Creating Vacancies And Their Functionalizations In Metal-Organic Frameworks

As a new type of porous material, metal-organic frameworks (MOFs) have been emerging as very promising multi-functional materials due to their powerful attributes from the porosity, capability of designing specific structures, and strong thermal stability, which lead them tailored to specific applications, such as gas storage/separation, catalysis, and drug delivery. Functionalizations of these materials have received tremendous attention. Currently, the main strategy to obtain MOFs with multi-functionalities is the postsynthetic modification. However, this method still has some limitations, such as reduced pore size and porosity, and low percentage of introduced metals or linkers, which are disorder. In this work, we create multi-functionalities in MOFs by designing innumerable ordered vacancies and then filling them with further linkers and metals precidely. This thesis is divided into the following three parts:1. We construct a three-dimensional cubic structure from Zn(â…¡) and 4-pyrazolecarboxylic acid, which undergoes elimination reactions by single-crystal to single-crystal transformation. The removal of one quarter of the metals and half of the linkers results in a new framework with orderd vacancies. The pore size and shape of the framework have been transformed through the process, which lead to distinct adsorption of dye molecules in the materials without vacancies and with vacancies.2. We introduce new metals with different atomic size and valence to occupy the metal vacancies in the framework to achieve multi-functional materials. Co(â…¡) and other new metals occupy the pre-existing vacancies, making any inorganic unit consist of two kinds of metals with ordered distribution. Meanwhile, we introduce different functionalized linkers, such as 3-methyl-4-pyrazole carboxylate, to fill the linker vacancies in the structure, generating several new multi-functional structure without vacancies. These new MOFs are in order for the new metals and linkers, which are inherited from the orderliness of the vacancies, and they can not be made by other methods.3. Based on the metal and linker vacancies in the framework, we introduce new metals and new linkers at the same time by a one-step reaction. After this reaction, we obtain new single crystal structures containing two different kinds of inorganic units and two different kinds of organic units. The multi-functionalities in MOFs are ordered, by creating innumerable ordered vacancies first and then filling them with new linkers and metals. Equivalent to functionalizing molecules in organic chemistry step by step, the system here demonstrated the capability of performing stepwise reactions in crystalline extended solids, and what is more, without destroying the structural integrity.