Planar tetra-, penta-, hexa-, hepta-, and octacoordinate silicons: a universal structural pattern.

A universal structural pattern has been presented at density function theory level to incorporate planar tetra-, penta-, hexa-, hepta-, and octacoordinate silicons in C2v B(n)E2Si series (E = CH, BH, or Si; n = 2-5) and D8h B8Si. The equivalence in valence electron counts and one-to-one correspondence of the delocalized pi and sigma valence orbitals with small boron clusters strongly support the optimized structures containing planar coordinate silicons. Planar B(n)E2Si series are predicted to be aromatic in nature, and the vertical detachment energies of their anions are presented to facilitate future photoelectron experiments. This structural pattern can be applied to form other planar coordinate nonmetals including Ge, P, As, Al, and Ga and needs to be confirmed in experiments to open a new branch of chemistry on planar coordinate main group elements.