Infrared and ab initio studies of molecules containing SiH bonds: Part I. A correlation between vis(SiH) and re (SiH)

Abstract

Isolated SiH stretching frequencies v is(SiH) are reported for the species SiHDX 2 (X = F or Cl), SiHD 2NMe 2, SiHD 2OMe, (SiHD 2NMe and (SiHD 2) 2S. IR spectra in the gas and solid phases are also shown for CHD 2OSiH 3. Splittings of v as(CH 3) in (CH 3) 2)SiH 2 and (CH 3) 3 SiH are reported, from which v is(CH) values are deduced. Evidence for the structures of these molecules is discussed. Ab initio structures have been determined using a 4–21G/3-3-21G basis set for the above molecules, and for SiH 4, SiH 3F, SiHF 3, SiH 3Cl, SiHCl 3, SiH 3Me, SiH 2Me 2, SiHMe 3, SiH 3CN, SiH 3CCH, SiH 3SiH 3, SiH 3CH 2CH 3, SiH 3CH 3Cl, SiH 3CHCH 2 and CH 3CH 2CH 3. The r e(SiH) and r e(CH) values are tabulated. A good correlation is found between v is(SiH) and r e(SiH) r e(SiH)(Å) = 1.9089 − 1.998 × 10 −4 v is (SiH) (cm −1) Plots for SiH 2Cl 2, and SiHCl 3 reveal large anomalies, but SiH 3CN and SiH 3CCH behave normally. Results are compared with similar ones for CH bonds. The CH bond length asymmetry in Me 2SiH 2 and Me 3SiH revealed by the v as(CH 3) splittings is confirmed by the ab initio calculations. The effect of conformation on the β effect of methyl on SiH and CH bonds is explored.