Gallium and Indium β-diketonate complexes: AACVD of [In(thd)3] and the attempted synthesis of gallium and indium bis(β-diketonates)

Aerosol-assisted chemical vapour deposition (AACVD) of a suspension of [In(thd)3] (thd = 2,2,6,6-tetramethylheptane-3,5-dionate) in CH2Cl2 at 450 °C afforded thin crystalline films of indium oxide. The films were analyzed by scanning electron microscopy (SEM), glancing angle X-ray diffraction (XRD) and energy dispersive analysis of X-rays (EDX). Efforts to grow thicker films were hampered by the poor solubility of [In(thd)3], so the synthesis of heteroleptic compounds of the type [M(bdk)2X] (M = Ga, In; bdk = β-diketonate; X = chloride, hydride, methyl) was attempted such that the solubility could be improved by tuning the ligands surrounding the metal centre. Reaction of stoichiometric amounts of β-diketones [Hthd and 2,4-pentanedione (acetylacetone, Hacac)] with Lewis base-stabilized adducts of GaH3 resulted only in the isolation of the homoleptic gallium tris(β-diketonate) compounds [Ga(bdk)3], instead of the expected heteroleptic gallium bis(β-diketonate) hydride, [GaH(bdk)2]. An unexpected reduction of Hthd to 2,2,6,6-tetramethylheptane-3,5-diol was also observed. Other attempted syntheses of gallium bis(β-diketonate) compounds also resulted in the isolation of homoleptic [Ga(bdk)3] complexes and similar results were obtained for indium. The compounds were characterised by 1H NMR spectroscopy, mass spectrometry and elemental analysis and the structures of [In(thd)3] and 2,2,6,6-tetramethylheptane-3,5-diol were determined by X-ray crystallography.