17 O MAS NMR Study of the Bonding Mode of Phosphonate Coupling Molecules in a Titanium Oxo-Alkoxo-Phosphonate and in Titania-Based Hybrid Materials

17 O-enriched phenylphosphonic acid (PhP*O 3 H 2 ) was prepared from phosphonic acid dichloride and enriched water. This enriched phosphonic acid was used to prepare the titanium oxo-alkoxo-phosphonate Ti 4 (μ 3 -*O)(μ 2 -OPr i ) 3 (OPr i ) 5 (PhP*O 3 ) 3 ( 1 ) as a model compound, and titanium oxide/phenylphosphonate hybrids either by sol−gel processing with Ti(OPr i ) 4 or by surface modification of a titania support. For comparison a gel sample was prepared using nonenriched PhPO 3 H 2 and enriched water. The 17 O 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 OTi x . These spectra give direct evidence for the presence of extensive Ti−O−P bonding in the hybrid materials.