Digallane

Digallane
Names
	IUPAC name digallane(6)
	Other names Di-μ-hydrido-tetrahydridodigallium; Gallane dimer
Identifiers
CAS Number	12140-58-8 ;
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). verify (what is ?) Infobox references

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

References

^ Anthony J. Downs; Michael J. Goode; Colin R. Pulham (1989). "Gallane at last!". Journal of the American Chemical Society. 111 (5): 1936–1937. doi:10.1021/ja00187a090.
^ ^a ^b ^c ^d Pulham C.R.; Downs A.J.; Goode M.J; Rankin D.W.H. Roberson H.E. (1991). "Gallane: Synthesis, Physical and Chemical Properties, and Structure of the Gaseous Molecule Ga₂H₆ As Determined by Electron Diffraction". Journal of the American Chemical Society. 113 (14): 5149–5162. doi:10.1021/ja00014a003.
^ N.N. Greenwood (2001). "Main group element chemistry at the millennium". J. Chem. Soc., Dalton Trans. (14): 2055–2066. doi:10.1039/b103917m.
^ Wiberg E.; Johannsen T. (1941). "Über einen flüchtigen Galliumwasserstoff der Formel Ga₂H₆ und sein Tetramethylderivat". Naturwissenschaften. 29 (21): 320. Bibcode:1941NW.....29..320W. doi:10.1007/BF01479551. S2CID 44840674.
^ Shriver, D. F.; Parry, R. W.; Greenwood, N. N.; Storr, A; Wallbridge, M. G. H. (1963). "Some Observations Relative to Digallane". Inorg. Chem. 2 (4): 867–868. doi:10.1021/ic50008a053.

[1] Anthony J. Downs; Michael J. Goode; Colin R. Pulham (1989). "Gallane at last!". Journal of the American Chemical Society. 111 (5): 1936–1937. doi:10.1021/ja00187a090.

[Pulham-2] Pulham C.R.; Downs A.J.; Goode M.J; Rankin D.W.H. Roberson H.E. (1991). "Gallane: Synthesis, Physical and Chemical Properties, and Structure of the Gaseous Molecule Ga₂H₆ As Determined by Electron Diffraction". Journal of the American Chemical Society. 113 (14): 5149–5162. doi:10.1021/ja00014a003.

[3] N.N. Greenwood (2001). "Main group element chemistry at the millennium". J. Chem. Soc., Dalton Trans. (14): 2055–2066. doi:10.1039/b103917m.

[4] Wiberg E.; Johannsen T. (1941). "Über einen flüchtigen Galliumwasserstoff der Formel Ga₂H₆ und sein Tetramethylderivat". Naturwissenschaften. 29 (21): 320. Bibcode:1941NW.....29..320W. doi:10.1007/BF01479551. S2CID 44840674.

[5] Shriver, D. F.; Parry, R. W.; Greenwood, N. N.; Storr, A; Wallbridge, M. G. H. (1963). "Some Observations Relative to Digallane". Inorg. Chem. 2 (4): 867–868. doi:10.1021/ic50008a053.

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Digallane

Preparation

Structure and bonding

References

Information related to Digallane

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