Digallane | |
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digallane(6) |
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Other names
Di-μ-hydrido-tetrahydridodigallium |
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Identifiers | |
CAS number | 12140-58-8 |
Properties | |
Molecular formula | Ga2H6 |
Molar mass | 145.494 g/mol |
(verify) (what is: / ?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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Infobox references |
Digallane is a chemical compound of gallium and hydrogen with the formula 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]
Contents |
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 Me3SiH. This step was followed by a further reduction with LiGaH4, solvent free, at −23 °C, to produce digallane, Ga2H6 in low yield.
Digallane is volatile and condenses at −50 °C into a white solid.
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:
The reactions with Lewis bases are similar to those of diborane, but the larger size of gallium is indicated by its ability to form 2:1 adducts. Thus, with trimethylamine both 1:1 and 2:1 adducts are formed (i.e. Me3N·GaH3 and (Me3N)2·GaH3, respectively. With phosphine a 1:1 adduct H3P·GaH3 is formed. The trimethylamine adducts have been known for some time. [6][7] These adducts are prepared by the reaction of LiGaH4 with trimethylammonium chloride, Me3NHCl, the 2:1 adduct is formed at low temperatures:
The monomeric structure of Me3N.GaH3 has been confirmed in both the gas and solid phases. In this regard, the 2:1 adduct contrasts with the corresponding alane complex, Me3N.AlH3 which in the solid is dimeric with bridging hydrogen atoms. [8] A range of other 1:1 adducts have been prepared and their stabilities determined.[9]