Mossbauer Quadrupole Splitting Research Articles

119Sn Mössbauer spectroscopy of the time-resolved evolution of SnCl3− ligand structure on the surface of growing platinum nanoparticles

The importance of stabilizing ligands cannot be understated for the colloidal synthesis of nanoparticles as well as their dispersion and assembly into macro-structures such as electrodes. We have recently demonstrated a novel all-inorganic ligand approach to Pt nanoparticle synthesis where surface-adsorbed Sn serves as both reducing agent and stabilizing ligand, producing remarkably monodispersed nanoparticles. By eliminating the need to remove organic surfactants prior to nanoparticle incorporation into electrodes, we were able to use electrostatic assembly to achieve well-defined nanoparticle dispersions in contrast to the aggregated structures common in the field. The approach has allowed us to elucidate the nature of structure sensitivity for electrocatalytic oxygen reduction reaction in acidic and alkaline media. In this paper, we provide a detailed investigation of the evolution of surface-adsorbed Sn-Pt ligand interaction during Pt nanoparticle growth. We show that surface adsorbed SnCl3− exists as pyramidally coordinated to the Pt nanoparticle through Sn-Pt bond formation, resulting in a distorted tetrahedrally coordinated Sn-moiety. Furthermore, we show the shift in the bond charge distribution as the Pt is reduced from its initial Pt2+ state to its metallic state. Direct evidence for the distorted tetrahedral coordination of Pt-SnCl3− and the shift in Sn-Pt bond charge during nanoparticle growth emerges from the 119Sn Mossbauer quadrupole splitting (QS) and Isomer-shift (IS) respectively. Evolution of the structure and chemistry of inorganic complexes during nanoparticle growth has never before been demonstrated and our work is the first to identify the strength of the Sn-Pt interaction in these systems. Such an understanding of nanoparticle surface chemistry will permit extension of this technique to other metals and macro-structures.

A study of the pressure vessel steel of the WWER-440 unit 1 of the Kozloduy nuclear power plant

A comparison between highly neutron irradiated samples from the region of weld № 4 and low irradiated samples from weld № 1 taken from the pressure vessel of the WWER-440 Unit № 1 of the Kozloduy NPP has been performed. Measurements of the residual activity of samples from the outer surface of the reactor pressure vessel bottom corpus reveal very low activity of 60Co. Insofar as there the base and weld metal appear to be exposed to a very low neutron fluence, the samples from these locations can be considered as practically not affected and may serve as a reference basis for comparison with highly irradiated pressure vessel regions. The Mossbauer parameters isomer shift (IS) and quadrupole splitting (QS) were found to be absolutely irradiation insensitive. A stepwise reduction of the internal hyperfine magnetic field Bhf, each by about 2.6 T, was observed. This can be attributed to the replacement of one or two surrounding iron atoms as first nearest neighbors by non-iron alloying atoms. The Mossbauer experimental line widths for irradiated and non-irradiated samples are practically the same, which is a quite unexpected result. The area fraction ratio for the three main Zeeman sextet subspectra S1:S2:S3 shows very high irradiation sensitivity. For the bottom low irradiated region of the reactor vessel the values are S1:S2:S3 = 50.1:40.0:9.4. After seven years of operation between the pressure vessel annealing in 1989 and the autumn of 1996 when the samples from weld № 4 were taken the ratio changes strongly to S1:S2:S3 = 56.4:34.7:8.5. A possible explanation of this result is that neutron irradiation gives rise to a precipitation process involving predominantly alloying atoms as Ni, Mn, Cr, Mo and V which become mobile and precipitate in the form of carbides and/or P-rich phases and alloying atom aggregates. This “refinement” process lowers the partial area of subspectra S2 and S3 where alloying atoms are involved and leads to a higher area fraction of the pure iron component S1, which is the major experimental result. For a more complete Mossbauer investigation on the processes of generation of structure defects caused by the neutron fluence, a new series of measurements will be performed by using a set of so-called surveillance specimens with different irradiation histories which are available only for the WWER-1000 reactors of the Kozloduy NPP.

