Selective synthesis and structural study of amino amide trichlorozincates

Abstract

Herein, we report the synthesis of (2-((2-ammoniopropanamido)methyl)-1H-benzimidazol- κN3) trichlorozincate (1-) 1a, (2-(1-(2-ammoniopropanamido)ethyl)-1H-benzimidazole-κN3)trichlorozincate (1-) 2a, and (2-((2-ammonio-3-methylbutanamido)methyl)-1H-benzimidazole-κN3)trichlorozincate (-1) 3a in a controlled pH environment (pH = 4.0). NMR studies reveal that the N→Zn bond is stronger in 1a and 3a than 2a and that the acid–base equilibria of the amino amides in the presence of Zn(II) result from the formation of various anionic species within the system (Cl−, ZnnClm2−). Crystallography studies show that intramolecular CH•••Cl interactions play a relevant role in the strength of the coordination bond. Furthermore, the cocrystallization of solvent molecules is essential to stabilize the supramolecular structure of 1a and 2a. The infrared spectroscopy corroborated the presence of solvent molecules giving rise to complex hydrogen-bond networks. Moreover, the vibrational spectra indicate that the C10-H10•••Cl3 interactions preferentially occur through the charge transfer phenomena n(Cl3)→σ*C10H10. Additionally, unlike 2a, the displacement in the scissor vibration of the methylene group between 1a and 3a corroborates that the charge transfer phenomena n(Cl3)→σ*C10H10 dominate the C10-H10•••Cl3 interaction.