MOLECULAR-STRUCTURE AND MOLECULAR VIBRATIONS OF 3,5,7,-TETRAMETHYL-2,4,6,8,9,10-HEXATHIAADAMANTANE

The molecular structure and vibrations of 3,5,7,-tetramethyl-2,4,6,8,9 ,10-hexathiaadamantane have been determined by a joint computational, gas-phase electron diffraction, and spectroscopic investigation. The g eometry and harmonic force field of the molecule was calculated at the Becke3-Lee-Yang-Parr/6-31G level. Vibrational analysis was performed using FT-IR and FT-Raman spectra recorded in the 4000-150 cm(-1) rang e and utilizing Pulay's DFT-based scaled quantum mechanical (SQM) meth od (DFT: density-functional theory). This SQM method was extended to m olecules containing C-S structural motifs. The joint computational and electron diffraction analysis resulted in an equilibrium geometry of T-d symmetry characterized by staggered orientation of the methyl grou ps with respect to their adjacent C-S bonds, The electron diffraction study yielded the following bond lengths (r(g)) and bond angles (with estimated total errors): C-S, 1.820 +/- 0.004 Angstrom; C-C, 1.536 +/- 0.004 Angstrom; C-H, 1.119 +/- 0.005 Angstrom; C-S-C, 102.2 +/- 0.2 d egrees; H-C-H, 109.9 +/- 0.7 degrees. The barrier to methyl rotation w as computed to be 17 kJ/mol in good agreement with that estimated from the average methyl torsion (with respect to the staggered form) of 10 +/- 3 degrees from the electron diffraction analysis.