Digallane

"Gallium trihydride" and "Gallium(III) hydride" redirect here. For the mononuclear compound, see Gallane.

Digallane (systematically named digallane(6)) is an inorganic compound with the chemical formula GaH₂(H)₂GaH₂ (also written [{GaH₂(μ-H)}₂] or [Ga₂H₆]). 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] This compound is a colorless gas that decomposes above 0 °C.

Digallane

Names
IUPAC name digallane(6)
Other names Di-μ-hydrido-tetrahydridodigallium Gallane dimer
Identifiers
CAS Number	12140-58-8 Y
3D model (JSmol)	Interactive image
ChemSpider	24769416
InChI InChI=1S/2Ga.6H Key: GFQCQFDOQMRGIQ-UHFFFAOYSA-N
SMILES [GaH2]1[H] [GaH2] [H]1
Properties
Chemical formula	Ga2H6
Molar mass	145.494 g/mol
Appearance	White solid or colorless gas
Melting point	−50 °C (−58 °F; 223 K) (sublimes)
Boiling point	0 °C (32 °F; 273 K) (decomposes)
Solubility in water	Reacts to form gallium(III) hydroxide
Related compounds
Related compounds	Diborane Aluminium hydride Indium trihydride Thallium hydride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Preparation

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 trimethylsilane, Me₃SiH. This step was followed by a further reduction with Li[GaH₄] (lithium tetrahydrogallate), solvent free, at −23 °C, to produce digallane, Ga₂H₆ in low yield.

Ga₂Cl₆ + 4 Me₃SiH → (H₂GaCl)₂ + 4 Me₃SiCl

(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 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