title: Extended halogen bonding between fully fluorinated aromatic molecules.
abstract: Halogen bonding is a noncovalent interaction where an electrophilic cap on a halogen atom, the so-called σ-hole, attracts a nucleophilic site on an adjacent molecule. The polarizability of halogens relates to the strength of the σ-hole, and accordingly the halogen-halogen distance becomes shorter in the order of Cl, Br, and I. Fully fluoro-substituted aromatic molecules, on the contrary, are generally believed not to form halogen bonds due to the absence of a σ-hole. Here, we study atomic-scale in-plane F-F contacts with high-resolution force microscopy. Our ab initio calculations show that the attractive dispersion forces can overcome the electrostatic repulsion between the fluorine atoms, while the anisotropic distribution of the negative electrostatic potential leads the directional bond and even changes the gap. The coexistence of these two competing forces results in the formation of a "windmill" structure, containing three C-F···F bonds among neighboring molecules. While the σ-hole is absent, the scheme of the C-F···F bonding has a high similarity to halogen bonding.
authors.affiliation: †Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland.|‡PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Kawai
authors.affiliation: †Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland.|§Department of Physics, Shahid Beheshti University, Evin, 19839 Tehran, Iran.
authors.forename: Ali
authors.initials: A
authors.lastname: Sadeghi
authors.affiliation: ⊥Department of Applied Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan.
authors.forename: Feng
authors.initials: F
authors.lastname: Xu
authors.affiliation: ⊥Department of Applied Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan.
authors.forename: Lifen
authors.initials: L
authors.lastname: Peng
authors.affiliation: ⊥Department of Applied Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Orita
authors.affiliation: ⊥Department of Applied Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan.
authors.forename: Junzo
authors.initials: J
authors.lastname: Otera
authors.affiliation: †Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland.
authors.forename: Stefan
authors.initials: S
authors.lastname: Goedecker
authors.affiliation: †Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland.
authors.forename: Ernst
authors.initials: E
authors.lastname: Meyer
keywords: F−F contact; atomic force microscopy; chemical structure; halogen bonding; intermolecular interaction