View source for Digallane

{{redirect2|Gallium trihydride|Gallium(III) hydride|the mononuclear compound|Gallane}}
{{more citations|date=October 2022}}
{{chembox
| verifiedrevid = 429881396
| Name =
| ImageFile = Digallane-2D.png
| ImageFileL1 = Digallane-3D-balls.png
| ImageFileR1 = Digallane-3D-vdW.png
| ImageSize = 200 px
| IUPACName = digallane(6)
| OtherNames = Di-μ-hydrido-tetrahydridodigallium<br />Gallane dimer
| SystematicName =
| Section1 = {{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 12140-58-8
| ChemSpiderID = 24769416
| PubChem =
| SMILES = [GaH2]1[H] [GaH2] [H]1
| StdInChI=1S/2Ga.6H
| StdInChIKey=GFQCQFDOQMRGIQ-UHFFFAOYSA-N
 }}
| Section2 = {{Chembox Properties
| Formula = {{chem2|Ga2H6}}
| MolarMass = 145.494 g/mol
| Appearance = White solid or colorless gas
| Density =
| MeltingPtC = -50
| MeltingPt_notes = (sublimes)
| BoilingPtC = 0
| BoilingPt_notes = (decomposes)
| Solubility = Reacts to form [[gallium(III) hydroxide]]
 }}
| Section7 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
 }}
| Section9 = {{Chembox Related
| OtherCompounds = {{ubl|[[Diborane]]|[[Aluminium hydride]]|[[Indium trihydride]]|[[Thallium hydride]]}}
}}
}}

'''Digallane''' (systematically named '''digallane(6)''') is an [[inorganic compound]] with the [[chemical formula]] {{Chem2|GaH2(H)2GaH2}} (also written {{Chem2|[{GaH2(''μ''\-H)}2]}} or {{Chem2|[Ga2H6]}}). It is the [[Dimer (chemistry)|dimer]] of the monomeric compound [[gallane]]. The eventual preparation of the pure compound, reported in 1989,<ref>{{cite journal
| title = Gallane at last!
|author1=Anthony J. Downs |author2=Michael J. Goode |author3=Colin R. Pulham | journal =Journal of the American Chemical Society
| year = 1989
| volume = 111
| issue = 5
| pages = 1936–1937
| doi = 10.1021/ja00187a090
}}</ref><ref name = "Pulham">{{cite journal
| title = Gallane: Synthesis, Physical and Chemical Properties, and Structure of the Gaseous Molecule Ga<sub>2</sub>H<sub>6</sub> As Determined by Electron Diffraction
|author1=Pulham C.R. |author2=Downs A.J. |author3=Goode M.J |author4=Rankin D.W.H. Roberson H.E. | journal =Journal of the American Chemical Society
| year = 1991
| volume = 113
| issue = 14
| pages = 5149–5162
| doi = 10.1021/ja00014a003
}}</ref>
was hailed as a "tour de force."<ref>{{cite journal
| title = Main group element chemistry at the millennium
| author = N.N. Greenwood
| journal =J. Chem. Soc., Dalton Trans.
| year = 2001
| volume =
| issue = 14
| pages = 2055–2066
| doi =10.1039/b103917m
}}</ref> Digallane had been reported as early as 1941 by Wiberg;<ref>{{cite journal
| title = Über einen flüchtigen Galliumwasserstoff der Formel Ga<sub>2</sub>H<sub>6</sub> und sein Tetramethylderivat
|author1=Wiberg E. |author2=Johannsen T. | journal =Naturwissenschaften
| year = 1941
| volume = 29
| issue = 21
| page = 320
| doi = 10.1007/BF01479551
|bibcode=1941NW.....29..320W |s2cid=44840674 }}</ref> however, this claim could not be verified by later work by Greenwood and others.<ref>{{cite journal
| title = Some Observations Relative to Digallane
|author1=Shriver, D. F. |author2=Parry, R. W. |author3=Greenwood, N. N. |author4=Storr, A |author5=Wallbridge, M. G. H. | journal =Inorg. Chem.
| year = 1963
| volume = 2
| issue = 4
| pages = 867–868
| doi = 10.1021/ic50008a053
}}</ref> This compound is a colorless gas that decomposes above 0 °C.

__TOC__
==Preparation==
A two-stage approach proved to be the key to successful synthesis of pure digallane. Firstly the dimeric [[monochlorogallane]], {{chem2|(H2GaCl)2}} (containing [[Bridging ligand|bridging]] chlorine atoms and thus formulated as ({{chem2|H2Ga(''μ''\-Cl))2}}) was prepared via the hydrogenation of [[gallium trichloride]], {{chem2|GaCl3}}, with [[trimethylsilane]], {{chem2|[[Methyl group|Me]]3SiH}}. This step was followed by a further reduction with {{chem2|Li[GaH4]}} (lithium tetrahydrogallate), solvent free, at −23&nbsp;°C, to produce digallane, {{chem2|Ga2H6}} in low yield.

:{{chem2|Ga2Cl6 + 4 Me3SiH → (H2GaCl)2 + 4 Me3SiCl}}
:{{chem2|(H2GaCl)2 + 2 Li[GaH4] → 2 Ga2H6 + 2 LiCl}}

Digallane is volatile and condenses at −50&nbsp;°C into a white solid.

==Structure and bonding==
Electron diffraction measurements of the vapour at 255 K established that digallane is structurally similar to [[diborane]] with 2 bridging hydrogen atoms<ref name="Pulham"/> (so-called [[three-center two-electron bond]]s). The terminal Ga-H bond length is 152 pm, the Ga-H bridging is 171 pm and the Ga-H-Ga angle is 98°. The Ga-Ga distance is 258 pm. The <sup>1</sup>H [[Nuclear magnetic resonance|NMR]] spectrum of a solution of digallane in [[toluene]] shows two peaks attributable to terminal and bridging hydrogen atoms.<ref name = "Pulham"/>

In the solid state, digallane appears to adopt a polymeric or oligomeric structure. The vibrational spectrum is consistent with tetramer (i.e. {{chem2|(GaH3)4}}).<ref name = "Pulham"/> The vibrational data indicate the presence of terminal hydride ligands. In contrast, the hydrogen atoms are all bridging in [[aluminium hydride|α-alane]], a high-melting, relatively stable polymeric form of [[aluminium hydride]] wherein the aluminium centers are 6-coordinated. Digallane decomposes at ambient temperatures:
:{{chem2|Ga2H6 → 2 Ga + 3 H2}}

==References==
{{reflist}}

{{Gallium compounds}}
{{Hydrides by group}}

[[Category:Inorganic compounds]]
[[Category:Gallium compounds]]
[[Category:Metal hydrides]]
[[Category:Reducing agents]]
[[Category:Substances discovered in the 1980s]]