Fe Mossbauer spectroscopy

Fig. 3.19 Schematic illustration of the measurement geometry for Mossbauer spectrometers. In transmission geometry, the absorber (sample) is between the nuclear source of 14.4 keV y-rays (normally Co/Rh) and the detector. The peaks are negative features and the absorber should be thin with respect to absorption of the y-rays to minimize nonlinear effects. In emission (backscatter) Mossbauer spectroscopy, the radiation source and detector are on the same side of the sample. The peaks are positive features, corresponding to recoilless emission of 14.4 keV y-rays and conversion X-rays and electrons. For both measurement geometries Mossbauer spectra are counts per channel as a function of the Doppler velocity (normally in units of mm s relative to the mid-point of the spectrum of a-Fe in the case of Fe Mossbauer spectroscopy). MIMOS II operates in backscattering geometry circle), but the internal reference channel works in transmission mode...

For a comparison of experimental Mossbauer isomer shifts, the values have to be referenced to a common standard. According to (4.23), the results of a measurement depend on the type of source material, for example, Co diffused into rhodium, palladium, platinum, or other metals. For Fe Mossbauer spectroscopy, the spectrometer is usually calibrated by using the known absorption spectrum of metallic iron (a-phase). Therefore, Fe isomer shifts are commonly reported relative to the centroid of the magnetically split spectrum of a-iron (Sect. 3.1.3). Conversion factors for sodium nitroprusside dihydrate, Na2[Fe(CN)5N0]-2H20, or sodium ferrocyanide, Na4[Fe(CN)]6, which have also been used as reference materials, are found in Table 3.1. Reference materials for other isotopes are given in Table 1.3 of [18] in Chap. 1. 

Miinck, E. Aspekts of Fe Mossbauer spectroscopy. In Que, L. (ed.) Physical Methods in Bioinorganic Chemistry, p. 287. University Science Books, Sausalito (2000)... 

The magnetic properties of the new solid solution series SrFe Rui 3 3, (0 < X < 0.5) with distorted perovskite structure, where iron substitutes exclusively as Fe(in) thereby causing oxygen deficiency, has also been studied by Greenwood s group [147] using both u and Fe Mossbauer spectroscopy. Iron substitution was found to have little effect on the magnetic behavior of Ru(IV) provided that X remains small (x < 0.2). 

Et4N]2[Fe2lr2(CO)i2] cluster precursor, which exhibit a high activity in the synthesis of methanol from CO and H2, were studied by Ir and Fe Mossbauer spectroscopy. The study extends from the precursors via the fresh to the aged catalysts. The presence of iridium in the metallic state as well as the presence of trivalent, divalent and alloyed iron is detected. Representative Ir and Fe Mossbauer spectra are shown in Fig. 7.69. Information about the adsorption on the surface of MgO... 

Fe2fr2(CO)i2 t3- Au(PPh3) ] [Fe2lr2(CO)i2 tt3-Au(PPh3) ], which has a trigonal bipyramidal core consisting of five atoms of three different Mossbauer isotopes, was studied by Ir, Au and Fe Mossbauer spectroscopy. The nature and the chemical character of the atoms located at the different sites are discussed with respect to their Mossbauer spectra... 

The interplay between magnetic coupling and ST in 2,2 -bipyrimidine (bpym)-bridged iron(ll) dinuclear compounds has been studied by magnetic susceptibility and Fe Mossbauer spectroscopy [24]. The molecular stmctures of [Fe(bpym) (NCS)2]2(bpym) and [[Fe(bt)(NCS)2]2(bpym) (bt = 2,2 -bithiazoline) are shown in Fig. 8.12. The magnetic behavior in the form of XmT versus Tplots, being the... 

Fe Mossbauer Spectroscopy Unusual Spin and Valence States... 

By far the most utilized Mossbauer isotope is Fe, particularly in (bio)inorganic chemistry. Most iron compounds are found in the oxidation states iron(ll) and iron (III), either with low-spin or high-spin electron configuration. The literature on the application of Fe Mossbauer spectroscopy in this field of research has been reviewed in several textbooks, which are referenced in Chap. 1. The present chapter is intended as a survey of the Mossbauer studies on iron compounds with less common, nevertheless increasingly interesting, valence and spin states. 

Schroder, C. et at. 2006. Fe Mossbauer spectroscopy as a tool in astrobiology. Planetary and Space Science, 54, 1622-1634. 

L.H. (1990) Magnetic properties of some selected, sod-related iron oxides and oxyhydroxides as probed by Fe Mossbauer spectroscopy. In Stanek, J. Pedziwiatr, A.T. (eds.) Condensed matter studies by nuclear methods. Proc. XXIV Zakopane School on Physics. 

