Oligomeric structures of the crystalline dimethylamine adducts Me2(H)N·MH3 (M = Al or Ga) and the dimethylamido derivative [Me2NGaH2]3

Introduction to twinning

“…Further examples of non-merohedral twinning problems are given by Dauter (2003), Choe et al (2000), Colombo et al (2000), Gaudin et al (2000), Guelylah et al (2001), and Tang et al (2001). A worked example (Herbst-Irmer & Sheldrick, 1998) is available from http:// shelx.uni-ac.gwdg.de/~rherbst/twin.html.…”

Formation and Characterization of the Cationic Gallane Derivatives [(RH2N)2GaH2]Cl (R = Me or iPr) and [{(iPrH2N)GaH2NHiPr}2GaH2]Cl

“…Firstly, the Ga-N bonds between the central Ga atom, Ga(1), and the NHiPr bridging groups measure 2.0068(14) Å, while the corresponding bonds between each of the terminal Ga atoms, Ga (2), and the NHiPr bridges and coordinated NH 2 iPr ligands measure 1.9884 (14) nificantly in length from those found in cyclic amidogallanes of the type [RRЈNGaH 2 ] n (R, RЈ = H or an organic group; n = 2 or 3) which fall in the range 1.96-2.10 Å. [6,7,[28][29][30] Secondly, it is noteworthy that the NGa(1)-N and Ga(1)-N-Ga(2) angles of 105.14(8) and 111.19(6)°are also close to those found in the skew-boat Ga 3 N 3 ring of the neutral amidogallane [MeHNGaH 2 ] 3 (101.4 and 113.2°). [7] In other words, the horseshoe shape of the new cation, supported by hydrogen bonding to a Cl -anion, prefigures closely the structures adopted by neutral amidogallanes of the type [RRЈNGaH 2 ] 3 .…”

“…[7] In other words, the horseshoe shape of the new cation, supported by hydrogen bonding to a Cl -anion, prefigures closely the structures adopted by neutral amidogallanes of the type [RRЈNGaH 2 ] 3 . [6,7,28,29] Such compounds are, in turn, normally accessed through elimination reactions of amine complexes of gallanes. [1,[4][5][6][7] This suggests that the cation [{(iPrH 2 N)GaH 2 NHiPr} 2 GaH 2 ] + may well exemplify a key intermediate in the formation of amidogallanes.…”

“…[4,5,12,13] By contrast with the corresponding reactions of LiGaH 4 , the reaction of LiAlH 4 with an excess of the amine hydrochloride [RNH 3 ]Cl (R = Me or tBu) in an ether solution proceeds mainly with H 2 elimination and formation of the imidoalane anion [(RN) 4 (AlH 2 ) 6 ] 2-possessing the adamantoid Al 6 N 4 skeleton I. [13] On the other hand, the main product of the reaction between LiAlH 4 and [iPrNH 3 ]Cl under similar conditions is the neutral, hexameric imidoalane [iPrNAlH] 6 (II). [13] Here we report the isolation, in [(MeH 2 N) 2 GaH 2 ]Cl (1) and [(iPrH 2 N) 2 GaH 2 ]Cl (2), of two further examples of cationic gallane complexes, the structures of which have been authenticated by X-ray analysis.…”

“…Previous research carried out in our laboratories has shown that gallanes formally of the type GaH 2 X (X = GaH 4 , BH 4 , or halogen) [1,4,[5][6][7][8]15,16] resemble analogous boranes [1,17,18] in many ways in adding to amine and other donor molecules L to form (i) molecular 1:1 complexes L·GaH 2 X and (ii) 1:2 complexes with either a molecular (L 2 GaH 2 X) or an ionic formulation ([H 2 GaL 2 ] + X -). The corresponding alanes likewise form 1:1 complexes L·AlH 2 X that are molecular in nature, but 1:2 complexes are typically also molecular with a pentacoordinate metal atom.…”