Solution Chemistry of Cyclotrigallazane:  Supercritical Ammonia and Lewis Base Catalyzed Dehydrogenation To Produce Poly(imidogallane)

The polymeric hydrido gallium imide [HGaNH] n , or poly(imidogallane), was isolated as an intermediate in the conversion of cyclotrigallazane, [H2GaNH2]3, to gallium nitride in supercritical ammonia. Poly(imidogallane) can be converted to nanocrystalline GaN via solid-state pyrolysis or by extended thermolysis in supercritical ammonia. Characterization by IR spectroscopy, elemental analysis, and X-ray and electron diffraction suggests that the structure of poly(imidogallane) is a layered solid with a coherent length of approximately 15 nm. The interaction of [H2GaNH2]3 and various Lewis bases leads to the isolation of [HGaNH] n and gallane−Lewis base adducts, H3Ga·base, rather than the expected gallazane adducts, H2GaNH2·base. Experiments involving the use of ND3 resulted in the isolation of [H2GaND2]3 and suggest that the donor−acceptor complex H2Ga(NH2)(ND3) was present in solution. It was proposed that these gallazane−base adducts equilibrate via a ligand redistribution reaction and that the formation of [HGaNH] n results from NH3 elimination from a diamidogallium hydride. The proposed mechanism is used to explain the catalytic role of ammonia in the conversion of [H2GaNH2]3 to [HGaNH] n .