NMR and IR Spectroscopic Examination of the Hydrolytic Stability of Organic Ligands in Metal Alkoxide Complexes and of Oxygen Bridged Heterometal Bonds

Abstract

IR and 13C NMR investigations of the hydrolytic stabilities of the saturated and unsaturated s-keto ligands acetylacetone (ACAC), ethylacetoacetate (EAA), allylacetoacetate (AAA), methacryloxyethyl-acetoacetate (MEAA) of the Al-, Ti- and Zr-butoxide complexes show a strong dependence on the type of the metal alkoxide and the structure of the organic ligands. The hydrolytic stabilities of the ligands decrease in the order Al->Zr->Ti-alkoxide and ACAC>AAA>EAA≥MEAA. Sol-gel reactions of complexes having a weak ligand stability leads to a larger water consumption and to larger particle sizes in sols than those with stable ACAC ligands. Heterometal bonds, i.e. Si-O-Al, Si-O-Ti and Si-O-Zr, in the system diphenylsiloxanediol/ metal alkoxide (complex) proved by 29Si and 17O NMR are hydrolysed to a different extent depending on the water amount, the type of the Si-O-M bond and the structure of the heterometal species. The degradation of the heterometal bonds leads to a separation of MO-M and Si-O-Si bonds which can entail a decreased homogeneity of the materials at a molecular level.