Structure of Fe CO

The gas-phase photochemistry of pentacarbonyliron has received considerable attention on the femtosecond timescale. When irradiated in the gas phase with 260 nm radiation for 120 fs, the parent ion [Fe(CO)5] is observed along with dissociation products [Fe(CO)s, t] (x= 1-5), whereas only Fe was observed using a 10 ns pulse. Similar results were obtained using a pump-probe technique at 400 and 800 nm with a 100 ns pulse. That study concluded that the ions [Fe(CO)5 .] occurred with concerted ligand loss, but that the loss of the last GO and formation of neutral Fe occurred in a stepwise fashion. These studies showed that [Fe(CO)5] was so short lived that it could not be observed when the timescale of the laser pulse was in the nanosecond regime. 

Electron attachment to Fe(CO)s leads to the formation of a series of cluster anions in the gas phase as determined by time-of-flight mass spectrometry. These clusters had the composition [Fe(CO)4] [Fe(CO)5]3, where 1, 2 b = 0-8, and these were analyzed as being van der Waals clusters in which the [Fe(CO)4] fragments function as ion cores. The clusters were examined by photoelectron spectroscopy. The spectra were all very similar with the threshold-binding energies and vertical-detachment energies varying linearly with cluster size. The data were consistent with electron ejection from the encapsulated [Fe(CO)4] unit. 

Iron carbonyls serve as catalysts for the isomerization of allylic alcohols to saturated carbonyl complexes as well as the conversion of allylic alcohols and formaldehyde to aldols. These processes were examined theoretically and the authors proposed that intermediate Fe(CO 3 was responsible for converting coordinated allyl alcohol into coordinated enol via two successive 1,3-hydride shifts. Several pathways for the subsequent reaction with formaldehyde were examined, but the most favorable involved direct attack of H2CO on the decomplexed enol.  

Unsaturated Fe(CO)4 was generated from Fe(CO)s and Mc3NO and reacted with alkynes to give corresponding cyclobutenediones or the anhydrides in yields of 50-75% after CuCl2 2H20 oxidation (Equation (4)).  

Syntheses and magnetic studies of iron nanorods and nanospheres have been reported using pentacarbonyliron. Spherical nanostructures formed by thermal decomposition of Fe(CO)s in the presence of stabilizing surfactant trioctyl-phosphine oxide (TOPO) at 340 °C were reported to give small spherical and rod-shape iron nanostructures. However, in the presence of both TOPO and trioctylphosphine (TOP) at 300 °C, FeP nanoparticles are obtained. Presumably, the coordination of the phosphorus of the TOP molecule direcdy to Fe activates it to loss of the organic substituents. 

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Tihay, F., Pourroy, G., Richard-Plouet, M., Roger, A. C., and Kiennemann, A. 2001. Effect of Fischer-Tropsch synthesis on the micro structure of Fe-Co-based metal/spi-nel composite materials. Appl. Catal. A 206 29 -2. 

Figure 22 Crystal structure of [Fe(CO)3(7 5-9-0(CH2)4-7-CB1oH11)]. Reproduced by permission of the American Chemical Society from Organometallics 2000, 19, 1993.

Two likely structures for Fe(CO)5 are the square pyramid and the trigonal bipyramid. Determine for both these structures the number of infra-red-active and Raman-active C—O stretching vibrations and then make use of the data given in Table 9.4 to decide on the structure of Fe(CO)5. 

The molecular structure of Fe(CO)5, determined on the solid compound below its freezing point (-20.5 °C) by X-ray diffraction, is trigonal bipyramidal D h symmetry). An... 

Iron Pentacarbonyl The structure of Fe(CO)s was first described37 in space group Cc, with four molecules per unit cell. The higher space group was rejected on the grounds that the molecule could not be centric. It was soon thereafter noticed38 that, within experimental error, the molecule does contain a twofold axis, and the structure was satisfactorily refined in C2/c. 

The second method utilizes in situ photolysis of stable metal carbonyls in inert gas matrices. For example, Poliakoff and Turner carried out UV photolysis of CO-enriched Fe(CO)5 in SF, and Ar matrices [Fe(CO)s- Fe(CO)4+CO], and concluded that the structure of Fe(CO)4 is C2 since it exhibits four i (CO) (2A + + JS ) in the infrared spectrum. 

Fe(CO)4 proceeds, that is, Fe(CO)s— excited Fe(CO)s— Fe(CO)4— Fe(CO)4, or Fc(CO)5— excited Fe(CO)5 — excited Fe(CO)s— Fe(CO)4. Fe(CO)4 was not observed in the low-temperature matrix experiments. Femtosecond UV laser excitation with time-of-flight mass spectrometric detection was able to show that photolysis of Fe(CO>5 at 267 nm proceeds via an excited singlet state to yield (in ca. 30 fs) Fe(CO)4, initially in an excited singlet state, which then rapidly decays to the lowest singlet state.Ultrafast electron diffraction experiments were able to determine a more precise structure of Fe(CO>4 and confirm the singlet pathway. 

Poliakoff M, Turner JJ (2001) The structure of [Fe(CO)4]—an important new chapter in a long-runtting story. Angew Chem Int Ed 40 2809-2812... 

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