Zirconium and Hafnium Twin Monomers for Mixed Oxides

The synthesis of Zr and Hf twin monomers of type [M(2-OCH₂ ^c C₄ H₃ O)₄ (x HOCH₂ ^c C₄ H₃ O)] (3, M=Zr, x=0; 4, M=Hf, x=1) and M[(2-OCH₂ -C₆ H₄ O)₂ (2-HOCH₂ -C₆ H₄ OH)] (5, M=Zr; 6, M=Hf) by reacting M(OR)₄ (M=Zr, R=ⁿ C₃ H₇ , 1; M=Hf, R=ⁿ C₄ H₉ , 2) with 2-furylmethanol or 2-hydroxybenzyl alcohol is discussed. Complexes 3-6 were homopolymerized under acidic conditions. Additionally, 5 and 6 were copolymerized with 2,2'-spirobi[4 H-1,3,2-benzodioxasiline] (SBS). Under acidic conditions SBS forms a phenolic resin/SiO₂ nanostructured material. The resulting hybrid materials from the homopolymerization of 3-6 and the copolymerized materials from 5 and 6 were characterized by standard solid-state analytics. The inorganic lattice of the MO₂ materials from the homopolymerized complexes 3-6 and SiO₂ /MO₂ from the copolymerization of 5 and 6 with SBS was obtained by air oxidation. The oxide materials were characterized by X-ray powder diffraction (XRPD) and energy-dispersive X-ray analysis, which proved their identity. The inner surface area was determined by N₂ adsorption/desorption studies, which revealed surface areas of 100 m²  g^-1 for MO₂ . The mixed oxides SiO₂ /MO₂ were additionally investigated by differential scanning calorimetry and variable-temperature XRPD to study the thermal behavior. It was found that crystallization of tetragonal MO₂ nanoparticles is characteristic within the SiO₂ matrix, but higher sintering temperatures caused crystallization of the SiO₂ lattice.