Temperature dependences of the hyperfine parameters of Fe2+in FeTiO3as determined by57Fe-Mössbauer spectroscopy

The temperature variations of the ferrous Mossbauer parameters for a synthetic ilmenite (FeTiO 3 ) have been determined and interpreted over a very wide temperature range (5–900 K). The Debye model of the lattice vibrations was used in interpreting the temperature dependence of the center shift, yielding a characteristic Mossbauer temperature of 350 ± 20 K and a zero-Kelvin intrinsic isomer shift of 1.30 ± 0.01 mm/s. The temperature dependence of the ferrous Mossbauer quadrupole splitting was interpreted using crystal field theory. A most adequate description of the experimental Δ E Q ( T ) curve was obtained assuming an energy shift of at the most ca. 500 ± 50 cm −1 for the highest orbital T 2g level relative to the lowest level within this T 2g triplet. The temperature dependence of the hyperfine field was interpreted within the molecular field theory of magnetism assuming the magnetic exchange energy being a function of interatomic spacing, indicating a first-order magnetic transition at the magnetic-paramagnetic transition temperature of 59.0 ± 0.5 K. This detailed presentation of Mossbauer parameters as a function of temperature can serve as a basis for easily detecting ilmenite ore at, for example, the lunar surface and for monitoring by means of Mossbauer spectroscopy the reduction process of the mined mineral, for the purpose of supplying a future Moon base site with oxygen and water.

Mössbauer, NMR, Geometric, and Electronic Properties in S = 3/2 Iron Porphyrins

Iron porphyrins with the intermediate spin S = 3/2 or admixed with S = 5/2 or 1/2 are models for a number of heme protein systems, including cytochromes c'. The (57)Fe Mossbauer quadrupole splittings and (1)H and (13)C NMR chemical shifts have been found to be useful probes of their electronic states. We present the results of the first successful quantum chemical calculations of the Mössbauer and NMR properties in various S = 3/2 iron porphyrin complexes, covering four-, five-, and six-coordinate states and three commonly seen porphyrin conformations: planar, ruffled, and saddled. Several interesting correlations among these useful experimental spectroscopic probes and geometric and electronic properties were discovered. These results should facilitate future investigations of related heme proteins and model systems.

Aluminum-Doped Perovskites As High-Performance Oxygen Permeation Materials

Previously unreleased compositions of (Ba0.5Sr0.5)(Fe1−xAlx)O3−δ perovskites in the range of 0≤ x ≤ 0.2 were synthesized and studied with respect to electronic and crystallographic structure, as well as oxygen permeation. The perovskite phase in all synthesized oxides was found to be cubic, without any impurities for aluminum fractions in the range x = 0.01−0.09. Electron energy-loss spectroscopy (EELS) revealed a significant amount of covalency by Fe-3d−O-2p hybridization and a mixed Fe3+ /Fe4+ valence state of iron for all synthesized perovskites, which was quantified by Mossbauer spectroscopy. Trivalent aluminum replaces a higher fraction of Fe4+ than of Fe3+ while both iron species are in high-spin state. The Mossbauer quadrupole splittings indicate a greater disorder around iron with increasing aluminum content and, together with the EELS result of an abatement of covalent character in the bonding of iron and oxygen, the observed lattice expansion can be understood. In situ XRD and TG/DTA measurement...

Mössbauer study of tektites

Room temperature 57Fe Mossbauer spectroscopy has been used to investigate the structural and oxidation state of Fe in tektites from different strewn fields. Spectra have been analyzed in terms of two quadrupole splitting distributions corresponding to Fe3 + and Fe2 + . All tektites show similar distribution of quadrupole splitting. Each distribution has one peak. The Fe2 + sites show a narrow region of Mossbauer line shift (δ) and quadrupole splitting (e), δ = 1.02–1.10 mm/s and e = 0.85–1.00 mm/s relative to α-Fe. These values have been assigned to intermediate coordination between tetrahedral and octahedral. The Fe3 + sites show wider regions of hyperfine parameters: δ = 0.25–0.45 mm/s and e = 0.65–0.90 mm/s. The Fe3 + /Fe2 + ratio was found to be 0.05–0.15.

