An iron hydride is a chemical system which contains
iron and
hydrogen in some associated form.
[
Because of the common occurrence of those two ]elements
Element or elements may refer to:
Science
* Chemical element, a pure substance of one type of atom
* Heating element, a device that generates heat by electrical resistance
* Orbital elements, parameters required to identify a specific orbit of ...
in the universe, possible compounds of hydrogen and iron have attracted attention. A few molecular compounds have been detected in extreme environments (such as stellar atmospheres) or detected in small amounts at very low temperatures. The two elements form a metallic alloy above of pressure, that has been advanced as a possible explanation for the low density of Earth's "iron" core.[ However those compounds are unstable when brought to ambient conditions, and eventually decompose into the separate elements.
Small amounts of hydrogen (up to about 0.08% by weight) are absorbed into iron as it solidifies from molten state.][ Although the H2 is simply an impurity, its presence can affect the mechanical properties of the material.
Despite the fleeting nature of binary iron hydrides, there are many fairly stable complexes containing iron-hydrogen bonds (and other elements).]
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 that is reported to survive 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
''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. T ...
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 FeH·).[ It may form a dimer and complexes with molecular hydrogen, such as FeH2(H2)2 and FeH2(H2)3.][
* What was once believed to be trihydridoiron () was later shown to be FeH bound to molecular hydrogen H2.][
]
Polymeric network compounds
* Iron(I) hydride
Iron(I) hydride, systematically named iron hydride and poly(hydridoiron) is a solid inorganic compound with the chemical formula (also written or FeH). It is both thermodynamically and kinetically unstable toward decomposition at ambient tempe ...
. It is stable at pressures exceeding 3.5 GPa.
* Iron(II) hydride
Iron(II) hydride, systematically named iron dihydride and poly(dihydridoiron) is solid inorganic compound with the chemical formula (also written )''n'' or ). ). It is kinetically unstable at ambient temperature, and as such, little is known abou ...
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
Iron pentahydride FeH5 is a superhydride compound of iron and hydrogen, stable under high pressures. It is important because it contains atomic hydrogen atoms that are not bonded into smaller molecular clusters, and may be a superconductor. Pairs ...
FeH5 is a polyhydride
A polyhydride or superhydride is a compound that contains an abnormally large amount of hydrogen. This can be described as high hydrogen stoichiometry. Examples include iron pentahydride FeH5, LiH6, and LiH7. By contrast, the more well known lit ...
, 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).magnesium iron hexahydride
Magnesium iron hexahydride is an inorganic compound with the formula Mg2FeH6. It is a green diamagnetic solid that is stable in dry air. The material is prepared by heating a mixture of powdered magnesium and iron under high pressures of hydrogen: ...
, , produced by treating mixtures of magnesium and iron powders with high pressures of H2.
* Di- and polyiron hydrides, e.g. Fe2(CO)8sup>− and the cluster Fe3(CO)11sup>−.
Complexes are also known with molecular hydrogen () ligands.
Biological occurrence
Methanogens, archaea
Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...
, bacteria and some unicellular eukaryote
Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...
s contain hydrogenase enzymes that catalyse metabolic
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
reactions involving free hydrogen, whose active site is an iron atom with Fe–H bonds as well as other ligands.[
]
See also
* Iron–hydrogen alloy
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
]
[A. S. Mikhaylushkin, N. V. Skorodumova, R. Ahuja, B. Johansson (2006)]
x (x=0.25; 0.50;0.75)"">"Structural and magnetic properties of FeHx (x=0.25; 0.50;0.75)"
. In: ''Hydrogen in Matter: A Collection from the Papers Presented at the Second International Symposium on Hydrogen in Matter (ISOHIM)'', AIP Conference Proceedings, volume 837, pages 161–167