Iron hydride

Overview

Solid solutions

Iron and iron-based alloys can form solid solutions with hydrogen, which under extreme pressure may reach stoichiometric proportions, remaining stable even at high temperatures and surviving for a while under ambient pressure, at temperatures below 150K.

Binary compounds

Molecular compounds

• Hydridoiron (FeH). This molecule has been detected in the atmosphere of the Sun and some red dwarf stars. It is stable only as a gas, above the boiling point of iron, or as traces in frozen noble gases below 30 K (where it may form complexes with molecular hydrogen, such as ).
• Dihydridoiron (). This compound has been obtained only in rarefied gases or trapped in frozen gases below 30 K, decomposing into the elements on warming. It may form a dimer and complexes with molecular hydrogen, such as and .
• What was once believed to be trihydridoiron () was later shown to be FeH bound to molecular hydrogen .

Polymeric network compounds

• Iron(I) hydride. It is stable at pressures exceeding 3.5 GPa.
• Iron(II) hydride or ferrous hydride. It is stable at pressures between 45 and 75 GPa.
• Iron(III) hydride or ferric hydride. It is stable at pressures exceeding 65 GPa.
• Iron pentahydride FeH5 is a polyhydride, where there is more hydrogen than expected by valence rules. It is stable under pressures over 85 GPa. It contains alternating sheets of FeH3 and atomic hydrogen.

Iron-hydrogen complexes

Complexes displaying iron–hydrogen bonds include, for example:

• iron tetracarbonyl hydride FeH2(CO)4, the first such compound to be synthesised (1931).
• FeH2(CO)2[P(OPh)3]2.
• Salts of the anion, such as magnesium iron hexahydride, , produced by treating mixtures of magnesium and iron powders with high pressures of H2.
• Di- and polyiron hydrides, e.g. [HFe2(CO)8]− and the cluster [HFe3(CO)11]−.

Complexes are also known with molecular hydrogen () ligands.

Biological occurrence

Methanogens, archaea, bacteria and some unicellular eukaryotes contain hydrogenase enzymes that catalyse metabolic reactions involving free hydrogen, whose active site is an iron atom with Fe–H bonds as well as other ligands.

References

J.V. Badding, R.J. Hemley, and H.K. Mao (1991), "High-pressure chemistry of hydrogen in metals: in situ study of iron hydride." Science, American Association for the Advancement of Science, volume 253, issue 5018, pages 421–424

Hiroshi Nakazawa, Masumi Itazaki "Fe–H Complexes in Catalysis" Topics in Organometallic Chemistry (2011) 33: 27–81.

Helga Körsgen, Petra Mürtz, Klaus Lipus, Wolfgang Urban, Jonathan P. Towle, John M. Brown (1996), "The identification of the radical in the gas phase by infrared spectroscopy". The Journal of Chemical Physics volume 104(12) page 4859

George V. Chertihin and Lester Andrews (1995), "Infrared spectra of FeH, , and in solid argon" Journal of Physical Chemistry volume 99, issue 32, pages 12131–12134

References

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