Quadrupole Splitting Values Research Articles

Determination of the coordination number and geometry of the coordination sphere of the central tin atom in stannatrane complexes by Mössbauer spectroscopy

The Mössbauer isomer shift (IS) and quadrupole splitting (QS) values of 35 strannatrane complexes of RSn(XCH 2CH 2) 3Y, R 2SN(XCH 2CH 2) 2Y and R 2Sn(OCOCH 2) 2Y composition were determined (R = alkyl or aryl groups, X = O, N or S, Y = N, NR, O or S). On the basis of the partial quadrupole splitting concept QS values were calculated assuming different coordination numbers, and, in the case of pentacoordination, different configuration of the compounds. The comparison of experimental and calculated QS values leads to the determination of the coordination number of tin, and in the pentacoordinated compounds to that of the configuration of the complexes. The data reflected the effect of the functional groups and donor atoms on the structure of the strannatranes.

Moessbauer Study of the Effect of Calcium Content on Iron Oxide Transformations in Fired Clays

Sixteen clays were studied by Moessbauer measurements in their unfired and fired forms. Thirteen of these clays were collected near ancient Greek sites and the remaining three in England and the United States. They were fired at 700°, 900°, and 1080°C to investigate the physicochemical transformations of the clay components in this temperature range. The results show distinctly different responses of the clays, according to their CaO content. Firing of the calcareous clays (>5 % CaO content) at 700°C produces small oxide particles (mainly hematite). This phase remains stable on further firing up to 1080°C, where it decreases slightly. Contrary to this behavior, the noncalcareous clays display a continuous increase of the amount and size of the oxide particles when fired up to 1080°C. This difference is attributed to stable calcium aluminosilicate phases which are formed in the calcareous clays as opposed to the continuous vitrification which occurs for the noncalcareous clays by firing up to 1080°C. The variation of the quadrupole splitting of the central doublet with firing temperature also differs for the two types of clays. The quadrupole splitting values among the clays span a range of 1.1 to 1.6 mm/s for a firing temperature of 700°C. Above this temperature, a distinct separation of the two groups occurs with the quadrupole splitting of calcareous clays lying higher.

M�ssbauer studies of synthetic and natural micas on the polylithionite-siderophyllite join

Mossbauer studies of micas on the polylithionite-side-rophyllite join show the existence of a relation between the quadrupole splitting (ΔEQ) values of Fe2+ high spin doublets and both cationic and anionic composition of micas. This linear relation is positive as Li2O content increases and negative as F content increases. In the lithium iron micas, the inner ferrous quadrupole doublet is assigned to the cis-site M(2), while the outer doublet is assigned to the trans-site M(1). A random distribution of Fe2+ is observed in fluorine-rich compositions, while slight enrichment of the M(1) site is noticed in hydroxyl compositions, perhaps due to a more sensitive oxidation in situ in M(2) than M(1) sites. The Mossbauer spectrum of siderophyllite K2(Fe42+Al2)(Si4Al4)O20(OH)4 shows the presence of only one ferrous doublet, which is assigned to M(2) sites. Hence from Mossbauer data we must consider a clintonite (“xanthophyllite”) structure for this mica. The ordered octahedral layer has two distorted ferrous cis-sites and one, more symmetrical, aluminum trans-site.

Dependence of the dynamic and hyperfine characteristics of Fe3+ ions on the rare-earth ion parameters in garnets above the Néel temperature

Nine rare-earth iron garnets R3Fe5O12 (R  Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm) are studied by the NGR method at 590 K. The approximation of experimental spectra by a theoretical curve obtained by computing the transmission integral allows to determine more exactly the hyperfine parameters of NGR spectra, while the values of the absolute Mössbauer factor for the majority of ferrites under study are determined for the first time. The value of quadrupole splitting is found to decrease with the increase of the radius of the rare-earth ion, which is indicative for the decrease of the polyhedron local distortions. The decrease of the absolute Mössbauer fraction with the increase of the mass of the rare-earth ion is also observed. Values of the Mössbauer effect in a- and d-sublattices are shown to be equal. [Russian Text Ignored].

