Synthesis, structural elucidation, characterization and theoretical DFT study of 1-(o-tolyl)biguanidium chloride

The structure of the new salt 1-(o-tolyl)biguanidium chloride, C₉H₁₄N₅⁺·Cl^-, has been determined by single-crystal X-ray diffraction. The salt crystallizes in the monoclinic space group C2/c. In this structure, the chloride and biguanidium hydrophilic ions are mostly connected to each other via N-H...N and N-H...Cl hydrogen bonds to form layers parallel to the ab plane around y = 1/3 and y = 2/3. The 2-methylbenzyl groups form layers between these layers around y = 0 and y = 1/2, with the methyl group forming C-H...π interactions with the aromatic ring. Intermolecular interactions on the Hirshfeld surface were investigated in terms of contact enrichment and electrostatic energy, and confirm the role of strong hydrogen bonds along with hydrophobic interactions. A correlation between electrostatic energy and contact enrichment is found only for the strongly attractive (N-H...Cl^-) and repulsive contacts. Electrostatic energies between ions reveal that the interacting biguanidium cation pairs are repulsive and that the crystal is maintained by attractive cation...Cl^- dimers. The vibrational absorption bands were identified by IR spectroscopy.