Fluorine as a Lewis acid: A symmetry‐adapted perturbation theory based on density functional theory and interacting quantum atoms study of noncovalent interactions in the NCF⋯NH₃ complex

Abstract

Different computational methods are used to investigate the nature of interaction in the NCFÁ Á ÁNH 3 model complex, in which the fluorine atom acts as a Lewis acid and forms a noncovalent bond with the ammonia (Lewis base). Symmetry-adapted perturbation theory based on density functional theory (SAPT(DFT)) indicates that the noncovalent interaction in the NCFÁ Á ÁNH 3 complex is mainly electrostatics. However, dispersion and induction terms also play important roles. Although fluorine noncovalent interactions are typically classified as halogen bonds, they are somewhat different from the well-known halogen bonds of iodine, bromine, and chlorine. The halogen bonds of NCClÁ Á ÁNH 3 and NCBrÁ Á ÁNH 3 are directional and the C X N (X = Cl or Br) angle tends to be linear. In contrast, the fluorine interaction in NCFÁ Á ÁNH 3 is not directional; the interaction energy shows no sensitivity to the angular (C F N) distortions, and the energy profile is flat over a wide angular range (from 180 to about 140 ). However, for the angles less than 130 , the energy curve shows a clear angular dependence and the interaction between NCF and NH 3 becomes stronger as the C F N angle decreases. It seems that at the tighter angles, a tetrel-bonded NCFÁ Á ÁNH 3 complex is preferred. Moreover, interacting quantum atoms (IQA) analysis shows that the competition between different intraatomic and interatomic interactions determines the geometry of NCFÁ Á ÁNH 3 complex.

On the Ability of Nitrogen to Serve as an Electron Acceptor in a Pnicogen Bond

“…Because the development of any positively charged region on the X atom is attenuated by higher electronegativity and reduced polarizability, the first-row F atom is seldom capable of generating a σ-hole. Nonetheless, although rare, there are instances of halogen bonds where F serves as electron acceptor − although the definition of some of these interactions as true halogen bonds has been disputed.…”

F-Halogen Bond: Conditions for Its Existence

“…Models can be devised, which are simple enough that any attractive forces can be unequivocally attributed to a target interaction such as an XB without complicating secondary interactions. There have been a number of quantum chemical studies ,− that considered the possibility of F XBs. However, each such study has limited itself to only a subset of possible systems in which such a bond might be present, different authors apply different levels of theory, and there have been some conflicting results from one study to the next, leaving this matter an open question.…”