Planar tetracoordinate carbon stabilized by heavier congener cages: The Si9C and Ge9C clusters

Using quantum chemical computations and analysis of electron distribution (MO, DOS, ELF) we showed that in some carbon-doped silicon and germanium clusters, it is possible to achieve a planar tetracoordinate carbon with enhanced stability. While the driving force for C-planarization in the square dications CX 4 2 + (with X = Si, Ge) is electron delocalization on X4 frame together with single bonds along C–X bonds, the larger neutral CSi9 and CGe9 clusters enjoy combined stabilization from both electronic effect and geometrical constraint of the X9 cages. In CX9, an additional electrostatic interaction reinforces stabilization within the CX4 moiety in maintaining the ptC configuration.