Colin R. Pulham," Anthon J. Downs,*-'. Michael J. Goode,l. David W. H. Rankin,**Ib. Contribution from the Inorganic Chemistry Loboratory, University of Oxford, ...
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J . Am. Chem. SOC.1991, 113, 5149-5162
Gallane: Synthesis, Physical and Chemical Properties, and Structure of the Gaseous Molecule Ga2H6As Determined by Electron Diffraction Colin R. Pulham," Anthon J. Downs,*-'. Michael J. Goode,l. David W. H. Rankin,**Ib and Heather E. Robertson
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Contribution from the Inorganic Chemistry Loboratory, University of Oxford, Oxford, OX1 3QR, U.K.,and the Department of Chemistry, University of Edinburgh, Edinburgh, EH9 3JJ, U.K. Received December 3, 1990
Abstract: The elusive binary hydride of gallium, [GaHJ, has at last been synthesized in rigorously conditioned all-glass apparatus by the reaction between monochlorogallane, [H2GaC1I2,and lithium tetrahydridogallate, LiGaH4, near -30 "C. The compound, which decomposes to the elements at ambient temperatures, has been characterized by chemical analysis, by its vibrational and 'H NMR spectra, and by chemical trapping with trimethylamine. The infrared spectra of the vapor species at low pressures (sampled directly at ambient temperatures or trapped in a solid inert matrix at ca. 20 K, and including the results of deuteration experiments) leave little doubt that the principal component is the diborane-like molecule H2Ga(p-H)2GaH2. Such a conclusion is endorsed by electron-diffraction measurements, carried out on the vapor at ca. 255 K these are consistent with an r, structure featuring the following parameters: r ( G a 4 a ) 258.0 (0.2),r(Ga-H,) 151.9 ( 3 3 ,and r(Ga-Hb) 171.0 (3.8) pm; and LGa-Hb-Ga 97.9 (3.2)" (H, = terminal H atom; Hb = bridging H atom). The molecule GazHs is highly susceptible to aggregation. The vibrational spectra of the solid suggest the presence of an oligomer [GaHJ, where n > 2 and possibly equal to 4, but still retaining terminal Ga-H bonds (cf. a-AIH,). A similar species is probably a major constituent of toluene-ds solutions of the gallane; at temperatures 120°).12913 experiment (including factors like the temperature, residence time, and proportions of the reaction mixture), however, it proved impossible to isolate a product which was entirely free from chloride. Thus, chemical analysis showed that proportion Ga:CI to be typically 251,and the 'H N M R spectrum of toluene-da solutions at low temperatures confirmed that the product contained more than one gallium hydride derivative. It appears, therefore, that a hydride-rich product including species like [GaH,], and [H2GaC1I2" is formed through the interaction of neat gallium(II1) chloride and a tetrahydridogallate, but only in very low yields (
