Showing papers by "Bruce O. West published in 2000"

The Influence of β-Diketones on the Hydrolysis and Growth of Particles from Zirconium(IV) n-Propoxide

Abstract: The influence of low ligand/Zr mole ratios (ρ = 0–0.1) on the hydrolysis and growth of oligomers from Zr(O n Pr)4 modified with a series of β-diketones (trifluoroacetylacetone, hexafluoroacetylacetone, benzoylacetone, dibenzoylmethane and dipivaloylmethane), and their subsequent aggregation to form uniform, dense spheres, has been investigated by light scattering and turbidometry. The addition of β-diketones results in a large increase in the induction time, t i (reduction in hydrolysis/condensation rates). A remarkable feature of the data is the dramatic reductions in rate observed even when a maximum of one in forty Zr–OR bonds have been replaced by the β-diketone and are no longer available for hydrolysis or further condensation. The largest effect is observed with dibenzoylmethane, which increases t i by a factor of 26 relative to acetylacetone. A mechanism rationalising the origin of the effect is discussed, which involves segregation of the β-diketone ligands on the surface of the growing particle, with subsequent particle growth restricted to those sites not occupied by the chelating ligands.