The selective surface modification by phosphonic acids of SiO 2 -TiO 2 supports at the micrometer and molecular scale was investigated. Under aqueous conditions, phosphonic acids bind to TiO 2 and not to SiO 2 surfaces. A micropatterned support was prepared by electron beam microlithography and selectivity, of the surface modification was evidenced using scanning Auger electron spectroscopy (SAES). The second support was a mesoporous SiO 2 -TiO 2 mixed oxide (10 mol % Ti) epoxidation catalyst prepared by sol-gel processing. Selectivity was deduced from the decrease of the catalytic activity upon modification and from chemical analysis; bonding modes to the surface were investigated using solid-state 29 Si and 31 P MAS NMR. The possibility to introduce different organic groups by successive treatments with a phosphonic acid and a silylating agent was illustrated in the case of the mixed oxide.

1H, 13C, 17O and 31P NMR parameters, including chemical shift tensors and quadrupolar parameters for 17O, were calculated for phenylphosphonic acid, C6H5PO(OH)2, under periodic boundary conditions. The results are in very good agreement with experimental data and permit the unambiguous assignment of all the sites present in the structure. In particular, the 17O NMR parameters of the P=O and P-OH environments were precisely determined, which should help in the characterization of the bonding mode of phosphonate molecules in hybrid solids. Moreover, the effect of intermolecular interactions on the NMR parameters were investigated by comparing the results of the calculations in the crystal and in an isolated molecule of phenylphosphonic acid.

17O-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 Ti4(μ3-*O)(μ2-OPri)3(OPri)5(PhP*O3)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 17O 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.