119Sn Mössbauer spectral studies in Sn(IV) and organotin(IV) substituted oxinates

Several Sn(IV) and organotin(IV) compounds of the type SnL 2X 2(X = Cl and HL = 5-acetyl-, benzol-, or phenylazo-, 8-quinolinol), SnX 4 · 2HL′(X = Cl or Br and HL′=8-quinolinol-N-Oxide), R 2SnL 2(R = CH 3, C 2H 5, C 4H 9, C 8H 17 or C 6H 5) and R 3SnL(R = C 6H 5) have been synthesized and characterized. The 119 m Sn Mössbauer spectra of these compounds have been recorded at 77°K and probable structures from the Mössbauer parameters are inferred. R 2SnL 2 chelates (Q.S = ca. 2.0 mm/sec.) are considered to have the two R-groups occupying cis-positions in the octahedral structure. The Mössbauer spectra of the compounds, SnX 4·2HL′ have been resolved graphically and the quadrupole splitting values ( ca. 0.75 mm/sec.) strongly suggest trans-configuration for the Sn(IV) tetrahalide adducts.

Mössbauer Spectroscopic Studies of Monosubstituted Pentacyano Ferrate(II) Complexes, Na3[Fe(CN)5RNH2] · nH2O

Abstract A series of compounds Na3[Fe(CN)5RNH2] · nH2O where R = -H, -CH3, -C2H5, n-C3H7, n-C4H9 and -CH2C6H5 and RNH2 = C5H5N have been studied by Mössbauer spectroscopy. Quadrupole splitting (⊿EQ) values vary in a limited range (0.68-0.80 mm/sec) indicating only small distortions in the octahedral geometry of the compounds with the substitution of various amino groups. Isomer shift (δ) values remain almost constant suggesting that s-electron density is not affected by substitution.

Mössbauer and ESR studies of non-bridging oxygens in potassium phosphate glasses

Mössbauer spectroscopic study was performed to investigate the behavior of non-bridging oxygens in the potassium phosphate glasses denoted by a formula of x K 2O(100− x)P 2O 5 7 Fe 2O 3. The quadrupole splitting values for Fe 2+ and Fe 3+ ions decreased continuously with the alkali content of the glasses in the alkali region of 0–30 mol.%, and increased in the higher alkali region. On the other hand, the Mössbauer absorption area for Fe 2+ increased continuously in the same alkali region ( x = 0–30 mol.%), and then decreased in the higher alkali region. The continuous decrease of the quadrupole splitting, i.e., the increase of the symmetry around the iron and the increase of the absorption area for the Fe 2+ ions are discussed in connection with the increase of non-bridging oxygens at site adjacent to the iron. ESR measurements for the γ-ray irradiated potassium phosphate glasses free from iron were also carried out to confirm the formation of the non-bridging oxygens in the glasses by observing PO 4 2− radicals produced by γ-ray irradiations. We conclude that the ESR absorption intensity for the PO 4 2− radicals linearly increases with the alkali content of the glasses, which was ascribed to the linear increase of non-bridging oxygens in the PO 4 tetrahedra.

Reinvestigation of the structure of the trimethyltin chloride 2,2′-bipyridine adduct

The structure of the complex, (CH 3) 3SnCl·bipy, was determined in the solid state using infrared and Mössbauer spectroscopies and in solution using the proton magnetic resonance spectrum recorded in CCl 4. The infrared and Mössbauer spectra indicated that, in the solid, the complex is a trigonal bipyramidal structure with coplanar methyl groups based on the quadrupole splitting values and the absence of the SnC symmetric vibration in the infrared spectrum. Upon dissolving in CCl 4, the structure is altered. The 1H NMR spectrum indicated that dissociation occurred upon dissolution based on the low value of the tin methyl hydrogen coupling constant.

Crystal structure of tricyclohexyltin chloride

The structure of tricyclohexyltin chloride has been determined by X-ray analysis. The compound crystallizes in the space group P2 1/ m with a 10.386(6), b 17.195(9), c 5.713(3) Å,β 104.26(9)° and Z = 2. It consists of discrete tetrahedral (cyclo-C 6H 11) 3SnCl units. The departure from the regular tetrahedral geometry is less than that in tricyclohexyltin acetate. The quadrupole splitting value (Δ 3.49 mm s −1), so large as to have been attributed to a penta-coordinated geometry, is shown to be consistent with the tetrahedral geometry when distortions are taken into account in the treatment of the point charge model.

