The organometallic complex dropSi-O-Zr(CH2C(CH3)(3))(3) was synthesized on the surface of silica dehydroxylated at 500degreesC and its reactivity towards oxygenated molecules was studied. The materials were characterized by IR, C-13 CP-MAS NMR, analysis of evolved gases and elemental analysis. Reaction with neopentyl alcohol ((CH3)(3)CCH2OH) leads to the quantitative formation of dropSi-O-Zr(OCH2C(CH3)(3))(3). Similarly, reaction with pivalic acid ((CH3)(3)CCOOH) leads to the quantitative formation of dropSi-O-Zr(OCOC(CH3)(3))(3). Addition of dry oxygen at 25degreesC to dropSi-O-Zr(CH2C(CH3)(3))(3) leads to the formation of dropSi-O-Zr(OCH2C(CH3)(3))(3). When heated at 200degreesC under oxygen, the alkoxy ligands transform into carboxylate species ((CH3)(3)CCOO)(-) probably coordinated to zirconium. These results, together with molecular modelling studies of the adsorption of hydrocarbons on mordenite modified by such complexes, explain the different behaviours observed in presence of air or inert gases. (C) 2003 Elsevier Science B.V. All rights reserved.