Ternary 14-electron XB2Be2 (X = Si, Ge, Sn, Pb) clusters: a planar tetracoordinate silicon (ptSi) system and its ptGe/Sn/Pb congeners

A class of ternary 14-electron clusters, XB2Be2 (X = Si, Ge, Sn, Pb), have been computationally predicted with a planar tetracoordinate silicon (ptSi) unit, as well as its heavier ptGe/Sn/Pb congeners. These pentaatomic ptSi/Ge/Sn/Pb species are established as global-minimum structures via computer global searches, followed by electronic structure calculations at the PBE0-D3, B3LYP-D3, and single-point CCSD(T) levels. Molecular dynamics simulations indicate that they are also kinetically stable against isomerization or decomposition. Chemical bonding analyses show that the clusters have double 2 pi/2 sigma aromaticity. The latter concept underlies the stability of ptSi/Ge/Sn/Pb clusters, overriding the 14-electron count or its variants, such as the 18-electron rule. No sp(3) hybridization occurs in these species, which naturally explains why they are ptSi/Ge/Sn/Pb (rather than traditional tetrahedral) systems.

Automated summary

A class of ternary 14-electron clusters, XB2Be2 (X = Si, Ge, Sn, Pb), have been computationally predicted to have stable planar tetracoordinate silicon and its heavier congeners. These clusters maintain stability through a unique aromaticity rather than the traditional 14-electron count rule.