The polyoctahedral silsesquioxane (POSS) 1,3,5,7,9,11,13,15-octaphenylpentacyclo[9.5.1.1(3,9).1(5,15).1(7,13)]octasiloxane (octaphenyl-POSS).

Solvent-free single crystals of 1,3,5,7,9,11,13,15-octaphenylpentacyclo[9.5.1.1(3,9).1(5,15).1(7,13)]octasiloxane (abbreviated as octaphenyl-POSS), C48H40O12Si8, were obtained by dehydration/condensation of the tetrol Si4O4(Ph)4(OH)4. The powder pattern generated from the single-crystal data matches well with the experimentally measured powder pattern of commercial octaphenyl-POSS. The geometry of the centrosymmetric molecule in the crystal was compared with that in the gas phase, and had shorter Si-O bond lengths and a broader range of Si-O-Si bond angles. The average Si-O bond length [1.621 (3) Å], and Si-O-Si and O-Si-O bond angles [149 (5) and 109 (1)°, respectively] were within the same range measured previously for octaphenyl-POSS solvates.