Planar Hypercoordinate Carbons in Alkali Metal Decorated CE3 2- and CE2 2- Dianions

After exploring the potential energy surfaces of M_m CE₂ ^p (E=S-Te, M=Li-Cs, m=2, 3 and p=m-2) and M_n CE₃ ^q (E=S-Te, M=Li-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 CE₂ ^2- and Y-shaped CE₃ ^2- 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.