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.