Molecular Routes to Group IV Magnesium and Calcium Nanocrystalline Ceramics.

The effect of alkaline-earth-metal alkoxides on the protonolysis of Cp2M'Cl2 (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 [M2M'2(μ3-OEt)2(μ-OEt)4(OEt)6(EtOH)4] with M = Mg and M' = Ti (1), Zr (2), and Hf (3), [Ca6Ti4(μ6-O)2(μ4-O)2(μ3-OEt)12(OEt)12(EtOH)6Cl4] (4), and [M2M'2(μ4-O)(μ-OEt)5(OEt)4(EtOH)4Cl]n with M = Ca and M' = Zr (5) and Hf (6) were prepared via elimination of the cyclopentadienyl ring from Cp2M'Cl2 as CpH in the presence of M(OEt)2 and ethanol (EtOH) as a source of protons. Meanwhile, similar reactions involving the initial substitution of Cl ligands by OEt groups in Cp2M'Cl2 (M' = Ti, Zr, Hf) resulted in the formation of [M2M'2(μ3-OEt)2(μ-OEt)4(OEt)6(EtOH)4] 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 MgTiO3 along with small amounts of Mg2TiO4, Mg2Zr5O12, or Mg2Hf5O12 binary metal oxides. The thermolysis of calcium compounds 4 and 7-9 led to highly pure CaTiO3, CaZrO3, or CaHfO3 perovskite-like oxide particles with diameters of 20-30 nm.