# Digallane
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{{redirect2|Gallium trihydride|Gallium(III) hydride|the mononuclear compound|Gallane}}
{{more citations|date=October 2022}}
{{chembox
| verifiedrevid = 429881396
| Name =
| ImageFile = Digallane-2D.svg
| ImageFileL1 = Digallane-3D-balls.png
| ImageFileR1 = Digallane-3D-vdW.png
| ImageSize = 200 px
| IUPACName = digallane(6)
| OtherNames = Di-μ-hydrido-tetrahydridodigallium
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](/source/gallium(III)_hydroxide)
}}
| Section7 = {{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt =
}}
| Section9 = {{Chembox Related
| OtherCompounds = {{ubl|[Diborane](/source/Diborane)|[Aluminium hydride](/source/Aluminium_hydride)|[Indium trihydride](/source/Indium_trihydride)|[Thallium hydride](/source/Thallium_hydride)}}
}}
}}
'''Digallane''' (systematically named '''digallane(6)''') is an [inorganic compound](/source/inorganic_compound) with the [chemical formula](/source/chemical_formula) {{Chem2|GaH2(H)2GaH2}} (also written {{Chem2|[{GaH2(''μ''\-H)}2]}} or {{Chem2|[Ga2H6]}}). It is the [dimer](/source/Dimer_(chemistry)) of the monomeric compound [gallane](/source/gallane). The eventual preparation of the pure compound, reported in 1989,[{{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
}}][{{cite journal
| title = Gallane: Synthesis, Physical and Chemical Properties, and Structure of the Gaseous Molecule Ga2H6 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
}}]
was hailed as a "tour de force."[{{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
}}] Digallane had been reported as early as 1941 by Wiberg;[{{cite journal
| title = Über einen flüchtigen Galliumwasserstoff der Formel Ga2H6 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 }}] however, this claim could not be verified by later work by Greenwood and others.[{{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
}}] 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](/source/monochlorogallane), {{chem2|(H2GaCl)2}} (containing [bridging](/source/Bridging_ligand) chlorine atoms and thus formulated as ({{chem2|H2Ga(''μ''\-Cl))2}}) was prepared via the hydrogenation of [gallium trichloride](/source/gallium_trichloride), {{chem2|GaCl3}}, with [trimethylsilane](/source/trimethylsilane), {{chem2|[Me](/source/Methyl_group)3SiH}}. This step was followed by a further reduction with {{chem2|Li[GaH4]}} (lithium tetrahydrogallate), solvent free, at −23 °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 °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](/source/diborane) with 2 bridging hydrogen atoms