Cyanide complexes of iron

There is often a need to monitor cyanide in air, water, solid waste, food, and other environmental samples. The cyanide present in these samples may include free (noncomplexed) cyanide such as hydrogen cyanide (or hydrocyanic acid in water solution), cyanogen (C2N2), cyanogen chloride, cyanide salts, or complexed cyanide such as metal-cyanide complexes of iron, nickel, copper, mercury, silver. Complexed cyanides are less toxic because they are less bioavail-able, but they may break down producing free cyanide, for example, as a result of the ultraviolet radiation in daylight. Analytical techniques for free... 

To determine cyanide and total cyanides (containing both simple and metal-cyanide complexes) in solutions, more drastic conditions are necessary to decompose the complexes before the HCN is distilled off. Several metal-cyanide complexes such as Cd, Cu, Ni, and Zn react almost as readily. But, cyanide complexes of iron show resistance to decompose under the same condition. Cobalt cyanides decompose very slowly. Conversion of metal cyanides to HCN is facilitated by the presence of magnesium and mercury salts. A useful form of distillation was developed by Serf ass et al. [4]. They used magne-sium(ll) and mercury(ll) chlorides with H2SO4 to decompose complex cyanides. These reduced hexacyanoferrate(ll) and hexacyanoferrate(III) to magnesium(II) and mercury(II)... 

The Ferric low-spin cyanide complexes of iron-bound haemin and haemoproteins are characterized by a great paramagnetic shift of the enriched cyano group (up to = 1200 ppm). (M 29, M 30, M 49, M 50, M 51 ). ... 

Traces of many metals interfere in the determination of calcium and magnesium using solochrome black indicator, e.g. Co, Ni, Cu, Zn, Hg, and Mn. Their interference can be overcome by the addition of a little hydroxylammonium chloride (which reduces some of the metals to their lower oxidation states), or also of sodium cyanide or potassium cyanide which form very stable cyanide complexes ( masking ). Iron may be rendered harmless by the addition of a little sodium sulphide. 

Table XVI shows a selection of stability constants and redox potentials for iron(II) and iron(III) complexes. This Table covers a wide range of the latter, showing how the relative stabilities of the iron(II) and iron(III) complexes are refiected in. B (Fe /Fe ) values. A more detailed illustration is provided by the complexes of a series of linear hexadentate hydroxypyridinonate and catecholate ligands, where again high stabilities for the respective iron(III) complexes are refiected in markedly negative redox potentials (213). The combination of the high stabilities of iron(III) complexes of hydrox5rpyridinones, as of hydroxamates, catecholates, and siderophores, and the low stabilities of their iron(II) analogues is also apparent in Fig. 8. Here redox potentials for hydroxypyranonate and hydroxypyridinonate complexes of iron are placed in the overall context of redox potentials for iron(III)/iron(II) couples. The -(Fe /Fe ) range for e.g., water, cyanide, edta, 2,2 -bipyridyl, and (substituted) 1,10-phenanthrolines is...

Such cyanide complexes are also known for several other metals. All the fer-rocyanide complexes may be considered as the salts of ferrocyanic acid H4Fe(CN)e and ferricyanide complexes are that of ferricyanic acid, H3Fe(CN)e. The iron-cyanide complexes of alkali and alkaline-earth metals are water soluble. These metals form yellow and ruby-red salts with ferro-cyanide and ferricyanide complex anions, respectively. A few of the hexa-cyanoferrate salts have found major commercial applications. Probably, the most important among them is ferric ferrocyanide, FeFe(CN)e, also known as Prussian blue. The names, formulas and the CAS registry numbers of some hexacyanoferrate complexes are given below. Prussian blue and a few other important complexes of this broad class of substances are noted briefly in the following sections ... 

Nitroprusside is a complex of iron, cyanide groups, and a nitroso moiety. It is rapidly metabolized by uptake into red blood cells with liberation of cyanide. Cyanide in turn is metabolized by the mitochondrial enzyme rhodanase, in the presence of a sulfur donor, to the less toxic thiocyanate. Thiocyanate is distributed in extracellular fluid and slowly eliminated by the kidney. 

Leita, L., De Nobili, M., Catalano, L., Moira, A., Fonda, E., and Vlaic, G. (2001). Complexation of iron-cyanide by humic substances. In Understanding and Managing Organic Matter in Soils, Sediments and Waters, Swift, R. S., and Sparks, K. M., eds., International Humic Science Society, St. Paul, MN, pp. 477 82. 

Proton Affinities of Some Cyanide and Aromatic Diimine Complexes of Iron Ruthenium and Osmium. J. Am. Chem. Soc. 85, 904 (1963). 

Very recently Geus and co-workers [44, 45] have applied another method based on chemical complexes. This is the complex cyanide method to prepare both monocomponent (Fe or Co) and multicomponent Fischer-Tropsch catalysts. A large range of insoluble complex cyanides are known in which many metals can be combined, e.g. iron(n) hexacyanide and iron(m) hexacyanide can be combined with iron ions, but also with nickel, cobalt, copper, and zinc ions. Soluble complex ions of molybdenum(iv) which can produce insoluble complexes with metal cations are also known. Deposition precipitation (Section A.2.2.1.5) can be performed by injection of a solution of a soluble cyanide complex of one of the desired metals into a suspension of a suitable support in a solution of a simple salt of the other desired metal. By adjusting the cation composition of the simple salt solution, with a same cyanide, it is possible to adjust the composition of the precursor from a monometallic oxide (the case when the metallic cation is identical to that contained in the complex) to oxides containing one or several foreign elements. 

Porphyrin Basicity. The reduction rate is decreased significantly as the porphyrin is made more basic (Figure 6). The bis-cyanide complex of ferric octaethyl porphyrin, the more basic porphyrin, is reduced the slowest while the bis-cyanide complex of ferric TPP, the least basic (16), is reduced the fastest. Increasing the porphyrin basicity places more electron density on the iron, making it more difficult to accept another electron. 

Certain classical coordination complexes (see Coordination Complexes) of iron (e.g. Prussian blue) will be dealt with in other articles (see Iron Inorganic Coordination Chemistry and Cyanide Complexes of the Transition Metals), as will much of the chemistries of iron carbonyls (see Metal Carbonyls) and iron hydrides (see Hydrides) (see Carbonyl Complexes of the Transition Metals Transition Metal Carbonyls Infrared Spectra, and Hydride Complexes of the Transition Metals). The use of organoiron complexes as catalysts (see Catalysis) in organic transformations will be mentioned but will primarily be covered elsewhere (see Asymmetric Synthesis by Homogeneous Catalysis, and Organic Synthesis using Transition Metal Carbonyl Complexes). 

Table 4. Selected IR properties of some carbonyl and cyanide complexes of nickel and iron with the PS3 and PS3 ligands [70, 71).

R. B. Grieves and D. Bhattacharyya, Foam separation of cyanide complexed by iron. 

An alternative interference removal step was developed by Ledo de Medina et al. who developed an IC method for phosphate in natural waters in the presence of high concentration of sulphates. This interference was avoided by first precipitating sulphate as lead sulphate prior to 1C analysis. Samples with high iron content were investigated by Simon. Interferences caused by the precipitation of iron hydroxides from air oxidation of ferrous iron in anoxic water samples and from the alkaline eluent used in IC, were found to affect the determination of phosphate and other inorganic anions in riverine sediment interstitial water samples with high concentrations of dissolved iron (0.5 to 2.0 mmol/1). To eliminate this interference the complexation of iron with cyanide was used prior to IC analysis. ... 

---