Die chromatographische Trennung und Bestimmung von 51Cr, 54Mn, 60Co und 59Fe

Ohne Zusammenfassung     

Hyperfine interactions at 57Fe in octaethylhaemin

Mössbauer measurements on octaethylhaemin have been made between 4.2 and 300 K, and (at the lower temperature) in applied magnetic fields of up to 50 kG. From a spin hamiltonian treatment the saturation value of the hyperfine field at the ⁵⁷Fe nucleus is found to be 495 kG, and the splitting parameter for the ferric ion levels by the axial ligand field is D = 8.0 cm^?1. The electric field gradient 1/2e²qQ = +0.93 mm s^?1.     

Mössbauer spectroscopy of 57Fe in NH4MnCl3, NH4FeCl3 and NH4CoCl3

The Mössbauer spectra of ⁵⁷Fe doped NH₄MnCl₃ reveal that this compound undergoes a crystallographic phase transition at 258°K and becomes magnetic at 105°K. No crystallographic transition appeared either in NH₄FeCl₃ or in ⁵⁷Fe:NH₄CoCl₃; the latter orders magnetically around 27°K.     

57Fe Mössbauer study of volcanic hornblende

A Mössbauer study has been made of Fe sites in volcanic hornblende of chemical composition (Si_5.7Al_2.3) (Al_1.5Ti_0.4Fe_0.5³⁺Fe_0.6²⁺Mn_0.01Mg_3.2)(Ca_2.0Na_0.5K_0.4P_0.01)(O, OH, F)₃₂ obtained from inside a volcanic bomb in the ash ejecta of Eifel region in Germany. The spectrum has been computer fitted to two quadrupole doublets and assigned to Fe²⁺ and Fe³⁺ oxidation states at the octahedral M₁, M₂ and M₃ sites; the M₄ site being considered to be occupied primarily by Ca atoms.     

Eu0.5RE0.5Fe0.5Mn0.5O3的57Fe Msosbauer谱研究

利用固相反应合成了Eu0.5RE0.5Fe0.5Mn0.5O3(RE=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Er,Tm,Yb,Y)等化合物。测量了其XRD谱及57FeMssbauer谱。实验发现,随着RE原子序数的增加,样品的晶胞体积减小,Fe在化合物中处于Fe3+的高自旋状态,57Fe的四极裂矩与样品的畸变参数D成线性关系。     

Direct observation of 57Fe chemical shifts in diamagnetic organoiron complexes

⁵⁷Fe NMR spectra of 35 organoiron complexes predominantly of the type [Fe(CO)₃(diene)] have been measured by direct detection at 2.9 MHz and at natural isotope abundance (2.2%). The ⁵⁷Fe chemical shift range so far observed is 3000 ppm, corresponding to about 9 KHz. The majority of the resonances are at higher frequency than that of Fe(CO)₅, which is proposed as a secondary standard. The ⁵⁷Fe resonance frequencies are also reported as ratios relative to the ⁷³Ge frequency of GeCl₄.The ⁵⁷Fe shielding is discussed qualitatively in terms of charge distribution in the complexes, very large deshielding effects being observed for cationic olefinic ligands. For η⁴-diene complexes, the shielding also depends upon ligand geometry and decreases with increasing ring size or CCC bond angle. Two types of ferrocenylcarbenium ions may be distinguished, indicated by high- or low-frequency shifts relative to ferrocene. For a number of [Fe(CO)₃(olefin)] complexes ¹J(⁵⁷Fe, ¹³C) coupling constants involving the carbonyl carbon are also reported.     

Zur simultanen Bestimmung von 55Fe und 59Fe in biologischen Proben

Ohne Zusammenfassung     

Mössbauer 57Fe spectra exhibiting “ferrous character”

The term “ferrous character” reported extensively in the literature for the Mössbauer spectroscopy of octahedrally coordinated iron atoms in chalcogenides and antimonides is critically evaluated. The significance of a formal valence state for the iron is examined. The magnitude of the isomer shift is shown to provide a guide not only to the existence of high-spin versus low-spin states, but also to localized versus itinerant electrons or to extended electrons within FeXM interactions (M = transition metal and X = anion). The existence of a quadrupole splitting for iron atoms in intrinsically cubic fields is only possible where the β-spin electron outside a closed α-spin half-shell is localized and Jahn-Teller coupled to lattice vibrations to form vibronic states. This situation is distinguished from quadrupolar fields associated with local-site symmetries deformed from cubic symmetry as well as from the case where the formation of itinerant β-spin electrons inhibits the formation of vibronic states.     

