Functional Design & Characterization Of Polycarboxylatic Metal-Organic Hybrid Materials

Crystal engineering provides varieties of methods to achieve the designability and controlled synthesis of the molecular accumulation, and further realizes the functionalization of the materials. Metal-organic frameworks, as an important object in the research of crystal engineering, have advantages of structural stability, design variety and the ease of synthesis, thus attracting widespread attention. The carboxylates can easily chelate with metal ions forming stable structures, so polycarboxylic acid type ligands are generally considered as excellent structural units to constructe metal-organic frameworks.In this paper, we use hydrothermal and solvothermal synthesis methods. By controlling the reaction temperature, changing the ligand, adjusting the ratio of reactants, p H adjustment strategies and so on, we finally synthesize 6 polycarboxylatic metal-organic frameworks. We use single X-ray diffraction to determine the atomic structures of crystals obtained. Properties of the products are analyzed by powder X-ray diffraction, infrared spectroscopy, thermal gravimetric analysis, and gas absorption and calorimetry analysis. The main contents are as follows:1. Design and synthesis of dicarboxylic frameworks, and study of their gas adsorption selectivity. Through solvothermal method, 1,3-H2 bdc and 1,4-H2 bdc are respectively applied into In(NO3)3. Then, we obtain two kinds of metal-organic hybrid materials, with different microporous structures, compound 1 and 2:[H2In3O(OH)3(1,3-bdc)3](1)[HIn(1,4-bdc)2](2)The pores in compound 1 are blocked by the benzenes, so it does not show good ability in absorbing gases. However, compound 2 has good adsorption selectivity ofCO2 over N2 under 1 atm, and its stability in the capacity and structure is also good.2. Energy storage and p H-control release. By introducing bpp ligand into Co(Ac)2 and 1,2,4,5-H4 btec, compound 3 can be easily obtained through hydrothermal method. Under normal temperature and pressure(NTP: ~298 K, 1 atm), put samples of compound 3 into acid water, then we can obtain compounds 4, 5 and 6 in this order:[Co5(OH)2(bpp)(btec)2]2?H2O(3) [Co2(H2O)4(bpp)2(Hbtec)2]?5H2O?H2bpp(4) [Co2(H2O)2(OH)(bpp)2(Hbpp)(btec)]?5H2O(5) [Co3(H2O)4(Hbpp)2(btec)2]?6H2O(6)Worthy to note, if the raw materials are mixed without hydrothermal treatment and kept under normal temperature and pressure(NTP: ~298 K, 1 atm), compound 6 will be obtained directely. Besides, if compound 6 is put in water for another hydrothermal treatment, we will obtain compound 3 again.Among the transformation procudure, the energy change of the system can be verified by the fluctuations in temperature of the system and the theoretical calculation. Subsequent experiments show that such transformation process can be controlled by adjusting the p H values of the system.