Tuning the Formations of Metal–Organic Frameworks by Modification of Ratio of Reactant, Acidity of Reaction System, and Use of a Secondary Ligand

Abstract

Four porous coordination networks (PCNs), {[Zn3O(H2O)3(adc)3]·2(C2H6NH2)·2(DMF)·3(H2O)}n (PCN-131), Zn2(DMA)2(adc)2]·2(DMA)}n (PCN-132), {[Zn3O(DMF)(adc)3(4,4′-bpy)]·2(C2H6NH2)·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 (H2adc) 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 m2 g–1, it shows a selective adsorption of CO2 over CH4.