Si−E (E = N, O, F) Bonding in a Hexacoordinated Silicon Complex: New Facts from Experimental and Theoretical Charge Density Studies

The concept of hypervalency in molecules, which hold more than eight valence electrons at the
central atom, still is a topic of constant debate. There is general interest in silicon compounds with more
than four substituents at the central silicon atom. The dispute, whether this silicon is hypervalent or highly
coordinated, is enlightened by the first experimental charge density determination and subsequent topological
analysis of three different highly polar Si−E (E = N, O, F) bonds in a hexacoordinated compound. The
experiment reveals predominantly ionic bonding and much less covalent contribution than commonly
anticipated. For comparison gas-phase ab initio calculations were performed on this compound. The results
of the theoretical calculations underline the findings of the experiment.