The study of bonding in silicon compounds by Fenske-Hall molecular orbital calculations and photoelectron spectroscopy

Calculations with and without silicon 3d orbitals were performed for three series of small silanes, SiH(4-x)Yx, SiHCl(3-x)(CH3)x, and for pentacarbonyl manganese silanes, Y3Si(Mn(CO)5 and Cl(3-x)(CH3)xSiMn(CO). The PE spectra was measured for the SiHCl(3-x)(CH3)x and the manganese compounds. For the small silanes, the silicon 3d orbital contributed only to the higher occupied orbitals. Electron density was acquired by the silicon 3d orbitals by rearrangement of electron density from the silicon 3s and 3p orbitals and by transfer of electron density from the atoms bonded to the silicon. Most of the electron density acquired by the Si 3d orbitals, through transfer, resulted from dpi-ppi interactions; however, the amount of dpi-ppi bonding is small, and did not correlate with the electronegativity of the atoms. The silicon 3d orbitals had an indirect effect on the character of the molecular orbitals by changing the energy of the other basis orbitals.