Oligomeric Rods of Alkyl- and Hydridogallium Imides

Abstract

Reaction of [RGa(NMe(2))(2)](2), where R = Me, Et, Bu, and Hx, with ammonia at 150 degrees C in an autoclave produced insoluble white powders formulated as oligomers of [RGaNH](n). The analogous reaction between NH(3) and MeGa[N(SiMe(3))(2)](2) at low temperature (<25 degrees C) formed an isolable intermediate, [MeGa(mu-NH(2))N(SiMe(3))(2)](2), that was characterized using single-crystal X-ray diffraction. Infrared spectroscopy and X-ray diffraction of the oligomers were consistent with a rodlike structure comprised of six-membered, [RGaNH](3) rings stacked perpendicular to the long axis of the rod. The method of synthesis, formula, and diffraction results suggested a structural similarity between the alkyl, [RGaNH](n)(), and the previously reported hydride, [HGaNH](n). The structural and electronic properties of rods having the general formula H(3)[(HXYH)(3)](n)H(3) (XY = GaN, GeC; n = 1-9) were investigated using density functional theory. Atomic electronegativity differences between the group 13/15 and 14/14 systems were found to play important roles in the geometrical structures of the two rods and also caused significant differences in the electronic structures. Energetically, it was found to be increasingly favorable to add additional cyclotrigallazane rings to the GaN rods, while for the GeC rods, there was a roughly constant energy cost associated with each additional ring. The electric dipole moments of the GaN rods increased substantially with length; in the GeC rods, charge separation occurred to a much smaller extent and had a polarization opposite to that found in GaN. In addition, increased dipole moments correlated with smaller electronic excitation energies, as predicted by time-dependent density functional theory. All of the powders exhibited luminescence in the visible spectrum at room temperature. Structure observed in the photoluminescence spectra of [HGaNH](n) and [MeGaNH](n) was interpreted as arising from rods of different length.

Unusual reaction pathways of gallium(III) silylamide complexes

“…The Ga1-C1 bond length is similar to those observed for other complexes with one methyl group coordinated to gallium bearing (trimethylsilyl)amide/imide ligands [1.953(4) Å for [MeGa = NSiMe 3 ] 4 (Kühner et al, 1997) and 1.957(3) Å for [MeGaN(SiMe 3 ) 2 (μ -NH 2 )] 2 (Kormos et al, 2005)]. Me 2 GaN(Ph)SiMe 3 (Waezsada et al, 1998) and Me 3 Ga (Lustig and Mitzel, 2004) exhibit longer Ga-C bonds with Ga-C1 1.974(3) and Ga-C2 1.978(3) Å for the silylamide complex and an average Ga-C bond length of 1.975 Å for the gallium alkyl.…”

Electronic properties of binary and mixed [RMNH]n (R=H,CH3, M=Al,Ga,In) oligomers

“…End effects are considered comparing electronic structures of the open and closed forms of binary rods with M=Ga where R=CH 3 or H. From the Table 1 one can see that the open forms of the oligomers are heavily polarized that is in consistence with previous report [4]. While the energy gap of the closed rods with R=H is stabilized at value 6.7±0.1 eV after elongation with n>7, H 3 [GaHNH] 3n H 3 exhibits steadily decreasing magnitude of the gap at least up to n=18, where the gap is 2.3 eV.…”

“…The reliability of the method was justified by comparison with results obtained by CCSD/QZVP method on the example of the smallest [GaRNH] 4 (R=H,CH 3 ) clusters. SVP as well TZVP basis sets [2] were utilized.…”

The role of the bis-trimethylsilylamido ligand, [N{SiMe3}2]−, in main group chemistry. Part 2: Structural chemistry of the metallic p-block elements

“…In contrast the solid-state structure of the amido-amine stabilized gallane, GaH(N{SiMe 3 } 2 ) (N(H)CH 2 CMe 2 CH 2 NMe 2 ) was dimeric with a central Ga 2 N 2 group involving the 2 [44]. This compound was described as an intermediate in the transamination reaction of GaMe(N{SiMe 3 } 2 ) 2 with ammonia, where gallium starting materials with the smaller amido-ligand, GaR(NMe 2 ) 2 (R = Me, Et), proceeded with loss of two equivalents of HNMe 2 to afford polymeric [RGaNH] n .…”