Digallane (systematically named digallane(6)) is an inorganic compound with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbol ...

(also written or ). It is the

dimer Dimer may refer to: * Dimer (chemistry), a chemical structure formed from two similar sub-units ** Protein dimer, a protein quaternary structure ** d-dimer * Dimer model, an item in statistical mechanics, based on ''domino tiling'' * Julius Dimer ...

of the monomeric compound

gallane Gallane, also systematically named trihydridogallium, is an inorganic compound of gallium with the chemical formula (also written as ). It is a photosensitive, colourless gas that cannot be concentrated in pure form. Gallane is both the simplest ...

. The eventual preparation of the pure compound, reported in 1989, was hailed as a "tour de force." Digallane had been reported as early as 1941 by Wiberg; however, this claim could not be verified by later work by Greenwood and others. 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 Me₃SiH. 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 Diborane(6), generally known as diborane, is the chemical compound with the formula B2H6. It is a toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Diborane is a key boron compound with a variety of applications. It has attracte ...

with 2 bridging hydrogen atoms (so-called

three-center two-electron bond A three-center two-electron (3c–2e) bond is an electron-deficient chemical bond where three atoms share two electrons. The combination of three atomic orbitals form three molecular orbitals: one bonding, one ''non''-bonding, and one ''anti''-b ...

s). 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 Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with ...

spectrum of a solution of digallane in

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon. It is a colorless, water-insoluble liquid with the smell associated with paint thinners. It is a mono-substituted benzene derivative, consisting of a methyl group (CH3) a ...

shows two peaks attributable to terminal and bridging hydrogen atoms. In the solid state, digallane appears to adopt a polymeric or oligomeric structure. The vibrational spectrum is consistent with tetramer (i.e. (GaH₃)₄). 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 Aluminium hydride (also known as alane and alumane) is an inorganic compound with the formula Al H3. Alane and its derivatives are common reducing (hydride addition) reagents in organic synthesis that are used in solution at both laboratory ...

wherein the aluminium centers are 6-coordinated. Digallane decomposes at ambient temperatures: : Ga₂H₆ → 2 Ga + 3 H₂

References

{{Hydrides by group Inorganic compounds Gallium compounds Metal hydrides Reducing agents Substances discovered in the 1980s