Chemical Tailoring In The Glass Formation Process And Stability Of Metal Complex

With the development of technology,glass has been widely used in daily life and high-tech fields.Furthermore,it has become the important model for some major issues in condensed matter physics.Recently,a new type of glass-MOF glass has been discovered.What's more,the structure,morphology,pore size,porosity,physical and chemical properties of MOF glass can be controlled through tailoring of chemical bonds.In order to provide a theoretical basis for the synthesis of new MOF glass by clarifying the structural origin of ZIF-4 phase transition?desolvation,amorphization,recrystallization,melting?and the nature of glass.In addition,the chemical stability and hydrolysis mechanism of MOF material have been explored.This provides a theoretical basis for guiding the design and synthesis of MOF materials that can adapt to different environments.The main work and conclusions of this paper are as follows:This paper adopts solvothermal synthesis method to prepare iso-structural ZIF-4with only different central ions?M=Zn,Co?.The two isostructural ZIF-4 exhibited different phase transitions by using calorimetric and thermogravimetric analysis.Upon heating,the framework of Co-ZIF-4 crystal undergoes the crystal-to-amorphous phase transition at 590 K,which is somewhat lower than the corresponding transition previously reported in the corresponding Zn-ZIF-4.In addition,the recrystallization rate for amorphous Co-ZIF-4 is relatively higher than the corresponding one of Zn-ZIF-4.Finally,the forming Co-zni crystal begins to melt at about 824 K,accompanying by quick decomposition,whereas Zn-zni undergoes complete melting which finishes at around 850 K without any decomposition.The structure,morphology and coordination environment of Zn-and Co-ZIF-4were characterized by means of XRD,SEM and XPS.What's more,the structure origin of ZIF-4 phase transition was elucidated.Because the ion radius of Co²⁺?0.67??is smaller than that of Zn²⁺?0.68??and the crystal field stabilization energy of Co²⁺is greater than that of Zn²⁺,leading to the stronger interaction between Co²⁺and organic ligands,the recrystallization rate of the Co-ZIF-4 compound is greater.In addition,the reason for the lower amorphous and melting temperature of Co-ZIF-4compounds is the greater degree of distortion of CoN₄ tetrahedron than that of ZnN₄tetrahedron,which is determined by Jahn-Teller effect.ZIF-62 was found to have better chemical stability by comparing the ZIF-4 and ZIF-62.On the one hand,because of the greater steric hindrance and higher hydrophobicity of benzimidazole compared with imidazole,ZIF-62 is more difficult for water molecules to enter into the framework.On the other hand,the better chemical stability of ZIF-62 mainly relates to the greater strength of the M-N bond,which is due to the benzene ring in benzimidazole can transmit electrons to imidazole ring.