Synthesis, structures, and luminescence of two 2-D microporous metal-organic frameworks in the zinc (cadmium)-dicarboxylate-imidazolate system

Abstract

Two 2-D microporous metal–organic frameworks, [Zn(BDC)(MbIm)]·2DMF (1) and [Cd3(BDC)3(MbIm)2(DMF)2]·2DMF (2), have been synthesized by solvothermal reaction of 1,4-benzenecarboxylic acid (H2BDC) and 2-methylbenzimidazole (MbIm) with zinc/cadmium nitrate. Single-crystal X-ray diffraction analysis indicates that 1 consists of the well-known zinc paddle-wheel motif which is linked by bridging dicarboxylates to form 2-D square grids. The 2-D layers stack offset due to the effect of the spatial structure of MbIm ligand and hydrogen-bonding interaction between MbIm and guest molecules. Similarly, 2 is constructed by six-connected Cd3(μ-O2CR)6(MbIm)2 units and bridging carboxylates, resulting in a 2-D layer structure with triangular grids. Topology analysis reveals that 1 exhibits a 2-D tetragonal plane network with {44·62} topology symbol, while 2 possesses a six-connected {36·46·53} topological network. Analysis of the luminescence spectra demonstrates that the complexes have good luminescent intensities with greater red-shift (82 nm for 1 and 69 nm for 2) corresponding to free MbIm. Elemental analyses, infrared spectra, powder X-ray diffraction, and thermogravimetric analyses of 1 and 2 have been investigated.