On Mössbauer effect in polypyrrole doped with selected metal halides

The reaction of partially oxidized polypyrrole [(C₄H₃N)₄⁺Cl₋]_n with FeCl₃ and SnCl₄ leads to the insertion of only one type metal halide species namely FeCl₄⁻ and SnCl₅⁻. The reaction with stannic halide is acid-base in nature whereas the reaction with ferric chloride may be either redox or acid-base. The use of SbCl₅ results in the insertion of two non-equivalent antimony halide species: SbCl₆⁻ and SbCl₃. Much simpler Mössbauer spectra can be obtained if in the doping reactions SbCl₅ or SbF₅ are replaced by NO₂⁺SbF₆⁻. Only one type of antimony with Mössbauer parameters characteristics of SbF₆⁻ is observed in this case. The Mössbauer lattice temperatures, θ_M, calculated from the temperature dependence of the recoil free fractions are 94 K and 105 K for FeCl₃ and SnCl₄ doped polypyrrole respectively. The obtained values are within the range typically observed for other conducting polymeric systems.     

Isotope-selective laser photodetachment for 129I accelerator mass spectrometry

2D coordination polymer iron(II) spin crossover complexes containing 3,5-lutidine with host framework Fe(3,5-lutidine)₂Ni(CN)₄were synthesized. Their spin crossover properties were studied by temperature dependent ⁵⁷Fe Mössbauer spectroscopy. Materials show gradual incomplete spin crossover with distinct thermochromism, while only 25 % of iron(II) ions are switched to the low spin state at 80 K, as determined by a detailed ⁵⁷Fe Mössbauer study.     

Magnetic and Mössbauer studies of cyanide-bridged bimetallic assembly [Mn(cyclam)][Fe(CN)6]·3H2O

Cyanide-bridged bimetallic assembly [Mn(cyclam)][Fe(CN)₆]·3H₂O (cyclam=1,4,8,11-tetraazacyclotetradecane) was synthesized from the reaction of trans-[MnCl₂(cyclam)]Cl with K₃Fe(CN)₆. A linear chain structure consisting of alternating [Mn(cyclam)]³⁺ and [Fe(CN)₆]³⁻ units was indicated by the IR and Mössbauer spectra. The variable-temperature magnetization and Mössbauer measurements revealed that this complex exhibited a long-range ordering below 6.8 K. The magnetic behavior of the complex was based on intrachain ferromagnetic and interchain antiferromagnetic interactions.     

Low spin Fe(IV) arising from electron transfer in a mixed-valence compound: A Mössbauer study

Co(en)₃Fe(CN)₆ a mixed-valence compound, where ‘en’ corresponds to ethylene diamine, exhibits a heteronuclear charge transfer between iron and cobalt ions; both the ions being in oxidation state III. An ⁵⁷Fe Mössbauer investigation confirms the creation of the rare species Fe(IV) as a result of charge transfer.     

Correlation between Mössbauer isomer shifts and XPS binding energies

A series of low-spin pentacyanoferrates (‖) of the type Na₃[Fe-(CN)₅L] (L = phosphine or phosphite) have been characterized by⁵⁷Fe Mössbauer spectroscopy and X-ray photoelectron spectroscopy. The Fe?P bond in Na₃[Fe(CN)₅L] is discussed in terms of a correlation between the isomer shift and the binding energy. It has been demonstrated that the isomer shift increases with the decreasing Fe2p_3/2 binding energy. The Mössbauer isomer shift reflects the total electron density at the nuclear site, while the chemical shift in the binding energy is concerned with the electron density on the atom of interest. The increasing Fe-to-P back donation leads to an increase of the s-electron density at the iron nucleus, i.e. a decrease of the isomer shift. The increasing tendency in the Fe2p_3/7 binding energy is interpreted by the increasing Fe-to-P back donation.     

Mössbauer,EPR and susceptibility studies of highly conducting polypyrrole doped with iron chloride

The results of Mössbauer, EPR and static magnetic susceptibility measurements on polypyrrole doped with FeCl₃ are presented. They indicate that iron chloride tetrahedra are interacting with the polymer matrix by hydrogen bonding. This interaction increases with dehydration of the samples. The susceptibility showed a maximum near 5 K, which is an indication for antiferromagnetic interaction, probably between paramagnetic iron and polarons.     

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.

     

Study of the FeII ion role in the magnetic properties of the AFM ring Cr7Fe using Mössbauer spectroscopy

In recent years the synthesis of antiferromagnetic rings traced a path to the observation of interesting quantum coherence phenomena in heterometallic Single Molecule Magnets. Because of the presence of different magnetic centers, it is crucial to understand the distribution of the molecular spin on all the sites. ⁵⁷Fe Mössbauer spectroscopy is an efficient and powerful technique to contribute to this knowledge in antiferromagnetic wheels containing iron ions. We analyze the Cr₇Fe^II wheel: the Mössbauer line shape evolution of low temperature spectra (2.1 K) at different external fields is illustrated and the mean spin value of the iron ion is evaluated.     

