Tuning the Formations of Metal-Organic Frameworks by Modification of Ratio of Reactant, Acidity of Reaction System, and Use of a Secondary Ligand
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abstract
Four porous coordination networks (PCNs), {[Zn 3O(H 2O) 3(adc) 3]2(C 2H 6NH 2)2(DMF)3(H 2O)} n (PCN-131), Zn 2(DMA) 2(adc) 2]2(DMA)} n (PCN-132), {[Zn 3O(DMF)(adc) 3(4,4-bpy)] 2(C 2H 6NH 2)S} n (PCN-131), and {[Zn(adc)(4,4-bpy) 0.5]S} n (PCN-132), have been synthesized by the assembly of anthrancene-9,10-dicarboxylic acid (H 2adc) with Zn(II) under different reaction conditions, including modifications of reactant ratio, acidity variations, and the use of a secondary ligand. Single-crystal X-ray diffraction studies reveal that PCN-131, obtained from the dimethylformamide (DMF) solution under acid condition, has a three-dimentional (3D) framework structure with one-dimensional (1D) honeycomb channels. PCN-132 isolated from dimethylacetamide (DMA) solution without adding acid in synthesis is a two-dimensional (2D) layer compound. By employing 4,4-bipyridyl (4,4-bpy) as a secondary ligand, PCN-131 and PCN-132 were synchronously synthesized as a mixture outcome with more PCN-131 than PCN-132. In PCN-131, 4,4-bpy acting as a secondary ligand is arranged inside the honeycomb channel of the 3D PCN-131, resulting in an effective improvement of thermal stability of the network, while in PCN-132, 4,4-bpy ligands link 2D layers of PCN-132 to form a pillared-layer 3D framework. Gas adsorption has been performed for selected materials. The results show that the framework of PCN-131 is thermally unstable after removing the solvent molecules coordinated to their metal sites. While PCN-131 is stable for gas uptake, with an evaluated Langmuir surface area of 199.04 m 2 g -1, it shows a selective adsorption of CO 2 over CH 4. 2011 American Chemical Society.
