Construction And Fluorescence Properties Of Coordination Polymers Based On Novel Biphenyl Carboxylic Acid/Pyrazole Ligands

Coordination polymers(CPs),are a class of crystalline materials formed through the self-assembly between metal ions and organic ligands,which has been widely explored in many material fields because of its inherent advantages of ordered and designable structures Porous CPs was also known as metal-organic frameworks(MOFs).CPs that possess excellent gas adsorption,fluorescence,magnet and catalytic properties,have been widely designed and synthesized by researchers.However,the self-assembly process of CPs is a very complicated process,many factors,such as organic ligand size,the type and spatial structure will play a decisive role in the construction of target functional complexes.The aromatic carboxylic acid organic ligand has several coordination sites,in which the carboxyl oxygen atoms can give rise to a variety of coordination modes,such as bridging,monodentate and chelating Meanwhile,the carboxylic acids can also provide hydrogen bonds as donors or receptors under different conditions,thus changing the entire structure of complexes,and providing a lot of choices for the design and synthesis of functional complexes.In contrast,pyrazole(Hpz)ligand has a simpler coordination mode,it is most typical that one pyrazole adopts two N atoms in a bridging manner to bind two metal ions,which makes it easier to construct CPs with a desired topology.Therefore,there are unique characters for the coordination modes of the ligands containing carboxyl and pyrazole,and these types of ligands have attracted the intensive attention of researchers in CP constructions.Based on the above consideration,5-(2-nitro-4-carboxyphenyl)isophthalic acid(H3L)ligand and 3,5-diethyl-4-(4-pyridyl)-pyrazole(Hdeppz)ligand were selected as organic linkers for CP constructions.According to the principle of self-assembly of crystal engineering,eight CPs were successfully synthesized by solvothermal method{[Ln2(L)2(DMF)2(H20)4]·H2O·DMF}n(Ln=Dy(1),Eu(2),Tb(3),Nd(4)),{[Ba3(L)2(DMF)(H20)5]·H2O}n(5),{[Ca3(L)2(DMF)2(H20)2]?2DMF·H2O}n(6),[Cd(Hdeppz)2(Cl)2]n(7),and[Cu4ICuII(Deppz)4(Cl)2]n(8).The crystal structure was determined by X-ray single crystal diffraction,and the fluorescence and sensing properties were studied focusedly.Complexes 1-4 are a series of lanthanide CPs(Ln-CPs),which have the similar 3,6-connected scu-3,6-Pbcn topological structures and exhibit fluorescence properties.In particular,complex 2 shows a highly sensitive quenching effect on nitrobenzene molecules,which can be used as a fluorescent probe to identify nitrobenzene from other organic small molecules.Complexes 5 and 6 are two alkali-earth metal-based frameworks,which contain the infinite metal-carboxylate two-fold helix chain building units.The two CPs possess different three-dimensional(3D)framewoks because of the influence of different metal ion radii.Complexes 5 and 6 show strong fluorescence properties,Inparticular,complex 6 shows a good quenching effect on Cr2O7-anions.In complexes 7 and 8,the difference of coordination habits between Cd2+ and Cu2+ ions and the different linear and Y-type coordination modes of Hdeppz lead to different structures between them.Complex 8 contains a rare-(Cu?Cl2Cu?4)n-supramolecular chain with the mixed valence states of Cu+ and Cu2+ions.Under the influence of coordination effect,both 7 and 8 show higher thermal stability and stronger fluorescence than free Hdeppz ligands.In this paper,the synthesized complexes were characterized by powder X-ray diffraction(PXRD),Infra-red spectrum(IR)and thermogravimetricanalysis(TGA),and their fluorescence and sensing properties were studied according to the different structures and metal ions of complexes.