Bernard T. Wilkins

Bonding studies of compounds of boron and the group IV elements : X. Photoelectron spectra of compounds Me4M (MC, Si, Ge, Sn, or Pb) and the lack of participation of M d-orbitals

The question of d-orbital participation by the central metal M in molecules containing second and higher row elements is critically examined in relation to the photoelectron spectra of the Group IV compounds Me4M. It is shown that the splitting between the two strictly symmetry-determined CH levels 1t1 and 1e drops monotonically from 1.35 eV in neopentane to approximately zeor in tetramethyl-plumbane, as is consistent with the decreasing through-space interactions in the (CH3)4 tetrahedron. Within the limits of the spectroscopic resolution, d-orbital participation is therefore discounted, as this would tend to increase the separation between these two levels on going down the series.

Bonding studies of compounds of boron and the group IV elements: XI. Photoelectron spectra of strained cyclic organosilicon compounds

The He(I) photoelectron (PE) spectra of a series of silacyclobutanes XX′-SiCH2CH2CHR and of a 1,3-disilacyclobutane Me2SiCH2SiMe2CH2 are reported and analysed. The ionisation potentials (IPs) of the uppermost ring molecular orbitals (MOs) (a1 and b1 within the C2v point group) are definitively assigned on the basis of symmetry arguments, comparisons with simpler systems such as SiX4 and (CH2)n, and extended Huckel theory (EHT) calculations, and comments are made on the origin of some of the other bands. The effects on these MOs of changes in the substituents X, X′, and R are discussed; they correlate well with the assignments and calculations. The effects of transannular interactions are assessed by comparisons with the spectrum of 1,1-dimethylsilacyclopentane.

Energy level trends in 1,3,5,7-tetrasilaadamantanes (“carborundanes”) and related molecules from photoelectron spectroscopy

Abstract The photoelectron spectra of 1,3,5,7-tetrasilaadamantane and its tetrafluoro, -chloro and -methyl derivatives are presented and most of the bands out to 16 eV assigned by correlating them with those of other T d molecules having known orbital sequences. Bands due to ionization from ring SiC, exocyclic SiC and SH levels are well separated in the T d molecules, but overlap strongly in the carbosilane Si 7 C 16 H 36 of C 2 v symmetry whose PE spectrum is also reported. Despite the diffuseness of the spectra, fairly unambiguous estimates for transannular SiCSiC and through-space CHCH interaction parameters could be obtained. The energy level trends across the series appear to be dominated by the inductive effect of the substituents.