The prediction of the nuclear quadrupole splitting of 119Sn Mössbauer spectroscopy data by scalar relativistic DFT calculations

The electric field gradient components for the tin nucleus of 34 tin compounds of experimentally known structures and (119)Sn M?ssbauer spectroscopy parameters were computed at the scalar relativistic density functional theory level of approximation. The theoretical values of the electric field gradient components were used to determine a quantity, V, which is proportional to the nuclear quadrupole splitting parameter (DeltaE). In a subsequent linear regression analysis the effective nuclear quadrupole moment, Q, was evaluated. The value of (11.9+/-0.1) fm(2) is a significant improvement over the non-relativistic result of (15.2+/-4.4) fm(2) and is in agreement with the experimental value of (10.9+/-0.8) fm(2). The average mean square error DeltaE(calcd)-DeltaE(exptl)=+/-0.3 mm s(-1) is a factor of two smaller than in the non-relativistic case. Thus, the approach has a quality which provides accurate support for the structure interpretation by (119)Sn spectroscopy. It was noted that geometry optimization at the relativistic level does not significantly increase the quality of the results compared with non-relativistic optimized structures. The accuracy in the approach called on us to consider the singlet-triplet state nature of the electronic structure of one of the investigated compounds.     

Variable-temperature 119Sn Mössbauer study of tin phthalocyanines

Variable-temperature ¹¹⁹Sn Mössbauer spectroscopic (VTMS) data for six tin phthalocyanine (pc) derivatives have been collected in order to ascertain the restrictions imposed by the macrocyclic ring on the vibrational motion of the tin atom. Thermal condensation of [(t-Bu)₄pc]Sn(OH)₂ yields the co-facially stacked polymer {[(t-Bu)₄pc]SnO}_n which can be distinguished in the VTMS experiment by the enhanced rigidity of its structure.     

Structural applications of the 119Sn Mössbauer quadrupole splitting of tin tetrahalide complexes

A correlation is reported between the Mössbauer quadrupole splitting and the values for νSnCl (from vibrational spectra) for cis-octahedral tin tetrachloride complexes. It is shown that resolved doublets in the Mössbauer spectra of some octahedral tin (IV) halide adducts are consistent with a cis configuration, so that structural assignments based on the resolvable or unresolvable nature of the Mössbauer quadrupole splitting must be taken with considerable caution.     

119Sn Mössbauer spectroscopy of Sn–O nanoparticles prepared by levitation-jet aerosol synthesis

Sn–O nanoparticles were prepared by levitation-jet aerosol synthesis and found to exhibit ferromagnetic behavior. X-ray powder diffraction analysis and ¹¹⁹Sn Mössbauer spectroscopy confirmed these nanoparticles consist of β-Sn, SnO and SnO₂ phases. The maximum specific magnetization was observed for nanoparticles containing the SnO/SnO₂ interface.     

Surface oxidation of tin chalcogenide nanocrystals revealed by 119Sn-Mössbauer spectroscopy

Narrow band gap tin(II) chalcogenide (SnS, SnSe, SnTe) nanocrystals are of high interest for optoelectronic applications such as thin film solar cells or photodetectors. However, charge transfer and charge transport processes strongly depend on nanocrystals' surface quality. Using (119)Sn-M?ssbauer spectroscopy, which is the most sensitive tool for probing the Sn oxidation state, we show that SnS nanocrystals exhibit a Sn((IV))/Sn((II)) ratio of around 20:80 before and 40:60 after five minutes exposure to air. Regardless of the tin or sulfur precursors used, similar results are obtained using six different synthesis protocols. The Sn((IV)) content before air exposure arises from surface related SnS(2) and Sn(2)S(3) species as well as from surface Sn atoms bound to oleic acid ligands. The increase of the Sn((IV)) content upon air exposure results from surface oxidation. Full oxidation of the SnS nanocrystals without size change is achieved by annealing at 500 °C in air. With the goal to prevent surface oxidation, SnS nanocrystals are capped with a cadmium-phosphonate complex. A broad photoluminescence signal centered at 600 nm indicates successful capping, which however does not reduce the air sensitivity. Finally we demonstrate that SnSe nanocrystals exhibit a very similar behavior with a Sn((IV))/Sn((II)) ratio of 43:57 after air exposure. In the case of SnTe nanocrystals, the ratio of 55:45 is evidence of a more pronounced tendency for oxidation. These results demonstrate that prior to their use in optoelectronics further surface engineering of tin chalcogenide nanocrystals is required, which otherwise have to be stored and processed under inert atmosphere.     

