Last updated
IUPAC name
Other names
Gallane dimer
3D model (JSmol)
  • InChI=1S/2Ga.6H
  • [GaH2]1[H][GaH2][H]1
Molar mass 145.494 g/mol
AppearanceWhite solid or colorless gas
Melting point −50 °C (−58 °F; 223 K) (sublimes)
Boiling point 0 °C (32 °F; 273 K) (decomposes)
Reacts to form gallium(III) hydroxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Digallane (systematically named digallane(6)) is an inorganic compound with the chemical formula GaH
(also written [{GaH
or [Ga
). It is the dimer of the monomeric compound gallane. The eventual preparation of the pure compound, reported in 1989, [1] [2] was hailed as a "tour de force." [3] Digallane had been reported as early as 1941 by Wiberg; [4] however, this claim could not be verified by later work by Greenwood and others. [5]



A two-stage approach proved to be the key to successful synthesis of pure digallane. Firstly the dimeric monochlorogallane, (H2GaCl)2 (containing bridging chlorine atoms and thus formulated as (H2Ga(μ-Cl))2) was prepared via the hydrogenation of gallium trichloride, GaCl3, with Me 3SiH. This step was followed by a further reduction with LiGaH4, solvent free, at −23 °C, to produce digallane, Ga2H6 in low yield.

Ga2Cl6 + 4 Me3SiH → (H2GaCl)2 + 4 Me3SiCl
1/2 (H2GaCl)2 + LiGaH4 → Ga2H6 + 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 with 2 bridging hydrogen atoms [2] (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 1H NMR spectrum of a solution of digallane in toluene shows two peaks attributable to terminal and bridging hydrogen atoms. [2]

In the solid state, digallane appears to adopt a polymeric or oligomeric structure. The vibrational spectrum is consistent with tetramer (i.e. (GaH3)4). [2] 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:

Ga2H6 → 2 Ga + 3 H2

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