Crystal Transformation Of Alkaline Earth Metal Ions,Mn²⁺,Pb²⁺-based MOFs Containing3,3',5,5'-tetracarboxylic Acid

In order to obtain the possible formation process and mechanism of Metal-Organic Frameworks?MOFs?,in this paper,we chose the 3,3',5,5'-biphenyltetracarboxylic acid?H₄BPTC?as the organic ligand to react with calcium nitrate,strontium chloride,barium nitrate,manganese chloride and lead nitrate,respectively,in the mixed solvents,and observed the formation processes of the final block-like crystals derived from the needle-like intermediates.Also,these intermediates and target products can be obtained by hydrothermal method.Further investigations on the dimension and shape of single crystals,IR spectra,XRD,crystal structures and thermal stability of the intermediates and target products indicates the crystal transformation reason and driving forces.The experimental factors,such as material ratio of reactants,the type of mixed solvents and their composition,pH value,temperature and reaction time,play an important role in the formation of the target compounds.The main contents of this thesis are given as follows:1.The organic ligand H₄BPTC was selected to react with calcium nitrate,strontium chloride and barium nitrate in different mixed solvents by oil-bath method,respectively,and the crystal-to-crystal transformation from a needle-like 1-D [Ca?H₂BPTC?₂?H₂O?₄]n?Ca-MOFs-1?to a block-like 3-D[Ca3?BPTC?1.5?H₂O?6·1.5H₂O]n?Ca-MOFs-2?,a needle-like 3-D [Sr2?H2BPTC?2?H₂O?6]n?Sr-MOFs-1?to a plate-like 3-D [Sr3?BPTC?1.5?H₂O?6]n?Sr-MOFs-2?and a needle-like 3-D [Ba?H2BPTC??H₂O?2]n?Ba-MOFs-1?to a block-like 3-D [Ba₅?BPTC?₃?H₂O?₁₃]n?Ba-MOFs-2?were found.These three pairs of MOFs based on alkaline earth metal ion are from needle-like crystals to block-like crystals.The transformation of crystal-to-crystal was analyzed according to the competition between the inorganic connectivity and connectivity of metal ions and the ionic radius of metal ion,which is vital to coordinate.2.The organic ligand H₄BPTC was used to react with manganese chloride in the mixed solvents using by oil bath method.Three-steps crystal transformation process from simple 3-D[Mn₂?H₂BPTC?₂?DMF??H₂O?₃]n?Mn-MOFs-1?to 3-D {[Mn₂?BPTC??DMF?₂?H₂O?]·DMF}n?Mn-MOFs-2?to complex 3-D [Mn2?BPTC??H₂O?2]n?Mn-MOFs-3?was found.The dehydrogen of H₄BPTC was verified,and the experimental factors such as material ratio of reactants have a great influence on the crystal-to-crystal transformation process of Mn-MOFs.3.The organic ligand H₄BPTC was used to react with lead nitrate in the mixed solvents by oil bath method and the crystal-to-crystal transformation from a 3-D needle-like [Pb₂?BPTC??H₂O?]n?Pb-MOFs-1?to a 3-D block-like [Pb₃?BPTC?2·4?H₂O?]n?Pb-MOFs-2?was found.The crystal-to-crystal transformation process of Pb-MOFs was discussed according to the their thermal stabilities.