How to Accomplish a Square C(N)(4) Substructure of the Planar Tetracoordinate Carbon

[Image: see text] Nitrogen-based groups are usually not used as ligands to coordinate to the ptC atom. However, here we reported only nitrogen-based ligands to accomplish a theoretically successful square planar C(N)(4) substructure. The first difficulty in accomplishing a square ptC(N)(4) substructure is to conquer the tremendous strain from the planar to tetrahedral arrangements, and the second is to restrict it in a suitable system with the right symmetry. We designed several neutral molecules with the square ptC(N)(4) substructures, and the molecules were studied using the density functional theory method at the B3LYP/6-311++G(3df,3pd) and TPSSh/6-311++G(3df,3pd) level of theory. The results of this work show that the molecules are all real minima on the potential energy surface and successfully achieved the square ptC(N)(4) substructure in the theoretical method. The group orbitals among the square ptC(N)(4) arrangement in the D(2d) symmetry have been discussed and used to investigate the bonding interactions among all atoms in the square ptC(N)(4) substructure. Usually, the ptC systems have 18 valence electrons, but the present ptC systems mentioned in this work have 24 valence electrons, which is unusual for ptC.