Synthesis, structure determination, and sol-gel processing of heterometallic heteroleptic alkoxide complexes of late transition metals

摘要

The thesis describes synthesis of single-source precursors (SSP) for sol-gel preparation of thin films and nanocomposites. The structures of the SSPs were determined by single-crystal X-ray studies and a new group of heterometallic heteroleptic alkoxide complexes have been described, the MII2MV2(acac)2(OR)12 complex, MII= Co, Ni, Zn or Mg, and MV= Ta or Nb, R= Et or Me. Changing to molybdenum oxomethoxide, MoO(OMe)4, instead of tantalum or niobium alkoxide, in the reaction with cobalt acetylacetone provided Co2Mo2O2(acac)2(OMe)10. Nickel acetylacetonate in the reaction with MoO(OMe)4 provided Ni2Mo2O2(acac)2(OMe)10. In order to improve solubility, the acetylacetonate complex was exchanged for Ni(ORN)2 (RN= CHMeCH2NMe2) and the reaction provided Ni2Mo2O2(ORN)2(OMe)10. The structure of Ni2Mo2O2(L)2(OMe)10, L= acac or ORN, was determined by EXAFS. Nanocomposite powder was produced by hydrolysis and condensation of the SSPs, with toluene as solvent. The xerogel powders from Ni2Mo2O2(ORN)2(OMe)10 were annealed at different temperatures and showed increasing degree of crystallization of the material. At 700 °C, crystallized grains could be seen, with low porosity but a large surface area provided by the grain size (175-250 nm). The oxide powders obtained at 650 °C and 800 °C from Co2Ta2(acac)2(OMe)12 showed dense and well-faceted xerogel particles with an even size distribution. Small islands of a crystallized oxide phase could be seen on the surface of the particles. Thin films were produced by spin-coating on Si and SiO2. SEM images of the oxide films from Co2Ta2(acac)2(OEt)12 revealed smooth and evenly distributed films on the substrates. The different layers were not seen, indicating uniform depositions. Zeolite Y (12 Å pores) was used for implementation of MII2MV2(acac)2(OMe)12. The implemented zeolite complex was studied by EXAFS and the catalysis ability was tested. For modelling experiments, synthesis between Co2Nb2(acac)2(OMe)12 and cyclohexylsilsesquioxane was performed and resulted in Co[(C6H11)7Si7O12]2H4. According to the very similar FT of the EXAFS analyses of the implemented zeolite and the Co-silsesquioxane complex, the metallasilsesquioxane complex can serve as a zeolite Y analogue with implemented metal atoms.