title: Structural investigations on the hydrolysis and condensation behavior of pure and chemically modified alkoxides. 1. Transition metal (Hf and Ta) alkoxides.
abstract: Structural investigations on the hydrolysis and condensation behavior of hafnium and tantalum alkoxides were for the first time performed by means of X-ray absorption fine structure and Raman spectroscopy. The studies reveal that both of the alkoxides are dimeric in nature and instantaneously undergo hydrolysis and condensation reactions upon the addition of water. The results indicate that the chemical reaction of the alkoxides with acetylacetone occurs immediately with an increase from 6- to 8-fold coordination around the metal. As a consequence of the coordination by a bidentate ligand, hydrolysis and condensation reactions are hindered in solutions of the chemically modified Hf(OnBu)4 and Ta(OEt)5. Furthermore, the investigations demonstrate that the structure of metal alkoxides is not altered after mixing with prehydrolyzed silicon tetraethoxide, and even after 48 h, both of the species remain as separate entities in the mixture. The addition of water to this mixture starts the hydrolysis and condensation reactions instantaneously and leads to the formation of a M-O-M homocondensation product due to the different reactivity of the two alkoxides.
authors.affiliation: Institute of Physical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany. v.krishnan@ipc.uni-stuttgart.de
authors.forename: Venkata
authors.initials: V
authors.lastname: Krishnan
authors.forename: Silvia
authors.initials: S
authors.lastname: Gross
authors.forename: Sonja
authors.initials: S
authors.lastname: Müller
authors.forename: Lidia
authors.initials: L
authors.lastname: Armelao
authors.forename: Eugenio
authors.initials: E
authors.lastname: Tondello
authors.forename: Helmut
authors.initials: H
authors.lastname: Bertagnolli