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The gas-phase molecular structure of cyclopropyltrifluorosilane as studied by electron diffraction and ab initio calculations

1994; Elsevier BV; Volume: 320; Linguagem: Inglês

10.1016/0022-2860(93)07856-r

1872-8014

Marwan Dakkouri, Volker Typke,

Inorganic Fluorides and Related Compounds

The gas-phase molecular structure of cyclopropyltrifluorosilane was investigated by electron diffraction and ab initio calculations. The major bond distances (ra) and the valence angles (rα) with uncertainties (3σ) obtained from diffraction data are as follows: C1C2 = 1.522(8) Å, CSi = 1.807(2) Å, SiF = 1.572(3) Å, CH = 1.104(3) Å, SiC(ring plane) = 124.5(9)°, SiCH = 116(4)°, CSiF6  112.3(10)°, CSiF7 = 111.6(10)°. The difference ΔCC = (C1C2)  (C2C3) = 0.032 Å obtained from ab initio calculations was treated as a constant parameter in the analysis of the diffraction data. The present study has shown that the fluorination of the silyl group leads to a significant shortening of the SiC bond by about 0.03 Å in comparison to cyclopropylsilane. The analysis of the diffraction data was performed with the rα-representation of the molecular structure applying a dynamical model, which treats the torsional vibration of the SiF3 group as large amplitude motion. The required vibrational mean square amplitudes and corrections ra — rα as well as their torsional dependence have been calculated from a normal coordinate analysis on the basis of the ab initio force field (6–31G*).