Quadrupole Splitting Data Research Articles

197Au Mössbauer Spectroscopy Studies of Some Cyclometalated Gold Dimers

Abstract The oxidation states and structures of a series of cyclometalated gold complexes derived from oxidative addition reactions of the digold(I) complex [Au2(μ-C6H3-2-PPh2-6-Me)2] have been determined by 197Au Mössbauer spectroscopy. The spectra for the binuclear gold(I)/gold(I) and gold(II)/gold(II) complexes indicate the presence of equivalent gold atoms, whereas the gold(I)/gold(III) and gold(III)/gold(III) spectra show signals due to two inequivalent metal centers. The coordination spheres of metal centers in the complexes have been determined from isomer shift and quadrupole splitting data.

NMR structural analysis of incommensurate modulated systems with multiple active symmetry modes: A case study of deuterated bis-(4-chlorophenyl)-sulfone

We report single-crystal deuteron NMR measurements both in the normal (N) and the incommensurate (IC) phase of bis-(4-chlorophenyl)-sulfone (BCPS). From the quadrupole splitting data obtained in the N phase, the quadrupole coupling (QC) tensors of all deuterons in BCPS are derived. The central part of the paper is concerned with the analysis of the deuteron NMR frequency distributions observed in the IC phase as a function of the orientation of the applied magnetic field relative to the BCPS crystal. This analysis is carried out in terms of the amplitudes and phases of the rotational symmetry modes that contribute to the fundamental IC modulation wave in BCPS, i.e., directly in terms of the structural changes associated with the IC phase transition. Both a semiquantitative graphical, and a fully quantitative numerical approach are given. The former is used to identify particularly simple and therefore particularly informative crystal orientations. The latter uses as an input the deuteron QC tensors measured in the N phase. Quantitative and complete structural information about the rotational displacements that atoms experience in an N--IC phase transition is deduced from NMR spectra. Our results are in full agreement with corresponding data of an x-ray-diffraction study. We also report on measurements of the spin-lattice relaxation time ${T}_{1}$ across the deuteron NMR frequency distributions. The results are at variance with the established theory and this is traced back to the fact that multiple rotational modes are contributing to the IC modulation wave in BCPS.

Cation Distribution and Magnetic Interactions in Substituted Iron-Containing Garnets: Characterization by Iron-57 Mössbauer Spectroscopy

Some new compounds with garnet-related structures have been examined by57Fe Mössbauer spectroscopy. The results show that in compounds of the type YCa2SbFe4−xGaxO12(x= 2, 3) the gallium is distributed over both the octahedral and tetrahedral sites. In these compounds, together with materials of composition Y3−2xCa2xSbxFe5−xO12(x= 1.25, 1.5) and Y3−xCaxSnxFe5−xO12(x= 1, 2), the results show evidence of more than one tetrahedral environment for the Fe3+ions. The quadrupole splitting data for the Fe3+ions in tetrahedral sites in some of these compounds are significantly larger than those previously reported for Fe3+in tetrahedral sites in other garnets. The compounds YCa2SbFe4O12and Y2CaSnFe4O12magnetically order at similar temperatures and show comparable octahedral- and tetrahedral-hyperfine magnetic fields at 18 K. The substitution of Fe3+by diamagnetic Sb5+on the octahedral sites results in a considerable lowering of the magnetic ordering temperature. The compounds Y0.5Ca2.5Sb1.25Fe3.75O12and Ca3Sb1.5Fe3.5O12show magnetic ordering on both the octahedral and tetrahedral sublattices at 18 K. A similar effect is observed in the compound YCa2SbFe3GaO12where 33% of the Fe3+ions located at the tetrahedral sites are substituted by diamagnetic Ga3+ions. The importance ofa–dantiferromagnetic superexchange interactions is demonstrated in compounds of the type YCa2SbFe2Ga2O12and YCa2SbFeGa3O12where the Ga3+ions substitute the Fe3+ions on both the octahedral and tetrahedral sites. In these compounds the dilution of the magnetic ions at the tetrahedral sites results in the frustration of magnetic ordering on both thed- anda-sublattices. The compound YCa2Sn2Fe3O12which does not contain Fe3+on the octahedral sites shows magnetic ordering on thed-sublattice in the absence of magnetic ions on theasublattice. The result demonstrates the importance ofd–dantiferromagnetic superexchange interactions.

