DETERMINATION OF THE MOLECULAR-STRUCTURE OF TRIS(TRIMETHYLSILYL)PHOSPHINE IN THE GAS-PHASE BY ELECTRON-DIFFRACTION, SUPPORTED BY MOLECULAR MECHANICS CALCULATIONS

The molecular structure of tris(trimethylsilyl)phosphine in the gas phase has been determined by electron diffraction. Results of three refinements are reported. In the first refinement, overall C3 symmetry and local C3 symmetry for the SiMe3 groups were assumed, but these groups were allowed to tilt away from one another so that their C3 local axes no longer coincided with the PSi bonds. The major geometrical parameters were ra(PSi) 225.9 (1), r(SiC) 188.2(1) pm, ∠ SiPSi 105.1(2) and ∠ CSiC 107.9(1)°. The tilt angle was 5.9(3)°, and the SiMe3 groups were twisted 17.2(2)° away from the staggered position, at which the overall molecular symmetry was C3v; the PSiC angles were therefore 106.8, 109.3 and 116.7°. In the other two refinements the restriction of C3 symmetry within the SiMe3 groups was removed, and the differences between SiC distances and between CSiC angles were first fixed at values calculated by molecular mechanics (MM2), and then these new restrictions were partially relaxed. Neither of these refinements fitted the experimental data quite as well as the first one. © 1990.