The Synthesis And Structural Analysis Of Phosphonate-Bridged Polytungstate Oligomers

Since the beginning of the 21st century,polyoxometalates have been widely used in the fields of catalysis,pharmacology,electrochemistry,photochemistry and magnetism due to their unique properties.It has gained increasing attention over the years among researchers from different backgrounds and gradually became one of the hottest areas of scientific research.In the field of polyoxometalates,polyoxotungstates(POTs)are the most predominant,with diverse structures and good stability.Therefore,POTs are selected as the inorganic precursor ligands in this study.It is expected that,with appropriate choices of substituting metals and bridging organic ligands,a series of novel structures can be obtained,thereby enable their properties to be modified and their applications to be expanded.The main research focus of this project is to use vacant POTs as inorganic ligands.They are introduced with transition metals such as Ni,which are then connected with various organic ligands into oligomeric structures.In this thesis we first prepared number of precursor materials required for the syntheses,including polyoxometalates ligands and organic bridging ligands,and these compounds were fully analyzed by using infrared spectroscopy,nuclear magnetic resonance spectroscopy,and thermogravimetric analysis.The results confirmed that the synthesized materials are the target products in question.In the synthesis of inorganic polytungstate ligands,four different types of polytungstates Na10[A???Si W9O34]?18H2O(referred to as A???Si W9 for short),Na9[B??? PW9O34]?9H2O(B???PW9),Na10[A???Si W9O34]?23H2O(A???Si W9)and Na12[B???P2W15O56]?24H2O(B???P2W15)were obtained.In the choice of organic bridging ligands,we synthesized three a,w-alkyldiphosphonic acids of different chain lengths: H2O3P(CH2)4PO3H2(referred to as C4),H2O3P(CH2)5PO3H2(C5)and H2O3P(CH2)6PO3H2(C6).The first group of oligomeric molecules,compound 1 and compound 2,designed and synthesized in this work was obtained by reacting the Ni2+ ion,the trivacant polyoxotungstate A - ? - Si W9 with the organic ligands C4 and C6.The structures of the above two compounds were first determined by single crystal Xray diffraction analysis,and then characterized by infrared spectroscopy,elemental analyses and thermogravimetric measurements to confirm that the molecular formula are [{(Ni4O4)4(PO3(CH2)4PO3)2(CO3)2(A???Si W9O34)4})44?(1)and [{(Ni4O4)4(PO3(CH2)6PO3)2(CO3)2(A???Si W9O34)4}]44?(2).The oligomer of a second type,compound 3,was prepared by hydrothermal reactions from Ni2+,lacunary polyoxotungstate A-?-Si W9 and terephthalic acid.Its molecular formula was similarly determined to be [{(Ni4O4)4(PO3(C6H4)PO3)2(CO3)2(A???Si W9O34)4}]44?(3).In this thesis we use different organic phosphonate ligands to systematically design and synthesize three oligomeric structures and then analyze and characterize them.This approach not only led to novel molecular structures but also new synthesis methods.The three oligomers obtained are related in structure design and their molecular length/shape can be regulated by varying linker ligands,laying the foundation for a targeted synthesis of molecular structures in the future,that is,the controlled design and synthesis of molecules.