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Triiron dodecacarbonyl
Triiron dodecacarbonyl
IUPAC name
Other names Iron tetracarbonyl trimer
CAS number 17685-52-8 Yes check.svgY
Molecular formula Fe3CO12
Molar mass 503.66 g/mol
Appearance dark green crystals
Melting point

165 °C

Boiling point


Solubility in water insoluble
Related compounds
Other cations Triruthenium dodecacarbonyl
Triosmium dodecacarbonyl
Related iron carbonyls Iron pentacarbonyl
Diiron nonacarbonyl
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Triiron dodecarbonyl is the chemical compound with the formula Fe3(CO)12. It was one of the first metal carbonyl clusters synthesized.[1] It is a more reactive source of iron(0) than is iron pentacarbonyl.


General properties

Fe3(CO)12 is a dark green solid, which sublimes under a good vacuum, albeit with significant decomposition. It is soluble in nonpolar organic solvents to give intensely green solutions. Most low nuclearity clusters are pale yellow or orange. Hot solutions of Fe3(CO)12 decompose to an iron mirror, which can be pyrophoric in air. The solid decomposes slowly in air, and thus samples are typically stored cold under an inert atmosphere.


It was occasionally obtained from the thermolysis of Fe(CO)5:

3 Fe(CO)5 → Fe3(CO)12 + 3 CO

Traces of the compound are easily detected because of its characteristic deep green colour. UV-photolysis of Fe(CO)5 produces Fe2(CO)9, not Fe3(CO)12.

An efficient synthesis of Fe3(CO)12 proceeds via the reaction of Fe(CO)5 with base:[2]

3 Fe(CO)5 + (C2H5)3N + H2O → [(C2H5)3NH][HFe3(CO) 11] + 3 CO + CO2

followed by oxidation of the resulting hydride with acid:

[(C2H5)3NH][HFe3(CO) 11] + HCl + CO → Fe3(CO)12 + H2 + [(C2H5)3NH]Cl

The original synthesis, by Walter Hieber, entailed the reaction of H2Fe(CO)4 with MnO2. The cluster was formulated merely as "Fe(CO)4".[3]


Fe3(CO)12 consists of a triangle of iron atoms surrounded by 12 CO ligands. Ten of the CO ligands are terminal and two span an Fe---Fe edge, resulting in C2v point group symmetry. By contrast, Ru3(CO)12 and Os3(CO)12 adopt D3h-symmetric structures, wherein all 12 CO ligands are terminally bound to the metals. Overall, it can be appreciated that these three clusters formally arise from condensation of three 16-electron M(CO)4 fragments, akin to the condensation of CH2 units into cyclopropane.

Elucidation of the structure of Fe3(CO)12 proved to be challenging because the CO ligands are disordered in the crystals. Early evidence for its distinctive C2v structure came from Mößbauer spectroscopic measurements that revealed two quadrupole doublets with similar isomer shifts but different (1.13 and 0.13 mm s-1) quadrupolar coupling constants.

The anion [HFe3(CO)11]- is structurally related to Fe3(CO)12, with the hydride replacing one bridging CO ligand. The bonding in the Fe-H-Fe subunit is described using concepts developed for diborane.


Like most metal carbonyls, Fe3(CO)12 undergoes substitution reactions, making, for example, Fe3(CO)11{P(C6H5)3} upon reaction with triphenylphosphine.

Heating Fe3(CO)12 gives a low-yield of the carbido cluster Fe5(CO)15C. Such reactions proceed via disproportionation of CO to give CO2 and carbon.

Fe3(CO)12 reacts with 1,3-Propanedithiol to form air-stable µ-(1,3-Propanedithiolato)-hexacarbonyldiiron in which both thiol sulfur atoms form a bridge between two iron atoms. This compound is a model compound for certain all-iron hydrogenases[4].


Like all metal carbonyls Fe3(CO)12 is hazardous as a source of volatile iron and as a source of carbon monoxide. Solid samples, especially when finely divided, and residues from reactions can be pyrophoric, which can ignite the organic solvents used for such reactions.


  1. ^ Elschenbroich, C.; Salzer, A. ”Organometallics : A Concise Introduction” (2nd Ed) (1992) from Wiley-VCH: Weinheim. ISBN 3-527-28165-7
  2. ^ McFarlane, W.; Wilkinson, G. W. (1966). "Triiron dodecacarbonyl". Inorganic Syntheses 8: 181–3. doi:10.1002/9780470132395.ch47.  
  3. ^ Hieber, W.; Leutert, F. (1932). "Über Metallcarbonyle. XII. Die Basenreaktion des Eisenpentacarbonyls und die Bildung des Eisencarbonylwasserstoffs (Metal carbonyls. XII. The Reaction of Iron Pentacarbonyl with Bases and the Formation of Iron Hydrocarbonyl)". Zeitschrift für anorganische und allgemeine Chemie 204: 145–64. doi:10.1002/zaac.19322040115.  
  4. ^ Synthesis, Purification, and Characterization of a µ-(1,3-Propanedithiolato)-hexacarbonyldiiron Laboratory Experiment or Mini-Project for Inorganic Chemistry or Integrated Laboratory Carmen F. Works 836 Journal of Chemical Education Vol. 84 No. 5 May 2007 Abstract


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