Novel pentagonal silicon rings and nanowheels stabilized by flat pentacoordinate carbon(s)

Abstract

It is predicted by accurate density functional and coupled-cluster theory that planar Si5C2- and Si5C1- rings can be stabilized by flat pentacoordinate carbon-silicon bonds. The energy difference of the Si5C2- dianion from the lowest energy three-dimensional isomer is about 12.2 kcalmol at the level of the density functional theory using the Becke 3-parameter (exchange), Lee, Yang and Parr functional, and the triple- doubly polarized basis sets. Stable composite Si5C2 structures are formed either as nanowheels with axial C-C bonds of 1.51 Å or as isoenergetic pentagonal graphiticlike layers with double C-C distance (3.02 Å) and almost double aromaticity index, based on nucleus independent chemical shifts. Both of these structures are at least 12 kcalmol lower in energy than the lowest energy Si 10C2 structure reported in the literature, but about 5 kcalmol higher than the lowest energy structure found here. © 2011 American Institute of Physics.