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<p>The crystal structures of 9-aminoacridinium 3-halobenzoate salts (X = Cl, Br, I) were compared in terms of molecular packing and intermolecular interactions. All three compounds crystallize in the monoclinic <i>P</i>2₁/<i>c</i> space group, are isomorphous, and exhibit a high degree of structural similarity with closely related packing motifs. Analysis of geometric parameters confirms proton transfer from the carboxylic group of the acid to the endocyclic nitrogen atom of 9-aminoacridine, consistent with Δp<i>K</i>a predictions indicating salt formation. Analysis of intermolecular interactions shows that the crystal packing is stabilized by a network of N–H⋯O and C–H⋯O hydrogen bonds, as well as π–π stacking, C–H⋯halogen, and halogen⋯π interactions. Geometric analysis of the halogen⋯π contacts indicates that these interactions can be classified as weak n–π* interactions. Energy framework calculations demonstrate that the energetic stability of the crystals increases with halogen size (I &gt; Br &gt; Cl), in agreement with the observed melting points, and highlight the dominant role of dispersion forces in stabilizing the supramolecular architecture across all three structures.</p>

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The role of π–π, C–H⋯halogen, and halogen⋯π interactions in the crystal packing of 9-aminoacridinium 3-halobenzoate salts: an experimental and theoretical investigation

  • 期刊论文

  • 发表日期：

    2026年3月9日

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  • Patryk Nowak,
  • Artur Sikorski,
  • Artur Mirocki

摘要

The crystal structures of 9-aminoacridinium 3-halobenzoate salts (X = Cl, Br, I) were compared in terms of molecular packing and intermolecular interactions. All three compounds crystallize in the monoclinic P2₁/c space group, are isomorphous, and exhibit a high degree of structural similarity with closely related packing motifs. Analysis of geometric parameters confirms proton transfer from the carboxylic group of the acid to the endocyclic nitrogen atom of 9-aminoacridine, consistent with ΔpKa predictions indicating salt formation. Analysis of intermolecular interactions shows that the crystal packing is stabilized by a network of N–H⋯O and C–H⋯O hydrogen bonds, as well as π–π stacking, C–H⋯halogen, and halogen⋯π interactions. Geometric analysis of the halogen⋯π contacts indicates that these interactions can be classified as weak n–π* interactions. Energy framework calculations demonstrate that the energetic stability of the crystals increases with halogen size (I > Br > Cl), in agreement with the observed melting points, and highlight the dominant role of dispersion forces in stabilizing the supramolecular architecture across all three structures.