Quadrupole Splitting Values Research Articles

Detection of vacant tetrahedral sites in thiospinels by 57Fe Mössbauer spectroscopy and diffuse reflectance

The spinel In 2 S 3, in which one-third of the tetrahedral cation sites is unoccupied, is used as a host lattice for solid solutions within the ternary systems In 2S 3—Cu 2S—CuS and In 2S 3—SnS—SnS 2. The number of vacant tetrahedral sites per unit cell can be varied within these solid solution regions, between zero and 2.66 and between 2.24 and 4, respectively. 57Fe introduced as a local probe allows these vacancies to be detected by means of Mössbauer spectroscopy. Several typical values of quadrupole splittings are observed which can be related to the number of vacant tetrahedral sites around an iron atom. Diffuse reflectance spectra reveal an absorption band at about 5000 cm −1 which appears in both systems. The intensity of this band is related to the number of vacant tetrahedral sites per unit cell.

Solubilization of Nonionic Polymers in a Lyotropic Lamellar Mesophase: Lecithin-Water-Polyethylene Oxide System

Soybean lecithin forms a homogeneous lamellar liquid crystalline phase with water at concentrations of less than 33 wt% water. The solubilization of water-soluble polyethylene oxide polymer into the lamellar phase is studied by 2 H and 31P NMR and polarizing microscopy methods. Between 20 and 33 wt% of water, the liquid crystalline phase is unable to solubilize any appreciable amounts of polymer and the mesophase is destabilized by the addition of about 0.5% of polymer, whereas the solubilization of the polymer increases drastically in the lamellar phase (e.g., 18% polymer at 10% water) with water content less than 10%. The 2H NMR quadrupole splitting values, as well as the 31P NMR chemical shift anisotropy, remain unaffected by replacement of lecithin or water with polymer. The results indicate that the binding of water to the interface and the molecular organization of the choline headgroup are little affected by the presence of polymer molecules in the mesophase.

Auger electron spectroscopic study of binary nickel(II)-iron(III) hydroxides

Surface analysis of coprecipitated binary Ni(II)-Fe(III) hydroxide solid solutions using Auger electron spectroscopy and depth profiling has revealed redistribution of the components (nickel and iron) within the surface layers showing significantly increased iron-to-nickel ratios, as compared to the corresponding gross averaged values in the bulk. The results are compared with transmission Mössbauer spectroscopic data obtained earlier for these systems, which are interpreted in terms of the presence of surface-related iron(III)-containing forms featured by essentially higher quadrupole splitting values. The surface analysis data presented are also discussed in connection with the high electrocatalytic activity of composite nickel-iron hydroxide systems towards anodic oxygen evolution in alkaline electrolytes revealed previously.

Quadrupole Interactions and Vibrational Anisotropy of Tetrahedral Fe(III) in the "123" Derivative LnSr2Cu2Ga1-xFexO7 (Ln = Y, Ho)

The layered copper oxides Ln Sr2Cu2Ga1-xFexO7 (Ln = Y, Ho) have been synthesized for 0 ≤ x ≤ 1. An orthorhombic structure (S.G. Ima2, a ≈ 22.9 Å, b ≈ 5.5 Å, c ≈ 5.4 Å) forms in the oxides prepared in Ar atmosphere for x rising up to 0.95. The transition from orthorhombic to tetragonal "123" structure (S.G. P4/mmm, a123 ≈ 3.84 Å, c123 ≈ 11.4 Å) in the range of 0.6 < x < 0.95 is induced by heating in an oxygen flow. The Mössbauer study reveals that iron exhibits the predominant tetrahedral coordination in the orthorhombic phase, but the pyramidal coordinations in the oxygenated tetragonal LnSr2Cu2FeO7.5. The characteristic Mössbauer quadrupole doublet associated with the tetrahedral "Ga" site turned out to be asymmetric suggesting an anisotropic thermal vibration of iron in this site. The anisotropy of recoil-free fraction is consistent with a large distortion of the tetrahedral site, where the EFG is parallel to the a direction of the unit cell. The negative sign of Vzz and the large value of quadrupole splitting (|ΔEQ| ≈ 1.93 mm/sec) suggest a similarity between the geometry of FeO4 tetrahedra in both oxides Ln Sr2Cu2Ga1-xFexO7 and Ln Ba2Cu3-xFexO-y.

