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

Reactions of 2-(aminomethyl)benzimidazole di-hydrochloride (1·2HCl) and glycine with 3Zn(OH)2·2ZnCO3 or Cu(OAc)2·H2O led to the synthesis of the quaternary coordination complexes 2 and 3. X-ray diffraction showed that these complexes are composed of 2a = [Zn(L)Cl(L′)] and 2b = [Zn(L)(H2O)2(L′)], and of 3a = [Cu(L)(H2O)0.25Cl(L′)] and 3b = [Cu(L)(H2O)1.5(L′)], respectively, where L = 2-(aminomethyl)benzimidazole and L′ = glycinate. Zn(II) in 2a has an intermediate geometry between a square-pyramid and a trigonal bipyramid structure. However, the geometry about the metal ion of units 2b, 3a, and 3b is distorted octahedral. Moreover, the supramolecular structures for 2 and 3 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 π–π stacking interactions between aromatic rings contribute to the stabilization of the supramolecular structure of 2 and 3. The Zn and Cu complexes were studied by infrared and Raman spectroscopy, which indicated that 2 and 3 have similar molecular structures in the solid state. Ultrasound activation at the end of the reaction was necessary to yield 2.