Perfluorohalogenated naphthalenes: synthesis, crystal structure, and intermolecular interaction

Abstract

Perfluorohalogenated naphthalenes (PFXNaPs) are unique small molecules with great potential to exhibit a new type of σ-hole and π-hole bonding, owing to the incorporation of multiple F atoms onto the naphthalene ring. In this study, we develop a synthetic protocol for PFXNaPs, conduct crystal engineering investigations, and explore the intermolecular interactions of PFXNaPs through π-hole and σ-hole bondings. We successfully synthesise PFXNaPs using Mg amide-mediated halogenation reactions of electron-deficient F₇ and F₆ naphthalenes, achieving good to excellent yields. Crystal structure analyses of 3,6-I₂F₆ naphthalene unveil intermolecular π-hole stacking between two C atoms in the naphthalene ring, involving cooperation with the σ-hole bonding of two I atoms. This intermolecular interaction mode has not been classified in previous reports. Computational studies show that the π-hole bonding in PFXNaPs is substantially enhanced compared to corresponding benzene molecules without diminishing the σ-hole bonding. The unique stacked interaction in PFXNaPs is primarily governed by electrostatic interaction and dispersion correction energies, with the contribution of C⋯C contacts being 10 times greater than that in benzene analogs. The results enable further applications of PFXNaPs in the fields of perfluorohalogenated arenes and organic crystalline materials.