{{chembox | Name = Iron(II) hydride | SystematicName = Dihydridoiron(4•) | Section1 = {{chembox Identifiers | CASNo = 33485-98-2 | CASNo_Ref = | PubChem = 141155 | PubChem_Ref = | SMILES = [FeH2] | ChemSpiderID = 124509 | StdInChI = 1S/Fe.2H | StdInChIKey = FUEZNWLRTWZOHC-UHFFFAOYSA-N }} | Section2 = {{chembox Properties | Formula = FeH₂^4• | MolarMass = 57.861 g mol⁻¹ }} }} '''Iron(II) hydride''' (also called '''ferrous hydride''' and '''iron dihydride''') is an unstable [[chemical compound]] of [[iron]] and [[hydrogen]] with the [[chemical formula|formula]] FeH₂. It is considered a [[free radical]] with four unsatisfied [[valence bond]]s; its formula may be written {{chem|FeH|2|4•}} to emphasize that fact. Iron(II) hydride has been isolated only in small quantities, trapped in frozen inert gases at extremely low temperatures, and dissociates into the elements in ambient conditions. It is one of the few known [[iron hydride|compounds of iron and hydrogen]]s, and the lightest dihydride of an element from group 8 of the [[periodic table]]. There are however several [[coordination compound]]s of iron where H₂ is one of the [[ligand]]s, which may be regarded as complexes of FeH₂. A complex with two hydrogen molecules, {{chem|FeH|2|({{chem|H|2}})|2}}, produced by the evaporation of iron into hydrogen gas, is said to be stable. ==Structure== Iron(II) hydride is structurally analogous to [[iron(II) fluoride]], FeF₂. It has a quasi-linear H−Fe−H structure (''D''_∞'''h''') with an equilibrium distance between the iron atom and the hydrogen atoms of 165 pm. The ground electronic state is [[molecular term symbol|⁵Δ_g]]. The antisymmetric stretching vibration ν₃ has a frequency of 50.20683 THz (1674.7196 cm^-1. ==Stability and reactions== As a radical, FeH₂ is thermodynamically unstable with respect to the loss of a hydrogen atom{{citation needed|February 2013}} and exists only transiently at above cryogenic temperatures. It decomposes, by successively releasing the two hydrogen atoms, into another similarly unstable radical, [[Iron(I) hydride|FeH]], and then into of iron in the form of [[nanocrystal]]s. == Production == Iron(II) hydride has been produced by several means, including: * By reaction of {{chem|FeCl|2}} and PhMgBr under a hydrogen atmosphere (1929). * Electrical discharge in a mixture of [[iron pentacarbonyl|pentacarbonyliron]] and dihydrogen diluted in helium. * Evaporation iron with a [[laser]] in a hydrogen atmosphere and condensing the products on a [[frozen gas matrix|matrix]] of frozen [[argon]]. * Decomposition product of excited [[ferrocenium]] ions. == Spectrum ==

Transitions of 56FeH2 ν3 fundamental band
'''Transition'''	'''Wavenumber cm−1'''	'''Frequency THz'''
P4(10)	1614.912	48.41
P4(7)	1633.519	48.9717
Q4(4),Q3(3)	1672.658	50.145
Q4(4),Q4(5),Q3(3)	1676.183	50.2507
R4(4)	1704.131	51.0886
R4(5)	1707.892	51.2013
R4(8)	1725.227	51.721
R4(9)	1729.056	52.8358

== References == Rod S. Mason and Lara J. Kelly (), [http://www.arkat-usa.org/get-file/45359/ "Synthesis of protonated ferrocene isomers in the gas phase and their study by mass spectrometry"]. Arkivoc, volume 2012, issue 7, pages 137-157. Helga Körsgen, Petra Mürtz, Klaus Lipus, Wolfgang Urban, Jonathan P. Towle, John M. Brown (1996), "The identification of the {{chem|FeH|2}} radical in the gas phase by infrared spectroscopy". The Journal of Chemical Physics, volume 104, issue 12, page 4859 ISSN 00219606 {{doi|10.1063/1.471180}} {{cite journal|last=Hieber|first=W.|coauthors=F. Leutert|year=1931|journal=Naturwissenschaften|volume=18|issue=32|page=360}} George V. Chertihin and Lester Andrews (1995), "Infrared spectra of FeH, {{chem|FeH|2}}, and {{chem|FeH|3}} in solid argon". Journal of Physical Chemistry, volume 99, issue 32, pages 12131–12134 {{doi|10.1021/j100032a013}} Xuefeng Wang and Lester Andrews (2009), "Infrared Spectra and Theoretical Calculations for Fe, Ru, and Os Metal Hydrides and Dihydrogen Complexes". The Journal of Physical Chemistry A, volume 113, issue 3, pages 551–563 issn:1089-5639 {{doi|10.1021/jp806845h}} {{iron compounds}} [[Category:iron compounds]] [[Category:metal hydrides]]