A well-defined silica-based material with a homogeneous nanolayer presenting identical pairs of vicinal silanols has been prepared by reaction of the surface organometallic species[ SiOZr(CH2CMe3)(3)], obtained on a silica dehydroxylated at 900 degrees C, with the double-decker-shaped silsesquioxane (OH)(2)DD(OH)(2). The surface structure has been established using extensive NMR characterization (H-1, C-13, Si-29, HETCOR, double-quantum, triple-quantum). Treatment with Zr(CH2CMe3)(4) leads to the first well-defined single-site bipodal grafted bis-neopentyl zirconium complex.