Studies On The Syntheis And Phase Transition For Zn（Im）₂ Framework Materials

Zeolitic imidazolate frameworks (ZIFs) is a new kind of porous material, which is provided with structural diversity, novelty and also the high chemical and thermal stability. Because of the excellent performance and its application in adsorption and separation, ZIFs have attracted more and more significant attention. ZIF-Zn(Im)2 is a sort of zeolitic imidazolate frameworks, based on transition metal Zn and imidazolate ligands.Take advantage of single metal and ligand as well as the temperature and solvent have the greatest impact on the structure of Zn(Im)2 materials, in this thesis, we studied the synthesis and temperature-, solvent-induced phase transition of Zn(Im)2 in solvent system of dialkyl amides, moreover, rules of the synthesis and phase transition of Zn(Im)2 has been summarized. The products were characterized by X-ray single crystal diffraction, X-ray powder diffraction, solid-state 13C NMR, infrared spectroscopy, thermogravimetry-differential thermal and elemental analysis. The main contents and conclusions are as follows:1. Under solvothermal conditions of four typical dialkyl amide we synthesized five ZIF-Zn(Im)2 compound 1-5 with new topologys. Single crystal structures of compound 1,3,4 are obtained as follows:compound 1: Zn(Im)(HIm)2 · AcOH, monoclinic, space group P 121/c 1 (14). compound 3: Zn10(Im)20· 5DBF, orthorhombic, space group P2(1)2(1)2(1). compound 4: Zn4(Im)8 · 2DBF, triclinic, space group P-1. There are ten independent Zn atoms in the structure of zeolite-like compound 3, which has the most independent coordinated and the largest ring in the Zn(Im)2 materials. Compound 1 has an one-dimensional zigzag chain structure.2. The rule of synthesis of Zn(Im)2 in solvent system of dialkyl amides has been researched. The role of solvent was obvious at low temperature, large-sized solvent molecule results porous Zn(Im)2 with a novel topology and rich material structures. The role of temperature was paramount at high temperature, thermal stable and high density Zn(Im)2 was easily obtained.3. Sample 1 was synthesized by molten reaction has the same structure with compound 1, as the parent linear chain, phase transition of Zn(Im)2 from 1D to 3D was investigated and temperature-, solvent-induced transition have been proved.4. Phase transition occurs in DMA at 100℃ and in DMF at 150℃ results sample 4 with crb topology and sample 3 with coi topology respectively. Guest molecule in the framework of samples, thus, the transformation were induced by solvent. Phase transition occurs in air at high temperature and in DMA at 180℃ results sample 2,5 respectively with dense zni topology. There was no guest molecule in the framework, thus, the transformation at high temperature were induced by temperature.