A topological study of homonuclear multiple bonds between the elements of group 14

Abstract

A study of the Electron Localization Function (ELF) for [REER] and [R₂EER₂] (E = Si, Ge, Sn; R = H, CH₃) has been undertaken. It has long been appreciated that the bonding in the heavier group 14 analogues of alkynes and alkenes has a different nature from that in simple carbon-containing molecules. Unlike their carbon analogues they have non-linear and non-planar structures respectively and the EE bonds cannot be described as normal double and triple bonds. There has been much discussion and disagreement concerning the nature of these bonds. We have made an ELF and an AIM study of these molecules to attempt to shed further light on this problem. For all systems the nature of the ligand (H or Me) does not significantly change the bonding picture. Our results reinforce previous experimental and theoretical studies in reproducing the non-linear and non-planar geometries. They show that the ELF results do not lead to quantitative values for the bond orders but indicate that the bond orders are less than three for the REER molecules and less than two for the R₂EER₂ molecules. These conclusions are made more quantitative by the AIM results. We attribute this decrease in bond order to the decreasing ability of these larger and less electronegative elements to attract electrons into the bonding region so that an increasing fraction of the electron density remains as essentially non-bonding or lone pair density.