Correlation of Fe 2+ isomer shifts with bond lengths and bond strengths in neso- and sorosilicates

An evaluation of Mbssbauer isomer shift and quadrupole splitting data of Fe2+ in a number of structurally well characterized neso- and sorosilicates is presented. It is found that the nearly linear correlations exist both between the isomer shift and the bond length and between the isomer shift and the bond strength. These correlations are discussed on the basis of the variation of the s-electron density at the Fe2+ nuclei with the chemical bond characteristics.

Transition metal Schiff-base complexes as ligands in tin chemistry. Part 2. A tin-119 Mössbauer spectroscopic investigation of the adducts SnBunxCl3–x(OR)·ML (x= 0 or 1; R = H or alkyl; M = CuIIor NiII; L = quadridentate Schiff-base ligand)

The compound SnCl3(OEt)·EtOH reacts with the complexes ML [M = CuII or NiII; H2L =N,N′-ethylene-bis(salicylideneimine), N,N′-o-phenylenebis(salicylideneimine), or derivatives of these] to give the adducts SnCl3(OEt)·ML. Hydrolysis of the ethoxo adducts in chloroform under ambient conditions yields the adducts SnCl3(OH)·ML. Chloroform solutions of the adducts SnCl4·ML gives similar hydroxo adducts under ambient conditions when M = CuII but not when M = NiII. The compound SnBunCl2(OH)·H2O reacts with ML at –10 °C to give 1 : 1 adducts, but at higher temperatures SnBunCl(OH)2·H2O and SnBunCl3·ML are formed. The compound SnBunCl2(OMe)·MeOH reacts with ML in chloroform to yield the adducts SnBunCl2(OMe)·ML. The replacement of chloride by hydroxide or alkoxide in either SnBunCl3 or SnCl4 results in a reduction of the Lewis acidity at tin. Mossbauer quadrupole-splitting data for SnBunCl2(OH)·ML and SnBunCl2(OMe)·ML were analysed in terms of the point-charge model from which it was established that the donor oxygen and carbon atoms practically always adopt fac geometry about tin; this contrasts with the mer geometry preferred by many adducts SnBunCl3·ML.

Tin–bromine bond lengths and mössbauer quadrupole splittings of tin(IV) bromide complexes. Crystal structure of pyridinium tetrabromodiphenylstannate(IV)

Mössbauer and crystallographic data have been obtained for pyridinium tetrabromodiphenylstannate(IV). The Sn atom is six-co-ordinated in the centrosymmetric trans-[SnBr4Ph2]2– anion with bond distances Sn–Br(1) 2.7592(3), Sn–Br(2) 2.7737(3) and Sn–C(11) 2.158(3)Å. The average Sn–Br distance for five octahedral tin(IV) bromide complexes, SnBr4L2, is related to the partial quadrupole splitting (p.q.s.) of the ligands by means of the correlation d(Sn–Br)/Å=(–0.048 ± 0.002)(4 p.q.s.)+(2.589 ± 0.003). The relationship rationalises the experimental Sn–Br distances and quadrupole splitting data in terms of the donor properties of the auxiliary ligands (L) in such a way that weak donor ligands give rise to shorter Sn–Br distances. The Mössbauer quadrupole splitting can be useful in the assignment of v(SnBr) vibrations in the IR and Raman spectra of trans-SnBr4L2 compounds.

Magnetic susceptibility tensors and deuterium quadrupole coupling constants of the methyl halides

High-resolution 95.2 MHz deuteron NMR spectra were obtained from dilute ether solutions of the monodeuteromethyl halides (X = Cl, Br, I). Small quadrupole splittings were resolved, resulting from molecular alignment by the 14.57 T field. These splittings relate the deuterium quadrupole coupling constants (qcc) to the anisotropy in the molecular diamagnetic susceptibility (Δξ). The results are consistent with literature qcc and Δξ values for CH 3CI and CH 3 Br, but suggest that Δξ of CH 3I determined by microwave spectroscopy is high by about 14%. A survey of literature qcc data for the complete series of halomethanes is given. The data indicate a good agreement between qcc's found from gas-phase studies (microwave), low-temperature solid-state NMR and NQR experiments, and investigations using certain well-chosen liquid crystal mixtures. The values judged to be most accurate were combined with quadrupole splitting data to obtain molecular and bond susceptibilities for this series of compounds.