Pyridine base adducts of manganese(II) and iron(II) complexes of TTA and STTA

Octahedral high-spin adducts of the type ML 2B 2, where M = Mn(II) and Fe(II), L = thenoyltrifluoroacetone and monothiothenoyltrifluoroacetone and B = pyridine and γ-picoline, were isolated in the atmosphere and the properties of these adducts were investigated to clarify the effect of the sulfur-coordination. The assignments of the metal-ligand stretching bands in IR spectra were performed. The frequencies of these bands followed the Irving-Williams order in most cases and suggested the soft character of Fe(II) to sulfur atom. The values of isomer shift and quadrupole splitting of Mössbauer spectra in Fe(II) complexes of STTA revealed the contribution of π back-donation to a great extent.

Synthesis of Some Triethylammonium Dihalotriorganostannates

Abstract Three new triethylammonium dihalotriphenylstannates and four new triethylammonium dihalomethyldiphenylstannates were synthesized and characterized by IR, PMR, and Mössbauer spectroscopy. The quadrupole splitting values calculated for these compounds using the point-charge model were in close agreement to the experimental values.

Semiempirical calculations of model deoxyheme. Variation of calculated electromagnetic properties with electronic configuration and distance of iron from the plane

The electronic structure of deoxyheme units and the electric field gradient at the iron nucleus are calculated as a function of the displacement of the iron from the heme plane. The high spin state has a calculated minimum energy with the iron out of plane at a distance similar to that observed for metMb. This could correspond to a relaxed form of deoxyHb, while the greater displacement observed in the intact protein could be strained. The calculated electric field gradient is relatively insensitive to iron displacement from the heme plane. This insensitivity could account for the very similar values of quadrupole splittings observed in low-affinity deoxyhemoglobin A and its separate high-affinity alpha and beta subunits, and still allow small differences in iron displacement consistent with the stereochemical trigger mechanism of cooperativity.

Relationship between m�ssbauer spectra and defect structure in biotites from electric field gradient calculations

The electric field gradient at the octahedral sites in biotite is calculated by use of the point charge model for the ideal crystal structure. The contribution from the overlap distortions of cation orbitals by the surrounding ligands is included. The calculated values of the ferric quadrupole splittings are in good agreement with those obtained from Mossbauer spectra of micas. The effect of the neighbouring point defects and of real structure features of biotite on the electric field gradient are computed. It has been found that various point defects in adjacent sites produce varying values of ferric quadrupole splittings, which exceed the difference between the ideal parameters at the two distinct octahedral sites. A new interpretation of the biotite Mossbauer spectra is suggested.

Transition metal chemistry of oxime-containing ligands, VI: magnetic and structural properties of mono (pyridine-2-aldoxime) dithiocyanato iron (II) and mono (6-methylpyridine-2-aldoxime) dithiocyanato iron (II) complexes

The complexes of pyridine-2-aldoxime (HPOX) and 6-methylpyridine-2-aldoxime (HMPX) with iron (II) thiocyanate of the type [Fe(L)(NCS)2] (L=HPOX and HMPX) have been prepared and characterized. A study of X-ray, magnetic, vibrational spectra (conventional and far-infrared), electronic spectra andMossbauer spectra has indicated that these complexes have polymeric, pseudo octahedral, coordination geometry with linear bridging thiocyanate ligands. The electronic spectra of mono complexes show a larger, low symmetry, ligand field than that present in [Fe(L)2(NCS)2] complexes. UnperturbedMossbauer spectra show a large quadrupole splitting, ΔEQ, and smaller isomer shift values in these iron (II) thiocyanate complexes. The magnetically perturbedMossbauer spectra of these iron(II) thiocyanate complexes at room temperature show that the principal component of the electric field gradient tensor is positive and corresponds to ad xy (5B2) ground state.

13C NMR studies on M(CN)5Xn− complexes

The 13C chemical shifts for a variety of M(CN)5Xn− complexes are reported. These chemical shifts correlate extremely well with the MC and CN stretching frequencies and Mössbauer isomer shifts and quadrupole splitting values for the iron complexes. However, the calculated shielding constants do not correlate well with the observed shifts.

Mössbauer studies of some new hexacoordinate iron(II) complexes with isocyanides, phosphines and halides

Mössbauer parameters have been determined, at 80 K, for some new complexes of the type [FeX(CNR) 5-nL n]ClO 4( n  3, 2, 0; X  Br -, I -; L  PhP(OEt) 2; R  4-CH 3C 6H 4, 2-CH 3C 6H 4, C 6H 5, 4-NO 2C 6H 4, 4-CH 3OC 6H 4, 2,6-(CH 3) 2C 6H 3 and [FeX 2(4-CH 3C 6H 4NC) 4]. Treatment by the point-charge model has been carried out to rationalize quadrupole splitting and centre shift values for chloro, bromo and iodo derivatives. The structural assignments, by pqs parameters, are consistent with X-ray and IR data.

