Modification of Different Zirconium Propoxide Precursors by Diethanolamine. Is There a Shelf Stability Issue for Sol-Gel Applications?

Modification of different zirconium propoxide precursors with H(2)dea was investigated by characterization of the isolated modified species. Upon modification of zirconium n-propoxide and [Zr((OPr)-Pr-n)((OPr)-Pr-i)(3)((PrOH)-Pr-i)](2) with a mol equivalent of H(2)dea the complexes [Zr-2((OPr)-Pr-n)(6)(OCH2CH2)(2)NH](2) (1) and [Zr-2((OPr)-Pr-n)(2)((OPr)-Pr-i)(4)(OCH2CH2)(2)NH](2) (2) were obtained. However, H-1-NMR studies of these tetranuclear compounds showed that these are not time-stable either in solution or solid form. The effect of this time instability on material properties is demonstrated by light scattering and TEM experiments. Modification of zirconium isopropoxide with either or 1 equivalent mol of H(2)dea results in formation of the trinuclear complex, Zr{eta(3)mu(2)-NH(C2H4O)(2)}(3)[Zr((OPr)-Pr-i)(3)](2)(iPrOH)(2) (3) countering a unique nona-coordinated central zirconium atom. This complex 3 is one of the first modified zirconium propoxide precursors shown to be stable in solution for long periods of time. The particle size and morphology of the products of sol-gel synthesis are strongly dependent on the time factor and eventual heat treatment of the precursor solution. Reproducible sol-gel synthesis requires the use of solution stable precursors.