title: Periodic ab initio approach for the cooperative effect of CH/pi interaction in crystals: relative energy of CH/pi and hydrogen-bonding interactions.
abstract: The bonding property of the CH/pi interaction in organic crystals has been investigated by the means of a periodic ab initio method. The energy of the CH(sp(2))/pi interaction in crystals, estimated with periodic RHF/6-21G*, showed a reasonable attractive CH(sp(2))/pi interaction owing to a cooperative effect, whereas the results calculated with RHF/cc-pVDZ indicate a negligibly small or repulsive interaction. The relative contribution of the CH(sp(2))/pi interaction to the column packing energy was found to be roughly half of the energy of a conventional hydrogen bond. The calculation of the charge distributions on the aromatic rings participating in the CH(sp(2))/pi interaction in crystals revealed that the atoms were more ionic than those in the gas phase. These theoretical calculations suggest a hydrogen-bonding characteristic for the CH(sp(2))/pi interaction in crystals, which does not occur in solution nor gas phase. We present computational evidence of the existence of the cooperative effect of CH(sp(2))/pi interaction in crystals.
authors.affiliation: Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Saigo