17O MAS NMR study of the bonding mode of phosphonate coupling molecules in a titanium oxo-alkoxo-phosphonate and in titania-based hybrid materials

O-17-enriched phenylphosphonic acid (PhP*O3H2) was prepared from phosphonic acid dichloride and enriched water. This enriched phosphonic acid was used to prepare the titanium oxo-alkoxo-phosphonate Ti-4(mu(3)-*O)(mu(2)-OPri)(3)(OPri)(5)(PhP*O-3)(3) (1) as a model compound, and titanium oxide/phenylphosphonate hybrids either by sol-gel processing with Ti(OPri)(4) or by surface modification of a titania support. For comparison a gel sample was prepared using nonenriched PhPO3H2 and enriched water. The O-17 MAS NMR spectra of these 5 solids have been recorded at various magnetic fields (7, 9.4, and 17.6 T) and the isotropic chemical shifts and quadrupolar constants have been determined for the different oxygen sites: P=O, P-O-H, P-O-Ti, and OTix. These spectra give direct evidence for the presence of extensive Ti-O-P bonding in the hybrid materials.