Structural transitions in a TiNiFe shape memory alloy

Results for resistance versus temperature, differential scanning calorimetry (DSC), Mössbauer spectroscopy, and magnetic susceptibility measurements in a Ti 50Ni 47Fe 3 sample are presented. The resistance versus temperature curve shows a sharp increase at 245K and then rises slowly until a maximum is attained at ∼150K. The DSC curve also exhibits a peak at the former temperature. The room temperature Mössbauer spectrum consists of a single line. As the temperature is lowered to 270K, a small asymmetric quadrupole doublet appears. The isomer shift and quadrupole splitting values of this doublet increase with decreasing temperature until almost constant values are achieved at temperatures ∼100K. The magnetic susceptibility curve shows a sharp decrease that begins at 255K and then an unexpected increase at 90K. We relate these observations with a charge density wave-driven premartensitic transition in this system, and with the final martensitic phase.

Crystal, molecular, and electronic structure of carboxylate [Fe3O(CH3COO)6(H2O)3]NO3·4H2O

Results of X-ray structural analysis, IR spectroscopy, and quantum chemical study of the [Fe3O(CH3COO)6(H2O)3]NO3·4H2O complex are reported. The crystal belongs to the monoclinic system with a=15.688(3), b=11.767(2), c=15.318(4) A, γ=92.54(3)o, space group P21/a, R=0.078. The molecule has a trinuclear structure: three iron atoms occupy the vertices of an equilateral, triangle with an Fe−Fe distance of 3.29 A and are bonded by the μ3-oxo and μ-CH3COO− (O,O′) ligands. To each iron atom, one water molecule is coordinated. Using the obtained values of populations on 3d AO of Fe (d xy 1.34 ; d xz 1.39 ; d yz 1.46 ; $$d_{z^2 }^{1.31} $$ ; $$d_{x^2 - y^2 }^{1.40} $$ ) and charges on oxygen atoms (O c −0.5 ; O ac −0.31 ; O w −0.31 ), we estimated the values of isomeric shift and quadrupole splitting (0.75 and 0.70 mm/sec, respectively; these are close to the experimental values of 0.75 and 0.58 mm/sec, (300 K)).

Coordination complexes of dimethyltin dichloride with C-nitroso compounds

Coordination complexes of five nitrosoanilines with dimethyltin dichloride have been prepared and studied by 13C, 15N and 199Sn solid state NMR spectroscopy and by Mössbauer spectroscopy. The 13C resonances of the CH 3-Sn groups, the 199Sn resonances and the Mössbauer quadrupole splitting values permit assignment of the two classes of coordination complexes. The C-NO resonances decrease on coordination. The 15N resonances demonstrate that coordination is accompanied by an enhancement of the quinonoid contribution in the ligand itself

Mössbauer Study of Some Iron Organo-Metallic Complexes

Abstract Mossbauer absorption spectra were obtained for ferric complexes of urea and thiourea derivatives with dibasic acids. The complexes were prepared in the two ratios 1:1 and 2:1 metal to ligand. The Mossbauer parameters were analysed inconsistent with the structural data obtained from I.R. spectra. It was found that changing the metal -ligand ratio has nearly no effect on both the isomer shift and quadrupole splitting values.

Sulfidation of Co/Al 2O 3 and CoMo/Al 2O 3 Catalysts Studied by Mössbauer Emission Spectroscopy

The sulfidation of uncalcined and calcined alumina-supported cobalt and cobalt-molybdenum catalysts was systematically studied by means of in situ Mössbauer emission spectroscopy (MES) at room temperature. The spectra obtained during the stepwise sulfidation of the uncalcined catalysts clearly resemble those observed for carbon-supported ones. Hence, the interpretation of the spectra of the alumina-supported catalysts is based on the conclusions drawn from the MES studies of the carbon-supported catalysts, which are less complex because Co ions do not diffuse into the support. It is demonstrated that not only in sulfided CoMo/Al 2O 3, but also in sulfided Co/Al 2O 3, catalysts Co-sulfide species with a "Co-Mo-S"-type quadrupole splitting can be formed. It is concluded that the Co-sulfide species formed in sulfided Co/Al 2O 3 and CoMo/Al 2O 3 catalysts are essentially the same, only the particle size and ordering of the Co-sulfide species may differ, as in the case of Co/C and CoMo/C catalysts. The function of the Mo, which is present as MoS 2, is merely to stabilize very small Co-sulfide particles, which in the limit contain only one single Co atom. Furthermore, it turns out that the value of the electric quadrupole splitting (Q.S. value) of the Co-sulfide phase in the sulfided catalysts depends on the sulfiding temperature and Co content. This observation leads to the conclusion that large Q.S. values point to the presence of very small Co-sulfide entities or particles (the lower limit being "particles" containing only one Co atom, such as proposed in the "Co-Mo-S" model), whereas small Q.S. values point to the presence of large Co-sulfide particles (the upper limit being crystalline Co 9S 8).

