Theoretical studies on the pentaatomic planar tetracoordinate carbon molecules CGa3Si and CGa3Si−

The pentaatomic molecules CGa3Si and CGa3Si− were studied with quantum chemical calculations. Six planar geometry isomeric structures have been found, and global minima structures 1 possess planar tetracoordinate carbons. Three different types of neutral-anion energy separations reported in this work are the adiabatic electron affinity (AEA), the vertical electron affinity (VEA), and the vertical detachment energy (VDE). Natural bonding orbital (NBO) analysis indicates strong donating and back-donating carbon-ligand interactions. The nucleus independent chemical shifts (NICS) and electron localization function (EFL) values suggest that structures 1 possess σ and π aromaticity. This analysis suggests that the presence of 18 valence electrons is crucial for the planar geometries to be stable and preferred over tetrahedral structures.