title: Surprising enhancing effect of methyl group on the strength of O⋯XF and S⋯XF (X=Cl and Br) halogen bonds.
abstract: The role of methyl group in H(2)O⋯XF and H(2)S⋯XF (X=Cl and Br) halogen-bonded complexes has been investigated with quantum chemical calculations. The halogen bond in the H(2)O⋯XF complexes is stronger than that in the H(2)S⋯XF complexes. However, the S⋯X halogen bond is stronger than the O⋯X one with the increase of methyl number. The result shows that the methyl group in the halogen acceptor has a positive contribution to the formation of halogen bond and there is a positive nonadditivity of methyl groups. Surprisingly, the methyl groups in dimethyl sulfide causes an increase of 150% for the interaction energy of S⋯Cl halogen bond. The natural bond orbital analyses have been performed to unveil the mechanism of the methyl group in the halogen bonding formation.
authors.affiliation: The Laboratory of Theoretical and Computational Chemistry, Science and Engineering College of Chemistry and Biology, Yantai University, Yantai 264005, People's Republic of China. liqingzhong1990@sina.com
authors.forename: Qingzhong
authors.initials: Q
authors.lastname: Li
authors.forename: Bo
authors.initials: B
authors.lastname: Jing
authors.forename: Zhenbo
authors.initials: Z
authors.lastname: Liu
authors.forename: Wenzuo
authors.initials: W
authors.lastname: Li
authors.forename: Jianbo
authors.initials: J
authors.lastname: Cheng
authors.forename: Baoan
authors.initials: B
authors.lastname: Gong
authors.forename: Jiazhong
authors.initials: J
authors.lastname: Sun