Novel polyhedral structures were prepared with a butterfly‐shape composed of oligosiloxane wings and a double‐decker silsesquioxane (DDSQ) body. The compounds were synthesized in two steps from commercially available alkoxysilanes, and their structures were confirmed using spectroscopic methods and X‐ray crystallography. Not like other phenyl‐substituted cage silsesquioxanes, these butterfly cages show very good solubility in common organic solvents. The crystal structures clearly showed their unique features: a larger space with longer siloxane chains and a very flexible framework. Moreover, these compounds are thermally stable with a Td5 (5 % weight loss temperature) over 320 °C.

Symmetric and asymmetric (Janus‐type) new “lantern cage” siloxanes (PhSiO1.5)4(Me2SiO)4(RSiO1.5)4 (R=Ph or iBu) were synthesized through reaction of all‐cis‐[PhSi(OSiMe2Br)O]4 with all‐cis‐[RSi(OH)O]4 (R=Ph or iBu). These precursors were obtained by facile two or three‐step reactions from commercially available compounds. The spectroscopic properties of the resulting products were fully characterized and they showed high thermal stability and sublimation without decomposition. The crystal structures clearly indicated that the internal vacancy volumes of the lantern cages are considerably larger than that of octaphenylsilsesquioxane (PhSiO1.5)8. DFT calculations of the lantern cage showed a distinctly different electronic state from that of octasilsesquioxane. These results suggest that lantern cage siloxanes have a characteristic “field” in the molecule.

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