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J Phys Chem A. 2007 Aug 16;111(32):7980-6. Epub 2007 Jul 26.

Cation-pi-anion interaction: a theoretical investigation of the role of induction energies.

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Center for Superfunctional Materials, Department of Chemistry, Pohang University of Science and Technology, San 31, Hyojadong, Pohang 790-784, Korea.


Cation-pi and the corresponding anion-pi interactions have in general been investigated as binary complexes despite their association with counterions. However, a recent study of the ammonia channel highlights the important but overlooked role of anions in cation-pi interactions. In an effort to examine the structural and energetic consequences of the presence of counterions, we have carried out detailed ab initio calculations on some model cation-pi-anion ternary complexes and evaluated the nonpair potential terms, three-body contributions, and attractive and repulsive energy components of the interaction energy. The presence of the anion in the vicinity of the pi system leads to a large redistribution of electron density and hence leads to an inductive stabilization. The resulting electronic and geometrical changes have important consequences in both chemical and biological systems. Compared to cation-pi-anion ternary complexes, the magnitude of the cation-pi interaction in pi-cation-anion ternary complexes is markedly lower because of charge transfer from the anion to the cation.

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