STRUCTURES AND MOLECULAR-PROPERTIES OF ST ERICALLY OVERCROWDED MOLECULES .37. HEXAKIS(TRIMETHYLSILYLMETHYL)BENZENE C6[CH2SI(CH3)3]6

Both the low first vertical ionization energy of only 740 eV, determin ed by PE spectroscopy for C6[CH2Si(CH3)3]6, and the blocked substituen t rotation in its radical cation as proven by ESR/ENDOR spectroscopy s uggest considerable steric over-crowdedness. To further substantiate t his interpretation of the molecular properties, the crystal structure (hexagonal R3BAR, 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 care twisted b y +/-9-degrees. Due to the angles CCSi widened to 115-degrees, however , the intramolecular distances C(H)...(H)C between non-neighboured met hyl groups of 443 and 452 pm even slightly exceed their van der Waals radii sum of 400 pm and thus avoid severe spatial congestion.