Syntheses,characterizations And Properties Of Lanthanide Coordination Polymers Based On Symmetric Tetracarboxylic Acid Ligands

Coordination polymers(CPs)are a kind of high molecular crystal material with periodic and high order,connected by suitable ligand bonds and other weak bonds,formed by metal ions or metal clusters with organic ligands,some of which with a 3D network also known as metal-organic frameworks(MOFs).As a new family of materials with various skeleton structures and rich porosity,CPs show potential applications in gas separation and storage,catalysis,sensing and luminescence.Recently,Ln-CPs have attracted persistent attention for their unique properties.However,the directional design and synthesis of Ln-CPs with excellent optical properties still remain great challenges.As well known,it is crucial to select proper organic ligands for the construction of multifunctional CPs.Aromatic polycarboxylic acid ligands are increasingly used in the synthesis of Ln-CPs.For one thing,polydentate ligands can provide more coordination sites;for another,lanthanide ions are easy to coordinate with O-donor groups,which lead to numerous carboxylic acid coordination polymers.Ln-CPs based on the two symmetrical four carboxylic acid ligand,3,5-bis-(3,5-dicarboxyl phenyl)-pyridine and 3,3′,5,5′-(1,3-diphenyl)tetracarboxylic acid are seldom reported.The above ligands have similar structures,with four sites distribution,high degree of symmetry and large space ductility.It is potential to use the two ligands building LnCPs with unique structures and good performances.Therefore,in this paper,we select trivalent lanthanide ions as the metal centers,3,5-bis-(3,5-dicarboxyl phenyl)-pyridine(H4DPP)and 3,3′,5,5′-(1,3-diphenyl)tetracarboxylic acid(H4DPB)as organic ligands.Four series of Ln-CPs were synthesized by solvothermal method.Their adsorption properties,optical properties and chemical sensing properties were further studied.The main research results include the following aspects:1.By using H4 DPP ligand and Ln(NO3)3,five new isomorphic Ln-CPs,{(Me2NH2+)[Ln(DPP)(H2O)2]}n(1–5)[Ln=Eu(1),Tb(2),Gd(3),Sm(4),Pr(5)] were solvothermally prepared.In 1,Eu O7(H2O)2 tricaped trigonal prism connect with ligand DPP4-,forming an 2D bilayer structure in the direction of the a axis,which can be simplified as(4,4)-connected hexagonal honeycomb structure.Its Sch?fli symbol is {43·63},calculated by TOPOS 4.0.Solid state luminescent studies illustrate that 1,2 and 4 exhibit the characteristic emission of the corresponding Ln3+ ions,while 3 reveals blue emission arising from the organic ligand and 5 shows characteristic luminescence emission bands of Pr3+ ions in near-infrared region(NIR).Notably,1 exhibits good luminescent sensing for metal ions,such as Cr2O72-ions,Mn O4-ions,Fe3+ ions,and small organic molecules,including acetone and trinitrophenol(TNP).2.By using H4 DPB ligand and Ln(NO3)3,12 isomorphic Ln-CPs were solvothermally prepared,namely {[Ln(HDPB)(H2O)2]·(H2O)2}n [Ln = Eu(6),Tb(7),Gd(8),Sm(9),Dy(10),Nd(11),Pr(12),Er(13),Y(14),La(15),Yb3+(16),Ho3+(17)].In 6,Eu O7(H2O)2 tricapped trigonal prism forms a dimer Eu2O12(H2O)4.This dimer is connected by HDPB3-ligand to form(3,6)-connected 2D bilayered structure.Its Sch?fli symbol is {415·66} calculated by TOPOS 4.0.6 exhibits good thermal stability and acid and alkaline resistance.Compounds 6-17 show a variety of energy transition forms in ultraviolet visible region and near-infrared region.6 shows the characteristic red emission peaks of Eu3+,7 shows the characteristic green emission peaks of Tb3+.Compounds 10-13,16 and 17 have strong luminescence in the near-infrared region.By adjusting the doping ratio of Tb/Eu/Gd,white light and tunable light emitting materials were successfully synthesized.In addition,compounds 6 and 7 show good sensing properties for p H,small organic molecules,metal ions,anions and nitro explosives.3.By using H4 DPB and Ln(NO3)3,3D Ln-CPs {[Ln(DPB)(H2O)](Me2NH2+)}n [Ln = Eu(18),Tb(19),Gd(20),Sm(21),Nd(22),Yb(23),Pr(24)and Ho(25)] were solvothermally prepared.In compound 19,two adjacent Tb O7(H2O)dicapped trigonal prism form a Tb2O14(H2O)2 dimer.The adjacent Tb2O14(H2O)2 dimer is linked by L4-,forming a(4,8)-connected three-dimensional network structure.Subsequently,With 1,10-phenanthroline hydrate(phen)as second ligand,we successfully synthesized [Ln(HDPB)(phen)]n [Ln = Eu(26),Tb(27),Pr(28)and Ho(29)].In compound 27,the adjacent Tb O6N2 dicapped trigonal prism form a Tb2O12N4 dimer,which is connected by the ligand HL3-to form a(3,6)-connected 3D shubnikov net.Stability study for 18,showed that the skeleton can resist acid,alkali and high temperature.The solid state fluorescence spectra of CPs 18-29 were studied.18 can detect Fe3+ ions and p-nitrophenol(PNP)effectively.Meanwhile,18 is an anionic framework,which can selectively adsorb the cationic dye methylene blue.After 5 cycles of adsorption and desorption,the crystal structure remains intact.With the introduction of the large chromophore 1,10-phenanthroline ligand,the blue light emission of 27 significantly enhanced.By modulating the excitation wavelength,27 can generate tunable light emission from yellow-green to blue.