Fe = O complexes

A fascinating approach to the synthesis of pyridine heterocycles has been discovered by using (arene)Fe(O) complexes to catalyze [2+2+2] cycloaddition reactions. The proposed method consists of a cross cyclization of alkynes and nitriles [45]. An example of such a reaction is depicted in Scheme 25. In the presence of (Ty -l,5-cyclooctadiene)(Ty -phosphinine)Fe(0) 85, butyronitrile 86 combines with two molecules of methyl propargyl ester 87 yielding a mixture of isomeric pyrroles 88 and 89. The reaction proceeds at ambient temperature, but relatively long reaction times are required to obtain good yields. The symmetric... 

The Fe(IV) dihydroxide complex further evolved in solution to the formation of the [Fe O] complex with the transfer of a proton to the bulk solution ... 

Scheme 6.8 Cyclotrimerization reaction with an -phosphinine-Fe(O) complex...

As with EDTA, which we encountered in Chapter 9, o-phenanthroline is a ligand possessing acid-base properties. The formation of the Fe(o-phen)3 + complex, therefore, is less favorable at lower pH levels, where o-phenanthroline is protonated. The result is a decrease in absorbance. When the pH is greater than 9, competition for Fe + between OH and o-phenanthroline also leads to a decrease in absorbance. In addition, if the pH is sufficiently basic there is a risk that the iron will precipitate as Fe(OH)2. 

This experiment describes the use of FIA for determining the stoichiometry of the Fe +-o-phenanthroline complex using the method of continuous variations and the mole-ratio method. Directions are also provided for determining the stoichiometry of the oxidation of ascorbic acid by dichromate and for determining the rate constant for the reaction at different pH levels and different concentration ratios of the reactants. 

FIGURE 16.16 When potassium cyanide is added to a solution of iron(ll) sulfate, the cyanide ions replace the H.O ligands of the [Fe(H20), - + complex (left and produce a new complex, the hexacyanoferrate(ll) ion, Fe(CN)(l 4 (right). The blue color is due to the polymeric compound called Prussian blue, which forms from the cyanoferrate ion. 

The Fe—O distances in hematite are 1.99 and 2.06 A. The (Mn,Fe)—O distances in bixbyite are expected to be the same in case that (Mn, Fe) has the coordination number 6, and slightly smaller, perhaps 1.90 A, for coordination number 4. The radius of 0= is 1.40 A, and the average O—O distance in oxide crystals has about twice this value. When coordinated polyhedra share edges the O—O distance is decreased to a minimum value of 2.50 A, shown by shared edges in rutile, anatase, brookite, corundum, hydrargillite, mica, chlorite, and other crystals. Our experience with complex ionic crystals leads us to believe that we may... 

Catalysis by Iron in Half Sandwich Complexes 2.1 Fe(O)- and Fe(I)-Catalysts... 

Properties of FeCr,o solid samples have been studied by X-ray diffraction, 57Fe Mossbauer spectroscopy and magnetic measurements to stimulate the interaction of Fe with fullerene. FeCr,o samples have been prepared by decomposition of the 1,3-dipolar cycloadduct of the fullerene and ferrocene nitrile oxide. The components exhibit super paramagnetic properties originating from an interaction between FeCr,o complexes within the nano-particles. Each nano-particle consists of hundreds to thousands complexes (546). 

The Fe(III) complexes of R-substituted salicylaldehyde thiosemicarbazone (R-thsa2- Fig. 6) are among the most studied spin crossover materials of this family. The crystal structures of several of them have been determined at various temperatures. The iron-donor atom distances are compiled in Table 2. The Fe(III) ion is in a distorted FeS2N202 octahedron formed by two thiosemicarbazone ligands, which are geometrically arranged in such a way that the S and O atoms are located in cis positions, whereas the N atoms occupy trans positions, i.e. each tridentate molecule coordinates in an equatorial plane [101]. 

Using one of your standards and the Spectronic 20, or other single-beam visible spectrophotometer, obtain an absorption (or transmittance) spectrum of the Fe-o-phenanthroline complex ion (instructor will demonstrate use of instrument). Determine the wavelength of maximum absorbance from the spectrum and use this wavelength to obtain absorbance readings of all the solutions. (Use the blank for the 100% transmittance setting.)... 

---