197Au Mössbauer study of Au 2S and gold adsorbed onto As 2S 3 and Sb 2S 3 substrates

197Au Mössbauer spectra were measured for crystalline Au 2S and for gold adsorbed onto colloidal As 2S 3 and Sb 2S 3 substrates. The spectrum for Au 2S is characterised by a quadrupole split doublet which has been deconvoluted into two overlapping doublets. The spectra for adsorbed gold on colloidal As 2S 3 and Sb 2S 3 are similar in appearance to that of Au 2S and have isomer shifts (IS) and quadrupole splitting (QS) values which are characteristic of gold in the +1 oxidation state, coordinated to two sulphur electron donors in an approximately linear geometry. The 197Au Mössbauer data confirm that the gold occurs on the As 2S 3 and Sb 2S 3 substrates as a surface complex and has not been electrochemically reduced to elemental gold (Au 0). These data further emphasize the role of surface chemistry in the scavenging and concentrating of gold by sulphide mineral surfaces from hydrothermal fluids in high-temperature ore-forming systems (e.g., epithermal environments), as well as in seafloor hydrothermal systems, where sulphide minerals are precipitating near the seafloor-seawater interface.

MACROBICYCLIC d-METAL TRIS-DIOXIMATES OBTAINED BY CROSS-LINKING WITH p-BLOCK ELEMENTS. PART X. THE FIRST CRYSTAL AND MOLECULAR STRUCTURE OF CLATHROCHELATE TRIS-DIOXIMATES WITH NONSYMMETRICAL DIOXIMES:merISOMERS OF AN IRON (II) COMPLEX WITH A MACROBICYCLIC PHENYLBORON PHENYLGLYOXIMATE LIGAND

Abstract Single crystals of the FePhm3 (BC6H5)2 · BF3 complex contain two mer isomers with different orientations of phenyl substituents in dioxime fragments have been obtained by the template cross-linking of three phenylglyoximate (H2Phm) molecules with two phenylboric acid molecules in the presence of boron trifluoride. They crystallize in space group P1, a = 13.962(5), b = 13.519(2), c = 12.343(6) Å, α = 63.63(7), β = 100.78(4), γ = 79.88(7)˚, V = 1959.9 Å3, Z = 2. The structure has been determined by X-ray methods. The trigonal prismatic coordination polyhedron formed by six nitrogen atoms of the macrobicyclic ligand has a distortion angle of 21.8˚. The Fe-N bond length (1.91 Å) and the bite angle (39.2˚) are typical for clathrochelate tris-dioximates of iron(II). A comparison between the value of quadrupole splitting in Mössbauer (57Fe) spectra obtained experimentally and its calculated value has been made.

Mössbauer study of 57Fe-doped La 2SrCu 2O 6

The Mössbauer spectra of La 2SrCu 1.95 57Fe 0.05O 6 were measured at various temperatures between 372 and 5 K. The spectrum measured at room temperature consists of two paramagnetic quadrupole doublets with similar Mössbauer parameters. The values of IS and small quadrupole splitting values indicate that high spin Fe 3+ ions are in octahedral sites. The spectrum measured at 5 K consists of a broad sextet and a minor paramagnetic component. The distribution function of H hf shows two peaks of 520 and at 440 kOe. The magnetic susceptibility shows no distinct anomaly in this temperature range. Magnetic ordering seems to take place over a wide range of temperature.