Effect of FeCl3 and acetone on the structure of Na–montmorillonite studied by Mössbauer and XRD measurements

⁵⁷Fe Mössbauer spectroscopy, X-ray diffraction, X-ray fluorescence spectroscopy and infrared spectroscopy were used to study the effect of FeCl₃ and acetone on the structure of a Na–bentonite. XRD indicated the incorporation of Fe³⁺ ions into the interlayer space since the basal lattice spacing of montmorillonite increased to 1.6 from 1.24 nm after treatment with FeCl₃ dissolved in acetone. Interlayer Na⁺ ions could be exchanged to Fe³⁺. Magnetically split Mössbauer subspectra with internal magnetic fields 41 and 46 T at 74 K, were associated with two main Fe³⁺ microenvironments within the interlayer regions. The resultant Fe–montmorillonite was successfully applied as a catalyst in the preparation of 1,1-diacetates from aromatic aldehydes and acetic acid anhydride.     

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.     

Alignment of iodine species in stretched polyacetylene films

The¹²⁹I Mössbauer spectroscopy has been applied to iodine-doped highly conducting polyacetylene. For the unstretched polyacetylene films, the iodine species of I^?, I ₃ ^? and I ₅ ^? are observed. The polyiodides have symmetrical charge population. In addition to these anions, a small amount of iodines is covalently bonding to the carbon atoms, breaking the double bonds of the main chain. For the stretched polyacetylene films, the measurements were done under the condition that the stretch direction was parallel or perpendicular to the direction of incident ψ-rays. The relative change of the intensities of the Mössbauer quadrupole-split lines reveals the alignment of the polyiodine anions in the stretched film.     

Effect of particle size and alloying with different metals on 57Fe Mössbauer spectra

Iron nanoparticles of various sizes have been synthesized using the chemical route which involves the preparation of iron bipyridine complexes in presence of different capping agents followed by thermal decomposition at 450°C in inert atmosphere. The bimetallic nanoalloys of Fe with Mg and Pd have also been prepared by following the same route. The resulting nanoparticles have been characterized by EDX-RF, XRD, AFM and ⁵⁷Fe Mössbauer spectroscopy. The appearance of quadrupole doublets in the Mössbauer spectra of Fe nanoparticles indicates the absence of magnetic interaction and variation in parameters is due to the varying particle size. The Mössbauer spectrum of Fe–Mg₂ bimetallic nanoalloy shows two doublets indicating the presence of superparamagnetism. The two doublets can be attributed to change in s-electron density of iron resulting from its two neighboring magnesium atoms. Fe–Pd nanoalloy Mössbauer spectrum is characterized by having a superparamagnetic doublet and a ferromagnetic sextet.     

Mössbauer study of Tl containing highT c superconductors

Mössbauer spectroscopy, X-ray diffractometry, ESR and electrical resistivity measurements, were used to study highT _c (above 100 K) superconducting materials in order to get information about the effect of the preparation circumstances as well as about the anomalous behaviour in⁵⁷Fe and¹¹⁹Sn doped TlBaCaCu(⁵⁷Fe)O_4.5+δ and TlBaCuCu(¹¹⁹Sn)O_4.5+δ superconductors. We have found that the Mössbauer parameters strongly depend on the preparation circumstances. In many cases the presence of Mössbauer lines of nonsuperconducting oxide phases indicated that the iron and tin could not entirely built in into the lattice of superconductor. Four valence state tin and four valence state iron sites were identified in the superconducting phases. We have found anomalous temperature dependent changes in the⁵⁷Fe Mössbauer spectra of TlBaCaCu(⁵⁷Fe)O_4.5+δ samples around theT _c between 105–135 K. In this temperature range the total area of the spectrum temporary increases.     

Mössbauer Studies of Nanosize CuFe2O4 Particles

⁵⁷Fe Mössbauer spectra of pulsed-laser deposited (PLD) films of CoFe₂O₄ of 0.3 µm thickness is investigated using transmission geometry is reported. Mössbauer parameters were determined for the tetrahedral (A) and octahedral (B) sites. The PLD processed films gave measurable spectra with no visible evidence of clustering or multiple phases present. Results on the films agreed with those of the bulk material. The films exhibited magnetic hyperfine and quadruple splittings similar to that of bulk CoFe₂O₄. This work demonstrates that measurable transmission Mössbauer spectra may be obtained for PLD deposited CoFe₂O₄ thick films.     

A study of the system Ag3−xTlxFe(CN)6, (x =0, 1, 2, 3) by Mössbauer spectroscopy

The ferricyanides Ag_3−xTl_xFe(CN)₆, (x = 0, 1, 2, 3) have been measured by Mössbauer spectroscopy. The results indicate a negative EFG for all samples except for x = 1, that is positive. The isomer shift for Tl₃Fe(CN)₆ is the more negative, indicating a strong contribution from the empty p-orbitals of Tl⁺ ions.     

