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Planar hexacoordinate carbon in chemistry describes a molecular geometry featuring a planar arrangement of carbon with six surrounding atoms. No actual chemical compounds having this particular hexacoordinate configuration have been reported but quantum mechanical methods have demonstrated that these molecules are a possibility. Examples of molecules investigated with computational methods are the B6C dianion, the CN3Be3 ion, the CO3Li3 ion and the CN3Mg3 ion. A simulated Be2C monolayer is reported to consist of quasi-planar hexacoordinate carbon atoms.
On the other hand, experimental research has confirmed that the pentagonal-pyramidal hexamethylbenzene ion, C66, contains a hexacoordinate carbon atom. Furthermore, a heptacoordinate carbon atom has been predicted to be involved in a stable hexagonal-pyramidal configuration of tropylium trication,.