Theoretical interpretation of Mössbauer spectra of 19Sn compounds

Experimental Mössbauer spectra of a series of Sn(II) and Sn(IV) compounds are interpreted in terms of MO theory. On the basis of the self-consistent charge (SCC)-X-MO method electronic charge densities (0) and electric field gradients V _zz at the ¹¹⁹Sn nucleus are computed and related with experimental isomer shifts and quadrupole splittings E _q. From this correlation values for the fractional change R/R in the nuclear charge radius and for the nuclear quadrupole moment Q of ¹¹⁹Sn are obtained as R/R=1.61 · 10^–4 and Q=–0.0615b, respectively. The results of our MO calculations indicate that large isomer shift differences in ¹¹⁹Sn compounds are due to a lone-pair MO, which exists in Sn(II) compounds but is absent in Sn(IV) compounds. This lone-pair MO causes an increase mainly in the 5s orbital population, resulting in a large electronic charge density (0). Furthermore, our results show the limits of the applicability of simple electrostatic models or phenomenological schemes to the interpretation of the experimental data when different coordination numbers of Sn are involved.     

Mössbauer and NMR characterization of tin octoate: Neat and residues in RTV foams

We have investigated hydrolysis and oxidation effects on tin octoate and on tin-octoate residues in RTV polysiloxane foams by means of Nuclear Magnetic Resonance (NMR) and Mössbauer spectroscopy (MS). ¹¹⁹Sn NMR showed the presence of various tin species whereas ¹¹⁹Sn MS detected the presence of two oxidation states: Sn(II) and Sn(IV). The relative abundance of Sn(IV) increased as both the tin octoate and the foam aged. Foams were also solvent extracted and no selective extraction of one tin oxidation state was observed; both oxidation states were detected. ¹³C NMR indicated that octanoic acid is present in the tin octoate and in the foams as a residue. MS data showed that aging treatments of the foams and of the neat catalyst have a great effect on the tin oxidation state. The two spectroscopic methods complement each other in following the effects of hydrolysis and oxidation.     

Characterization by X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy of a new alluaudite-like phosphate:: Na4CaFe4(PO4)6

A single crystal of a new sodium calcium iron (III) phosphate, Na₄CaFe₄(PO₄)₆, has been synthesized by a flux method and characterized by X-ray diffraction, Mössbauer spectroscopy and magnetic susceptibility measurements. The compound crystallizes in the monoclinic space group C2/c(a=12.099(5) Å, b=12.480(5) Å, c=6.404(2) Å, β=113.77(3)°, Z=2, R₁=0.022, R_w2=0.066). The crystal structure belongs to the alluaudite type, characterized by the X(2)X(1)M(1)M(2)₂(PO₄)₃ general formula. The open framework results from Fe₂O₁₀ units of edge-sharing FeO₆ octahedra, which alternate with M(1)O₆ octahedra (M(1)=Na+Ca) that form infinite chains. These chains are linked together through the common corners of PO₄ tetrahedra yielding two distinct tunnels of sodium cation occupation. This compound is antiferromagnetic with a Néel temperature of 35 K. Mössbauer parameters are consistent with the structural results.     

A comparative study of the magnetic properties and phase separation behavior of the rare earth cobaltates, Ln0.5Sr0.5CoO3 (Ln=rare earth)

A comparative study of the magnetic properties of a few members of the Ln_0.5Sr_0.5CoO₃ family with different radii of the A-site cations, 〈r_A〉, in the range 1.19-1.40 Å has been carried out. The apparent T_c (where the magnetization undergoes an abrupt increase) decreases markedly with 〈r_A〉 as well as the size-disorder arising from the mismatch in the size of the A-site cations. The value of the magnetization at low temperatures decreases markedly with decrease in 〈r_A〉 or increase in size-disorder, suggesting that the relative proportion of the ferromagnetic (FM) species decreases relative to that of the paramagnetic (PM) species. Such a variation of the FM/PM ratio with composition and temperature is evidenced from the Mössbauer spectra of La_0.5Sr_0.5CoO₃ as well. The variation of the FM/PM ratio with 〈r_A〉 and size-disorder, as well as a local-probe study using ⁵⁹Co Nuclear magnetic resonance spectroscopy suggest that electronic phase separation is an inherent feature of the Ln_0.5Sr_0.5CoO₃ type cobaltates, with the nature of the different magnetic species in the phase-separated system varying with 〈r_A〉 and size disorder.     

