Iron III Compounds

Alkylthiocyanates and alkylselenocyanates are obtained by treatment of trialkylboranes with potassium thiocycanate (260) and sodium selenoisocyanate (261), in the presence of iron(III) compounds, respectively. Unsymmetrical trialkylboranes react preferentially at the more highly branched alkyl group. Alkenylphenyl selenides are obtained by the reaction of alkenylboronic acids with phenylselenyl bromide (262). 

Eisen-oxydverbindung, /. ferric compound, iron(III) compound, -pastille, /. (Pharm.) reduced iron lozenge, -pecherz, n. limonite pitticite tripUte. -phosphor, n. iron phosphide. -probe, /. iron test iron sample, -pulver, n. iron powder, -quarz, m. ferriferous quartz, -rahm, m. a porous form of hematite. 

Ferri-verbindung, /. ferric compound, iron(III) compound, -zyan, n. ferricyanogen. 

Iron centers that are more electron-deficient than iron(III) compounds are used for efficient and highly specific oxidation reactions in, for example, heme and nonheme enzymes [166-172]. Most iron(IV)-complexes found in biological reaction cycles possess terminal or bridging 0x0 groups as is known from a large number of structural and spectroscopic investigations. With the exception of iron(IV)-nitrido groups, nonoxo iron(IV) centers very rarely take part in such reactions. 

The Discovery of the Spin Crossover Phenomenon for Iron(III) Compounds 261... 

Since the appearance of the first reports by Cambi and Szego [1, 2], the tris(N,AT-dialkyl-dithiocarbamato)iron(III) compounds have been extensively studied and the later work has included detailed structural characterisation by X-ray diffraction methods. In addition, new dithiocarbamato-based Fe(III) spin crossover materials have been prepared, those having the alkyl substituents as part of a ring system being of particular note. A schematic representation of the structure of tris(N,AT-disubstituted-dithiocarbama-to)iron(III) is given in Fig. 1, and relevant crystallographic and magnetic data are compiled in Table 1. 

Table 1 Crystallographic and magnetic data of tris(N,N-disubstituted-dithiocarbamato)iron(III) compounds... 

Tris(dithioacetato)iron(III) compounds are purely low spin over the temperature range 93-293 K [83]. 

Iron(III) compounds of 3-OEt-salAPA have been widely studied [127, 128, 139-145]. Both the anion and the incorporated solvent molecule influence the spin crossover behaviour of the complex salts. Thus T1/2 for [Fe(3-OEt-salAPA)2]ClC>4 is 295 K, whereas that for the dichloromethane solvate is 152 K [140]. The transition in [Fe(3-0Et-salAPA)2]C104 and [Fe(3-OEt-salA-PA)2]BPh4 is more gradual and occurs at a somewhat higher temperature than that for the benzene solvate [Fe(3-0Et-salAPA)2]C104-C6H6 [141]. 

The electron relaxation is usually field dependent and the main mechanism for electron relaxation is the modulation of transient ZFS caused by collisions with solvent molecules. Small static ZFS have been estimated for several manganese(II) and gadolinium(III) proteins, and somewhat larger ones for iron(III) compounds. In such low symmetry systems, it is reasonable to expect the magnitude of transient ZFS to be related to that of the static ZFS, as the former can be seen as a perturbation of the latter. As a consequence, systems with increasing static ZFS experience faster electron relaxation rates. Modulation of static ZFS by rotation could be an additional mechanism for relaxation, which may coexist with the collisional mechanism. 

The first iron-containing silsesquioxanes which appeared in the literature were compounds containing ferrocenyl units as side-groups.However, these are not within the scope of this review as iron is not part of the metallasilsesquioxane skeleton. Meanwhile, several ferrasilsesquioxane complexes have been synthesized. The first iron(III) compound of this type was prepared in our laboratory according to Scheme 56. ° In 161, the coordination sphere of iron is completed by TMEDA (N,N,N, N -tetramethylethylenediamine) as a chelating amine ligand. Pale yellow, crystalline 161 was isolated in 80% yield and structurally characterized by X-ray diffraction. This compound was later used by Maxim et to prepare iron... 

Nickel (II) oxide Cobalt (II) oxide Iron (III) compounds Tin (TV) oxide Gold (ni) oxide... 

Soon after the introduction of dimethylglyoxime as a specific reagent for nickel by Tschugaeff-Kraut-Brunck (1905-1907), Baudisch discovered a compound which precipitates copper and iron quantitatively from acid solutions.82 He appropriately named this reagent as cupferron . It is the water soluble ammonium salt of nitrosophenylhydroxylamine (5). When dissolved in chloroform, the whitish-grey copper compound gives a bright yellow solution and the brown yellow iron(III) compound a deep red solution. This behaviour reveals the inner complex character of these derivatives (6). 

By considering electron configurations, suggest a reason why iron(III) compounds are readily prepared... 

Although the S = % system with ZFS is difficult to understand completely in terms of electron relaxation as several different electron transitions are operative, we can conclude that the effective electron relaxation time (as defined in Eqs. (3.11) and (3.12)) is of the order of 10 10 s at low fields and that it increases with increasing the field. Under these circumstances there are no hopes to investigate iron(III) compounds with small ZFS by high resolution NMR. On the contrary, Fe(III) complexes have also been investigated as possible contrast agents for MRI [11]. 

A variation on the (dioxygen)iron(II) complex, an Fe Fe111 intermediate, was proposed by Aust and coworkers as the instigator of oxyradical damage [37,51]. There is no thermodynamic data available that allows one to calculate how oxidising such a complex would be. It is conceivable that an equal mixture of iron(II) and iron(III) compounds imposes a reduction potential on the system that is favourable for catalysis of lipid peroxidation. 

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