Cation Distribution and Local Configuration of Fe 2+ Ions in Structurally Nonequivalent Lattice Sites of Heterometallic Fe(II)/ M(II) ( M = Mn, Co, Ni, Cu, Zn) Diaquadiformato Complexes

57Fe Mössbauer investigations are carried out on a wide series of heterometallic diaquadiformato Fe(II)/ M(II) complexes with M = Mn, Co, Ni, Cu, and Zn to provide a local picture of the coordination environment of the 57Fe 2+ ions as a function of (i) the nature of the host cation and (ii) the relative amounts of both metals in the matrix (between 50 and 0.25 at.% Fe). Information is obtained on the quantitative distribution of both metals between the two structurally nonequivalent lattice sites and on the local geometry around the dopant atom in each crystal site. In the mixed Fe-Cu complexes. Fe 2+ ions are preferentially incorporated in the tetrahydrated site; in Cu-rich Fe x Cu 1- x (HCO 2) 2· 2H 2O, the 57Fe 2+ ions located in the hexaformato-coordinated site are surrounded by an axially compressed octahedron of formate ligands which contrasts with the elongated configuration observed in the pure iron compound and in the other mixed systems. Semiquantitative estimations of the tetragonal field splitting and of the extent of metal-ligand interactions are proposed from the temperature dependence of the quadrupole splitting values.

Quadrupole Splittings in Trigonal-prismatic Iron(II) Complexes: the Possibility of Obtaining Absolute Partial Quadrupole Splittings

An attempt to determine the absolute values of partial quadrupole splittings (PQS) by investigating trigonal-prismatic low-spin iron(II) complexes has been made; all PQS values obtained are positive.

Co-ordination number, symmetry of the co-ordination sphere of tin(IV) and oligomerization in carbohydrate complexes of dibutyltin(IV)

Dibutyltin(IV) complexes with 19 different carbohydrates were prepared and studied by Mossbauer spectroscopy. Comparison of the experimental quadrupole splitting values with those calculated on the basis of the partial quadrupole splitting concept revealed that the complexes are of four types: with the central tin(IV) atoms surrounded by donor atoms in a trigonal-bipyramidal, octahedral, both a trigonal-bipyramidal and octahedral or a tetrahedral arrangement. This procedure also distinguished between the different structural isomers of both trigonal-bipyramidal and octahedral complexes. Conclusions could therefore be drawn as to the factors determining which of the isomers is formed in the systems. The changes in the room-temperature Debye–Waller factors and the integral intensities of the Mossbauer doublets assigned to the tin(IV) in different surroundings reflected the oligomerization in the systems. The Mossbauer spectra revealed a temperature-dependent Goldanski–Karyagin effect.

M1, M2 site populations and distortion parameters in synthetic Mg-Fe orthopyroxenes from M�ssbauer spectra and X-ray structure refinements

Synthetic orthopyroxenes free of trivalent cations Mg x Fe 2-x Si2O6 (x=0; 1; 1.6) were investigated using both Mossbauer spectroscopy (MS) and single-crystal X-ray diffraction (XRD) in order to compare the results obtained on the same samples by the two techniques. The Mg-Fe distribution over M1 and M2 octahedral sites was determined on compounds with x = 1 and x=1.6, unheated and annealed at 650, 850 and 1040° C for 29 to 42 hours to obtain different degrees of order. The data obtained by the two techniques are in very good agreement, thus suggesting, for these compositions, the absence of systematic errors. The investigation of a synthetic compound with x=0 (ferrosilite) confirmed that the accuracy of both methods is very good. The observed small discrepancies between the results are not significant if compared with the relevant standard deviations which, for both methods, were derived by leastsquares calculations. The best fit is obtained for Fe(M1)/ Fe(tot) parameters that, in both methods, are directly calculated without using data from chemical analysis. For the unheated samples the values by MS and XRD are respectively: 0.185(9) and 0.180(4) for x = 1.6; 0.282(8) and 0.285(2) for x=1; 0.503(7) and 0.502(1) for x=0. For all the investigated samples the correlation between the geometrical distortion parameters, calculated by X-ray refinement, and the quadrupole splitting values, measured by Mossbauer spectroscopy, agrees with the theoretical model of Ingalls (1964).

Beziehungen zwischen Kristallstruktur und 197AuMößbauereffekt ternärer AlkalimetallGold(I)Chalkogenide

197Au-Mössbauer results are reported for a series of alkali metal gold chalcogenides: Na 3AuS 2, KAuS, CsAuS, K 4Au 6S 5, KAuSe, NaAuTe, KAuTe, RbAuTe and CsAuTe. Isomeric shifts (ISs) and quadrupole splittings (QSs) correspond to the region expected for gold atoms of oxidation state + 1 in the QSIS correlation diagram. The compounds with linearly coordinated gold atoms exibit a marked linear relationship between IS and QS. The highest values of QS and IS are found for Na 3AuS 2. Progressively lower values are manifested as the chalcogen atom is changed from sulphur to selenium to tellurium or when the alkali metal is exchanged for a less electronegative element respectively. Correspondingly the parameters of alkali metal gold chalcogenides with a smaller content of alkali metal are smaller. The Mössbauer spectra of the ternary tellurides show the expected difference between the threefold-coordinated gold atoms of the layer structures and the twofold-coordinated gold atoms of the chain structures. Eventual AuAu interactions could not be proved by these Mössbauer measurements. The short AuAu distances, detected by X-ray analysis, are possibly van der Waals contacts.