Murad, E. (1990) Application of Fe Mossbauer spectroscopy to problems in clay minerals and soil science possibilities and limitations. Adv. Soil Sci. 12 125-157... 

Bacfer, 36 414-415, 449-451 amino acid sequences, 36 468 Fe Mossbauer spectroscopy, 36 423... 

The association of sulfur and iron into simple to more complex molecular assemblies allows a great flexibility of electron transfer relays and catalysis in metalloproteins. Indeed, the array of different structures, the interactions with amino-acid residues and solvent and their effect on redox potential and spectroscopic signatures is both inspiring for chemists and electrochemists, and of paramount importance for the study of these centers in native conditions. Most of the simpler natural clusters have been synthesized and studied in the laboratory. Particularly, the multiple redox and spin states can be studied on pure synthetic samples with electrochemical and spectroscopic techniques such as EPR or Fe Mossbauer spectroscopy. More complex assembhes still resist structural... 

Fe Mossbauer spectroscopy has been used extensively to characterize catalysts, constituting the large majority of the Mossbauer investigations of catalysts. The... 

Because of the broad coverage of this article, we will limit ourselves to the study of stmctural and electronic properties of iron centers by Fe Mossbauer spectroscopy. If the reader is interested in the determination of dynamic properties both by conventional and synchrotron-based Mossbauer spectroscopy, we refer them to the articles by Parak, and Paulsen et as well as to the contribution of Scheidt and Sage in this volume see Nuclear Resonance Vibrational Spectroscopy (NR VS)). 

For liquid solutions containing iron compounds or proteins, the Mossbauer-Lamb factor goes to zero, and therefore Fe Mossbauer spectroscopy on solutions is only possible in the frozen state. Since the natural abundance of Fe is only 2%, it is advisable to perform Mossbauer studies on solutions with Fe-enriched samples. For protein studies, Fe enrichment is essential. Typical sample volumes can range from 0.25-1.0mL. In some cases, frozen solution studies can be performed down to an Fe concentration of 0.1 mM, but taking a Mossbauer spectrum of such a sample can take weeks depending on the shape of the spectrum and the outcome is uncertain. Therefore, it is strongly recommended that the concentration of Fe be at least 1 mM. Samples with Fe concentrations of, for example, 10 mM can very conveniently be measured in a couple of hours—such samples the Mossbauer spectroscopists like the most. In any case, for... 

Wood B. J. and Virgo D. (1989) Upper mantle oxidation state ferric iron contents of Iherzolite spinels by Fe Mossbauer spectroscopy and resultant oxygen fugacities. Geochim. Cosmochim. Acta 53, 1277-1291. 

As with other organophosphorus compounds, NMR spectroscopy represents the most useful diagnostic tool in the characterization of dppf complexes. From P and H NMR spectroscopic data, information can be obtained on the coordination site, the symmetry and the fluxional behavior of these complexes. Possible iron-metal interaction and ring conformational changes of the ferrocenyl moieties can also be studied using " Fe Mossbauer spectroscopy. 

A number of transition metal nuclei can be studied by Mossbauer techniques (e.g., Fe, Ni, Ru, W, Os, Ir, and Pt). Of these, only Ir, Ru, and Fe have been used to study nitrosyl bonding. The most detailed studies have been on the well-known iron complexes [Fe(CN)5(NO)] - (87. 89) and [Fe(NO)(dtc)z] (88-90) (dtc is N,N-dialkyldithiocarbamato). In the latter, high-spin/low-spin equilibria can be followed by Fe Mossbauer spectroscopy, and the Mossbauer parameters agree well with data from electron spin resonance (ESR) spectroscopy in determining the ground states of these complexes. 

A variety of spectroscopic and physical techniques have been used to investigate the nature of these redox centers. EPR, Fe Mossbauer spectroscopy, and Mo and Fe X-ray absorption spectroscopy Mo, Fe, and H electron-nuclear double resonance (ENDOR) linear electric field effect and magnetic circular dichroism (MCD) have provided information about the environment of the Mo and Fe nuclei and their interaction with the unpaired spin of electrons in paramagnetic species of the MoFe proteins. 

The major iron storage protein, ferritin, has been extensively studied (48) and shown to consist of a hollow, spherical proteinaceous shell surrounding an iron(III) oxide core. The other iron storage protein, hemosiderin, has received rather less attention, but, for normal hemosiderin, techniques such as Fe Mossbauer spectroscopy and electron diffraction (49) indicate the presence of a smaller ferritin-like core. 

The idea that in vivo bacfer may serve as an electron store has been investigated by Fe Mossbauer spectroscopy. Cells of P. aeruginosa grown to the stationary phase on Fe-enriched media were shown to contain bacfer in which at least 90% of the iron was oxidized (72). Therefore, bacfer is unlikely to act simply as an electron store. 

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