Crystal Structure And Fluorescence Properties Of Coordination Polymers Based On Pyridine Formyl Ligands

Coordination polymers are very promising functional material because of their controllable structure,function and easy cutting.Optical coordination polymers are optical functional materials capable of satisfying various specific structures and specific functions that are urgently needed by the rapid development of today's society.The nitrogen-oxygen heterocyclic ligands have rich coordination nodes based on the coordination advantages of nitrogen and oxygen.Pyridine formyl ligands are nitrogen-oxygen heterocyclic ligands.Using pyridine formyl ligands to construct optical coordination polymers is expected to become a new generation of optical functional materials.Three pyridine formyl ligands were synthesized.The first two ligands were synthesized from 2,6-pyridinedicarboxylic acid by esterification reaction and hydrazine solution reaction.Then condensation reaction with pyridine-2-formaldehyde and 2-acetylpyridine,respectively.Two kinds of picolinyl bis-schiff base ligands were obtained with several coordination nodes.The third ligand synthesized from potassium 2-picolinate as the raw material and modified by introducing substituents at different positions of pyridine through oxidation,acidification,nitration and other reactions.In this paper,crystals were mainly cultured by the ordinary solution method.Self-assembled coordination polymers by selecting appropriate solvents and transition metal ions.Eight coordination polymers were obtained,of which three were grid structures,four of them were one-dimensional chain structures and one was two-dimensional network structure.The crystal data of these coordination polymers have been obtained by X-ray single crystal diffraction analysis and have characterized their basic properties such as infrared and powder XRD.Their thermal stability and optical properties have been studied by thermogravimetry,ultraviolet spectrum and fluorescence spectrum.The chemical formulas of the eight crystals synthesized list as follows:[Cd₆?L1?₂?Ac?₈?H₂O?₆]·4H₂O?1?{[Zn_1.5?L1?_0.5]·2Ac}_n?2?[Cd₉?L2?₆]?NO₃?₆·2DMF?3?[Zn₉?L2?₆]?NO₃?₆?4?[Zn?L3?₂]_n?5?[Mn?L3?₂]_n?6?[Cd?L3?₂?H₂O?]_n?7?{[Pb₂?L3?₄?H₂O?]·H₂O}_n?8?In these chemical formulas,L1 = deprotonation N,N'-bis?pyridine-2'-ylmethylene?pyridine-2,6-dicarbohydrazide;L2 = deprotonation N,N'-bis?2'-acetylpyridine?-2,6-pyridine dicarbohydrazide;L3 = deprotonation 2-carboxylic acid-4-nitropyridine-1-oxide.X-ray single crystal diffraction analysis of the above crystals shows that crystal 1is a 2×2 “?” structure in Chinese,triclinic system,and P??? space group.The ligand is bridged with cadmium through the coordination modes of ?-N-N and ?-O.The cadmium ion adopts N₂O₅ and N₃O₄ configurations to form a distorted pentagonal double cone configuration,connecting two adjacent molecules into a one-dimensional chain structure through hydrogen bonds and extending adjacent one-dimensional molecular chains into a three-dimensional supramolecular structure through ?-? stack.Crystal 2 is a one-dimensional wheatlike chain structure,its structural unit is 2×2“ ? ” structure in Chinese,monoclinic system,C2/c space group.Acetate ions are bridged with zinc ions through the coordination mode of ?-O.Zinc ion adopts N₃O₂ and N₂O₃ configuration to form a distorted tetragonal coordination configuration.There are ?-? stacking between molecules,which expands adjacent one-dimensional molecular chains into three-dimensional supramolecular structures.Crystals 3 and 4 are 3×3 “?” structures in Chinese.Crystal 3 belongs to the triclinic system,P??? space group.Crystal 4 belongs to the monoclinic system and the P2₁/c space group.The ligands are bridged to the metal ions through the coordination mode of ?-O.The metal ions adopt three configurations,namely N₄O₂,N₃O₃ and N₂O₄ configurations,all of which form a distorted octahedral configuration.There are a large number of hydrogen bonds in crystal 3 and three-dimensional supramolecular structures are formed between adjacent molecules through hydrogen bonds.Crystals 5 and 6 are all one-dimensional “ladder” structures,all of which belong to the monoclinic system,P2₁/c space group.The ligand is connected to the metal ion through a coordination mode of ?₂-?¹: ?².The metal ions adopt the MO₆ configuration to form an octahedron.Two adjacent One-dimensional chain forms a three-dimensional supramolecular structure through hydrogen bonds.Crystal 7 is a one-dimensional “butterfly” chain structure,monoclinic system,P2₁/c space group.The ligand is linked to the cadmium ion through a coordination mode of ?₂-?²: ?¹.The cadmium ion adopts the CdO₇ configuration to form a twisted pentagonal double cone configuration.Two adjacent one-dimensional chain forms a three-dimensional supramolecular structure through hydrogen bonds.Crystal 8 is a two-dimensional network structure,which belongs to the monoclinic system,P2₁/c space group.It is connected by the coordination mode of?₄-?²: ?²,?₃-?¹: ?² and ?2 and adopts the PbO₆ coordination configuration to form a quadrangular double cone configuration,three-dimensional supramolecular structure formed by intermolecular hydrogen bonds between two adjacent molecules.The thermal stability and fluorescence properties of eight crystals have been studied.Thermogravimetric analysis shows that the weight loss of eight coordination polymers corresponds to its structure and the thermal stability is good.The fluorescence spectrum shows that the coordination polymers have all undergone a certain degree of red shift.