Understanding the Nature and Energetics of C–H···F Interactions in Crystalline Propamides

Abstract

Intermolecular interactions play a pivotal role in crystal engineering, enabling the creation of novel materials with tailored properties. While strong hydrogen bonds have traditionally been the primary focus, recent attention has shifted toward weaker interactions, such as C–H···F interactions. Fluorine, previously believed to be incapable of forming hydrogen bonds, has now been recognized for its ability to engage in weak C–H···F interactions, significantly influencing crystal packing. This study explores the intricate nature of C–H···F interactions and their relationship in the presence of other intermolecular interactions. We have synthesized and structurally characterized six new fluorine-containing organic compounds and examined how the positions of fluorine and trifluoromethyl groups (ortho, meta, and para) affect intermolecular interactions. The solid-state structures of these compounds have been explored by investigating the noncovalent interactions present in the crystal. The weak C–H···F interactions, shaped by the electronic environment and the acidity of the donor hydrogen atoms, contribute to the enhanced stability of the crystal structure. To quantify these interactions, we have evaluated the lattice energies via PIXELC, performed the topological analysis via the QTAIM approach, and analyzed the molecular electrostatic potential (MESP) as well. The thermal stability of the compounds has been assessed in the context of noncovalent interactions present in the crystal structure. By elucidating the role of C–H···F interactions, this research aims to contribute to the advancement of supramolecular chemistry and crystal engineering of interactions involving organic fluorine. The study investigates only six fluorinated compounds, which significantly limits its ability to represent the broader and more complex trends within crystal engineering.