Structural study by X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy of the Na2Mn2(1 − x)Cd2xFe(PO4)3 (0 ≤ x ≤ 1) solid solution

Na₂Mn_{2(1 − x)}Cd_2xFe(PO₄)₃ (0 ≤ x ≤ 1) phosphates were prepared by solid state reaction and characterized by powder X-ray diffraction, magnetic susceptibility and Mössbauer spectroscopy. The X-ray diffraction patterns indicated the formation of a continuous solid solution which crystallizes in the alluaudite structural type characterized by the general formula X(2)X(1)M(1)M(2)₂(PO₄)₃. The cation distribution, deduced from a structure refinement of the x = 0, 0.5 and 1 compositions, is ordered in the X(2) sites and disordered in the remaining X(1), M(1) and M(2) sites. The magnetic susceptibility study revealed an antiferromagnetic behaviour of the studied compounds. The ⁵⁷Fe Mössbauer spectroscopy confirmed the structural results and proved the exclusive presence of Fe³⁺ ions.     

Mössbauer, NMR and ATR-FTIR spectroscopic investigation of degradation in RTV siloxane foams

The combination of experimental techniques allowed for a comprehensive study of aging processes occurring in RTV siloxane foams. ¹¹⁹Sn Mössbauer spectroscopy demonstrated that tin residues are composed of Sn(II) and Sn(IV) species. The 27-year-old foams showed only Sn(IV) species with a quadrupole-splitting parameter larger than that observed for SnO₂. Solid-state ²⁹Si NMR differentiated between the various functional linkages in the foams, and showed no significant change of the di- to trifunctional linkage ratios. High-resolution NMR, on solvent extract of foams, showed the presence of water, catalyst, plasticizer, and some silicone oligomers. ATR-FTIR demonstrated changes near the surface of the foam when aged with water and with the presence of the tin catalyst. Gamma irradiation at a low dose had little effect on compression sets. The main changes observed for artificially aged and aged in service foams were related to the presence of the tin catalyst.     

Aluminium substitution in iron(II-III)-layered double hydroxides: Formation and cationic order

The formation and the modifications of the structural properties of an aluminium-substituted iron(II-III)-layered double hydroxide (LDH) of formula (OH)₁₂ SO₄, 8H₂O are followed by pH titration curves, Mössbauer spectroscopy and high-resolution X-ray powder diffraction using synchrotron radiation. Rietveld refinements allow to build a structural model for hydroxysulphate green rust, GR(SO₄²⁻), i.e. y=0, in which a bilayer of sulphate anions points to the Fe³⁺ species. A cationic order is proposed to occur in both GR(SO₄²⁻) and aluminium-substituted hydroxysulphate green rust when y<0.08. Variation of the cell parameters and a sharp decrease in average crystal size and anisotropy are detected for an aluminium content as low as y=0.01. The formation of Al-GR(SO₄²⁻) is preceded by the successive precipitation of Fe^III and Al^III (oxy)hydroxides. Adsorption of more soluble Al^III species onto the initially formed ferric oxyhydroxide may be responsible for this slowdown of crystal growth. Therefore, the insertion of low aluminium amount (y∼0.01) could be an interesting way for increasing the surface reactivity of iron(II-III) LDH that maintains constant the quantity of the reactive Fe^II species of the material.     

