Carboranyl units bringing unusual thermal and structural properties to hybrid materials prepared by sol-gel process

Abstract

Strategies for the preparation of carboranyl-containing hybrid materials by hydrolytic sol-gel process were investigated with carboranyl-containing poly-trialkoxysilyl precursors: 1,2-[(CH2)3Si(OEt) 3]2-1,2-C2B10H10 (P1) and 1-R-2-Si[(CH2)2Si(OEt)3]3,-1,2- C2B10H10 (R = Me, P2 or Ph, P3). When P1 is used, the integrity of the precursor is preserved whatever is the catalyst (F-, H+), while for P2 and P3, cleavage of the Ccluster-Si bond is observed with F- and OH- as catalysts. Such Si-Ccluster bond cleavage leads t porous hybrid materials templated by the carborane, which is further eliminated from the material and totally recovered. In contrast, nonporous materials are obtained when carborane is preserved in the materials. Part of this hybrid material exhibits a lamellar structure in relation to the presence of the carborane units. In dry air, high thermal stability is observed for such materials and results in a very limited oxidation of the material at 1200 °C (weight gain of <5%). In an inert atmosphere, high thermal stability combined with several chemical transformations leads to a limited weight loss, graphitization, and oxide and under-oxide mixtures. Materials were characterized by IR, solid-state NMR ( 29Si, 13C), porosimetry, X-ray diffraction, SEM, TEM, TGA, and XPS. © 2006 American Chemical Society.