Zur Darstellung von hochspezifischem 64Cu, 65Ni und 56Mn

Ohne Zusammenfassung     

57Fe Mössbauer effect study of a presumed singlet-triplet transition in [Fe(P4)X]BPh4 complexes,X = Br,I

The ⁵⁷Fe Mössbauer effect in the solid compounds [Fe(P₄)X]BPh₄ (X = Br, I; P₄ = hexaphenyl-1,4,7,10-tetraphosphadecane) has been studied between 4.2 and 298 K. A single temperature dependent doublet is observed. For the iodo complex, ΔE_Q = 2.25 mm s^?1, δ^IS = +0.13 mm s^?1, V_tzz 0, η ≈ 0.8 at 4.2 K, whereas ΔE_Q = 1.81 mm s^?1, δ^IS = +0.20 mm s^?1 at 298 K. The results are consistent with a singlet-triplet transition with k > 10⁹ s^?1.     

An 57Fe Mössbauer effect study of magnetic ordering in the Fe2O3Cr2O3 system

⁵⁷Fe Mössbauer effect spectra have been obtained as a function of temperature for a series of Fe₂O₃Cr₂O₃ compositions in the range 0.2–75% Fe₂O₃. From 30% of Fe₂O₃ upwards, the dependence of the reduced internal magnetic field $\text{H}{}_{\mathrm{<mtext>eff</mtext>}}\text{(T)}\text{H}{}_{\mathrm{<mtext>eff</mtext>}}\text{(T = 0)}$ on reduced temperature, $\text{T}\text{T}{}_{\mathrm{N}}$, was found to be identical with that for α-Fe₂O₃, indicating the persistence of Fe₂O₃-type ordering over this composition range. For 0.2% of ⁵⁷Fe₂O₃ in Cr₂O₃, the reduced field values fall far below those for α-Fe₂O₃ or Cr₂O₃, and weak coupling of Fe₃⁺ with Cr³⁺ has been inferred.A Morin transition similar to that for α-Fe₂O₃ was not present for samples containing 75% of Fe₂O₃. Quadrupole shifts ? were found to be negative and diminishing between 75 and 30% Fe₂O₃, and positive between 20 and 0.2%. The limiting value at lowest dilution of 0.113 ± 0.010 mm/sec corresponds to a nuclear quadrupole coupling constant e²qQ of 0.45 ± 0.04, approximately half that for α-Fe₂O₃. Cone angles for Fe³⁺ spin vectors in the spin-spiral arrangements for intermediate compositions have been derived, and are similar to, but less extreme than those deduced from neutron diffraction data.     

Origin of the quadrupole splitting in the Mössbauer 57Fe spectrum of cubic (disordered) LiFeO2

The room-temperature Mössbauer ⁵⁷Fe spectrum of polycrystalline disordered cubic α-LiFeO₂ contains a quadrupole splitting |Δ_obs| of 0.65(2) mm/sec. This value is relatively large for an Fe atom in an essentially Fe³⁺_HS state. To account for its magnitude, the distribution of the electric-field gradient (EFG) values associated with the Fe atoms was investigated by means of exact geometric analysis involving the 12 nearest cation neighbors (model A) as well as large-scale computer simulation involving more distant cations (models B to E). It is found that (1) the major contribution to |Δ_obs| comes from the distribution of +1 and +3 charges among the 12 nearest cation neighbors of a reference Fe atom; (2) this contribution by itself largely accounts for |Δ_obs|; (3) the contribution from cations beyond the seventh-nearest neighbors is marginal; (4) displacing the oxygen atoms from their lattice sites toward adjacent Fe atoms produces a significant effect on the distribution of EFG values at a reference Fe atom, while incipient cation ordering appears to have a relatively small effect; and (5) the contribution of the EFG = 0 component to model |EFG| distributions will be overemphasized unless cations beyond the first-nearest neighbors are included in the EFG summation. The 144 distinct (up to rotation and reflection) Li¹⁺_12?kFe³⁺_k configurations on the coordination cuboctahedron of nearest cation neighbors (required for the examination of model A) are listed, together with their symmetries and multiplicities, and it is shown that the 144 configurations engender only 17 distinct |EFG| values. Observations are also made on various geometric aspects of calculating EFG at ⁵⁷Fe³⁺_HS on cubic lattices.     