Effects of pH on the speciation of several triorganotin compounds in Anacostia River sediments using Mössbauer spectroscopy

The effects of pH on the speciation of some tributyltin and triphenyltin compounds in spiked sediments from the Anacostia River were studied. The compounds included tributyltin chloride, oxide, and acetate as well as triphenyltin chloride, hydroxide, and acetate. Mossbauer spectroscopy was used to measure the speciation of the triorganotin compounds in the spiked sediments. In general, for the three pHs (5, 7, and 9) studied, the Mossbauer parameters, quadrupole splitting, and isomer shift, varied depending upon the sediment site and the pH. The ρ-values (ratio of quadrupole splitting to isomer shift), which indicate the co-ordination of the tin atom, were greater than 2.1 in all cases, indicating that the co-ordination around the tin atoms in all the spiked sediments is greater than four. The variation in the Mossbauer parameters with pH at different sites in the Anacostia River reflects the variation in the components of the sediments.

Crystallographic report: Bis(triphenyltin) oxalate

AbstractThe centrosymmetric structure of bis(triphenyltin) oxalate contains essentially four‐coordinated tin and monodentate carboxylate moieties despite a Mössbauer quadrupole splitting of 2.8 mm s−1 and a 119Sn NMR chemical shift of −503 ppm. Copyright © 2003 John Wiley & Sons, Ltd.

57Fe Mössbauer Quadrupole Splittings and Isomer Shifts in Spin-Crossover Complexes: A Density Functional Theory Investigation

We report the results of density functional theory (DFT) calculations of the 57Fe Mossbauer quadrupole splittings ΔEQ and isomer shifts δFe of both the high-spin (HS) and low-spin (LS) states of tw...

Synthesis, properties and Mössbauer spectra of bisaxially co-ordinated iron(II) phthalocyanine low-spin complexes: the first semi-quantitative explanation of the influence of the character of axial ligands on the spectral parameters †

A series of bisaxially co-ordinated low-spin iron(II) phthalocyanine complexes (pc)FeL2 with different types of nitrogen bases as axial ligands has been prepared and characterised by electronic, 1H NMR and Mossbauer spectroscopies. The influence of electronic and steric effects of the axial ligands on Mossbauer quadrupole splitting (ΔEQ) and isomer shift (δ), NMR parameters, and metal-to-ligand charge transfer (MLCT) band position are discussed. Mossbauer partial quadrupole splitting (p.q.s.) and partial isomer shift (p.i.s.) parameters for different ligands have been estimated and rationalised with the overall data for (pc)FeL2 and (nx)2FeL2 (nx = nioxime) complexes. A semi-empirical AM1 method and the cone angle concept were used to factorise σ- and π-electronic and steric effects of the ligands. A good correlation between the predicted and experimental MLCT band position of (pc)FeL1L2 complexes, as well as predicted and experimental p.i.s. and p.q.s. values for different ligands, has been observed.

Studies of the bonding in iron(II) cyclopentadienyl and arene sandwich compounds. Part 5. An interpretation of the 57Fe Mössbauer spectroscopic data of dibromoborylferrocenes, and related molecules

Abstract The Mossbauer spectroscopic parameters of three dibromoboryl ferrocenes and of a related dichloroboryl ferrocene are reported. The results are discussed in relation to the known crystal structures, the Mossbauer parameters and the correlation of the latter with Hammet substituent constants. These data are also compared with those of other ferrocenes that form ferrocenyl carbocations (–CR 2 + is isoelectronic with –BX 2 where X=halogen) as well as protonated ferrocenyl ketones. It is concluded that normal ferrocenyl carbocations, though nominally isoelectronic with the similarly substituted dibromoboryl ferrocenes, bond in a very different manner involving a change in structure where the two cyclopentadienyl rings are no longer parallel. However, the protonated ferrocenyl ketones show Mossbauer quadrupole splittings that are similar to those of the dibromoboryl ferrocenes; this is interpreted to suggest that the former cations have significant carbocationic character and parallel cyclopentadienyl rings. The nature of the Fe–B interactions are discussed in terms of the overall C–B bonding, particularly in the case where four dihaloboryl groups are present.

'Tg-.DELTA. Rule' Applied to Semiconducting Vanadate Glasses Containing Different Amounts of Fe2O3.

