Journal of Sol-Gel Science and Technology 8, 603-607 (1997) 9 1997 Kluwer Academic Publishers. Manufactured in The Netherlands. Chemistry of Hybrid Organic-Inorganic. Access to Silica Materials through Chemical Selectivity PIERRE M. CHEVALIER AND ROBERT J.E CORRIU Prdcurseurs Organomgtalliques de Mat~riaux, CNRS- UMR 44, Ddpartement de Chimie Organique Fine, Universit~ MontpeUier II, Sciences et Techniques du Languedoc, 34095 Montpellier, Cedex 05, France JOEL J.E. MOREAU AND MICHEL WONG CHI MAN Laboratoire de Chimie Organomdtallique, ENS Chimie Montpellier, 8 Rue de l'Ecole Normale, 34053 Montpellier, Cedex 01, France Abstract. Hybrid organic-inorganic materials containing labile organic fragments with various structural features have been prepared. The mild cleavage of SiC bonds allowed removal of the organic moities. It led to silica which pore structure varied according to the nature of the organic component eliminated. Keywords: sol-gel, silsesquioxanes, hybrid organic-inorganic materials, silicas, pore structure, Si--C bond cleavage, alkynyl silanes 1. Introduction Crystalline micro or mesoporous alumino-silicates are currently obtained in a controlled way by using tem- plate organic molecules [ 1]. The introduction of molec- ular or macromolecular templates to generate porosity in amorphous inorganic materials, also constitute an attractive approach [2]. In this respect, organic-inorganic hybrids are of in- terest for the preparation of materials with controlled porosity. The control of the pores size of silica via the temporary introduction of organic polymers in a silicate matrix was successfully obtained upon pyrolysis of a silica gel hybrid containing a starburst dendrimer [3]. The removal of the organic component in silsesquiox- ane hybrid network was also achieved by oxidative re- actions [4, 5]. The plasma oxidation of the hydrocarbon template in silsesquioxanes led to silica gels showing a coarsening of the existing porosity [5]. Compared to the hybrid precursor, the post-plasma material had a higher pore diameter and a lower surface area. In order to avoid the use of sacrificial organic com- ponent for porosity control, we studied the preparation of hybrid silsesquioxane network containing fragile silicon-carbon bonds. We previously showed [6] that hybrid silica gels can be obtained from alkoxysilanes containing mono- or diyne units (Eq. (1)). (MeO)3Si ( - - ) x Si(OMe)3 H2o [O1.5Si SiOl.5]~ H20/MeOH/60~ (SiO2)~ THF 2 mol.% NH2F (1) The sol-gel condensation of the alcoxysilanes led to a molecularly defined hybrid network. Then, the mild hydrolytic cleavage of the Si--C bond, in the presence of a fluoride catalyst, led to the elimination of acety- lene, leaving silica behind [6]. The produced porous silica had a higher N2 BET surface area than that of the originating hybrid gel. We wish to report here a "controlled" synthe- sis of silica, under mild reaction conditions, based on the temporary introduction of different acetylenic molecules as part of the hybrid network of silsesquiox- anes gels.