Nano Building Blocks via Iodination of [PhSiO1.5]n, Forming [p-I-C6H4SiO1.5]n (n = 8, 10, 12), and a New Route to High-Surface-Area, Thermally Stable, Microporous Materials via Thermal Elimination of I2

摘要

We describe the synthesis and characterization of the homologous p-iodophenylsilsesquioxanes (SQs) [p-I-C₆H₄SiO_1.5]_n (n = 8, 10, 12) via ICl-promoted iodination (−40 to −60 °C) with overall yields of 80−90% and >95% para selectivity following recrystallization. Characterization by NMR, FTIR, TGA, and single-crystal X-ray diffraction are reported and compared to data previously published for I₈OPS. Coincidentally, we report a new synthesis of the elusive pentagonal decaphenyl SQ (dPS) [C₆H₄SiO_1.5]₁₀ and its characterization by NMR and single-crystal X-ray studies. These unique macromolecules possess equivalent chemical functionality but varying symmetries (cubic, pentagonal, and D_2d dodecahedral), offering the potential to develop homologous series of functionalized star and dendrimer compounds with quite different core geometries and thereby providing the potential to greatly vary structure−property relationships in derivative compounds and nanocomposites made therefrom. We find that all three compounds decompose on heating to 400 °C/N₂ with loss of I₂ to form robust, microporous materials with BET surface areas of 500−700 m2/g, pore volumes of 0.25−0.31 cm3/g, average pore widths of 8 Å, and oxidative stabilities ≥500 °C and with solid-phase morphologies varying from crystalline to mostly amorphous, as indicated by powder XRD and SEM studies. These latter findings point to important symmetry effects relating directly to packing in the crystalline phase prior to thermolysis.