‘Tg-Δ rule’, i.e., a linear relationship between the glass transition temperature (Tg) and the Mossbauer quadrupole splitting (Δ), is applied to semiconducting 10K2O⋅(90-x)V2O5⋅xFe2O3 and 25K2O⋅(75-x)V2O5⋅xFe2O3 glasses (henceforth denominated glass A and B, respectively). Slopes of the straight lines obtained from the plot of Tg vs. Δ (i.e., 685 and 690°C (mm·s-1)-1 for glass A and glass B, respectively) imply that the Fe(III) atoms substitute tetrahedral V(IV) or V(V) atoms and play a role of network former. Both Tg and Δ values increase with the Fe2O3 content, suggesting that Fe(III) causes an increase in the distortion of VO4 tetrahedra. Fourier-transform infrared (FT-IR) spectra prove that Fe(III) does not essentially change the network structure. These experimental results are discussed together with the ‘Tg-Δ rule’ that was recently applied to aluminate, gallate and borosilicate glasses.

Mössbauer spectra of tin(IV) iodide complexes

The first examples of compounds containing the [SnR2I3]– anion, i.e. [Bun4N][SnR2I3] (R = Me or Ph), have been prepared and characterized by IR, Raman and 119Sn Mossbauer spectroscopies, and X-ray powder diffraction data. The experimental data are consistent with a trigonal bipyramidal structure, with the R groups in equatorial positions, for the [SnR2I3]– anions. Octahedral [SnR2I4]2– anions could not be isolated and it is shown that the previously reported [Bun4N]2[SnMe2I4] is actually a 1∶1 mixture of Bun4NI and [Bun4N][SnMe2I3]. The X-ray powder structure of Cs2SnI6 has been refined by the Rietveld method. The compound crystallises in the cubic Fm3m space group with a = 11.6410(3) A and a Sn–I distance of 2.864(1) A. The Sn–I distances in Cs2SnI6, SnI4(bipy), SnI4(Ph3PO)2 and SnI4(Ph2SO)2 are related to the Mossbauer quadrupole splitting, showing that ligands that are weaker donors than I– (i.e. have a more positive partial quadrupole splitting) give rise to Sn–I distances that are shorter than for the [SnI6]2– anion.

Correlating Mössbauer and Solution- and Solid-State 117Sn NMR Data with X-ray Diffraction Structural Data of Triorganotin 2-[(E)-2-(2-Hydroxy-5-methylphenyl)-1-diazenyl]benzoates

A series of R3SnO2CR' compounds, where R = Me (1), Et (2), Bu-n (3), Ph (4), and cHex (5) and R'CO2 is the carboxylate residue of 2-[(E)-2-(2-hydroxy-5-methylphenyl)-1-diazenyl]benzoic zoic acid, has been shown by multinuclear magnetic resonance studies to be monomeric in solution. Crystallography shows that monomeric four-coordinate species are found in the solid state for 4 and 5 but polymeric structures with five-coordinate tin atoms are found for 1-3. The different behavior is ascribed to the steric demands of the tin-bound substituents. A fair correlation is found between the difference in Sn-117 chemical shift between the solution and solid states and the carbonyl oxygen-tin distance of the compounds 1-5, only when the data of 4, R = Ph, are omitted. This indicates that the mesomeric effect of the phenyl group does not express its influence to the same extent in the solid and solution states, unlike the inductive effects. By contrast, a good correlation including 4 is found between the Mossbauer quadrupole splitting and the difference in Sn-117 chemical shift between the solution and solid states. This shows that the nature of the organic group on the tin atom contributes to similar extents to the values of the Sn-117 chemical shifts in solution and solid state, independently of the existence or not of mesomeric effects, and that the parallel behavior of QS and Sn-117 chemical shifts is geometry independent.

Electric Field Gradients at 57Fe Nuclei in the Sr3Fe2Ge4O14 Trigonal Germanate

A computation of the lattice electric field gradient tensor at the octahedral and tetrahedral Fe 3+ sites in the Sr 3 Fe 2 Ge 4 O 14 trigonal germanate is performed, taking into account the fractional ionic charges provided by the valence summation procedure. The correlation of the calculated Mossbauer quadrupole splittings with those found experimentally shows the role of the local environment distortion in the quadrupole interaction of iron nuclei in this structure.

