Synthesis, Structure And Characterization Of Dicarboxylic Acid Lanthanide Coordination Polymer

Organic carboxylic acids possess the hard-base oxygen atoms that are affinitive toward rare earth metal ions and so are commonly used for synthesis of rare earth metal complexes. Pyrazine-2,3-dicarboxylic and pyridine-2,3-dicarboxylic acids, like benzen-1,2-dicarboxylic acid, have flexible coordination and so can be applied for construction of diverse structured and functionalised coordination polymers of rare earth metals. The dissertation, in the principles of molecule design and self-assembly of supramolecular chemistry and by hydrothermal reactions using azohetero aromatic bicarboxylic acids as main ligands, obtained a series of coordination polymers, which have been characterized by microanalysis, X-ray single crystal and powder diffractions, IR, and so on. Some of the polymers, showing fine photoluminescence have also been investigated in purpose of providing more evidences to the studies on such a kind of compounds.With coordination of 2,2'-bipyridine-3,3'-dicarboxylic acid as main ligand to La and Nd,two 2D coordination polymers, {[Ln2(bpdc)3(H2O)2]·4.5H2O}n ( Ln=La , Nd ) were synthesized. Furthermore, by adding different second ligands to these reactions, six more products with mix ligands ({[Nd2(bpdc)3(H2O)2]·2H2O·(bpy)}n,[Ln(bpdc)(Ho-phic)]n ( Ln=La , Nd ),{[Ln(bpdc)(Ho-phic)]·2H2O}n(Ln=Eu,Tb),{[La(bpdc)(adi)0.5(H2O)2]·3 H2O }n) were isolated. Structures of these complexes reveal that rare earth metal ions are coordinated by oxygen of bpdc only, leaving nitrogen atoms free. This offers an evidence supportive to Lewis acid-base theory. More than that, from the isolated compounds, it is seen that the metal ions are all nine coordinated, except for 8. Under the given conditions, bpdc exhibits three coordination modes, two of which lead to one-dimensional (1D) chain and the remaining one leads to 2D network. If add phthalic acid as second ligand to reaction, owing to the closeness of two carboxylates which lead to chelation and hindrance, the polymers are usually 1D structured. Besides, we found also that coordination mode of ligand is influence by many other factors, for examples, presence of auxiliary ligand, nature of metal ion, and reaction conditions, such as temperature, stoichiometry, pH value, etc.. Pyrazine-2,3-dicarboxylic acid (pzdc), like 2,2'-bipyridine-3,3'-dicarboxylic acid, belongs to azo-containing aromatic ligand, but structurally it is more rigid. This part describe the use of pzdc as main ligand to obtain complexes of neodymium ({[Nd2(pzdc)3(H2O)]·2H2O}n and{[Nd2(pzdc)3(H2O)7]·1.5H2O}n). The effort revealed a diversity of polydentate coordination modes of pzdc and meanwhile found that coordination of pzdc with rare earth metal present higher coordination numbers and more complicated modes than coordination to transition metal ion. With increase of coordination number and complication of coordination mode of pzdc, the complexes show more complex structures. After that, we introduced flexible ligand, hexanoic acid-into the reactions, therewith obtaining a porous coordination polymer, {[La(pzdc)(adi)0.5(H2O)]·2H2O}n. It implicates that introduction of flexible aliphatic acid as second ligand into the reaction, when condition is suitable, can form structurally regular porous coordination frameworks.With consideration of the free coordination of nitrogen atoms of dicarboxylic acids in the synthesized rare earth metal complexes and selectivity of metal ions, we added transition metal ions, combined with rare earth metal, into the reactions and so were afforded four coordination polymers, [LnNi(bpdc)3(H2O)4]n(Ln=La,Nd)and {[Ln2Ni2(bpdc)5(H2O)7]·5H2O}n(Ln=La,Nd). These 3D metal-organic frameworks show an assembly from 1D and 2D structures. What is more, the endeavour obtained also two groups of complexes of 3d-4f with combination uses of rigid pydc with flexible butanoic and hexanoic acids. The resultant coordination polymers are highly porous, possessing the accessible voids up to 28.2 and 41.8% respectively. On basis of the observation, it is predictable that fabrication of MOF with various pore sizes is possible through adjusting the lengths of ligands.