Synthesis and structure of Zn(II) and Cu(II) complexes derived from 2-(aminomethyl)benzimidazole and glycine

<div><p>Reactions of 2-(aminomethyl)benzimidazole di-hydrochloride (<b>1</b>·2HCl) and glycine with 3Zn(OH)₂·2ZnCO₃ or Cu(OAc)₂·H₂O led to the synthesis of the quaternary coordination complexes <b>2</b> and <b>3</b>. X-ray diffraction showed that these complexes are composed of <b>2a</b> = [Zn(L)Cl(L′)] and <b>2b</b> = [Zn(L)(H₂O)₂(L′)], and of <b>3a</b> = [Cu(L)(H₂O)_0.25Cl(L′)] and <b>3b</b> = [Cu(L)(H₂O)_1.5(L′)], respectively, where L = 2-(aminomethyl)benzimidazole and L′ = glycinate. Zn(II) in <b>2a</b> has an intermediate geometry between a square-pyramid and a trigonal bipyramid structure. However, the geometry about the metal ion of units <b>2b</b>, <b>3a</b>, and <b>3b</b> is distorted octahedral. Moreover, the supramolecular structures for <b>2</b> and <b>3</b> were assembled through N–H⋯O and O–H⋯Cl hydrogen bonds. In these complexes, H₂O and N–H groups serve as proton donors, whereas chloride and C=O groups serve as proton acceptors. Also <i>π</i>–<i>π</i> stacking interactions between aromatic rings contribute to the stabilization of the supramolecular structure of <b>2</b> and <b>3</b>. The Zn and Cu complexes were studied by infrared and Raman spectroscopy, which indicated that <b>2</b> and <b>3</b> have similar molecular structures in the solid state. Ultrasound activation at the end of the reaction was necessary to yield <b>2</b>.</p></div