Influence of intermolecular interactions on the Mössbauer quadrupole splitting of organotin(IV) compounds as studied by DFT calculations

The influence of intermolecular interactions on the M?ssbauer quadrupole splitting (Delta) of 119Sn was investigated in detail by density functional theory (DFT) calculations. Six organotin(IV) complexes [Me2Sn(acac)2 (1), Ph3SnCl (2), Me3Sn-succinimide (3), Me3Sn-phthalimide (4), Me3SnCl (5), and cHex3SnCl (6)] of known solid-state structures and quadrupole splittings were selected. Theoretical Delta values were calculated for both fully optimized geometries and experimental solid-state structures of different size, and the results were compared to the experimental Delta values. Compared to a synthetic procedure described in the literature for compound 4, a more convenient synthesis is reported here. The experimental Delta of this compound has also been redetermined at 80 K. For compounds with negligible intermolecular interactions in the solid state, calculated Delta values obtained did not vary significantly. In contrast, the calculated Delta values turned out to be very sensitive to the size of the supramolecular moiety considered in the crystal lattice. The crystal structure of compound 2 shows no significant intermolecular interactions; however, the calculated and the experimental Delta values remained very different, even when the supramolecular moiety considered was extended. Distortion of the coordination sphere of tin in the molecule of 2 toward a trigonal bipyramidal geometry was considered, and a possible weak intermolecular Sn...Cl interaction was included in the model. Steps of the distortion followed the new structure correlation function, which was found for the R3SnCl (R=alkyl, aryl) compounds. The experimental Delta value could be approached by this method. These results suggest that compound 2 is involved in some unexpected intermolecular interaction at 80 K.     

Solid-state 119Sn NMR and Mössbauer spectroscopy of "distannynes": evidence for large structural differences in the crystalline phase

The "distannynes" Ar'SnSnAr' (Ar' = C6H3-2,6(C6H3-2,6-Pr(i)2)2) and ArSnSnAr (Ar = C6H3-2,6(C6H2-2,4,6-Pr(i)3)2) were examined by solid-state (119)Sn NMR and M?ssbauer spectroscopy. The two compounds display substantially different spectroscopic parameters, while differing only in the absence (Ar'SnSnAr') or presence (ArSnSnAr) of a para-Pr(i) group in the flanking aryl rings of their terphenyl substituents. The spectroscopic differences can be interpreted in terms of a more trans-bent geometry and a longer Sn-Sn bond for ArSnSnAr in comparison to the wider Sn-Sn-C angle (125.24(7) degrees ) and shorter Sn-Sn bond length (2.6675(4)A) determined from the crystal structure of Ar'SnSnAr'. The differences are consistent with previously published calculations by Nagase and Takagi for ArSnSnAr.     

119Sn Mössbauer spectroscopic insight into the effect of surface-located tin dopant cations on the visible-light photocatalytic activity of anatase TiO2

The presence of Sn⁴⁺ dopant ions on the surfaces of titania crystallites results in a nearly fourfold increase in the rate constant of a white-light photocatalytic bleaching reaction of methyl orange. Thus, the positive effect of a Sn^II electronic lone pair, which was theoretically predicted in 2013 by Iwaszuk and Nolan for a SnO-nanocluster modified anatase model, can be experimentally revealed using catalyst powders containing surface-located oxidized Sn⁴⁺ species.     

The rearrangement of the defect structure of magnetite in a vortex magnetic field according to the Mössbauer spectroscopy data

The rearrangement of the defect structure of ferrosoferric oxide Fe₃O₄ (magnetite) was studied by Mössbauer spectroscopy after treatment in a vortex magnetic field. The experimental dependence of the degree of structure imperfection of magnetite s on the duration of treatment in a magnetic field t _MF was obtained. The s(t _MF)function nonmonotonically oscillated over the range 0–100 s and experienced a relaxation transition to a new constant value, which was larger at t _MF ～ 300 s. The conclusion was drawn that very fast complex processes occurred in the crystal structure in a magnetic field, which caused irreversible changes in the defect structure of magnetite.     

Applications of Mössbauer spectroscopy to the study of electronic materials

A brief introduction to the methodology of the Mössbauer spectroscopy will be given. The main applications to the study of the intrinsic properties of the materials employed in the electronic technology are reviewed.The reported examples prove the effectiveness of this techniques in the study of semiconducting and magnetic materials.Evidence will be given also to the studies of preparation processes of crystalline and amorphous compound.     

Mn doping on Mössbauer spectroscopy of maricite-NaFePO4 as cathode material

Journal of Radioanalytical and Nuclear Chemistry - Transition metal ion substitution in sodium phosphate is effective in enhancing the performance of a cathode material. The...     

Successful location of tin dopant cations on surface sites of anatase-type TiO2 crystallites evidenced by 119Sn Mössbauer spectroscopic probe and XPS techniques