Further examples of 19e− sandwiches of Fe(I) studied by Mössbauer spectroscopy: Per-ethylated benzene complexes

The organometallic complexes C5H5 Fe(I) C6(C2H5)6 and C5(CH3)5 Fe(I)C6 H(C2H5)5 have been studied by Mossbauer spectroscopy. Hyperfine data are typical for 19e− systems with one electron on the e 1 * orbital. The thermal variation of the quadrupole splittings indicates vibronic reduction of the spin-orbit constant, in agreement with previous analyses of similar 19e− systems. The quadrupole splitting and recoil-free fraction data give evidence for phase transitions, which are discussed with respect to cooperative Jahn-Teller distortion and hindered rotations of the ethyl groups.

A study of quasi-crystalline Al–Fe alloys by Mössbauer-effect spectroscopy and diffraction techniques

After an introduction to quasi crystals, special attention is paid to icosahedral Al6(Cr0.7Fe0.3) and decagonal Al7(Mn1−xFex)2. These alloys have been studied with Mössbauer-effect spectroscopy and diffraction techniques. Isomer-shift and quadrupole-splitting data on the icosahedral alloys are successfully described with a Mackay cluster. The X-ray diffractogram of pure decagonal Al7(Mn1−xFex)2, x = 0 and 0.3, has been indexed with a basis-vector set that is closely related to the icosahedral set.

Transition metal Schiff-base complexes as ligands in tin chemistry. Part 1. A tin-119 Mössbauer spectroscopic investigation of the adducts SnX4·ML, SnMe2(NCS)2·ML, and SnRCl3·ML (X = halide; M = CuIIor NiII; L = quadridentate Schiff-base ligand; R = phenyl or n-butyl)

Mossbauer quadrupole splitting data for adducts SnX4·ML, SnRCl3·ML, and SnMe2(NCS)2·ML [R = Ph or Bun, X = Cl, Br, or I; M = CuII or NiII; L =NN′-ethylenebis(salicylideneiminate), NN′-o-phenylenebis(salicylideneiminate), or derivatives of these] are discussed in terms of the point-charge model, and calculated quadrupole splitting data are presented for 27 of the adducts SnRCl3·ML. For each adduct SnRCl3·ML the mer and fac calculated values differ substantially and one is generally in excellent agreement with the experimental value; on this basis geometry is assigned. Examples of mer and fac isomers occur with the former being favoured by the more strongly donating metal Schiff-base complexes. In the case of two complexes it proved possible to isolate both the mer and fac isomers.

The Mössbauer recoil-free fraction and structure: IV. Triphenyltin derivatives of methionine, penicillamine and cysteine and l-histidinatotin(II)

Tin-199 Mössbauer isomer shift, quadrupole splitting and resonance area data have been recorded in the temperature range 77–150 K for the four triphenyltin complexes, O-triphenylstannylmethionine (Ph 3Snmet), its methionine solvate, Ph 3Snmet·metH, O,S-bis(triphenylstannyl)penicillamine ((Ph 3Sn) 2pen) and O,S-bis(triphenylstannyl)cysteine ((Ph 3Sn) 2cys) as well as l-histidinatotin(II) (HisSn). In the solid state, the structure of I comprises mainly discrete monomeric molecules with four-coordinated tin together with a small amount of a one-dimensional polymeric modification containing five-coordinated tin. The methionine solvate, Ph 3Snmet·metH, also contains discrete monomeric molecules, which are involved in hydrogen-bonding with the methionine solvate molecules. Both (Ph 3Sn) 2 pen and (Ph 3Sn) 2)cys contain two chemically-distinct tin environments, one four-coordinate where the triphenyltin residue is bound to the thiol sulphur, and a five-coordinated site where bonding is to the carboxyl group. However, (Ph 3Sn) 2 pen appears to be monomeric in the solid, whereas (Ph 3Sn) 2cys comprises a one-dimensional polymer. An essentially monomeric structure is proposed for HisSn, but with some moderately weak intermolecular association.

