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Silsesquioxane
A silsesquioxane is an organosilicon compound with the chemical formula ()n (R = H, alkyl, aryl or alkoxyl). Silsesquioxanes are colorless solids that adopt cage-like or polymeric structures with Si-O-Si linkages and tetrahedral Si vertices. Silsesquioxanes are members of polyoctahedral silsesquioxanes ("POSS"), which have attracted attention as precursors to ceramic materials and nanocomposites. Diverse substituents (R) can be attached to the Si centers. The molecules are unusual because they feature an inorganic silicate core and an organic exterior. The silica core confers rigidity and thermal stability.
==Structure==
Silsesquioxanes are known in molecular form with 6, 8, 10, and 12 Si vertices, as well as polymers. The cages are sometimes labeled T6 T8, T10, and T12, respectiively (T = tetrahedral vertex). The T8 cages, the most widely studied members, have the formula ()8, or equivalently R8Si8O12.
In all cases each Si center is bonded to three oxo groups, which in turn connect to other Si centers. The fourth group on Si is usually an alkyl, halide, hydride, alkoxide, etc.
In the cubic clusters the Si-O-Si angles are about 145°, being bowed out, allowing the Si centers to better adopt tetrahedral geometry.〔Larsson, Kare "Crystal structure of octa(methylsilsesquioxane), (CH3SiO1.5)8" Arkiv foer Kemi 1960, vol. 16, pp. 203-8.〕〔Larsson, Kare "Crystal structure of (HSiO1.5)8 " Arkiv foer Kemi 1960, volume 16, pp. 215-19.〕〔 P. R. Chinnam, M. R. Gau, J. Schwab, M. J. Zdilla and S. L. Wunder "The polyoctahedral silsesquioxane (POSS) 1,3,5,7,9,11,13,15-octa-phenyl-penta-cyclo-()octa-siloxane (octa-phenyl-POSS)" Acta Cryst. 2014. vol. C70, pp. 971-974. 〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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