The present study provides the first experimental evidence for the stabilization of tin dopant cations immediately on the surface of an oxide having a tetragonal structure. ¹¹⁹Sn Mössbauer spectra of the dopant, introduced by air annealing into the bulk of anatase microcrystals, showed that it was located, in the tetravalent state, in somewhat distorted octahedral sites of a unique type. On the contrary, the reduced tin species, formed upon subsequent hydrogen annealing the Sn⁴⁺-doped samples, are found to occupy different sites being characterized by two sets of the isomer shift δ and quadrupole splitting ΔE_Q values (δ_I = 3.25 mm s⁻¹, ΔE_QI = 1.75 mm s⁻¹; and δ_II = 2.85 mm s⁻¹, ΔE_QII = 1.71 mm s⁻¹). Either of them implies both the divalent state of tin atoms and their presence at low-coordination sites that can be assigned to the surface of crystallites. Mössbauer spectra of Sn^4+←2+ daughter ions, formed upon contact with air of Sn²⁺, consist of a symmetrically broadened peak characterized by only slightly different average values of both the isomer shift (<δ> = 0.07 mm s⁻¹) and quadrupole splitting (<ΔE_Q> = 0.50 mm s⁻¹), as compared to the δ and ΔE_Q values for the bulk-located Sn⁴⁺. However, considerable broadening of Sn^4+←2+ doublet components (Γ = 0.97 mm s⁻¹) allows one to suggest that these secondary formed ions remain distributed over the non equivalent sites inherited from their Sn²⁺ precursors. The occurrence of Sn^4+←2+ at surface sites is independently proven by XPS measurements that revealed a greater than 10-fold enrichment with tin of 3–5 nm thick surface layers.     

Coprecipitation of iron and platinum(IV) hydroxo complexes as probed by Mössbauer spectroscopy

Stabilization of ⁵⁷Fe compounds in matrices of solid solutions of platinum(IV) superoxo- and hydroxo complexes was probed by Mössbauer spectroscopy. The ratio Fe^III/Fe^IV in these matrices is 20/1.     

Characterization of iron promoter in tungstated zirconia catalysts by Mössbauer spectroscopy at very low temperatures

A tungstated zirconia (WZ) catalyst with iron promoter used for the conversion of n-pentane into isopentane has been characterized by M?ssbauer spectroscopy. The M?ssbauer spectra have been recorded in zero magnetic field in the temperature range 0.05-295 K and with a magnetic field up to 7 T between 4.2 and 50 K. Both the recording of M?ssbauer spectra with an applied magnetic field and at extremely low temperature allowed for the demonstration that iron is present in the catalysts as (i) hematite (alpha-Fe2O3) particles a few 10 nm in size, (ii) very small oligomeric Fe(III) species, probably in solid solution in zirconia, and (iii) Fe(III) oxide clusters showing magnetic ordering, probably embedded in the first surface layer and thus forming "rafts". These latter clusters form two ensembles with quite different sizes: one with diameters of about 3 nm, the other with diameters larger than 30 nm. These results are in agreement with those recently obtained by X-ray absorption spectroscopy and electron paramagnetic resonance.     

Degradation of passive layers of iron studied by conversion electron Mössbauer spectroscopy

Integral electron Mössbauer spectroscopy (ICEMS) and additionally some electrochemical methods were used to characterize the passivation process of iron (low carbon steel) in sulfate, sulfate+sulfite (a possible model solution of acid rain) solutions and in phospate buffer. The phase compositions and thicknesses of the passive layers formed due to the electrochemical polarizations were analyzed in dependence on the duration of the anodic passivations and on the pH of the used electrolytes. The passive layer, as determined from the Mössbauer spectra, consists mainly of -FeOOH, however in sulfite containing sulfate aqueous solution at pH 3.5 Fe₃C and despite ex-situ circumstances FeSO₄·H₂O was detected after the shortest polarization time. The film thickness, which was found to grow nearly linearly with polarization time in pure sulfate solution and in phospate buffer, reached a maximum of 60–160 nm (depending on pH) in sulfate+sulfite solution after a passivation time of about 4 hours. It has been proved, that HSO₃ ^–-ion, which is contained by acid rain, initiate pit formation under acid conditions and so enforces the corrosion of iron. The experimental results furthermore suggest, that not the whole oxidic layer is responsible for the passivity but only a very thin intermediate layer formed between an inner oxide layer of a cubic structure and the rhombic oxide (-FeOOH) cover.     

<Superscript>119</Superscript>Sn Mössbauer study of the influence of a gas atmosphere on the valence state and distribution of tin atoms in the MgO structure

Analysis of the Mössbauer spectra of dopant ¹¹⁹Sn in cubic MgO has demonstrated that the Sn²⁺ ions can be stabilized on the surface of crystallites of an oxide with a structure differing from the corundum structure. The Mössbauer parameters (at 100 K, the isomer shift is δ = 2.50 ± 0.01 mm/s and the quadrupole splitting is Δ = 2.30 ± 0.02 mm/s) point to the stereochemical activity of the lone pair of Sn²⁺. Being in contact with oxygen at 295 K, tin is rapidly converted to the tetravalent state (δ = 0.08 ± 0.01 mms, Δ = 0.58 ± 0.01 mm/s). The lack of formation of Sn²⁺ on the surface of another cubic oxide (MnO) can be explained by rapid segregation of tin from the bulk of crystallites as stannate clusters.     

Application of the Mössbauer spectroscopy to the study of the oxidation state of azaferrocene derivatives

Azaferrocene has two active sites of iron and nitrogen atoms. Drastic change of the oxidation state in iodine oxidation of azaferrocene is observed by introducing the methyl substituents into the pyrrole ring, while all the N-methylates show a similar electronic state. It was revealed that an introduction of methyl substituent to the pyrrole ring promotes the oxidation of nitrogen atom in pyrrole ring more than the central iron atom.