Planar Hexacoordinate Carbon: A Viable Possibility

The viability of molecules with planar hexacoordinate carbon atoms is demonstrated by density-functional theory (DFT) calculations for CB ₆ ^2– , a CB ₆ H ₂ isomer, and three C ₃ B ₄ minima. All of these species have six π electrons and are aromatic. Although other C ₃ B ₄ isomers are lower in energy, the activation barriers for the rearrangements of the three planar carbon C ₃ B ₄ minima into more stable isomers are appreciable, and experimental observation should be possible. High-level ab initio calculations confirm the DFT results. The planar hexacoordination in these species does not violate the octet rule because six partial bonds to the central carbons are involved.