Global Planar Tetra-, Penta- and Hexa-coordinate Silicon Clusters Constructed by Decorating SiO₃ with Alkali Metals

The achievement of the rule-breaking planar hypercoordinate motifs (carbon and other elements) is mainly attributed to a practical electronic stabilization mechanism, where the bonding of the central atom p_z π electrons is a crucial issue. We have demonstrated that strong multiple bonds between the central atom and partial ligands can be an effective approach to explore stable planar hypercoordinate species. A set of planar tetra-, penta- and hexa-coordinate silicon clusters were herein found to be the lowest-energy structure, which can be viewed as decorating SiO₃ by alkali metals in the MSiO₃ ^- , M₂ SiO₃ and M₃ SiO₃ ⁺ (M=Li, Na) clusters. The strong charge transfer from M atoms to SiO₃ effectively results in [M]⁺ SiO₃ ^2- , [M₂ ]²⁺ SiO₃ ^2- and [M₃ ]³⁺ SiO₃ ^2- salt complexes, where the Si-O multiple bonding and structural integrity of the Benz-like SiO₃ framework is maintained better than the corresponding SiO₃ ^2- motifs. The bonding between M atoms and SiO₃ motif is best described as M⁺ forming a few dative interactions by employing its vacant s, p, and high-lying d orbitals. These considerable M←SiO₃ interactions and Si-O multiple bonding give rise to the highly stable planar hypercoordinate silicon clusters.