The proton-transfer complexes 2-amino-4-methoxy-6-methylpyrimidinium (2A4M6MP) 4-aminosalicylate (4AMSA), C6H10N3O+·C7H6NO3-, I, and 5-chlorosalicylate (5ClSA), C6H10N3O+·C7H4ClO3-, II, were synthesized by slow evaporation and crystallized. The crystal structures of both I and II were determined by single-crystal X-ray structure analysis. The crystal structures of both salts exhibit O-H...O, N-H...O, N-H...N and C-H...O interactions in their crystals. The 4AMSA and 5ClSA anions in combination with the 2A4M6MP cations form distinct synthons, which are represented by the graph-set notations R22(8), R42(8) and R22(8). Furthermore, the ΔpKa values were calculated and clearly demonstrate that 2A4M6MP is a good salt former when combined with carboxylic acids. Hirshfeld surface analysis was used to quantify the weak and strong interactions in the solid state, and energy framework calculations showed the stability of the hydrogen-bonding interactions. QTAIM (quantum theory of atoms in molecules) analysis revealed the nature of the chemical bonding in I and II, and the charge-density distribution in the intermolecular interactions in the crystal structures.
Keywords: Hirshfeld surface; charge density; crystal structure; fingerprint plot; intermolecular interaction; proton transfer; pyrimidinium; salicylate; salt.