“…20 Rings containing metals or hydrogen bonds can also form stacking interactions. 3,4,6,[11][12][13][14]21 Thus, planar metal-chelates with delocalized π-bonds can stack with aromatic species and with other metal-chelate rings, exhibiting large interaction energies. 3,4,6,11 Quasi-rings, formed by resonance-assisted hydrogen bonding, 12,21 can form π-stacking interactions.…”