Iron complexes cyano

Indeed, the oxidation of Fe(CN)g by O2 (as well as by H2O2 and BrOj) proceeds via the rds of dissociation of the hexa- to the penta-cyano complex. The value of k in (8.90) is 5.6 X lO M s at pH > 3.8. Traces of Fe from decomposition of the cyano complex promote catalytic oxidation (Prob. 19). A large number of complexes of the type Fe(CN)5X" for both Fe(II) and Fe(III) have been studied and cross-reaction redox kinetics abound. Care has to be exercised in the use of FeiCN) . Daylight can induce changes in the complex even within an hour and catalytic effects (traces of Cu Sec. 3.1.4) have to be considered. In addition, the sensitivity of the values of and rate constants to medium effects lessen the value of the iron-cyano complexes as reactant partners for the demonstration of Marcus relationships. Nevertheless, they, with other inorganic complexes, have been extensively employed to probe the peripheral characteristics of metallopro-teins. 

An interesting series of dinuclear iron-cyano complexes [(NC)5Fe—L—Fe(CN)5]4, 5, 6 in which the metal centres are bridged via bifunctional heterocyclic amines such as pyrazine, 4,4 -bipy-... 

An interesting series of dinuclear iron-cyano complexes [(NQjFe—L—Fe(CN)5] ... 

Probably the most extensively applied masking agent is cyanide ion. In alkaline solution, cyanide forms strong cyano complexes with the following ions and masks their action toward EDTA Ag, Cd, Co(ll), Cu(ll), Fe(ll), Hg(ll), Ni, Pd(ll), Pt(ll), Tl(lll), and Zn. The alkaline earths, Mn(ll), Pb, and the rare earths are virtually unaffected hence, these latter ions may be titrated with EDTA with the former ions masked by cyanide. Iron(lll) is also masked by cyanide. However, as the hexacy-anoferrate(lll) ion oxidizes many indicators, ascorbic acid is added to form hexacyanoferrate(ll) ion. Moreover, since the addition of cyanide to an acidic solution results in the formation of deadly... 

Structural models, which are synthesized to imitate features of the proposed structure of the active site. These may be used to demonstrate the chemical conditions, which allow such structures to exist, to investigate their chemical properties and to give a better understanding of the spectroscopic characteristics of the native proteins. Examples of these include the mixed carbonyl/cyano complexes of iron, used to verify the infrared spectra to the hydrogenases (Fig 7.4) (Lai et al. 1998) and the nickel-thiolate complexes which have low redox potentials like the hydrogenases (Franolic et al. 1992). 

Iron(II) and (III) cyano complexes provide very interesting mechanistic chemistry. The Fe(CN)5H20 ion is a popular substrate for study. It is easily prepared in situ by the dissolution of solid Na3[Fe(CN)jNH3] for 15 minutes at 25°C in aqueous solution. For a large variety of entering groups Y (unspecified charge) a D mechanism is favored (Prob. 18) ... 

The above mechanistic interpretation is in contrast with the one appearing in the coordination chemistry of NO on the very labile Fe(III) porphyrins and hemoproteins, which show water substitution-controlled kinetics at the iron(III) center (22,25). The latter Fe(III) moieties are, however, high-spin systems, whilst the cyano-complexes are low-spin. There is strong experimental evidence to support the dissociative mechanism with the Fe(III)-porphyrins, because the rates are of the same order as the water-exchange reactions measured in these systems (22d). Besides, the Fe(III) centers are less oxidizing than [Fein(CN)5H20]2- (21,25). 

The syntheses of iron isonitrile complexes and the reactions of these complexes are reviewed. Nucleophilic reagents polymerize iron isonitrile complexes, displace the isonitrile ligand from the complex, or are alkylated by the complexes. Nitration, sulfonation, alkylation, and bromina-tion of the aromatic rings in a benzyl isonitrile complex are very rapid and the substituent is introduced mainly in the para position. The cyano group in cyanopentakis(benzyl isonitrile)-iron(ll) bromide exhibits a weak "trans" effect-With formaldehyde in sulfuric acid, benzyl isonitrile complexes yield polymeric compositions. One such composition contains an ethane linkage, suggesting dimerization of the transitory benzyl radicals. Measurements of the conductivities of benzyl isonitrile iron complexes indicate a wide range of A f (1.26 e.v.) and o-o (1023 ohm-1 cm.—1) but no definite relationship between the reactivities of these complexes and their conductivities. 

Cyanopentakis(benzyl isonitrile)iron(II) bromide, which represents a new class of iron isonitrile complexes, was investigated in some detail. This complex is diamagnetic and dissociates in nitrobenzene into two univalent-univalent ions as indicated by cryoscopic and conductivity measurements. It exhibits two peaks in the triple bond region of the infrared spectrum one at 2200 cm.—1 assigned to the isonitrile groups and another at 2092 cm.-1 assigned to the cyano group. The structure proof of cyanopentakis (benzyl isonitrile) iron (II) bromide is ... 

The term iron blue pigments as defined in ISO 2495 has largely replaced a great number of older names (e.g., Paris blue, Prussian blue, Berlin blue, Milori blue, Turnbull s blue, toning blue, and nonbronze blue). These names usually stood for insoluble pigments based on microcrystalline Fe(II)Fe(III) cyano complexes many were associated with specific hues. A standardized naming system has been demanded by users and welcomed by manufacturers, and has led to a reduction in the number of varieties [3.177],... 

Thermal decomposition under hydrogen of a series of pentacyanocobaltate complexes (CN-, N02-, NO- or N3- ligands) revealed that the latter complex is the most exothermic by far. Presence of iron powder suppresses hydrogen cyanide formation. See related METAL AZIDES, METAL CYANIDES(AND CYANO COMPLEXES)... 

Formation of Ni(CO)4 or Co(CO)4- by the cyanide method depends upon the stepwise substitution of the anion of the cyano complex by the iso-electronic carbon monoxide molecule. By treating Co2(CO)8 with potassium cyanide we obtained cyanocarbonyls of cobalt of low oxidation number (83). In reactions of the nitrosyl carbonyls of iron and cobalt, Behrens (86) substituted all the CO groups with CN to give K3[Co(NO)(CN)3] or... 

In contrast to the case of inudazoles binding to tetraphenylporphyrins, Wang et have demonstrated that binding of cyanide to high-spin protoporphyrin IX iron(III) chloride in DMSO-c 6 is a two-step process as shown in equations (38) and (39), and whether DMSO acts as a sixth ligand for the mono-cyano complex is not known ... 

The acute toxicity of HCN and cyanide is a consequence of the affinity of these substances for various heavy metals, such as iron or copper, by forming cyano complexes. The effect on cytochromes, which results in an efficient inhibition of respiration, is most important. In addition, numerous other metabolic processes are affected (for a review, see Solomonson, 1981). The lefhal dose of cyanide for humans is considered to be about 1 mg per kg... 

The pentacyanonitrosylferrates, (the nitroprussides ) are of interest. Cyano complexes in general do not easily form mixed complexes by replacement of CN" groups and, in the hexacyano-complexes of iron, only one CN" can be replaced by NH3, HgO, CO, NOg (nitro) or NO (nitroso). Acidification of a K4Fe(CN)g--KN02 mixture gives first the pentacyanonitro-ferrate(II) ion, [Fe(CN)5N02] " ... 

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