57Fe Mossbauer studies

Fe Mossbauer study of iron distribution in zeolite A during zeolite crystallization process... 

Finch, J. Gainsford, A. R. Tennant, W. C. (1982) Polarized optical absorption and 57Fe Mossbauer study of pegmatitic muscovite. Amer. Mineral., 67,59-68. 

A 57Fe Mossbauer study of the mineral deerite, Fe 2Fe6+[Si12O40](OH)10, has been effected over a wide temperature range (5—500 K).339 The spectra... 

Properties of FeCr,o solid samples have been studied by X-ray diffraction, 57Fe Mossbauer spectroscopy and magnetic measurements to stimulate the interaction of Fe with fullerene. FeCr,o samples have been prepared by decomposition of the 1,3-dipolar cycloadduct of the fullerene and ferrocene nitrile oxide. The components exhibit super paramagnetic properties originating from an interaction between FeCr,o complexes within the nano-particles. Each nano-particle consists of hundreds to thousands complexes (546). 

The recoilless nuclear resonance absorption of y-radiation (Mossbauer effect) has been verified for more than 40 elements, but only some 15 of them are suitable for practical applications [33, 34]. The limiting factors are the lifetime and the energy of the nuclear excited state involved in the Mossbauer transition. The lifetime determines the spectral line width, which should not exceed the hyperfine interaction energies to be observed. The transition energy of the y-quanta determines the recoil energy and thus the resonance effect [34]. 57Fe is by far the most suited and thus the most widely studied Mossbauer-active nuclide, and 57Fe Mossbauer spectroscopy has become a standard technique for the characterisation of SCO compounds of iron. 

Fe HB(C2H2N3)3 2] has been obtained by dehydration under heating of the low-spin hexahydrate. The crystal structure for this hexahydrate has been determined at room temperature [17]. It clearly contains Fe(II) ions in the low-spin state (average Fe-N distance=1.99 A). The dehydrated derivative [Fe HB(C2H2N3)3 2] has been reported to exhibit a very abrupt spin transition between 334-345 K via variable temperature UV-vis and 57Fe Mossbauer spectroscopy studies [19]. After the publication of a preliminary magnetic study in 1994 [19], a more detailed report appeared in 1998 [20]. 

The spin transition in [Fe(salen)(NO)] has been studied by IR [171, 172], 57Fe Mossbauer [169, 173] and EPR spectroscopy [169]. IR spectra have also been recorded at room temperature for various pressures ranging from ambient up to 37 kbar. At 37 kbar conversion to the S=l/2 state is complete [172]. The quartet state is re-populated on relaxation of the pressure. 

De Endredy, A.S. (1963) Estimation of free iron oxides in soils and clays by a photolytic method. Clay Min. Bull. 5 209-217 de Faria, D.L.A. Venancio Silva, S. de Oliveira, M.T. (1997) Raman Microspectroscopy of some iron oxides and oxyhydroxides. J. Raman Spectrosc. 28 873-878 De Grave, E. Vandenberghe, R.E. (1986) 57Fe Mossbauer effect study of well-crystallized goethite (a-FeOOH) Hyp. Interact. 28 643-646... 

De Grave, E., Eeckhout S.G., McCammon, C.A. (1999a) Selected applications of 57Fe Mossbauer spectroscopy to mineral studies. Hyp. Interact. 122 21-38... 

FeMoco, both as a constituent of the FeMo protein and an isolated entity, has been the subject of detailed spectroscopic examination. 57Fe Mossbauer and EPR studies of the cofactor have been interpreted in terms of an S = centre that contains one molybdenum and ca. six irons in a spin-coupled structure. The EPR signal serves as a valuable fingerprint of FeMoco furthermore, release of FeMoco from the FeMo protein produces an EPR spectrum with broader features, but the same profile, thereby indicating that the core of this cluster is little changed by the extraction procedure. Treatment of FeMoco with ca. one equivalent of... 

Infrared- and 57Fe-Mossbauer-spectral studies indicated that substitution in these derivatives occurs exclusively at cobalt, with one ligand per cobalt atom in the trisubstituted derivatives (54). Only with the chelating dppe ligand was a tetrasubstituted product formed, Eq. (74). 

The time dependence of the anhydrous [Fe(paptH)2](N03)2, which was first reported on by Sylva and Goodwin109), has recently been studied in detail by 57Fe Mossbauer measurements161). The gradual conversion from sT2(Oh) to 1 A1(Oh) was found to be almost complete, when the sample was cooled slowly, the ST2 fraction being > 0.95 at 290 K and 0.067 at 105 K. A pronounced hysteresis of ATC =... 

In a single-domain particle of a-Fe203 the magnetization vector is held in the c-plane perpendicular to the c-axis by the magnetocrystalline field. Mossbauer studies use the 57Fe nucleus as the "observer to record when the relaxation time t becomes shorter than the period for precession of the nuclear spin about the direction of the effective field. Substitution into the equation for the Larmor frequency, or observer relaxation time, with an expression for the frequency factor proportional to the specific volume and anisotropy constant of the oxide gave (26, 27) the relationship ... 

Iron porphines constitute the active site of hemoproteins and as such are among the most important and most widely studied series of metal complexes. The syntheses of iron protoporphyrin (heme) and its derivatives are important for the reconstitution of hemoproteins (particularly when one wishes to incorporate 57Fe for Mossbauer studies), as well as for model studies. In addition to the naturally occurring porphyrins, iron complexes of both 5,10,15,20-tetraphenyl-21//,23//-porphine (H2tpp) and octaethyl-21//,23//-porphine (H2oep) are widely used in model studies of the natural systems. 

Combined EPR and 57Fe Mossbauer spectroscopic studies of the MoFe protein in various overall oxidation states39 40,42,44 48,49) have provided strong evidence for the presence of six metal clusters two M centers that are the protein-bound form of the FeMo-cofactor (a novel Mo-Fe-S cluster) and four unusual tetranuclear iron clusters referred to as the P clusters. These will be discussed separately below. In addition, Mossbauer spectra of MoFe proteins from Azotobacter vinelandii, Clostridium pas-teurianum, and Klebsiella pneumoniae all show an additional component termed S39 40 42, which accounts for 6% of the total Fe present (2 Fe per molecule) and which has Mossbauer parameters (AEq = 1.35 mm/s d = 0.60 mm/s) different from those expected for likely impurities such as high-spin Fe2+ or Fe3+ ( adventitious iron). At present, it is difficult to decide whether species S is an unusual and persistent impurity or an integral part of the MoFe protein. 

The existence of extensive Mossbauer studies of 57Fe in this material provides a motivation for detailed study, since theory and experiment can be closely compared [124]. One important result of the Mossbauer work is the observation of some Fe3+ on the octahedral sites, presumably to relieve stress due to misfit between ionic radius of Fe2+ and packing requirements of the structure. Since the hyperfine fields are known to be sensitive probes of the local environment, a comparison of results with different cluster sizes and boundary conditions will give a clear indication of convergence and reliability of the model, which can be applied more generally to silicates. 

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