Organotin biocides. X. Synthesis,structure and biocidal activity of organotin derivatives of 2-mercaptobenzothiazole, 2-mercaptobenzoxazole and 2-mercaptobenzimidazole

Ten organotin derivatives of 2-mercaptobenzothiazole (Hmbt), 2-mercaptobenzoxazole (Hmbo) and 2-mercaptobenzimidazole (Hmbi) have been synthesised and thier structures characterised by spectroscopic methods. Triorganotin derivatives are all S-bonded to the ligand and four-coordinate at tin except Bu₃Sn(mbo) which is five-coordinate trans-ONSnR₃ polymer at 78K. The crystal structure of Cy₃Sn(mbt) has been determined and confirms the tetrahedral geometry at tin. Bu₂Sn(mbt)₂ is weakly six-coordinate by N,S chelating ligands. Biocidal activity patterns are presented for Cy₃Sn(mbt), Ph₃Sn(mbt) and Ph₃Sn(mbo).     

Control of grain size and morphologies of nanograined ferrites by adaptation of the synthesis route: mechanosynthesis and soft chemistry

Nanocrystalline Fe-based spinels with composition Fe_2.5Ti_0.5O₄ can be synthesized using two different routes: soft chemistry and high-energy ball milling. This paper is focussed on the fact that each type of synthesis process can lead to powders with a crystallite size of about 15 nm but with significant differences in the grain size distribution and the agglomeration state. Whereas in the case of mechanosynthesis, the ball-milled powders consist of aggregates, those obtained by soft chemistry are very well dispersed. Moreover the chosen investigated nanopowders present a blocked/superparamagnetic transition depending on the grain size. The grain size morphologies obtained by the two techniques of synthesis can then be fully characterized by complementary experiments: in addition to high-resolution image processing, specific measurements adapted to the study of magnetic relaxation can be used for weighting differently their small and large size tails: namely, magnetization measurements and Mössbauer spectrometry.     

Mössbauer spectra as a “fingerprint” in tin-lithium compounds: Applications to Li-ion batteries

Several Li-Sn crystalline phases, i.e. Li₂Sn₅, LiSn, Li₇Sn₃, Li₅Sn₂, Li₁₃Sn₅, Li₇Sn₂ and Li₂₂Sn₅ were prepared by ball-milling and characterized by X-ray powder diffraction and ¹¹⁹Sn Mössbauer spectroscopy. The analysis of the Mössbauer hyperfine parameters, i.e. isomer shift (δ) and quadrupole splitting (Δ), made it possible to define two types of Li-Sn compounds: the Sn-richest compounds (Li₂Sn₅, LiSn) and the Li-richest compounds (Li₇Sn₃, Li₅Sn₂, Li₁₃Sn₅, Li₇Sn₂, Li₂₂Sn₅). The isomer shift values ranged from 2.56 to 2.38 mm s⁻¹ for Li₂Sn₅, LiSn and from 2.07 to 1.83 mm s⁻¹ for Li₇Sn₃, Li₅Sn₂, Li₁₃Sn₅, Li₇Sn₂ and Li₂₂Sn₅, respectively. A Δ−δ correlation diagram is introduced in order to identify the different phases observed during the electrochemical process of new Sn-based materials. This approach is illustrated by the identification of the phases obtained at the end of the first discharge of η-Cu₆Sn₅ and SnB_0.6P_0.4O_2.9.     

