Four benzimidazole-based Zn^II/Cd^II polymers extended by aromatic polycarboxylate coligands: synthesis, structure, and luminescence

Abstract

Four benzimidazole (bim)-based metal complexes, {[Zn₂(bim)₄(btec)] · DMF} _n (1), {[Zn(bim)(btc)] · Htea} _n (2), [Zn(bim)₂(bdc)] _n (3), and {[Cd₃(bim)₄(H₂O)₆(btc)₂] ⋅ 2H₂O} _n (4) (H₄btec = 1,2,4,5-benzenetetracarboxylic acid, H₃btc = 1,3,5-benzenetricarboxylic acid, H₂bdc = 1,4-benzenedicarboxylic acid, and tea = triethylamine), have been obtained by the introduction of benzene-based polycarboxylate as coligand and are structurally characterized by single-crystal X-ray diffraction, elemental analysis, IR spectra, thermogravimetric curves, and luminescence spectra. Controlled by the number and position of the carboxylates attached to the aromatic ring, all the four complexes exhibit polymeric structures from 1-D chain or ribbon for 1, 3, and 4 to 2-D layer for 2. In contrast, the neutral bim is a terminal ligand to complete the metal coordination sphere and it also helps to assemble the low-dimensional coordination skeleton into a high-dimensional ordered supramolecular architecture by N–H ··· O hydrogen-bonding and π–π stacking interactions. Additionally, the complexes exhibit strong emissions originating from the bim-based intraligand as well as photo-induced interligand charge transfer upon cation binding, suggesting potential applications as luminescent materials.

Keywords:

• Benzimidazole
• Mixed-ligand
• Crystal structure
• Fluorescent properties

Acknowledgments

This study was financially supported by the Key Project of Chinese Ministry of Education (grant no. 209003), the Program for New Century Excellent Talents in University (NCET-08-0914), the Natural Science Foundation of Tianjin (grant nos. 10JCZDJC21600 and 10JCYBJC04800) and the Academic Advance Project for Young Teachers of Tianjin Normal University, which are gratefully acknowledged.