On the interpretation of nuclear quadrupole interaction data for rare-earth nuclei at low symmetry sites

Expressions are given for all tensor components of the lattice- and 4f-shell electric field gradient contributions at a rare-earth nucleus and the influence of local symmetry is discussed. To demonstrate that a full tensor analysis is essential for monoclinic symmetry, the quadrupole splitting data for169Tm in Tm2O3 are re-analyzed, resulting in significantly different shielding factorsRQ and Υ∞.

ESR and Mössbauer studies of Fe 3+ ion in calcium boro-aluminate glasses

A correlated ESR and Mössbauer spectroscopic study of the glass system 2Ca O3B 2 O 3.Al 2 O 3.xFe 2 O 3 (0.1⩽ x⩽1) is reported. At low Fe contents ( x⩽0.1) Fe 3+ ions are found only in tetrahedral environments, giving a single, sharp ESR peak at g=4.13. For higher x, occupation by Fe 3+ of other-symmetry sites become possible, as seen by the evolution of g=2.0 and g=6.0 ESR features. A careful examination of Mössbauer isomer shift data has yielded an average value of 1.96 Å for the Fe 3+−O 2− distance, besides confirming the tetrahedral site symmetry. Using this value, and quadrupole splitting data the extent of angular distortion (α) from perfect tetrahedral symmetry has been deduced as 30° from a calculation based on Newman's superposition model.

Studies on mixed metal(II)-iron(II) chloride systems. Part 4. The Mössbauer and X-ray powder diffraction data for the CsM xFe 1−xCl 3·2H 2O (M = Mn, Co or Ni; x = 0, 0.5) system

The octahedral Fe(II) environment containing four chlorides and two cis water molecules is reported for the caesium materials which are demonstrated to be isostructural with RbM xFe 1−xCl 3·2H 2O (M = Mn, Co, Ni; x = 0, 0.5) [2]. The data for interatomic distances and hydrogen bonding in these materials are discussed in terms of the structure of CsMnCl 3·2H 2O from X-ray diffraction [30, 31] and CsFeCl 3·2H 2O from neutron diffraction [34] studies. The Mössbauer data for these compounds are reported. The chemical isomer shifts of all these materials are similar, but the quadrupole splitting data are slightly different. The data are explained in terms of changes in the site symmetry resulting in a change of orbital occupancy. The temperature dependence of the quadrupole splitting in these materials is discussed.

Mössbauer Spectroscopic Studies of Chlorostannate(II) Complexes in Frozen Aqueous Solutions

AbstractMössbauer parameters of frozen aqueous solutions of Sn(ClO4)2 in 0.5 M HClO4 did not change with the concentration of NaClO4, so that it was used to keep the ionic strength at the desired level. When NaCl was added into Sn(ClO4)2 solutions, isomer shift did not change, but quadrupole splitting did. Therefore, stability constants were calculated from the quadrupole splitting data, which were in good agreement with the published values. The observed spectra could be resolved into components.

Preparation and m�ssbauer studies of tetraaquabis[maleato(1-)]-iron(II)

Tetraaquabis[maleato(1-)]iron(II), Fe(C4H3O4)2 · 4H2O has been synthesised. The compound is monomeric and is isomorphous with the manganese(II) analogue. The temperature dependence of quadrupole splitting and optical spectral data giveca. 10000 cm−1,ca. 650 cm−1,ca. 190 cm−1 andca. 1400 cm−1 for the 10 Dq, tetragonal field, rhombic field and the splitting of the Eg level, respectively. The quadrupole splitting data indicate that distortion from cubic symmetry increases in the order oxalate < malonate < maleate. DTA, TGA and Mossbauer studies indicate elimination of one molecule of maleic acid at 235 °C. The resulting product shows a less distorted structure and this is attributed to the formation of maleato(2-)iron(II).

