Oxidation state of iron

The porphyrin ligand can support oxidation states of iron other than II and III. [Fe(I)Por] complexes are obtained by electrochemical or chemical reduction of iron(II) or iron(III) porphyrins. The anionic complexes react with alkyl hahdes to afford alkyl—iron (III) porphyrin complexes. Iron(IV) porphyrins are formally present in the carbene, RR C—Fe(IV)Por p.-carbido, PorFe(IV)—Fe(IV)Por nitrene, RN—Fe(IV)Por and p.-nittido, PorFe(IV)... 

The rate equation agrees with the experimental form, Eq. (6-14). However, it appears much less plausible than that in Eq. (6-14) in that it requires the intervention of two oxidation states of iron that are highly unusual and unstable under these reaction conditions. 

What is the oxidation state of iron in the alkaline earth ferrites ... 

Six-coordinate organoiron porphyrin nitrosyl complexes, Fe(Por)(R)(NO), were prepared from Fe(Por)R (Por = OEP or TPP R = Me, n-Bu, aryl) with NO gas. The NMR chemical shifts were typical of diamagnetic complexes, and the oxidation state of iron was assigned as iron(ll). ... 

The isomer shift is considered the key parameter for the assignment of oxidation states from Mossbauer data. The early studies, following the first observation of an isomer shift for Fe203 [7], revealed a general correlation with the (formal) oxidation state of iron. However, isomer shifts have also been found to depend on the spin state of the Mossbauer atom, the number of ligands, the cr-donor and the... 

Russo, U., Long, G.J. Mossbauer spectroscopic studies of the high oxidation states of iron. In Long, G.J., Grandjean, F. (eds.) Mossbauer Spectroscopy Applied to Inorganic Chemistry, pp. 289-329. Plenum, New York (1989)... 

The fact that Prussian blue is indeed ferric ferrocyanide (Fe4in[Fen(CN)6]3) with iron(III) atom coordinated to nitrogen and iron(II) atom coordinated to carbon has been established by spectroscopic investigations [4], Prussian blue can be synthesized chemically by the mixing of ferric (ferrous) and hexacyanoferrate ions with different oxidation state of iron atoms either Fe3+ + [Fen(CN)6]4 or Fe2+ + [Fem(CN)6]3. After mixing, an immediate formation of the dark blue colloid is observed. However, the mixed solutions of ferric (ferrous) and hexacyanoferrate ions with the same oxidation state of iron atoms are apparently stable. 

Figure 5.7 Relationship between the isomer shift, the quadrupole splitting and the oxidation state of iron.

The commonest oxidation states of iron in its complexes are II and III (electronic configuration d6 and d5, respectively), but, as we shall see, the I and IV oxidation states are also accessible. 

Stated that in the vast majority of cases, the Fe(III)/Fe(II) process is chemically reversible, we begin the survey of these two oxidation states of iron with tetracoordinated complexes. 

Table I. Relationship between Mossbauer Chemical Shift and Oxidation State of Iron and Tin...

MOssbauer spectroscopy has been used to investigate the oxidation state of iron in complexes such as [Fe(CN)6] " " intercalated in LDHs [176]. By means of MOssbauer spectroscopy, it has also been demonstrated that ferrocene sulfonates intercalated in LDHs decompose on attempted ion-exchange with sodium carbonate solutions and that the liberated Fe " ions become incorporated in the layers [189]. 

Figure 20. Electronic structure and transport in mixed conducting perovskites. (a) Band picture of electronic structure in the high-temperature metallic phase of Lai- r tCo03-(5. (Reprinted with permission from ref 109. Copyright 1995 Elsevier.) (b) Localized picture of electron/ hole transport in semimetallic Lai- 3r Fe03-(5, involving hopping of electrons and/or electron holes (depending on the oxidation state of iron).

The same transition metal may have different oxidation states in its compounds - for example, you know that the common oxidation states of iron are (11) and (111). In its compounds, copper is usually in oxidation state (11), but it can also have oxidation number... 

Samples 6 and 7 in table 5.32 are from the Zabargad peridotite (Red Sea) and are representative of the chemistry of upper mantle pyroxenes (Bonatti et al., 1986). The absence of Fe203 in these samples is due to the fact that microprobe analyses do not discriminate the oxidation state of iron, which is thus always expressed as FeO. It must be noted here that the observed stoichiometry (based on four oxygen ions) is quite consistent with the theoretical formula and that no Fe is required to balance the negative charges of oxygen. 

The environment and oxidation state of iron in borosilicate glasses has been probed by IR, Raman, and Mossbauer spectroscopies, in lead vanadate (Pb2V207) glasses by XRD and IR and Raman spectroscopies. " ... 

The most common oxidation states of iron are +2 (ferrous) and -i-3 (ferric). The standard electrode potential for Fe —> Fe2+ + 2e- is -0.440 volts. Thus, the metal can replace hydrogen from water at ordinary temperatures ... 

The oxidation state of iron may be either + 2 or + 3 and the importance of the Cytochrome lies in their ability to act as redox intermediates in electron transfer. 

Five oxidation states of iron, II-VI, are accessible in oxides. The principal oxidation states are II-IV these all carry spontaneous atomic magnetic moments in oxides the mixed-valence states of particular interest are associated with III/II and IV/III couples on crystallographically equivalent sites. The low-temperature disproportionation reaction 2 Fe — Fe Fe " in CaFe03 is also of fundamental theoretical interest. 

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. 

Figure 5.2 A Latimer diagram for the +3, +2 and 0 oxidation states of iron reduction potentials...

Dixneuf jnd coworkers have prepared Feltj -PhiPCH ClK)S](Tj -SCOMeKPI h3)(CO) which obeys the [8-electron rule.21 Confirm that it does and draw its struciure. What is the oxidation state of iron in this compound-1... 

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)]. 

Iron as a cofactor in catalysis is receiving increasing attention. The most common oxidation states of iron are Fe2+ and Fe3+. Iron complexes are nearly all octahedral, and practically all are paramagnetic (as a result of unpaired electrons in the 3d orbital). The most common form of iron in biological systems is heme. Heme groups (Fe2+) and hema-tin (Fe3+) most frequently involve a complex with protoporphyrin IX (fig. 10.19). They are the coenzymes (prosthetic... 

---