Complexes of iron

Perhaps the most important complex of iron(II) is heme (or haeme). Haemoglobin, the iron-containing constituent of the blood, consists essentially of a protein, globin, attached through a nitrogen atom at one coordination position of an octahedral complex of iron(II). Of the other five coordination positions, four (in a plane) are occupied by nitrogen atoms, each of which is part of an organic... 

Wet-Chemical Determinations. Both water-soluble and prepared insoluble samples must be treated to ensure that all the chromium is present as Cr(VI). For water-soluble Cr(III) compounds, the oxidation is easily accompHshed using dilute sodium hydroxide, dilute hydrogen peroxide, and heat. Any excess peroxide can be destroyed by adding a catalyst and boiling the alkaline solution for a short time (101). Appropriate ahquot portions of the samples are acidified and chromium is found by titration either using a standard ferrous solution or a standard thiosulfate solution after addition of potassium iodide to generate an iodine equivalent. The ferrous endpoint is found either potentiometricaHy or by visual indicators, such as ferroin, a complex of iron(II) and o-phenanthroline, and the thiosulfate endpoint is ascertained using starch as an indicator. 

This simple explanation accounts quite well for a variety of dithiocarbamato complexes of iron(III) whose magnetic moments rise gradually from about 2.3 BM (corresponding to low-spin d ) at very low temperatures to > 4BM (corresponding to roughly equal populations in the two states) above room temperature. 

Raymond, K. N., Muller, G., and Matzanke, B. F. Complexation of Iron by Siderophores A Review of Their Solution and Structural Chemistry and Biological Function. 123 49-102 (1984). 

Also, reactive silylene complexes of iron and chromium can be generated at low temperatures and subsequently derivatized by trapping reagents. In THF as solvent, first labile THF adducts are formed, which are converted to the more stable HMPA adducts. The THF complexes dimerize above —40 °C with loss of THF. The silylene complexes can be utilized for reactions if they are generated in the presence of reagents like dimethylcarbonate. The resulting reaction products... 

Polynuclear complexes of iron and their biological implications. T. G. Spiro and P. Saltman, Struct. Bonding (Berlin), 1969, 6, 116-156 (170). 

The nature of spin state transitions in solid complexes of iron(II) and the interpretation of some associated phenomena. E. Konig, G. Ritter and S. K. Kulshreshtha, Chem. Rev., 1985, 85, 219 (91). 

Complexation of iron by siderophores. A review of their solution and structural chemistry and biological function. K. N. Raymond, G. Muller and B. F. Matzanke, Top. Curr. Chem., 1984,123, 49 (227). 

If the complex has an overall negative charge (an anionic complex), the suffix -ate is added to the stem of the metal s name. If the symbol of the metal originates from a Latin name (as listed in Appendix 2D), then the Latin stem is used. For example, the symbol for iron is Fe, from the Latin ferrum. Therefore, any anionic complex of iron ends with -ferrate followed by the oxidation number of the metal in Roman numerals ... 

The earlier literature containing work on 1,1-dithio complexes of iron has been covered in depth by Coucouvanis 1), and, since 1968, interest in these iron complexes has increased. 

Several complexes of iron with the 1,1-ethenedithiolates have been isolated. These are mainly tris-Fe(III) complexes with the 1,1-dicyano-2,2-ethylenedithiolate ligand (1). Recently, however, Coucouvanis et al. (262) synthesized a new 1,1-dithiolate ligand (XVIII) from the reac-... 

Fe(Et2dtc)3]BF4 has the advantage that the product is completely free from by-products and is isolable in yields of 90%. The relationship between Ei,2 values and electronic structures has been described in terms of Ai - T2 crossover equilibrium (273). The rate of e transfer between [Fe(Me2dtc)3] and [Fe(Me2dtc>3]BF4 has been measured by H-NMR, line-broadening experiments (275). Mossbauer-spectral data have been published (276) for a series of (R2dtc) complexes of iron(IV). 

These complexes are stable (presumably to aerial oxidation), which is, perhaps, surprising, in view of the fact that the analogous complexes of iron(II) could not be isolated, oxidation to iron(III) taking place in each case. A number of interesting poly(bisdithiocarbamate) complexes of cobalt(II) and nickel(II) (XXI) have been prepared and... 

Rue E. L. and Bruland, K. W. (1995). Complexation of iron (111) by natural organic ligands in the Central North Pacific as determined by a new competitive ligand equilibration/adsorptive cathodic stripping voltammetric method. Mar. Chem. 50,117-138. 

Spiro G, Saltman P (1969) Polynuclear Complexes of Iron and Their Biological Implications. 6 116-156... 

Kusz J, Giitlich P, Spiering H (2004) Structural Investigations of Tetrazole Complexes of Iron(II). 234 129-153... 

Iron dextran injection contains a complex of iron hydroxide with dextrans of average molecular weight between 5000 and 7000, and is used for the treatment of iron-defieiency anaemia in situations where oral therapy is ineffeetive or impractical. The sodium salt of sulphurie aeid esters of dextran, i.e. dextran sodium sulphate, has anti-eoagulant properties eomparable with heparin and is formulated as an injection for intravenous use. 

The isotopic method has been used in conjunction with a flow apparatus by Stranks, to measure the exchange between the cyclopentadienyl complexes of iron (III) and iron (II) in methanol. Separation was based on the insolubility of Fe(C5H5) in petroleum ether at —80 °C. Using Fe(II) and Fe(III) 10 M and short reaction times ( msec), a rate coefficient 8.7 x 10 l.mole .sec at — 75 °C was obtained. The rate of exchange in the presence of chloride ions and inert electrolytes was found to be more rapid. Calculations using Marcus Theory showed reasonable agreement with the experimental observations. In deuterated acetone, line broadening measurements have led to an estimate of this rate coefficient of > 10 l.mole . sec at 26 °C. 

A stopped flow technique coupled with spectrophotometric analysis of the iron (II) complex formed has been used to investigate - the reactions of some organic complexes of iron(III) with the ion Fe ". The iron(III) was complexed with 1,10-phenanthroline, various substituted 1,10-phenanthrolines (5-methyl-, 5-nitro-, 5-chloro-, 5-phenyl-, 5,6-dimethyl-, 4,7-diphenyl-, and 3,4,7,8-tetramethyl-) and 2,2 -dipyridine, 4,4 -dimethyl-2,2 -dipyridine, and 2,2, 2"-tripyridine. The wavelengths used for the analysis lay in the region 500-552 m/i. 

Results of relaxation measurements on spin-state equilibria in solution are available for complexes of iron(II), iron(III), and cobalt(II). The results comprise values of relaxation time r, rate constants for the forward and reverse reactions feLH activation parameters AH and AS for the two opposed... 

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