Iron spin fluctuations in 57Fe-doped high-Tc superconductors (Bi,Pb)2Sr2Can-1CunO2n+4 with n=2,3

Bi-based superconductors of 2212 and 2223 type were doped with 1-3% 57Fe. 57Fe Mossbauer spectra were taken between 293 K and 2 K. In all samples indications for a slowing down of Fe spin fluctuations were found. In the 2223 superconductor doped with 3% Fe, a magnetically split spectrum with a hyperfine field of 40.5 T is measured at T=2 K. The Fe spins are aligned nearly parallel to the electric field gradient which is positive and lies close to the c axis. The Fe valence is +3 in all cases. The RT spectra are strongly dependent on the substitution of Pb for Bi. The spectra of both the Pb-containing 2212 and 2223 samples show one well-defined doublet with a quadrupole splitting value of 1.12 mm s-1. Without Pb substitution, the spectra of the 2212 system consist of two doublets with quadrupole splittings of about 0.6 mm s-1 and 1.7 mm s-1, with their relative intensities depending on the Fe concentration.

Site Occupancy in Nontronite Studied by Acid Dissolution and Mössbauer Spectroscopy

AbstractThe dissolution of two Ca2+-exchanged nontronite samples has been studied in 10% HCl. Early acid-dissolution studies (Osthaus, 1954) have indicated that after two hours of dissolution most of the octahedral Fe3+ (VIFe3+) would be removed leaving mainly tetrahedral Fe3+ (IVFe3+) in the nontronite structure. In the present study, 57Fe Mössbauer spectra of acid-treated samples were recorded and fitted with two octahedral Fe3+ (2 × VIFe3+) and two octahedral and one tetrahedral (2 × VIFe3+, 1 × IVFe3+) doublet models. The Mössbauer spectra of acid-treated Garfield nontronite samples could be adequately fitted with two-doublet models but acid-treated Hohen Hagen nontronite samples could not. Isomer shift and quadrupole splitting values obtained from the two-doublet models corresponded to VIFe3+ and not IVFe3+, as was suggested by the Osthaus (1954) experiment. When an IVFe3+ doublet was included in the model used to fit the Mössbauer spectra of acid-treated Garfield nontronite samples, a slight increase in the intensity of the IVFe3+ doublet occurred with increasing dissolution, but this was much lower than indicated by Osthaus (1954). No trend in the intensity of the IVFe3+ doublet was observed for acid-treated Hohen Hagen nontronite. Therefore, acid treatment appears to remove VIFe3+ and IVFe3+ from the nontronite structure at about the same rate. Mössbauer spectroscopy, infrared spectroscopy and X-ray powder diffraction data indicate that the nontronite that remains undissolved following acid treatment is structurally similar to the untreated nontronite.

Mössbauer parameters and structure correlations in five-coordinate iron complexes

Iron-57 Mössbauer spectroscopy data are reported for [Fe(Bu tNC) 5], [Fe(CO) 4 (Bu tNC)] and [(PPh 3) 2N][Fe(CO) 4(CN)] complexes in order to examine the bonding character and geometrical changes of several iron penta-coordinate complexes. The small quadrupole splitting value of 0.88 mm s −1 measured for the distorted trigonal bipyramidal [Fe(Bu tNC) 5] differs significantly from these found for regular geometries. As a consequence of this unusual result, a new correlation method of analysis was proposed for 13 known structures of five-coodinate [FeL 5], axially substituted [Fe(CO) 4L′] and [{Fe(CO) 4} nL″] n− complexes (L = CO or Bu tNC), on the basis of deviations from the idealized trigonal bipyramidal structure and changes in the quadrupole splittings. Furthermore, correlations involving Mössbauer data and IR carbonyl stretching frequencies were used to answer more detailed electronic and stereochemical questions.