Investigation Of Synthesis, Structure And Properties Of Organic Multi-Carboxylate Ligands Based Coordination Polymers

Coordination polymers represent a new class of hybrid organic-inorganic surpramolecular materials comprised of ordered networks formed from organic bridging ligands and inorganic metal cations. A large amount of coordination polymers have been generated and show the characteristics of high surface area, high porosity and easily tunable pore size which make them great potential applications in the areas of gas storage, separation and catalysis along with optics, electrics, magnetism. A large number of coordination polymers with novel structures have been designed and synthesized according to the crystal engineering approaches.In the present works, two kinds of coordination polymers with highly exposed mental cations were presented, we have selected aluminum or boron of sp3hybridization as the node,aromatic carboxylic acid or heterocyclic carboxylic acid as the organic ligand, constructed sixteen polymer materials in the form of one dimensional or multidimensional networks. Elemental analysis,1H NMR, XRD, TGA, SEM,TEM and BET were used for structural characterization of the product, in addition, N2and O2adsorption properties, the electrochemical properties (lithium ion conductivity, electrochemical stability window and ion transference number) of some compounds were studied preliminarily. The main research content is as follows:(1) We adopted benzene-1,4-dicarboxylic acid, benzene-1,3,5-tricarboxylic acid, benzene-1,2,4,5-tetracarboxylic acid and biphenyl-4,4’-dicarboxylic acid as the organic ligands, NaAl(OCH3)4and LiAl(OCH3)4as connected nodes and metal ion source, and constructed eight coordination polymers with novel structure, including [NaAl(BDC)2]n,[NaAl(BTC)2]n,[NaAl(PMA)2]n,[NaAl(BPDC)2]n (compound1-4) and [LiAl(BDC)2]n,[LiAl(BTC)2]n,[LiAl(PMA)2]n,[LiAl(BPDC)2]n (compound5-8). Each sp3aluminum is covalently bonded to four oxygen atoms that are associated with electron withdrawing groups via aromatic n-conjugation in the polymer backbones. This structural style allows the ionized charges from sodium atoms to be redistributed to the aromatic rings, leading to the enhanced mobility of sodium ions in the framework. Compound1-4has the similar thermal stability,microstructure and morphology with compound5-8respectively. By TGA test, the results showed that the eight coordination polymers all have good thermal stability, the decomposition temperature are all above400℃. The eight compounds all have a certain pore structure, wherein the compound1and compound5have an obvious microporous structure. Specific surface areas of compound5-8are higher than that of compound1-4and one of the highest is compound5which comes to284m2/g because the highly exposed lithium ion in the structure is more conducive to the adsorption of nitrogen compared to the sodium ion.N2and O2adsorption experiment of eight compounds were carried out under the pressure range of0-1.9MPa and the temperature of25℃,adsorption quantity of N2and O2are all on the rise with the increase of pressure. Within the scope of pressure, N2adsorption quantity of compound3and compound7are less than O2,and N2adsorption quantity of other six compounds are higher than that of O2which show some selective adsorption performance.Compound1and compound5present a relatively high adsorption capacity on the account of microrporous structure, N2and O2adsorption of compound1are1.08wt%and0.46wt%respectively at1.9MPa and compound5reach1.39wt%and0.72wt%respectively. At the same time, single ion polymer electrolyte membranes have been successfully prepared from compound5-8and PVDF-HFP by means of solvent thermal method, and their electrochemical performances have also been compared. Electrochemical performance test show that ion conductivity of four electrolytes all has an obvious increase when the temperature rises. The ionic conductivity of compound5are1.50×10-5S/cm and7.61×10-5S/cm respectively at20℃and70℃. The other three compounds are at the level of10-6s/cm at20℃and10-5S/cm at70℃. Electrochemical stability test show that the electrochemical stability of compound5and compound6are all above4.5v and meet the requirements of lithium ion electrolyte. Ion transference number of compound5is0.79,which is in line with the characteristics of a single ion polymer electrolyte. Adsorptive and electrochemical performance tests show that benzene-1,4-dicarboxylic acid should be the most suitable ligand for the network structure of the four ligands.(2) we adopted2,5-Pyridinedicarboxylic acid,2,6-Pyridinedi carboxylic acid, Thiophene-2,5-dicarboxylic acid and2,2’-Bipyridy1-4,4’-dicarboxylic acid as the organic ligands, LiAl(OCH3)4as connected node and lithium ion source, composited four coordination polymers with novel structure, including LiAl(2,5-PDC)2]n,[LiAl(2,6-PDC)2]n. LiAI(2,5-TDC)2]n and [LiAl(2,2’-4,4’-BPrDC)2]n(compound9-12) respectively. By TGA test, the results show that the four coordination polymers all have good thermal stability, the decomposition temperature are all above300℃,meeting the requirements of a polymer electrolyte. BET test show that compound9-12all have a small specific surface area,one of the highest is compound12which only comes to117m2/g. N2and O2adsorption at room temperature are all in a low level. Single ion polymer electrolyte membranes have been successfully prepared from compound9-12and PVDF-HFP by means of solvent thermal method. Electrochemical performance test show that ion conductivity of four electrolytes also has an obvious increase when the temperature rises. The ionic conductivity of compound9and compound10are1.21×10-5S/cm and4.80×10-5S/cm respectively at20℃,5.45×10-5S/cm and2.46×10-4S/cm respectively at70℃. Electrochemical stability test show that the electrochemical stability of four compounds are all above4.5v and meet the requirements of lithium ion electrolyte. Ion transference number of compound10is0.90,which is in line with the characteristics of a single ion polymer electrolyte.(3) Another four coordination polymers were synthesized from the same four heterocyclic carboxylic acid ligands, including LiB(2,5-PDC)2]n,[LiB(2,6-PDC)2]n, LiB(2,5-TDC)2]n and [LiB(2,2’-4,4’-BPrDC)2]n(compound13-16). LiB(OCH3)4provide connected nodes and lithium ion source, built a polymer framework similar to LiBOB in which each sp3boron atom is covalently bonded to four oxygen atoms. By TGA test, the results show that the four coordination polymers have good thermal stability and the decomposition temperature are all above300℃, meeting the requirements of a polymer electrolyte. Single ion polymer electrolyte membranes have been successfully prepared from compound13-16and PVDF-HFP by means of solvent thermal method. Electrochemical performance test show that ion conductivity of four electrolytes also has an obvious increase when the temperature rises.The ionic conductivity of compound13and compound14is1.41×10-5S/cm and6.98×10-5S/cm respectively at20℃,1.22×10-4S/cm and6.39×10-4S/cm respectively at70℃. Electrochemical stability test show that the electrochemical stability of four compounds are all above4.0v,of which compound14reaches5.3v and meets the requirements of lithium ion electrolyte. Ion transference number of compound14is0.92,which is in line with the characteristics of a single ion polymer electrolyte.