57Fe NMR Chemical shifts and 57fe, 13C coupling constants in α-ferrocenyl carbocations. Direct metal participation in the stabilization of metallocenyl carbocations

The ¹³C{⁵⁷Fe} double resonance method has been used to investigate ⁵⁷Fe-enriched samples of ferrocene derivatives, α-ferrocenyl carbocations and carbonyl complexes with various σ- and π-hydrocarbon ligands. In the α-ferrocenyl carbocations the ⁵⁷Fe resonances span a 1200 ppm range, being a sensitive tool of direct iron participation in the stabilization. The ⁵⁷Fe resonances in the carbocations [FcCH₂][HSO₄] (I), [FcCHMe][HSO₄] (II), [FcCHPh][HSO₄] (III), [FcCHC₅H₄ Mn(CO)₃][CF₃CO₂] (IV), [(Fc)₂CH][BF₄] (V), [FcCHC₅H₄RuC₅Hs][BF₄] (VI) and [FcCMe₂][HSO₄] (VII), ?523.6, ?219.3, 221.0, 368.7, 699.0, 405.0 and 288.5 ppm, respectively, relative to ferrocene, are interpreted in terms of rehybridization of the iron non-bonding d orbitals (shielding effect and the electron withdrawing effect of the substituent in the cyclic ligand (deshielding effect). The role of rehybridization of non-bonding iron orbitals in the low-frequency shift of the ⁵⁷Fe resonances, in addition to that in the previously investigated complex [(C₅H₅)₂FeH][BF₃OH] (?1109.3 ppm), has been demonstrated for bridge-substituted [3]ferrocenophanes, whose ring tilting induces a low-frequency shift of up to 340 ppm relative to their unbridged analogues.The ¹³C NMR spectra of carbocations V and VI reveal a temperature dependence due to the rotation around the C(1)C_α exocyclic bonds. In carbocation VI the ruthenium atom effectively competes with the iron atom to bond with C_α whereas in carbocation V two equivalent metal atoms possess the same ability for such bonding; as a result, complex V has a more pronounced “carbenium ion” nature than IV and VI, as indicated by the relative positions of the ¹³C_α resonances in carbocations IV, V and VI: δ 122.4, 147.2 and 116.9 ppm, respectively.The values of ⁵⁷Fe, ¹³C coupling constants for α-ferrocenyl carbocations exclude Fe-C_α σ-bonding and support a structure in which the iron atom is π-bonded with six carbon atoms of a fulvenoid ligand. According to the data on ⁵⁷Fe resonances and ⁵⁷Fe, ¹³C coupling constants in α-ferrocenyl carbocations the strength of FeC_α bonding is markedly influenced by the electronic effect of the substituent at C_α, being even lower in carbocation I than that of Fe-cyclopentadienyl carbon atoms.     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).     

Overlap contribution to internal conversion coefficients of the 14.4 keV M1 transition in 57Fe

It is suggested that while evaluating contact charge densities from internal conversion coefficients it is important to consider overlap effects. Ratios of the internal conversion coefficients

and

are evaluated as a function of interatomic separation for Fe³⁺ in an octahedral arrangement of Br^? ions.     

Mössbauer 57Fe isomer shift as a measure of valence in mixed-valence iron sulfides

An empirical formula relating the room-temperature isomer shift δ for high-spin iron in sulfur coordination to the effective iron valence 〈m +〉, of the form δ = A ? B 〈m +〉, has been refined for tetrahedral coordination and modified by an inclusion of orbital degeneracy into the definition of 〈m+〉; it has also been extended to include octahedral coordination by adding 0.17 mm/sec to A. For a given 〈m+〉, the I.S. is shown to be sensitive to nearest-neighbor anion coordination, but much less sensitive than the hyperfine field to the competitive bonding with these anions. However, the sign of the deviation from the empirical line indicates the direction of any net superexchange charge transfer to or from the iron atom. The utility of the relationship is illustrated by application to a wide range of problems.     

Superexcited states of CH4

The energy spectrum of a superexcited state (the different between the total photoabsorption and photoionization cross section) is calculated using ultraviolet photoelectron data for CH₄ and oscillator strength data for the iso-electronic atom, Ne. From this estimate we have concluded that the superexcited state of CH₄ is interpreted in terms of Jahn-Teller distortion of high Rydberg states referring to the ²T₂ state of CH⁺₄. The inconsistency between the data of the UV optical spectrum and results of other measurements or analyses is pointed out and discussed.     

Rydberg states of H4

Ab initio frozen core CEPA calculations have been performed in order to predict vertical energy levels and disccosiation energies for the Rydberg states of H₄ up to n_eff = 5. The electron correlation energies are analysed and discussed.     

Non-radiative decay of the benzene 1B2u and 3B1u states

Optic-acoustic measurements on high pressure benzene are presented, and are used to analyse the nature of the decay channels form the highly vibrationally excited ³B_1u state. The vibrationally relaxed benzene ³B_1u state is deactivated by n-pentane with a collisional efficiency of 3 × 10^?5. A model, introducing an intermediate state close in energy to the ³B_1u state, is shown to be in good accord with the results.