Synthesis, spectroscopic, and structural characterization of two malate zinc coordination polymers with imidazole or 2,2′-bipyridine

Abstract

Zinc(II) coordination polymers, [Zn(Hmal)(im)(H₂O)] _n · 2nH₂O (1) and [Zn(Hmal)(bpy)] _n · 3nH₂O (2) (H₃mal = malic acid, im = imidazole, bpy = 2,2′-bipyridine), were synthesized from aqueous solution and characterized by elemental analyses, infrared and fluorescence spectra, thermogravimetric analyses, and single-crystal X-ray structural analyses. In 1, zinc is coordinated by imidazole, water, and tridentate malate in octahedral geometry. The β-carboxy group of malate further bridges with the other zinc forming 1-D polymeric chains. A pair of 1-D chains self-assemble to generate a double chain by strong hydrogen bonds between imidazole and malate. Furthermore, neighboring pairs of double chains are extended to form the final 3-D framework through intermolecular hydrogen bonds. In 2, the malates link Zn in a bidentate–monodentate fashion to form spiral-shaped chains that extend into a 3-D supramolecular structure by π–π stacking interactions and intermolecular hydrogen bonds. Complex 1 exhibits strong fluorescence at room temperature.

Keywords:

• Zinc
• Malic acid
• Imidazole
• 2,2′-Bipyridine
• Coordination polymer

Acknowledgments

Financial supports provided by National Science Foundation of China (20571061, 20423002), the Ministry of Science & Technology (2005CB221408) and Scientific Research Funds for the Talents of China Three Gorges University (KJ2009B049) are gratefully acknowledged.