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

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 ₂ 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.