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Digallane
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<h2 id="preparation">Preparation</h2> <p>A two-stage approach proved to be the key to successful synthesis of pure digallane. Firstly the dimeric monochlorogallane, (H2GaCl)2 (containing <a href="/facts/Bridging_ligand/E4ytba8I">bridging</a> chlorine atoms and thus formulated as (H2Ga(<i>μ</i>-Cl))2) was prepared via the hydrogenation of <a href="/facts/Gallium_trichloride/gMs76FbG">gallium trichloride</a>, GaCl3, with <a href="/facts/Trimethylsilane/cgwLhNKs">trimethylsilane</a>, <a href="/facts/Methyl_group/fkM97EMD">Me</a>3SiH. 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. </p> Ga2Cl6 + 4 Me3SiH → (H2GaCl)2 + 4 Me3SiCl (H2GaCl)2 + 2 Li[GaH4] → 2 Ga2H6 + 2 LiCl <p>Digallane is volatile and condenses at −50 °C into a white solid. </p> <h2 id="structure-and-bonding">Structure and bonding</h2> <p>Electron diffraction measurements of the vapour at 255 K established that digallane is structurally similar to <a href="/facts/Diborane/k7egwbPf">diborane</a> with 2 bridging hydrogen atoms<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a> (so-called <a href="/facts/Three-center_two-electron_bond/1etgQjYh">three-center two-electron bonds</a>). 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 <a href="/facts/Nuclear_magnetic_resonance/pGYAn9Bz">NMR</a> spectrum of a solution of digallane in <a href="/facts/Toluene/Pzdt8dwD">toluene</a> shows two peaks attributable to terminal and bridging hydrogen atoms.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p><p>In the solid state, digallane appears to adopt a polymeric or oligomeric structure. The vibrational spectrum is consistent with tetramer (i.e. (GaH3)4).<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> The vibrational data indicate the presence of terminal hydride ligands. In contrast, the hydrogen atoms are all bridging in <a href="/facts/Aluminium_hydride/fprkHPdh">α-alane</a>, a high-melting, relatively stable polymeric form of <a href="/facts/Aluminium_hydride/fprkHPdh">aluminium hydride</a> wherein the aluminium centers are 6-coordinated. Digallane decomposes at ambient temperatures: </p> Ga2H6 → 2 Ga + 3 H2 <h2 id="references">References</h2> <ol> <li id="fn:1"><p>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 href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>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. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>N.N. Greenwood (2001). "Main group element chemistry at the millennium". J. Chem. Soc., Dalton Trans. (14): 2055–2066. doi:10.1039/b103917m. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>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. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>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. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>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. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>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. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>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. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> </ol>