Structural, magnetic, and spectroscopic studies of YAgSn, TmAgSn, and LuAgSn

The rare earth-silver-stannides YAgSn, TmAgSn, and LuAgSn were synthesized from the elements by arc-melting and subsequent annealing. The three stannides were investigated by X-ray powder and single-crystal diffraction: NdPtSb type, P6₃mc, Z=2, a=468.3(1), pm, wR₂=0.0343, 353 F² values, 12 variables for YAgSn, and ZrNiAl type, P6¯2 m, a=726.4(2), , wR₂=0.0399, 659 F² values, 15 variables for TmAgSn, and a=723.8(2), , wR₂=0.0674, 364 F² values, 15 variables for LuAgSn. Besides conventional laboratory X-ray data with monochromatized Mo radiation, the structures were also refined on the basis of synchrotron data with , in order to clarify the silver-tin ordering more precisely. YAgSn has puckered, two-dimensional [AgSn] networks with Ag-Sn distances of 278 pm, while the [AgSn] networks of TmAgSn and LuAgSn are three-dimensional with Ag-Sn distances of 279 and 284 pm for LuAgSn. Susceptibility measurements indicate Pauli paramagnetism for YAgSn and LuAgSn. TmAgSn is a Curie-Weiss paramagnet with an experimental magnetic moment of 7.2 μ_B/Tm. No magnetic ordering is evident down to 2 K. The local environments of the tin sites in these compounds were characterized by ¹¹⁹Sn Mössbauer spectroscopy and solid-state NMR (in YAgSn and LuAgSn), confirming the tin site multiplicities proposed from the structure solutions and the absence of Sn/Ag site disordering. Mössbauer quadrupolar splittings were found in good agreement with calculated electric field gradients predicted quantum chemically by the WIEN2k code. Furthermore, an excellent correlation was found between experimental ¹¹⁹Sn nuclear magnetic shielding anisotropies (determined via MAS-NMR) and calculated electric field gradients. Electronic structure calculations predict metallic properties with strong Ag-Sn bonds and also significant Ag-Ag bonding in LuAgSn.     

Organotin(IV) triazolates: Synthesis and their spectral characterization

Some organotin(IV) triazolates of general formula R_nSn(L)_4 − n (where R = Me, n-Bu and Ph for n = 2; R = Me, n-Pr and n-Bu for n = 3 and HL = 3-amino-5-mercapto-1,2,4-triazole) have been synthesized by the reaction of R₂SnCl₂/R₃SnCl with NaL in 1:2/1:1 molar ratio. Whereas, Oct₂SnL₂ has been synthesized azeotropically by the reaction of Oct₂SnO and HL in 1:2 molar ratio. As good single crystals were not obtained, a large number of experimental techniques, viz. UV/Vis, IR, far-IR, multinuclear (¹H, ¹³C and ¹¹⁹Sn) NMR and ¹¹⁹Sn Mössbauer spectroscopic studies, were used to accomplish a definitive characterization and determination of their most probable structures. In these compounds triazole acts as a monoanionic bidentate ligand, coordinating through S_exo and N(4). The IR and ¹¹⁹Sn Mössbauer spectroscopic studies allow us to deduce a highly distorted cis-trigonal-bipyramidal structure for R₃SnL and a distorted skew trapezoidal-bipyramidal structure for R₂SnL₂, in the solid state. However, ¹H, ¹³C and ¹¹⁹Sn NMR spectral studies revealed that weak bonding between tin and N(4) is further weakened in the solution leading to pseudo-tetrahedral/tetrahedral structure.     

Nanosized copper ferrite materials: Mechanochemical synthesis and characterization

Nanodimensional powders of cubic copper ferrite are synthesized by two-steps procedure of co-precipitation of copper and iron hydroxide carbonates, followed by mechanochemical treatment. X-ray powder diffraction, Mössbauer spectroscopy and temperature-programmed reduction are used for the characterization of the obtained materials. Their catalytic behavior is tested in methanol decomposition to hydrogen and CO and total oxidation of toluene. Formation of nanosized ferrite material is registered even after one hour of milling time. It is established that the prolonging of treatment procedure decreases the dispersion of the obtained product with the appearance of Fe₂O₃. It is demonstrated that the catalytic behavior of the samples depends not only on their initial phase composition, but on the concomitant ferrite phase transformations by the influence of the reaction medium.     

Study of the surface chemistry and morphology of single walled carbon nanotube-magnetite composites

The study of the morphologies of the single walled carbon nanotube (SWCNT), magnetite nanoparticles (MNP), and the composite based on them was carried with combined X-ray diffraction (XRD), Raman spectroscopy (RS), scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). These techniques together with thermogravimetric analyses (TGA) and diffuse reflectance infrared transform spectroscopy (DRIFTS) confirmed the production of pure single phases, and that the composite material consisted of MNP attached to the outer surface of the SWCNT. The Mössbauer spectroscopy (MS) research showed the presence of a large quantity of Lewis acid sites in the highly dispersed magnetite particles supported on the SWCNT outer surface. The DRIFTS carbon dioxide adsorption study of the composites revealed significant adsorption of carbon dioxide, fundamentally in the Lewis acid sites. Then, the Lewis acid sites were observed to be catalytically active. Further, the electron exchange between the Lewis acid sites and the basic or amphoteric adsorbed molecules could influence the magnetic properties of the magnetite. Consequently, together with this first ever use of MS in the study of Lewis acid sites, this investigation revealed the potential of the composites for catalytic and sensors applications.     

