Novel β-ketoiminato complexes of zirconium: synthesis, characterization and evaluation for solution based processing of ZrO2 thin films

Abstract

Treatment of tetrakis(diethylamido)zirconium(IV); [Zr(NEt₂)₄] with a series of β-ketoimines ({[RHN]C(CH₃)C(H)C(CH₃)O} where R is a functionalized side-chain; 4-(2-methoxyethylamino)pent-3-en-2-one, Hmeap; 4-(3-methoxypropylamino)pent-3-en-2-one, Hmpap; 4-(2-(dimethylamino)ethylamino)pent-3-en-2-one, Hdeap; 4-(3-(dimethylamino)propylamino)pent-3-en-2-one, Hdpap) leads to an amine substitution reaction that yielded novel monomeric heteroleptic mixed amido-ketoiminato complexes of the type bis(4-(2-methoxyethylamino)pent-3-en-2-onato)bis(diethylamido)zirconium(IV) (1), bis(4-(3-methoxypropylamino)pent-3-en-2-onato)bis(diethylamido)zirconium(IV) (2), and bis(4-(3-(dimethylamino)propylamino)pent-3-en-2-onato)bis(diethylamido)zirconium(IV) (3), and eight-coordinated homoleptic complexes tetrakis(4-(2-methoxyethylamino)pent-3-en-2-onato)zirconium(IV) (4) and tetrakis(4-(2-(dimethylamino)ethylamino)pent-3-en-2-onato)zirconium(IV) (5), depending on the ratio of the ligand to zirconium. Adopting a similar strategy with zirconium alkoxide, namely [Zr(OⁱPr)₄·ⁱPrOH], with β-ketoimine Hmeap, leads to the formation of a dimer, bis(μ₂-isopropoxo)bis(4-(2-methoxyethylamino)pent-3-en-2-onato)tetrakis(isopropoxo)dizirconium(IV) (6). The newly synthesised complexes were characterized by NMR spectroscopy, mass spectrometry, single crystal X-ray diffraction, elemental analysis and thermal analysis. The low decomposition temperature facilitated by the stepwise elimination of the ketominate ligand from the complex and the stability of the complexes obtained in air as well as in solution makes them highly suitable for solution based processing of ZrO₂ thin films, which is demonstrated using compound 5 on Si(100) substrates. High quality ZrO₂ films were obtained and were investigated for their structure, morphology, composition and optical properties. Low temperature crystallisation of ZrO₂ is achieved by a simple chemical deposition process using the new class of Zr precursors and the films exhibit an optical transmittance above 90%.