Synthesis, Crystal Structure, Unusual Non-covalent Interaction, and Hirshfeld Surface of 2-(2,2,3,3,3-Pentafluoropropoxy) Ethylammonium Iodide Salt

The crystal structure of 2-(2,2,3,3,3-pentafluoropropoxy) ethylammonium iodide (5F-EA-HI) was determined by using single-crystal X-ray diffraction at 100 K. The compound crystallized in the orthorhombic space group Pccn with unit-cell parameters a = 23.911(7) Å, b = 8.880(2) Å, c = 9.451(2) Å, and V = 2006.740(9) ų (Z = 8). Its cation, 5F-EAH⁺, adopts an extended conformation in which the pentafluoropropoxy tail is directed away from the ammonium head group, stabilized by a weak intramolecular non-classical C–H···F and an intramolecular classical N–H···O hydrogen bonding. The iodide anion serves as the principal supramolecular acceptor, forming three charge-assisted N–H···I classical hydrogen bondings that assemble the molecules into dimers and rhombic cyclic motifs. In addition, short intermolecular C–F···F–C interactions between neighbouring fluorinated tails generate both Type I and Type II halogen bond geometries, linking adjacent molecules into closed cyclic tetrameric assemblies. Hirshfeld surface analysis quantitatively confirms these intermolecular interactions with percentage contributions. A space-filling analysis of the crystal packing revealed the clear spatial segregation of fluorous, organic and inorganic (iodide-rich) phases, which are usually observed in fluorinated halide perovskites, but not in the organic spacer. These findings demonstrate how weak non-covalent interactions cooperate to direct the solid-state organization of a highly fluorinated ethylammonium salt and suggest that 5F-EA-HI may serve as a structurally well-defined model spacer for the design of moisture-resistant and thermally stable 2D halide perovskites.