Size-Selective Surface Organometallic Chemistry on Cagelike Mesoporous Silica (original) (raw)

Chemistry of Materials, 2007

Abstract

ABSTRACT Periodic mesoporous silicas SBA-1, SBA-2, and SBA-16 feature a unique cagelike pore topol. consisting of large supercages interconnected by smaller windows. Compared to channel-like mesoporous silica MCM-48, these cagelike silicas display a distinct reactivity toward magnesium silylamides {Mg[N(SiHMe2)2]2}2 and {Mg[N(SiMe3)2]2}2. All surface silanol groups ==Si-OH of MCM-48 can be derivatized with the magnesium grafting precursors, forming stable silicon-oxygen-magnesium linkages. The completeness of the reaction is evidenced by a dramatic loss of specific pore vol. (0.92 -> 0.27 and 0.30 cm3 g-1), disappearance of the OH stretching vibration in the IR spectrum and the magnesium content (3.5 and 4.0 wt %) of the hybrid materials Mg[N(SiHMe2)2]x@MCM-48 and Mg[N(SiMe3)2]x@MCM-48. In contrast, the amt. of magnesium that can be grafted onto the surface of cagelike silica SBA-1 does not exceed 0.3 wt %. The specific pore vol. of SBA-1 hybrid materials is only slightly decreased compared to the MCM-48 materials and the majority of the SiOH groups is still visible in the IR spectrum. We assume that the surface reaction is limited to the external surface of the SBA-1 silica particles. The remaining silanol functional groups located at the internal surface of SBA-1 are prone to further derivatization with small silylating reagents or small metalorg. compds. such as HN(SiHMe2)2 or Ti(NMe2)4 yielding org./metalorg. or heterobimetallic hybrid materials, resp. [on SciFinder (R)]

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