Intriguing pi(+)-pi Interaction in crystal packing.

The pi(+)-pi interactions are utilized to design the solid-state assembly of host-guest complexes where guests are anions. The doubly protonated MPTPH(2) (MPTP = 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine) complexed with H(2)O 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 pi(+)-pi and pi-pi interactions as well as H-bonding interactions. The planar structure of MPTPH(2)(Cl)(2).2H(2)O or MPTPH(2)(Br)(2).2H(2)O facilitates the crystal packing, since the pi(+)-pi interactions play an important role in the solid-state assembly.