Electron Diffraction Investigation of Dimethyl Diselenide

The molecular structure of dimethyl diselenide has been determined by an electron diffraction investigation of the vapor. A computerized background correction routine, satisfying the positivity and area criteria, was employed to reduce the data and obtain a final molecular intensity curve. The values for a set of nine distances and amplitudes were obtained from a least-squares fit to the final molecular intensity curve. The bonded distances are rg(C–H) = 1.131 ± 0.008 Å, rg(C–Se) = 1.954 ± 0.005 Å, and rg(Se–Se) = 2.326 ± 0.004 Å. The corresponding amplitudes are l(C–H) = 0.079 ± 0.007 Å, l(C–Se) = 0.054 ± 0.003 Å, and l(Se–Se) = 0.056 ± 0.002 Å. The ∠CSeSe = 98.9 ± 0.02° and the ∠HCSe = 108.4 ± 0.8°. The errors are estimated to be at the 99% confidence level. The methyl groups are unsymmetrically placed with respect to the CSeSe planes. They are rotated about the C–Se bonds such that one of the HCSe planes in each CH3Se moiety makes an angle of 36.1 ± 6° with the respective CSeSe plane. Dimethyl diselenide assumes a stable skew conformation with a dihedral angle of 87.5 ± 4°. The molecule contains a twofold axis of symmetry passing midway between the two selenium atoms in the plane bisecting the dihedral angle.