Studies on InFeMO4 (M=Mg, Co, Ni, Cu and Zn) compounds: Crystal structure and cation distribution

The crystal structure and the cation distribution in a series of InFeMO₄ compounds (M=Mg, Co, Ni, Cu and Zn) have been studied by means of X-ray powder diffraction and ⁵⁷Fe Mössbauer spectroscopy. The M=Mg, Co and Ni samples were confirmed to crystallize with the cubic spinel structure (space group Fd-3m), whereas the M=Cu and Zn samples adopted a hexagonal structure. For all the phases, the cation stoichiometry was found to deviate from the ideal molecular formula, InFeMO₄. The paramagnetic Mössbauer spectra of the samples were analyzed using a four-component fitting model suggested by a statistical simulation with point-charge calculation. The Mössbauer data confirmed the trivalent state for iron at both cation sites in all samples. The results from the fitting of the Mössbauer spectra were also employed in Rietveld refinement of the X-ray diffraction data for the determination of exact cation distribution. It was seen that the distribution of Fe at the A and B sites follows very closely the 1:2 ratio of the ideal formula AB₂O₄ for all samples, whereas trivalent indium was clearly seen to favor the A site and divalent M cation the B site.     

Hyperfine interactions and lattice dynamics of Sn21O6Cl16(OH)14

In this study, the tin(II) oxy-hydroxychloride Sn₂₁O₆Cl₁₆(OH)₁₄ has been synthesised and investigated. This compound is the synthetic equivalent of mineral abhurite, which was discovered in 1985 as a tin corrosion product formed on the surface of tin ingots after long immersion in seawater. The Mössbauer parameters of Sn₂₁O₆Cl₁₆(OH)₁₄ determined at various temperatures are reported and discussed for the first time. At room temperature, the isomer shift and the quadrupole splitting are, respectively, δ=3.22 mm s⁻¹ and Δ=1.71 mm s⁻¹, relative to the centroid of the spectrum of BaSnO₃. The Mössbauer recoil-free fraction has been also evaluated over a wide range of temperature. At 300 K, the recoil-free fraction of Sn₂₁O₆Cl₁₆(OH)₁₄ is f₃₀₀=0.09±0.02.     

Structure, magnetic properties and Mössbauer spectroscopy of GdRhSn

Polycrystalline GdRhSn was obtained by a reaction of the elements in a sealed tantalum tube in a high-frequency furnace. The sample was investigated by X-ray diffraction on powder and a single crystal: ZrNiAl type, space group , a=752.6(1),c=386.38(6) pm, wR₂=0.0353, 454 F² values and 14 variables. Both crystallographically independent rhodium atoms have a tricapped trigonal prismatic coordination, i.e. [Rh1Sn₃Gd₆] and [Rh2Sn₆Gd₃]. The shortest distances occur for the Rh-Sn contacts (274 and 283 pm). Together the rhodium and tin atoms build up a three-dimensional [RhSn] network in which the gadolinium atoms fill distorted hexagonal channels. The magnetic and electronic properties of GdRhSn have been studied by means of magnetic AC and DC susceptibility measurements as well as ¹¹⁹Sn and ¹⁵⁵Gd Mössbauer spectroscopy. A transition from a paramagnetic to an antiferromagnetic state with non-collinear magnetic ordering takes place at .     

