Stacking interactions between chelate and phenyl rings in square-planar transition metal complexes

Analysis of geometrical parameters in the crystal structure of square-planar complexes, with and without chelate rings, of all transition metals from Cambridge Structural Database shows that there are stacking interactions between the phenyl ring and the chelate ring with delocalized pi-bonds. Short distances between the metal and carbon atom of the phenyl ring and parallel orientation of phenyl ring with respect to the coordination plane were found in the crystal strucutres of complexes with chelate rings. There is a correlation of the distances between the centers of chelate and phenyl rings and the metal-carbon distances showing that the chelate and phenyl rings tend to overlap. In the crystal structures, there are mutual slipped-parallel orientations of the phenyl and chelate rings. The data show that the geometry of the stacking interaction between phenyl and chelate rings is similar to the geometry of the stacking interaction of two benzene rings, indicating that chelate rings can behave similarly to organic aromatic rings.