Conversion electron Mössbauer study of LiF implanted with 57Fe ions

Lithium fluoride crystals implanted with 57Fe ions at doses from 5×10 15 at/cm 2 to 6×10 16 at/cm 2 have been studied with conversion electron Mössbauer spectroscopy. It was found that iron enters the implanted zone in three well defined charge states: Fe 3+, Fe 2+ and Fe 0 (metal). At low doses the relative fractions of Fe 3+ and Fe 2+ are close to 80% and 20%, which corresponds to the respective ionic fractions in an iron doped LiF sample obtained by vacuum co-deposition. With the increase in the implantation dose the Fe 2+ and Fe 0 fractions increase to about 40% and 30%, respectively. Annealing in vacuum results in a growth of metallic iron precipitates, whereas annealing in the presence of oxygen leads to precipitation of superparamagnetic particles of some, still unidentified, ferric compound. The Mössbauer data were related to the role of F- and F 2-centres observed by optical absorption measurements. Good agreement has been achieved between the quadrupole splitting data for Fe 3+ in fluorides LiF, NaF and KF and the calculated values in frames of the model of V −-Fe 3+-V − defect clusters presented in our earlier work.

Studies on mixed metal(II)–iron(II) chloride systems. Part 2. Mössbauer and X-ray powder diffraction data for the potassium and rubidium M′M″xFe1–xCl3·2H2O (M′= K or Rb; M″= Mn, Co, or Ni; x= 0.5) systems

The potassium and rubidium complexes M′M″xFe1–x·2H2O (M′= K or Rb; M″= Mn, Co, or Ni; x= 0.5) have been studied by Mössbauer spectroscopy and X-ray powder diffraction. The first occurrence of an octahedral FeII environment containing four chlorides and two cis water molecules is reported for the Rb materials. The K materials contain octahedral FeII environments with trans water molecules. The 57Fe Mössbauer data for these compounds are presented. The chemical shifts of both sets of materials are similar, but the quadrupole splitting data are different. The data for the Rb materials are explained in terms of changes in site symmetry and orbital occupancy. The changes are brought about by changes in bonding due to ‘ pressure ’ effects. The occurrence of cis–trans isomers in the mother-solutions is discussed.

Investigation into diphosphine oxides as ligands in diorganotin(IV) adducts. Part 1. Synthesis and spectroscopic characterization of 1,2-bis(diphenylphosphoryl)ethane tin complexes and X-ray structure of [1,2-bis(diphenylphosphoryl)ethane]di-n-butyldichlorotin(IV)

1,2-Bis(diphenylphosphoryl)ethane (dppoe) forms complexes with diorganotin(IV) chlorides of the type SnR2Cl2(dppoe)(R = Prn, Bun, or Ph), the i.r. and tin-119 Mossbauer spectra of which have been recorded. The crystal structure of SnBun2Cl2(dppoe) has been determined from single-crystal X-ray data collected by counter methods and refined by full-matrix least-squares techniques to R= 0.0461 for 2 430 observed reflections. Crystals are triclinic, space group P, with unit-cell dimensions a= 11.775(5), b= 15.987(7), c= 11.006(5)A, α= 102.12(5), β= 114.55(6), γ= 101.69(5)°, and Z= 2. Tin is bonded to two Cl– ions, to two C atoms and to two O atoms, to one more loosely than the other. The weaker co-ordination of one of the two OP groups is also reflected in distortions of the geometry of the co-ordination polyhedron. The structure is polymeric in that the dppoe ligand forms bridges between adjacent tin atoms. Tin-119 Mossbauer spectra have been recorded for the three SnR2Cl2(dppoe) complexes in the temperature range 77–150 K, and for the complex (SnPh3Cl)2(dppoe) at 77 K. Quadrupole-splitting data for the former are consistent with a trans-SnC2X4 arrangement about the tin atom in each case. Recoil-free fraction temperature coefficients, a, have also been determined for the three SnR2Cl2 complexes; root-mean-square amplitudes of vibration, 〈x〉, and absolute recoil-free fractions, ƒ, have been estimated at various temperatures for SnBun2Cl2(dppoe).

Implantation induced diamond to amorphous-carbon transition studied by conversion electron Mössbauer spectroscopy

The implantation of 57Fe atoms into diamond and graphite matrices at an energy below 100 keV and in a dose range between 10 15 to 10 16 atoms/cm 2 is investigated at room temperature with conversion electron Mössbauer spectroscopy. The spectra indicate similar quadrupole-split broadened doublets in both matrices. The systematics of concentration dependences of the isomer shift and the quadrupole splitting data for Fe implanted in diamond and graphite, silicon and germanium is discussed. A strong influence of the atomic volume and compression effects in diamond is pointed out.