An additive treatment of 115In nuclear quadrupole coupling constants for organoindium compounds

Using previously measured 119Sn IV and 115In III e 2 Qq values, we use the additivity model to rationalize and calculate 115In e 2 Qq values for In III in a variety of coordination environments. A semiquantitative estimate of In III e 2 Qq values (in MHz) may be obtained by multiplying the 1 2 s 2Qq value (in mm sec −1) for the isostructural Sn IV compound by 310. Absolute partial quadrupole coupling constants ( pqcc) have been derived for the first time for linear ( sp hybridized metal) and trigonal planar ( sp 2 hybridized metal) species. The ratios of the pqcc values ( pqcc) Me tet:( pqcc) Me tba: ( pqcc) Me oct is 1.23:1.09:1. These are in good agreement with the corresponding 119Sn partial quadrupole splitting ( pqs) values. The relative pqce values for ligands in two to six coordination are in qualitative agreement with those expected from a simple molecular orbital approach. The pqcc parameters are used to calculate the expected e 2 Qq values for a number of methylindium species in four, five, and six coordination. These calculations should be very useful for structural elucidation. For the associated compounds MeInBr 2 and EtInI 2, these calculations suggest highly associated structures with In having a coordination number of greater than four. For the six coordinate Me 2In moieties, the trend in e 2 Qq with C-In-C angle is reproduced qualitatively by a simple distortion calculation.

Mössbauer spectroscopic studies of clusters Mn 2(CO) 8[μ-Sn(hal)Mn(CO) 5] 2 (hal = Cl, Br) and related Mn and Re compounds

In order to be acquainted with the nature of bonds at Sn involved in the title compounds, as well as to get information on the configuration of the strictly related derivatives I 2Sn 2Mn 4(CO) 18 and Cl 2Sn 2Re 4(CO) 18, the Mössbauer spectroscopic investigation reported in this paper has been carried out. The experimental parameters (isomer shifts, δ; nuclear quadrupole splittings, ΔE; for the bromide derivative only, the asymmetry parameter η and the sign of the nuclear quadrupole coupling constant e 2qQ) have been discussed in connection with data concerning compounds with tin-transition metal bonds, mainly hal 2Sn[Mn(CO) 5] 2 (hal = Cl, Br) and ClSn[Mn(CO) 5] 3. Rationalizations of ΔE and η have been effected by the point-charge model formalism. Deductions derived from Mössbauer-Zeeman spectral parameters have been interpreted in the light of informations extracted from the molecular structures and the application of the second-order hybridization concept. A s character sequence has been proposed for SnMn and Snhal bonds, as well as self-consistent sets of calculated absolute partial quadrupole splitting values, for the title compounds and quoted halotin-manganese pentacarbonyls.

MÖSSBAUER SPECTRA OF DEOXYGENATED HEMOGLOBIN IN R AND T STATES

Normal human deoxygenated hemoglobin (Hb) exhibits low oxygen affinity and cooperativity in ligand binding (T state). These functional properties are lost upon enzymatic removal of the two C-terminal amino acids of the P chains (Hb-CPA) or of the C-terminal amino acid of the a-chain followed by reaction with NEM (NES des-Arg-Hb) (R state). This last species recovers normal functional properties upon binding of IHP. The isomer shift and quadrupole splitting values at 78 K of Hb and HbCPA are very close and distinct from those relative to NES- des-Arg Hb and IPH + NES-des-Arg Hb. Thus Mossbauer parameters reflect changes in the ferrous ions electronic structure that cannot be directly related to the conformational state of the molecule.

Mössbauer Study of FexCo1-xRh2S4 with Spinel Structure

X-ray, magnetic, electrical and Mossbauer studies are made on Fe x Co 1- x Rh 2 S 4 (0≤ x ≤1.0). These compounds are found to be antiferromagnetic and semiconducting. For x ≤0.75, the Mossbauer spectra resemble to each other and show apparently superpositions of many spectra with different values of hyperfine fields and quadrupole splittings. On the assumptions that local tetragonal distoritions occur at all ferrous ion sites in the crystal and that a complex spin structure is formed independently of the distortions, fitting calculations for the observed spectra are made. For x =1.0, the observed spectra are complicated and can not be explained applying such a simplified model only.