Convenient Route to Heterometallic Group 4-Zinc Precursors for Binary Oxide Nanomaterials.

Abstract

In this study, simple and efficient synthetic routes to a family of uncommon group 4-zinc heterometallic alkoxides were developed. Single-source molecular precursors with the structures [Cp2TiZn(μ,η-OR)(THF)Cl2] (1), [Zr3Zn7(μ3-O)(μ3,η2-OR)3(μ-OH)3(μ,η2-OR)6(μ,η-OR)6Cl6] (2), and [Hf3Zn7(μ3-O)(μ3,η2-OR)3(μ-OH)3(μ,η2-OR)6(μ,η-OR)6Cl6] (3) were prepared via reduction of Cp2TiCl2 with metallic zinc or protonolysis of the metal-cyclopentadienyl bond in Cp2M'Cl2 (M' = Zr or Hf) in the presence of 2-methoxyethanol (ROH) and Zn(OR)2. This synthetic route enables the creation of compounds with well-defined molecular structures and therefore provides precursors suitable for obtaining group 4-zinc oxides. Precursors 1-3 were characterized by elemental analysis, nuclear magnetic resonance and infrared spectroscopies, and single-crystal X-ray diffraction. Compound 1 decomposed at 800-900 °C to give a mixture of binary metal oxides (i.e., Zn2Ti3O8, ZnTiO3, or Zn2TiO4) and common polymorphs of TiO2 and ZnO. After calcination at 1000 °C, only TiO2 and the high-temperature-stable phase Zn2TiO4 were observed. Thermolysis of compounds 2 and 3 gave mixtures of ZnO and ZrO2 or HfO2, respectively. The obtained ZnO-ZrO2 and ZnO-HfO2 mixed oxide materials have constant phase compositions across a broad temperature range and therefore are attractive host lattices for Eu3+ for applications as yellow/red double-light-emitting phosphors. It was established that Eu3+ ions were successfully introduced into the ZnO and ZrO2/HfO2 lattices. It was revealed that Eu3+ ions prefer to occupy low-symmetry sites in ZrO2/HfO2 rather than in ZnO.