EXAFS study of zirconium alkoxides as precursor in the sol-gel process: I. Structure investigation of the pure alkoxides

The properties of materials obtained by sol-gel processing show a certain dependence on the type of metal alkoxide and the solvent. Some authors assumed that these effects are caused by the degree of oligomerization of the metal alkoxides and their solvation. In order to obtain information on the structure and molecular complexity of the metal alkoxide we performed an EXAFS study on primary zirconium alkoxides Zr(OR)₄, with OR = n-propoxide and n-butoxide in solution of their parent alcohol. The EXAFS data for zirconium iso-propoxide have been used as a reference, because its solid state structure is known from X-ray analysis. The Zr-Zr correlations which were observed for all investigated systems provide evidence for an oligomeric structure. Because the analysis of the co-ordination spheres around the central Zr-atom revealed different Zr-O bond lengths, some of the formerly postulated structure models can be ruled out. We propose solvated dimers or trimers or mixtures of both species as possible structures of zirconium propoxide and zirconium butoxide in solution of their parent alcohol.