Synthesis and structural studies of amino amide salts derived from 2-(aminomethyl)benzimidazole and α-amino acids

• Amino amides were synthetized via condensation at height temperature.
• Amino amide-anion interactions were studied by experimental and theoretical methods.
• Experimental methods indicated that Cl− or ZnCl42− anions increase the acidity of N–H bonds.
• QTAIM studies evidenced that NO3− ions increase the ionic character of N–H bonds.

2-{[(Ammoniumacetyl)amino]methyl}-1H-benzimidazol-3-ium dichloride 4, 2-{[(2-ammoniumpropanoyl)amino]methyl}-1H-benzimidazol-3-ium dichloride 5, and 2-{[(2-ammonium-3-phenylpropanoyl)amino]methyl}-1H-benzimidazol-3-ium dichloride 6 amino amides were synthesized via condensation of 2AMBZ dihydrochloride with the corresponding amino acid. Compounds 7–12 were obtained by replacing chloride ions (in salts 4–6) with nitrate or tetrachlorozincate ions. The results of X-ray diffraction crystallographic studies indicated that the geometries, charges and sizes of the anions are essential for the formation of the strong hydrogen bond interactions of compounds 4, 5, 9–12. Moreover, in most cases, the presence of water and solvent molecules stabilizes the supramolecular structures of these compounds. Nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy indicated that the presence of chloride or tetrachlorozincate anions increases the acidity of the benzimidazolic and amide groups more significantly than the presence of nitrate anions. However, Quantum Theory of Atoms in Molecules (QTAIM) computations of the crystal structures demonstrate that amino amides interact more strongly with NO3− than with Cl− and ZnCl42− anions; this difference explains the spectroscopic results.

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