EXAFS study of zirconium alkoxides as precursors in the sol-gel process: II. The influence of the chemical modification

EXAFS studies of primary zirconium alkoxides Zr(OR)₄ with OR = n-propoxide and n-butoxide, dissolved in their corresponding alcohols and chemically modified with acetylacetone (Hacac) and acetic acid (HOAc) in different molal ratios, are presented. The EXAFS-spectroscopic results, supported by FT-IR-studies, indicate a different chemical behavior of the complexing agents. In contrast to acetylacetone, the addition of acetic acid does not change the oligomeric structure of the zirconium alkoxides. Amazingly, the modification with acetic acid leads, in comparison to the pure compounds, to a shortened metal centre distance, whereas in the reaction with acetylacetone the Zr-Zr distance is not changed. With the determined distances and a rough quantitative inclusion of the coordination numbers it was possible to deduce detailed structure models.