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Structures and Molecular Properties of Sterically Overcrowded Molecules, 37. - Hexakis(trimethylsilylmethyl)benzene C66
Bock, Hans,Meuret, Jochen,Ruppert, Klaus
, p. 2237 - 2242 (2007/10/02)
Both the low first vertical ionization energy of only 7.40 eV, determined by PE spectroscopy for C66, and the blocked substituent rotation in its radical cation as proven by ESR/ENDOR spectroscopy suggest considerable steric overcrowdedness.To further substantiate this interpretation of the molecular properties, the crystal structure (hexagonal R, Z = 2) has been determined at 100 K.Accordingly, the bulky trimethylsilyl groups are arranged alternatingly above or below the C6-ring plane, out of which the methylene C centers are twisted by +/- 9 deg.Due to the angles CCSi widened to 115 deg, however, the intramolecular distances C(H)...(H)C between non-neighboured methyl groups of 443 and 452 pm even slightly exceed their van der Waals radii sum of 400 pm and thus avoid severe spatial congestion. - Key Words: Sterically overcrowded organosilicon molecules/ Radical cation dynamics/ Silicon compounds
