is established by57Fe conversion electron Mossbauer spectroscopy (CEMS) that annealing under ultrahigh vacuum conditions does not lead to complete amorphization: only a maximum thickness of ≈14 A interfacial α-Fe is transfered into the amorphous phase between 620–660 K. This thin amorphous layer apparently acts as a diffusion barrier and prohibits further growth of the amorphous phase. The average composition of the amorphous interfacial layer was determined from the Mossbauer spectral parameters.

M�ssbauer spectra of iron carbonyl complexes of aromatic azines and schiff bases

1. The nature of the substituents at the methylenimino group carbon atom does not have a significant effect on the Mossbauer spectral parameters of binuclear complexes of iron with nitrogen bridges not containing a nitrogen-nitrogen bond. 2. The ortho-metallated complexes obtained from Schiff bases and aromatic azines have two structurally nonequivalent iron atom positions.

M�ssbauer effect characterization and thermal transformations of Fe(III) ions co-precipitated with praseodymium trihydroxide

Mossbauer studies at+27 and−196° C on 5 wt % Fe(III) ions co-precipitated with praseodymium trihydroxide and subjected to annealing for 24h at 100, 350, 600, 725, 825 and 1100° C are reported. Variations in Mossbauer spectral parameters and the results of thermal analysis, infra-red spectroscopy, electron microscopy and X-ray diffraction (XRD) studies on the samples have been used to follow and to gain insight into the nature of thermal and microstructural processes that occur during phase transitions. In the co-precipitate, Fe ions exist as ferric oxide hydrate gel-like species. In samples annealed at 100° C Fe ions exhibit an increase in dispersion strengthening in the lattice while in samples annealed at 350° C they become somewhat labile due to disruption of lattice planes on dehydroxylation. In samples annealed at 600° C magnetically split sixline Mossbauer spectra are observed, which in agreement with XRD analysis and electron paramagnetic resonance studies indicate the precipitation of PrFeO3 microphases in Pr6O11. Annealing to higher temperatures finally leads to a pronounced agglomeration of iron microphases and the establishment of a better crystallized host lattice.

ChemInform Abstract: SYNTHESIS, MAGNETIC SUSCEPTIBILITY, AND SPECTROSCOPIC PROPERTIES OF SINGLE‐ AND MIXED‐VALENCE IRON OXALATE, SQUARATE, AND DIHYDROXYBENZOQUINONE COORDINATION POLYMERS

AbstractDie polymeren Fe(II)‐Komplexe (I) werden durch Reaktion von FeSO4°C 7 H2O bzw. FeC12°C 4 H2O mit den Säuren in wäßrig‐alkoholischer Lösung z.T. bei Zugabe von Pyridin oder Pyrazin dargestellt.(keine Ausb.‐Angabe).