Iron in Fe

Effect of loading and method of preparation on the reducibility of iron in Fe/MgO catalysts... 

Cysteine can bind to either one or two metal ions, and is frequently found as a ligand to iron (in Fe-S clusters—see later) and to Cu+ (for example in the copper chaperones, which transfer copper to specific copper-binding proteins). Histidine can bind metal ions in two... 

Kanowitz, S. M. and Palenik, G. (1998). Bond valences in coordination chemistry. A simple method for calculating the oxidation state of iron in Fe-0 complexes. Inorg. Chem. 37, 2086-8. 

When [Fe4S3(NO)7] reacts with RS in DMF solution, then, for a range of substituents R, the products are (23) [Fe(NO)2(SR)2] , as formed from [Fe2(SR)2(NO)4], together with [Fe(NO)(SR)3] in this latter series (Table IV), although the A(14N) value depends upon R, no hyperfine coupling to the a-hydrogen atoms in R was resolved, so that all the spectra of [Fe(NO)(SR)3] comprise three lines only. The mono-nitrosyl complexes are fairly short lived, and within 2 days only the dinitrosyl complexes were detectable. Since the formal oxidation states of iron in [Fe(NO)2(SR)2] and [Fe(NO)(SR)3] are Fe(-I) and Fe(I), respectively, it is likely that [Fe(NO)2(SR)2] arises from the basal iron atoms in [Fe4S3(NO)7] , and that [Fe(NO)(SR)3] arises from the apical iron [Eq. (17)]. 

The situation for Fe11 porphyrin is rather similar, with the existence of 5 = 0, 1 and 2 states. The iron in Fe(TPP)(THF)2 lies in the plane of the porphyrin.647 This result is of considerable relevance to model systems for hemoglobin and the question of the trigger for the conformational change associated with the cooperative uptake of dioxygen. In this example the presence of a symmetrical weak axial field is the crucial factor. While this particular situation probably does not occur in any natural hemoprotein, these results demonstrate conclusively that high-spin Fe11 will fit into the porphyrin plane. 

Fig. 5.16. Backscattered electron compositional image of the transition zone between a Fe-Ni alloy and the aluminium melt saturated with the alloy constituents. Temperature 700°C, dipping time 3600 sec. The content of iron in Fe-Ni alloys is expressed in mass %. 

Figure 10.2. Acid-base speciation of (a) citrate, (b) aluminum, and (c) iron(III) as a function of solution pH at 25°C and in 0.01 mol L NaNOs solutions. The distributions were computed using a total soluble citrate (citys) concentration of 10 mol and total soluble aluminum (Aljs) and iron(in) [Fe(ni)Ts] concentrations controlled by gibbsite (A1(OH)3(x)) and goethite [FeOOH(x)]. (Relevant thermodynamic data from May and Murray, 2000 Baes and Mesmer, 1986 Liu and Millero, 1999.)...

Geochemical observations concerning the iron content of the calcite cements conform with the isotopic and petrofabric results. Both early and late calcite cements contain variable concentrations of iron, as indicated by our staining results and confirmed by the microprobe analyses of Hutcheon et al. (1985) for the Avalon Sandstone (range 1.5-4.4 wt% Fe). Possible sources are the reduction of iron in Fe-oxide and hydroxide coatings for the early ferroan calcite, the intrastratal solution of... 

Table 5.6 shows an example of process rates in a coastal marine sediment. In this comparison, it is important to keep in mind that the different oxidants are not equivalent in their oxidation capacity. When for example the iron in Fe(III) is reduced, the product is Fe + and the iron atoms have been reduced only one oxidation step from +3 to +2. Sulfur atoms in sulfate, in contrast, are reduced eight oxidation steps from +6 in SO/ to -2 in H S. One mol of sulfate, therefore, has 8-fold higher oxidation capacity than one mol of iron oxide. In order to compare the different oxidants and their role for organic carbon oxidation, their reduction rates were recalculated to carbon equivalents on the basis of their change in oxidation step. It is then clear that oxygen and... 

If the optical electronegatively (58, 60) of iron in Fe(acac)a is taken to be 2.3, then the optical electronegativity of the highest filled jr-orbitals of acetylacetonate anion is 2.7. This value is in agreement with that suggested from Cu(acac)2 if one assumes that the shoulder near 26,000 cm"i in Cu(acac) is a charge transfer band n dxy. However, Cotton and coworkers (61) have assigned this band as a dxy - n transition. The... 

Phytic Acid. Recent reviews (67,68,69) summarized the literature covering the relationship between phytic acid and mineral bioavailability in soy protein products. The formation of phytate-proteln-mineral complexes (particularly zinc chelates in flours, concentrates, and Isolates prepared from mature soybeans) may be responsible for reduced mineral availability. However, the iron in Fe-labeled mature soybeans is more available to iron-deficient rats than the iron in green-immature soybeans, even though mature soybeans contain three times more phytic acid (70). The factor(s) responsible for this difference in bioavallablllty has not been identified. 

The results from four different techniques indicate that the iron in Fe proteins is present as a single 4Fe4S cluster. Smith and Lang (1974) in their Mossbauer study of Kp2 showed that the spectrum of the reduced protein was similar in form and temperature behavior to that of bacterial ferredoxins in that all the Fe atoms were associated with unpaired electron spin. They interpreted the spectra in terms of a single 4Fe4S cluster operating between the -2 and -3 oxidation states. 

Klepka, M.T., Nedelko, N., Greneche, J.M., Lawniczak-Jablonska, K., Demchenko, I.N., Slawska-Waniewska, A., et al. Local atomic structure and magnetic ordering of iron in Fe-chitosan complexes. Biomacromolecules 9, 1586-1594 (2008)... 

Fe Mossbauer spectroscopy revealed that iron in Fe(NCSe)2(bpp)2 had a high-spin Fe" state at room temperature, while a small amount of low-spin Fe" v/as observed at 78 K, in addition to the large amount of high-spin Fe". In contrast, iron in Fe(NCSe)2(bpp)2 2(benzene) showed a temperature-independent high-spin Fe". In this case, powder X-ray diffraction pattern revealed a reversible structural change between ID and 2D interpenetrated structures, triggered by desorption and adsorption of benzene molecules. The Fe Mossbauer spectrum at 78 K revealed that a small amount of low-spin Fe" appeared when benzene molecules were desorbed from... 

Behavior of Na ions during discharge and charge of sodium-ion battery (SIB) was also investigated by means of Mossbauer spectroscopy intercalation (sorption) and deintercalation (desorption) of Na ions could be respectively confirmed as reduction and oxidation of iron in Fe "P04 [II]. 

Now let us turn to the compounds of transition elements. Iron compounds snch as iron oxide Fe Oj have its iron in Fe(III) state. Fe(Ill) has five electrons in its valence shell (d-shell), as we mentioned earlier. The d-shell consists of five d-orbitals and can accommodate as many as ten electrons. Since there are only five electrons in the d-sheU of Fe(III), the electron can be moved around within the d-shell by light. 

In each of these structures, we have obtained an uneharged metal atom, and some (fractional) double bonding for the Ni-C and Co-C bonds. To generate neutral iron in Fe(CO), we need to deloealize six electrons into antibonding C-0 orbitals. Because Fe in straeture (10) has only five lone-pairs of valence... 

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