Gas electron diffraction study of the vapour over dimethylamine–gallane leading to an improved structure for dimeric dimethylamidogallane, [Me₂NGaH₂]₂: a cautionary tale

Abstract

Dimethylamine-gallane is relatively slow to decompose in a closed system and vaporises at low temperature primarily as Me2(H)N.GaH3 molecules which can be trapped in a solid Ar matrix and characterised by their IR spectrum. Under the conditions needed to secure a useful gas electron diffraction (GED) pattern, however, the vapour was found to consist of dimeric dimethylamidogallane molecules, [Me2NGaH2]2, formed from the secondary amine adduct by elimination of H2, and the most reliable structure for which has been determined. Salient structural parameters (r(hl) structure) were found to be: r(Ga-N) 202.6(2), r(Ga-H) 155.6(8), r(N-C) 148.0(3), r(C-H) 111.2(6) pm; Ga-N-Ga 90.7(1), C-N-C 109.3(5), N-C-H 109.9(10) and H-Ga-H 119.4(42) degrees.

Synthesis and Characterization of Monocrystalline GaPSi3 and (GaP)y(Si)5–2y Phases with Diamond-like Structures via Epitaxy-Driven Reactions of Molecular Hydrides

“…They are not pyrophoric and decompose in air to form white residues. As indicated in ref , both molecules are volatile with ∼1 Torr vapor pressure and remain thermally stable at room temperature for several weeks without further decomposition, making them viable CVD sources of Ga atoms. Prior to growth, the precursors were examined by gas phase IR spectroscopy and the spectra were consistent with those of the dimeric materials mentioned above as described in ref .…”

“…However, we found that the adducts were not stable and steadily decomposed in their storage container via elimination of D 2 or H 2 over several days to produce the [D 2 GaN­(CH 3 ) 2 ] 2 or [H 2 GaN­(CH 3 ) 2 ] 2 derivative, respectively, in the gas phase. The latter are known to adopt dimeric structures in which the N atoms bridge the Ga­(D/H) 2 units to form four-membered rings, as illustrated in Figure . The starting materials are prepared as indicated in ref using standard inert atmosphere techniques and purified through a series of traps kept at −20, −78, and −196 °C.…”

“…The latter are known to adopt dimeric structures in which the N atoms bridge the Ga­(D/H) 2 units to form four-membered rings, as illustrated in Figure . The starting materials are prepared as indicated in ref using standard inert atmosphere techniques and purified through a series of traps kept at −20, −78, and −196 °C. The pure compounds were collected in the −20 °C trap as colorless liquids and then stored at −25 °C in a drybox.…”

Molecular structures of free quinuclidine and its adducts with metal trihydrides, MH3 (M = B, Al or Ga), studied by gas-phase electron diffraction, X-ray diffraction and quantum chemical calculations

“…While the MP2 calculations estimate the M-N distances well for 2 and 3 in the gas phase, the M-N bonds in the crystal structures are shorter than calculated by 0.022, 0.065 and 0.125 Å for 3 and 4, respectively, but this is rather common for adducts, for which crystallisation usually results in a significant shortening of the coordinate link. 8,9,33,34 It is interesting to observe that the three heavy-atom distance parameters of the quinuclidine fragment remain fairly constant on going from 2 to 4. This is particularly true for the calculated distances (largest difference 0.007 Å for MP2/6-311+G* calculations).…”

“…Furthermore, these same adducts of quinuclidine (in particular with alane and gallane) have found their way into the arsenal of synthetically useful compounds, since they allow relatively stereoselective reduction of ketones and oxiranes to the corresponding alcohols; the selectivity can be tuned by varying the metal centre. 7 The relative stability of the quinuclidine-gallane adduct under ambient conditions, compared with other amine-gallane adducts, 1,3,8, 9 significantly increases the usefulness of the compound.…”