Iron atom pentacarbonyl

The low-valent ferrate [Fe(CO)3(NO)] 76 or Hieber anion was discovered some 50 years ago by Hieber and Beutner [43, 44] in order to extend the Hieber base reaction [45,46], in which iron pentacarbonyl 78 reacts with alkaline bases to form the [Fe(CO)4] anion [47, 48]. Compared to its homoleptic analogue, the Hieber anion is more stable because the electron-withdrawing character of the nitrosyl ligand stabilizes the negative charge at the iron atom. 

The active catalytic species are iron clusters generated from the pentacarbonyl. They consist of about 40-50 iron atoms at a diameter of ca. 0.7nm. This corresponds roughly to the dimension of the smallest SWNT formed (also refer to Section 3.3.7). The iron particles generated from the catalyst attach to the outside of the carbon nanotubes and may contribute up to 7% to the overall mass of the product mixture (Figure 3.15). The metal clusters can, however, be removed by wet chemistry (Section 3.3.6) because they are not concealed deep inside the SWNTs, but usually surrounded by just two or three layers of carbon. 

From Fig. G.l we find that an iron atom in the elemental state has 8 valence electrons. We arrive at the oxidation state of iron in iron pentacarbonyl by noting that the charge on the complex as a whole is zero (it is not an ion), and that the charge on each CO ligand is also zero. Therefore, the iron is in the zero oxidation state. 

Treatment of Fe3(CO)i2 with pyridine JV-oxide in benzene at room temperature gives the brown pyrophoric [Fe(CsH5NO)4][Fe4(CO)i3] IS). Irradiation of iron pentacarbonyl with dimethylsulfoxide in benzene solution at 80° C gives the red-black, slightly air-sensitive [Fe(Me2SO)e] [Fe4(CO) 13] 18). Irradiation of iron pentacarbonyl with triphenylphosphine oxide or triphenylarsine oxide in benzene solution at 80° C gives dark red materials formulated as [Fe((/>3PO)2][Fe2(CO)g] and [Fe( 3AsO)3][Fe2 (CO)g], respectively 18). The apparently low coordination numbers of two or three for the cationic iron atoms in these two compounds seem peculiar. 

It consists of Pt with two NH3 molecules (neutral) and two CP ions, giving a neutral species. Iron pentacarbonyl, Fe(CO)5, is an example of a neutral species formed from a neutral iron atom and CO molecules. 

The first workers, while attempting to elucidate the structure of iron pentacarbonyl, treated Fe(CO)s with butadiene in a sealed tube at 150° C for several hours and obtained a product which analyzed as C4HjFe(CO)3. Although they were not able to assign a definite structure to this material they considered that the iron atom was bonded to the terminal carbon atoms of the diene and to three carbonyl groups. The cyclic structure (I) was proposed however, they stated that the alternative structure (II) could not be ruled out. 

The mononuclear metal carbonyls contain only one metal atom, and they have comparatively simple structures. For example, nickel tetracarbonyl is tetrahedral. The pentacarbonyls of iron, ruthenium, and osmium are trigonal bipyramidal, whereas the hexacarbonyls of vanadium, chromium, molybdenum, and tungsten are octahedral. These structures are shown in Figure 21.1. 

Iron oxide yellows, 19 399—401 Iron pellets, 14 498—499 Iron pentacarbonyl, 7 591 14 550 16 71 effective atomic number of noble gas, 7 590t... 

Thermal decomposition of iron pentacarbonyl. Very finely divided red iron oxide is obtained by atomizing iron pentacarbonyl, Fe(CO)5, and burning it in excess of air. The size of the particles depends on the temperature (580-800 °C) and the residence time in the reactor. The smallest particles are transparent and consist of 2-line ferri-hydrite, whereas the larger, semi-transparent particles consist of hematite (see Chap. 19). The only byproduct of the reaction is carbon dioxide, hence, the process has no undesirable environmental side effects. Magnetite can be produced by the same process if it is carried out at 100-400 °C. Thermal decomposition of iron pentacarbonyl is also used to coat aluminium powder (in a fluidized bed) and also mica platelets with iron oxides to produce interference or nacreous pigments. 

Transparent red iron oxides containing iron oxide hydrate can also be produced directly by precipitation. A hematite content of > 85 % can be obtained when iron(II) hydroxide or iron(II) carbonate is precipitated from iron(II) salt solutions at ca. 30 °C and when oxidation is carried out to completion with aeration and seeding additives (e.g., chlorides of magnesium, calcium, or aluminum) [5.271], Transparent iron oxides can also be synthesized by heating finely atomized liquid pentacarbonyl iron in the presence of excess air at 580-800 °C [5.272], [5.273]. The products have a primary particle size of ca. 10 nm, are X-ray amorphous, and have an isometric particle form. Hues ranging from red to orange can be obtained with this procedure, however, it is not suitable for yellow hues. 

Carbon monoxide has been found to be surprisingly reactive toward the metals in Group VIII, in both their oxidized and unoxidized states. A sizable number of compounds exist in which one or more CO molecules are attached to a metal atom through the carbon typical of these are nickel tetracarbonyl, Ni(CO)4, iron pentacarbonyl, Fe(CO) cobalt carbonyl hydride, Co(CO)4H platinum carbonyl chloride, Pt(CO)2Cl2 and more complicated molecules such as Co4(CO)i2. 

Insertion of isocyanide carbon atoms into the Cr—carbene bond of [(CO)5CrC(OMe)Me] gave aziridinylcarbene complexes (CIV), some reactions of which are summarized in Scheme 2 28, 198). Cyclic carbene groups (CV)-(CVIII), in which the carbene carbon atom is part of an aromatic six-electron Tr-system, have been reported to form pentacarbonyl chromium and tetracarbonyl iron complexes 383, 384). Related to carbene... 

---