Modification of Metal Alkoxide Precursors by Organofunctional Bidentate Ligands: Chemical Problems and Opportunities for Materials Syntheses

Bidentate ligands are potentially useful to modify metal alkoxides precursors for sol-gel processing. However, anionic bidentate ligands are needed to get a strong coordination, while diamines as neutral bidentate ligand form coordination polymers [Ti 2 (OR) 8 (diamine) 2 ]∞ when reacted with Ti(OR) 4 . The Lewis acidity of metal alkoxides may cause organic side reactions. The first is the formation of ester and water in the reaction with carboxylic acids, and therefore carboxylate-substituted metal oxide clusters of the general composition M n O x (OH/OR) y (OOCR) z are obtained instead of substituted monomeric precursors. The second side reaction discussed is the cleavage of β-diketones by metal alkoxides. Despite this side reaction, 3-acetyl-6-trimethoxy-silyl-hexane-2-one is a useful compound to prepare single-source precursos for silica/metal oxide composites.