Molecular orbital calculation of Mössbauer parameters for Sn(CH3)nH4−n (n=0, 1, 2, 3) and their photoproducts in low temperature matrices

Mossbauer parameters of tin compounds, Sn(CH3)2H4−n (n=0, 1, 2, 3, 4), isolated in low temperature matrices were related to electronic properties at the tin nuclei obtained by molecular orbital calculations. Structures of novel species, Sn(CH3)2 and Sn(CH3)H, produced via photodissociation of matrix-isolated Sn(CH3)3H and Sn(CH3)2H2, respectively, were determined on the basis of molecular orbital calculations as compared with Mossbauer parameters. The correlations between Mossbauer quadrupole splitting and calculated electric field gradient using STO-3G or MINI-4 were found to depend on the valence of tin atoms because of poor allowance for basis sets in describing highly polar molecules.

A correlation between mossbauer quadrupole splittings and 57Fe NMR chemical shifts of diamagnetic iron(II) porphyrinates

A correlation between mossbauer quadrupole splittings and 57Fe NMR chemical shifts of diamagnetic iron(II) porphyrinates

Molecular orbital calculation of Mössbauer parameters for tin compounds in low temperature matrices

Mossbauer parameters of tin compounds, Sn(CH3)nCl4−n (n=0, 1, 2, 3, 4), isolated in low temperature matrices are correlated with electronic properties at the tin nuclei obtained by molecular orbital calculations. The Mossbauer isomer shift and quadrupole splitting show good correlation with electron density and electric field gradient estimated by molecular orbital calculations, respectively. Structures of novel species (Sn(CH3)2CH2 and [Sn(CH3)2CH2]2) produced via photodissociation of Sn(CH3)4 in low temperature matrices were estimated by means of molecular orbital calculations as compared with Mossbauer parameters.

Tin-119 Mössbauer and nuclear magnetic resonance studies of organotin compounds. Part 2. Sterically crowded organotin halides and carboxylates

Tin-119 Mossbauer and 119Sn NMR data have been obtained for a number of novel organotin halides and carboxylates containing bulky organic ligands (adamantyl, triptycyl). The Mossbauer spectra are discussed in terms of distortions from tetrahedral geometries as a result of steric crowding. The largest distortions occur for the adamantyl derivatives. A detailed study of 119Sn NMR shifts revealed correlations with Mossbauer quadrupole splittings and with the electronegativities of the ligands concerned. The crystal structure of (E)-(but-2-enyl)triphenyltin was determined: triclinic, space group P, with a= 9.892(3), b= 10.196(4), c= 11.637(5)A, α= 107.16(2), β= 103.40(2), γ= 109.77(2)°. The crystals are composed of discrete non-interacting molecules. The structure was refined to R= 0.035 and R′= 0.043. The geometry around the tin centres is only slightly distorted from tetrahedral with bond angles ranging between 107.5(2) and 112.8(2)°, average 109.5°. The Sn–C(but-2-enyl) bond is significantly longer than the three Sn–C(phenyl) bonds. The structure is compared to those of other similar compounds.

Studies of the bonding in iron(II) cyclopentadienyl and arene sandwich compounds. Part 2. Correlations and interpretations of carbon-13 and iron-57 nuclear magnetic resonance and iron-57 mössbauer data

Carbon-13 NMR data for [Fe(η-C5H5)(η-C5H4X)] and [Fe(η-C5H5)(η-C6H5X)]+ and 57Fe NMR data for neutral substituted ferrocenes, ferrocenyl carbenium ions and ferrocenophanes have been analysed and correlations between these data sets and those of the 57Fe Mossbauer quadrupole splitting (q.s.) are discussed on the basis of concepts put forward previously. For substituted neutral ferrocenes there is a linear relationship between q.s. and chemical shift δ(57Fe). For ferrocenyl carbenium ions the relationship suggests a change in structure and bonding from species like [Fe(η-C5H5)(η-C5H4[graphic omitted]CMe2)] to the more fulvenoid structure [Fe(η-C5H5)(C5H4CH2)]+. Bridged ferrocenes (ferrocenophanes) show effects which are associated with ring tilting.