Structural Investigation of the Hydrolysis-Condensation Process of Titanium Alkoxides Ti(OR)(4) (OR = OPri, OEt) Modified by Acetylacetone. 1. Study of the Alkoxide Modification

Chemical modifications of alkoxides have been extensively used in sol-gel processing for a better control of the hydrolysis-condensation process. In this paper, the modification of titanium alkoxides (Ti(OPri)(4), Ti(OEt)(4)) with acetylacetone is investigated by using infrared, H-1 and C-13 NMR, and X-ray absorption (XANES-EXAFS) spectroscopies. The reaction with titanium isopropoxide leads to a unique species, Ti(OPri)(3)acac (acac = acetylacetonate), whose structure is precisely described. It appears to be a monomer with titanium in 5-fold coordination. The reaction between acetylacetone and titanium ethoxide leads to the existence of several species in equilibrium, monomers in 5-fold coordination and oligomers in 6-fold coordination. These structural differences are related to the ability of the alkoxy groups to behave as bridging ligands. A study of the dilution of the modified precursor Ti(OPri)(3)acac in ethanol is also presented. Substitution of isopropoxy groups by ethoxy groups occurs and leads to the formation of new monomeric and oligomeric species. These products were characterized by 1H NMR spectroscopy.