Digallane
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| Names | |||
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| IUPAC name
digallane(6)
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| Other names
Di-μ-hydrido-tetrahydridodigallium
Gallane dimer | |||
| Identifiers | |||
3D model (JSmol)
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| ChemSpider | |||
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| Properties | |||
| 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) | ||
| Reacts to form gallium(III) hydroxide | |||
| Related compounds | |||
Related compounds
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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 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.
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
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