{{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<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 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 chlorine atoms and thus formulated as ({{chem2|H2Ga(''μ''\-Cl))2}}) was prepared via the hydrogenation of gallium trichloride, {{chem2|GaCl3}}, with trimethylsilane, {{chem2|Me3SiH}}. 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 bonds). 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 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 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