Localisation of iron ions in NH4,Na-Y zeolite: A Mössbauer effect study

Localisation of Fe ions in deep-bed treated NH₄,Na-Y zeolite at 830K, 940K, and 1050K, as well as after reduction by hydrogen, and dealumination with subsequent calcination is studied by⁵⁷Fe Mössbauer spectroscopy. Most of the incorporated iron is present in the form of octahedrally coordinated ferric species with two distinct sets of hyperfine parameters assigned to atoms inside the zeolite structure and in extraframework positions. Fe²⁺ ions with high coordination are also detected and their amount increases with the temperature of deep-bed treatment. Low-temperature Mössbauer effect measurements at 77K and 4.2K were employed to facilitate the identification of iron sites.     

Use of X-ray photoelectron and Mössbauer spectroscopies in the study of iron pentacyanide complexes

A number of iron pentacyanide complexes of the Na_itn [Fe(CN)₅X] type have been synthesized. The compounds have been examined by X-ray photoelectron (ESCA) and Mössbauer spectroscopies. The influence of the nature of ligand X upon the properties of iron- (II) pentacyanide complexes has been studied. The donor properties of dinitrogen as a ligand have been compared with those of other nitrogen-containing ligands. A correlation has been established between the ESCA and Mössbauer data.     

Mössbauer study of SnO<Subscript>2</Subscript> powders doped with dilute <Superscript>57</Superscript>Fe prepared by a sol-gel method

SnO₂ powders, doped with various ⁵⁷Fe contents were prepared by a sol-gel method, and annealed finally at 500 °C and 650 °C. These samples were characterized by Mössbauer spectroscopy, vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) to investigate the relationship of magnetic properties, grain sizes, annealing temperatures and Mössbauer parameters. The particle sizes of SnO₂ powders reduced to less than 100 nm with the increase of Fe contents up to 5%. Rutile SnO₂ was the only phase obtained for all samples. Room temperature Mössbauer spectra suggest the presence of two different paramagnetic iron sites for all samples and one magnetically relaxed species for those samples with the lowest iron concentrations. The magnetization increased with the Fe content, but was reduced for the samples annealed at 650 °C perhaps due to a segregation of α-Fe₂O₃ doped with tin.     

In situ Mössbauer spectroscopic study of iron III chloride intercalated in graphite under reaction conditions

In situ⁵⁷Mössbauer spectroscopy has been used to study the process of reduction and Fischer-Tropsch reactions on FeCl₃ intercalated in graphite layers. It is found that on flowing H₂ on graphite intercalated by FeCl₃ at 400° C, FeCl₃ converts to FeCl₂ and partly to small particles of α-Fe. The Mössbauer spectra of the reduced sample are superposition of a sextuplet and two quadrupole doublets indicative of metallic iron and two species of FeCl₂. However, at room temperature and at 400° C for a short period of reduction the magnetic hyperfine splittings (ca. 295 kOe and 262 kOe respectively) are smaller than the corresponding parameters for bulk metallic iron. The differences have been attributed to the interaction between the monolayers of iron atoms and the carbon nets of the graphite support. When the reduction was carried out for a longer period, α-Fe was formed. When a sample reduced for a short period of time is heated at 400°C in the presence of the synthesis gas, part of the iron particles sinter, and α-iron is observed. On heating the above sample once again at 400°C in the presence of the synthesis gas, the remaining small particles of iron are totally converted to the bulk phase (α-Fe). Experimental observations indicate that α-Fe and FeCl₂ are present on the surface as well as inbetween the intercalated graphite layers.     

New Hofmann-like spin crossover compound with 3,5-lutidine

A new type III of 3,5-lutidine spin crossover coordination compound with formula Fe(3,5-lutidine)₂Ni(CN)₄·2[(H₂O)(3,5-lutidine)] 2c has been obtained. The ratio of the high spin state (HS) iron (II) changing to the low spin state (LS) iron (II) in 2c is higher than that of type I and type II 3,5-lutidine coordination polymer 2a and 2b previously reported. ⁵⁷Fe Mössbauer spectra of 2c show two different doublets which correspond to HS1 (inner doublet lines) and HS2 (outer doublet lines). The intensity of the HS1 doublet decreases on cooling to 80 K while the intensity of another component, the LS singlet, increases. The 90 % of the HS1 doublet change to the LS singlet is probably due to suitable environments of octahedral iron (II) ions coordinated by four nitrogen atoms of cyano groups and two nitrogen atoms of 3,5-lutidine ligands. We also prepared the Hofmann-like 3,5-dichloropyridine coordination compound Fe(3,5-dichloropyridine)₂Ni(CN)₄ ·2[(3,5-dichloropyridine)(H₂O)] 2d to compare it with 2c. ⁵⁷Fe Mössbauer spectra of 2d show that 2d is not a spin crossover coordination compound.