Molecular Routes to Group IV Magnesium and Calcium Nanocrystalline Ceramics.

The effect of alkaline-earth-metal alkoxides on the protonolysis of CpM'Cl (M' = Ti, Zr, Hf; Cp = cyclopentadiene) was investigated. This approach enabled the design of compounds with well-defined molecular structures to generate high-purity binary metal oxides. Single-source molecular precursors with structures of [MM'(μ-OEt)(μ-OEt)(OEt)(EtOH)] with M = Mg and M' = Ti (1), Zr (2), and Hf (3), [CaTi(μ-O)(μ-O)(μ-OEt)(OEt)(EtOH)Cl] (4), and [MM'(μ-O)(μ-OEt)(OEt)(EtOH)Cl] with M = Ca and M' = Zr (5) and Hf (6) were prepared via elimination of the cyclopentadienyl ring from CpM'Cl as CpH in the presence of M(OEt) and ethanol (EtOH) as a source of protons. Meanwhile, similar reactions involving the initial substitution of Cl ligands by OEt groups in CpM'Cl (M' = Ti, Zr, Hf) resulted in the formation of [MM'(μ-OEt)(μ-OEt)(OEt)(EtOH)] with M = Ca and M' = Ti (7), Zr (8), and Hf (9). The precursors were characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray structural analysis. Magnesium compounds 1-3 decomposed at 750-850 °C to give MgTiO along with small amounts of MgTiO, MgZrO, or MgHfO binary metal oxides. The thermolysis of calcium compounds 4 and 7-9 led to highly pure CaTiO, CaZrO, or CaHfO perovskite-like oxide particles with diameters of 20-30 nm.