Intriguing π⁺−π Interaction in Crystal Packing

The π+−π interactions are utilized to design the solid-state assembly of host−guest complexes where guests are anions. The doubly protonated MPTPH2 (MPTP = 4′-(4-methoxyphenyl)-2,2′:6′,2′′-terpyridine) complexed with H2O and Cl− or Br− are synthesized, crystallized, and characterized by X-ray analysis. By using the density functional theory calculations which can properly describe the dispersion energy, the assembling phenomena are analyzed in terms of π+−π and π−π interactions as well as H-bonding interactions. The planar structure of MPTPH2(Cl)2·2H2O or MPTPH2(Br)2·2H2O facilitates the crystal packing, since the π+−π interactions play an important role in the solid-state assembly.