Bildung siliciumorganischer Verbindungen. LIX. Die Kristall- und MolekülStruktur des Dodecamethyl-heptasila-[4,4,4]-propellans Si7C19H48

Formation of Organosilicon Compounds. LIX. Crystal and Molecular Structure of Dodecamethyl-heptasila-[4,4,4]-propellan Si₇C₁₉H₄₈ 1,1,3,3,7,7,9,9,11,11,13,13-Dodecamethyl-1,3,5,7,9,11,13-heptasila-[4,4,4]-propellan Si₇C₁₉H₄₈ crystallizes in the monoclinic space group P2₁/c with a = 11.499, b = 11.411, c = 22.171 Å, β = 96.95° and Z = 4 formula units. The three independent six-membered rings of the molecule have the same skew-boat-conformation. Along the central Si? C? bond the mean value of the torsion angle within the six-membered rings is 19°. The mean value for the bond length is Si-C = 1.893 Å, but the bond length diminishes within the polycyclic system from the axial C-atom to the outer members of the rings (1.916; 1.880; 1.864 Å). The interatomic distances between CH₃- groups and from CH₃- groups to CH₂- groups shows the twisted conformation to be a result of the contacts between these groups.