Synthesis, Structures And Properties Of Coordination Complexes With Pyridine Carboxylic Acid

Carboxylic acid ligands are classical both in inorganic chemistry and biochemistry. They have the characteristics of symmetry and variety. They are the biological active substances in biological bodies. Their complexes are broadly researched and applied in the following fields, including solid chemistry, structure, magnetism, spectrum kinetics, reaction mechanism, the reaction of ligands and analytical chemistry. There are many reports about complexes with pyridine dicarboxylic acid, and the research on pyridine tricarboxylic acid is just spring up in the recent years. However, there is no study in pyridine tetracaboxylic acid now. Because of the advantages of pyridine carboxylic acid ligands, there will be a wide space in researching of the complexes with tetracarboxylic acid.In this studies potassium pyridine-2,3,5,6-tetracarborxylate has been synthesized and characterized. Seven complexes and two ligands have been synthesized, K₃Cu₂H(PTA)₂·12H₂O (I) , K₂Zn₃(PTA)₂·12H₂O (II) , Mn₂H₂(PTA)2·8H₂O(III) (H₄PTA= 2,3,5,6-pyridine tetracarboxylic acid), and complexes with nickel(II) and cobalt(II) ions, (PATE), [NiL(H₂O)₃]·1.5H₂O (IV) (H₂L=4-hydroxy-pyridine-2,6- dicarboxylic acid), [FeLL' (H₂O)₂]·2.5H₂O (V) (H2L=4-hydroxy-pyridine-2,6- dicarboxylic acid(CAM), H2L'=4-hydroxy-pyridine-2,5-dicarboxylic acid), (CAM), characterized by IR spectrum, thermogravimetric (TG) analysis and single-crystal X-ray diffraction.The dramatic changes occurred under hydrothermal condition, where the carboxylate group in C6 position of 4-hydroxy-pyridine-2,6-dicarboxylic acid was transferred to C5 position to form 4-hydroxy-pyridine-2,5-dicarboxylic acid.Compound (I), (II) and (III) crystallize in the triclinic space group P-1. The structure of complex (I) is analyzed compared with 1,2,4,5- benzenetetracarboxylic acid. The different coordination modes of the carboxylate groups were displayed in coordinating with metal ions under different pH value. It resulted in diverse three dimensional structures of coordination complexes. The potassium ion played an inducement role in the molecular self-assembly.The complex (II) shows feeblish photoluminescence properties.