Structural characterization of titanium-oxo-polymers synthesized in the presence of protons or complexing ligands as inhibitors

The structure of sol–gel synthesized titanium oxo-polymers has been investigated using solid and liquid state 17O NMR and small angle X-ray scattering (SAXS). The growth of the titanium oxo-polymers has been controlled to produce sols and gels by adjusting two main parameters: the hydrolysis ratio H=[H2O]/[Ti] and the inhibitor ratio p=[H+]/[Ti] or a=[acacH]/[Ti] (acacH=acetylacetone). The combination of 17O NMR and SAXS techniques has allowed us to determine the structure of the oxo-polymers at a local and a semi local scale. The proposed model for the structure of these oxo-polymers is based on the condensation of sub-units with a mean composition Ti(OZ)x(OH)yO2 − (x + y)/2 (OZ=Acac+OBun) and having a gyration radius of about 20–25 Å. These sub-units are made with a titanium-oxo core built with μ2-O, μ3-O, μ4-O bridges and their surface is capped by the residual ligands OZ. Increasing the hydrolysis ratio H or decreasing the inhibitor ratio (p or a), mainly results in an increase of the size and the fractal dimension of the oxo-polymers, while the size and the mean composition of titanium oxo-core constituting the sub-units are apparently not modified.