New polynuclear compounds based on N-benzyliminodipropionic acid: solution studies,synthesis, and X-ray crystal structures

Three new polynuclear compounds based on a dicarboxylic acid ligand are reported. In particular, two Cu(II) coordination compounds, [Cu₂(H₂O)₆(Hbzlidp)₂](CF₃SO₃)₂·2H₂O (1) and [Cu(NO₃)(Hbzlidp)]_∞ (2) (bzlidp^2? = N-benzyliminodipropionate anion), and a Ni(II) dinuclear compound, [Ni₂(H₂O)₄(bzlidp)₂] (3), were synthesized and characterized by IR spectroscopy, elemental analysis and single crystal X-ray diffraction. Different structures were obtained depending on the reaction conditions. The structural analyses reveal that 1 was formed by dinuclear [Cu₂(H₂O)₆(Hbzlidp)₂]²⁺ units built by two copper(II) ions joined through two Hbzlidp^? ligands, while 2 was formed by pairs of Cu(II) centers bridged by four syn,syn carboxylate groups to generate “paddle wheel” units. The dinuclear copper units are arranged in a rhombus type grid, in a 2-D layer structure. In both cases, the N was protonated and not coordinated to the metal center. Compound 3 was formed by [Ni₂(H₂O)₄(bzlidp)₂] neutral dinuclear units, with octahedral Ni(II) centers. Solution studies of the ligand–M(II) systems (M(II) = Mn, Co, Ni, Cu, Zn, Cd, and Pb) were also carried out.     

Transition metal chemistry of oxime containing ligands,VII

Complexes of pyridine-2-aldoxime (Hpox) with iron(II) and chromium(III) of type, [Fe(Hpox)₂ X ₂] (X=Cl, Br, I or NCS); [Cr(Hpox)₃]Cl₃·3 H₂O; [Cr(Hpox)₂ X ₂]ClO₄ (X=F, Cl or Br) and [Cr(Hpox)₂(H₂O)₂]Br₃·H₂O were prepared and characterized by analytical X-ray powder diffraction, magnetism, vibrational (conventional and far-infrared) and electronic spectroscopy techniques. X-ray and electronic spectral data indicate that all the complexes except [Cr(Hpox)₃]Cl₃·3 H₂O havetrans-pseudo-octahedral microsymmetry around the metal ion. Infrared spectral data indicate that the ligand, Hpox, behaves like a neutral ligand and coordinates to the metal ion through pyridine nitrogen atom and oxime nitrogen atom in all these complexes. The magnetic susceptibilities of chromium(III) complexes, measured over a temperature range 300–78 K, are independent of temperature whereas the magnetic moments of iron(II) complexes over a temperature range 300–20 K are dependent of temperature. The observed temperature dependence of magnetic moments of iron(II) complexes was used to evaluate the magnitude of orbital reduction factor,k, the low-symmetry distortion parameter, , and the extent of reduction in spin-orbital coupling, . In all these iron(II) complexes the magnetic results indicate the presence of an orbitally non-degenerate,⁵B_2g, ground state. Magnetically unperturbed and perturbedMössbauer spectra of iron(II) complexes at various temperatures have also been reported. Magnetically perturbedMössbauer spectra of iron(II) complexes at 4.2 K in an axial field of 60kGauss indicate that the principal component of electric field gradient tensor is positive and consistent with⁵B_2g ground electronic state in a tetragonal (D _4h) local site symmetry.

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Übergangsmetallkomplexe mit Oxim-enthaltenden Liganden, VII. Elektronische und strukturelle Eigenschaften vonFe(II)-undCr(III)-Komplexen mit Pyridin-2-aldoxim

Zusammenfassung Es wurden Komplexe von Pyridin-2-aldoxim (Hpox) mit Fe(II) und Cr(III) vom Typ [Fe(Hpox)₂ X ₂] (X=Cl, Br, I, NCS), [Cr(Hpox)₃]Cl₃·3 H₂O, [Cr(Hpox)₂ X ₂]ClO₄ (X=F, Cl, Br) und [Cr(Hpox)₂(H₂O)₂]Br₃·H₂O hergestellt. Charakterisierung und Diskussion von Geometrie und Bindungsverhalten in den Komplexen erfolgte auf Grund von analytischen Daten, Röntgen-Pulveraufnahmen, Elektronenanregungsspektroskopie, Infrarotspektroskopie, magnetischen Messungen undMössbauer-Spektroskopie.