Parallel stacking interactions in square-planar transition-metal complexes containing fused chelate and C₆-aromatic rings

Stacking interactions in the crystal structures of square-planar transition metal complexes from the Cambridge Structural Database with five- and six-membered chelate rings fused with C_6-arom rings (arom = aromatic) were analyzed. The distribution of distances between the closest C_6-arom-C_6-arom and C_6-arom-chelate contacts shows that in a large fraction of the intermolecular interactions the C_6-arom ring of one molecule is closer to the chelate than to the C_6-arom ring of the other molecule. These results indicate a possible preference of the C_6-arom ring to form stacking contacts with the chelate rings. The preference is ubiquitous and does not depend on the metal type.