Tuning the formations of metal-organic frameworks by modification of ratio of reactant, acidity of reaction system, and use of a secondary ligand

摘要

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.