The global minima of thirteen combinations of atoms with formula CE 3 M 3 + (E=S-Te and M=Li-Cs) adopt a planar structure with carbon covalently bonded to three chalcogens and ionically bonded to the three alkali-metals to stabilize the first global minima structures containing planar hexacoordinate carbon atoms. File list (2) download file view on ChemRxiv planar_hexacoordinate_carbon.pdf (854.66 KiB) download file view on ChemRxiv Planar_hexacoordinate_carbon_SI.pdf (5.42 MiB)

Herein, the first global minima containing a planar hexacoordinate carbon (phC) atom are reported. The fifteen structures belong to the CE 3 M 3 + (E = S-Te and M = Li-Cs) series and satisfy both geometric and electronic criteria to be considered as a true phC. The design strategy consisted of replacing oxygen in the D 3h CO 3 Li 3 + structure with heavy and less electronegative chalcogens, inducing a negative charge on the C atom and an attractive electrostatic interaction between C and the alkali-metal cations. The chemical bonding analyses indicate that carbon is covalently bonded to three chalcogens and ionically connected to the three alkali metals.

After exploring the potential energy surfaces of M m CE 2 p (E=SÀ Te, M=LiÀ Cs, m = 2, 3 and p = m-2) and M n CE 3 q (E=SÀ Te, M=LiÀ Cs, n = 1, 2, q = n-2) combinations, we introduce 38 new global minima containing a planar hypercoordinate carbon atom (24 with a planar tetracoordinate carbon and 14 with a planar pentacoordinate carbon). These exotic clusters result from the decoration of V-shaped CE 2 2À and Y-shaped CE 3 2À dianions, respectively, with alkali counterions. All these 38 systems fulfill the geometrical and electronic criteria to be considered as true planar hypercoordinate carbon systems. Chemical bonding analyses indicate that carbon is covalently bonded to chalcogens and ionically connected to alkali metals.

<div>The global minima of thirteen combinations of atoms with formula CE₃M₃⁺ (E=S-Te and M=Li-Cs) adopt a planar structure with carbon covalently bonded to three chalcogens and ionically bonded to the three alkali-metals to stabilize the first global minima structures containing planar hexacoordinate carbon atoms.</div>

<div>The global minima of thirteen combinations of atoms with formula CE₃M₃⁺ (E=S-Te and M=Li-Cs) adopt a planar structure with carbon covalently bonded to three chalcogens and ionically bonded to the three alkali-metals to stabilize the first global minima structures containing planar hexacoordinate carbon atoms.</div>