Homoleptic gallium(iii) and indium(iii) aminoalkoxides as precursors for sol–gel routes to metal oxide nanomaterials

Abstract

New homoleptic aminoalkoxides of gallium(III) and indium(III) of the types M₄{(OC₂H₄)₂NMe}₆ [M = Ga (1), In (2)] and [Ga{(OC₂H₄)₃N}]_n (3), as well as a previously described Ga₂(OC₂H₄NMe₂)₆ (A) have been prepared by isopropoxo(chloro)-aminoalkoxo exchange reactions and characterised by elemental analyses, FT-IR and ¹H NMR spectroscopy. Formation of a star-shaped Ga[Ga{μ-η³:η¹-(OC₂H₄)₂NMe}₂]₃ (1·4CHCl₃) and a zigzag linear In₄{μ-η³:η¹-(OC₂H₄)₂NMe}₆ (2·6CHCl₃), as revealed by X-ray single crystal structures, reflects the structural diversity among N-methyldiethanolaminate derivatives. Their hydrolyses in boiling water, either in presence or absence of tetraalkylamonium bromide, have been studied and, for gallium derivatives, compared with similar hydrolytic reactions of Ga(OⁱPr)₃. The hydrolysed products were studied by FT-IR, TG-DTA and XRD techniques. For gallium derivatives, transition from orthorhombic Ga(O)OH phase of as-prepared powder to phase pure rhombohedral- and monoclinic-Ga₂O₃ occurred at about 500 °C and 700 °C, respectively, whereas cubic In(OH)₃ phase of as-prepared powder of 2 was converted to cubic In₂O₃ at 250 °C. Partial hydrolyses were also performed and evolution of the particle size in solution was recorded by light scattering measurements. Various sol–gel processing parameters such as concentration and hydrolysis ratio (h) were studied in order to stabilise nano-sized colloidal suspensions for access to thin films by spin coating. The N-methyldiethanolamine derivatives 1 and 2 were found to be the most suitable candidates for sol–gel processing. The transparent Ga₂O₃ and In₂O₃ films obtained on glass or Si wafers from spin-coating of 1 and 2, respectively, were characterised by SEM, EDX and XRD.