Structure Construction And Luminescence Properties Of Lanthanide Coordination Polymers Containing Aromatic Carboxylic Acid Ligands

In this work,we have mainly studied the syntheses,crystal structures and the luminescent properties of lanthanide coordination polymers.According to the luminescent characteristic of Ln³⁺ ions,we select different carboxyl groups ligands as main subjects,phenanthroline and oxalate as second ligands,and synthesize 24 lanthanide coordination polymers from dinuclear,one–dimensional chain,two–dimensional layer to three–dimensional framework under hydro?solvo?thermally conditions.X–ray single crystal diffraction,IR spectrum,elemental analyses and powder X–ray diffraction are used to characterize the crystal structures of these coordination polymers.Their performances have been measured by solid luminescent analyses,decay lifetimes,and energy transfer process.The influence of organic aromatic carboxylic acid ligands on the crystal structures has been analyzed;also the relationship between energy level of ligands and luminescent properties has been investigated.Two series nine lanthanide coordination polymers formulated as {[KEu?Hqlc??qlc??H₂O?6?OH?]²⁺·2Cl^-}n?1?,{[Eu?qlc?₂?phen??H₂O?₂]+·Cl^-}·CH3CN?2?,[Eu?qlc?₂?phen??NO3?]·H₂O?3?,[Ln?qlc?₂?H₂O?₄]·?qlc?·?H₂O??Ln = Eu?4?,Sm?5?,Gd?6?,Tb?7?,Dy?8?,Ho?9??have been synthesized under solvothermal conditions using quinoline–3–carboxylic acid?Hqlc?and 1,10–phenanthroline?phen?.Coordination polymer 1 exhibits two–dimensional hcb network connected by K atom.Coordination polymers 2–4 display three diverse dimer structures,due to the synergistic effect of coordination modes of Hqlc ligand and anion.These crystal structures are stabilized by hydrogen bonds and ?–? interactions,to form supramolecular net.We calculated the electron energy level of Hqlc ligand,indicating that the energy may transfer from qlc– to phen ligand and then sensitize coordination polymers 2 and 3.Moreover,the luminescent lifetime of 4 is increased from 283.70 ?s to 792.33 ?s after doped with PMMA.Therefore,the PMMA doping with the luminescent lanthanide complexes may be of potential application as light–emitting materials.In the following research,a rare two–dimensional CdCl2 type structure formulated as {[Tb₃?babi???3–OH?₇]·H₂O}n?10?was synthesized by precise pH value tuning,in which N,N?–bis?ethylacetate?biimidazole ligand occurred ester hydrolysis to produce N,N?–bis?ethylacetate?biimidazole?H₂babi?.–CH₂– group of H₂ babi could rotate to satisfy the coordination orientation of carboxylate group to ease the steric hindrance.Coordination polymer 10 is doped with PMMA matrix,which displays excellent luminescent properties with enhanced luminescent intensities,long lifetimes and thermal stability.Moreover,the VT–luminescence investigations confirm that 10@PMMA can be a kind of stable green luminescence material below 270 oC.The introduction of semi–rigid V–shaped 3–?2?,3?–dicarboxylphenoxy?benzonic acid?H3dpob?as main ligand,phenanthroline and oxalate as auxiliary ligands,nine lanthanide coordination polymers from one-dimensional to three-dimensional were hydrothermally synthesized.The empirical formulas are as follow: {[Eu?dpob??phen?]·H₂O}n?11?,{[Ln?Hdpob??ox?0.5?H₂O?₂]}n?Ln = Eu?12?,Sm?13?,Gd?14?,Tb?15??,{[Eu?dpob??H₂O?₂]·0.5H₂O}n?16?,{[Ln?dpob??H₂O?₂]·mH₂O}n?Ln = Eu?17?,Gd?18?,Tb?19?,m = 0.5 for 17 and 19;m = 1 for 18?.The topological structures were induced by concentration effect to realize converting from two-dimensional kgd to three-dimensional rtl type.Based on RGB primary principle,a long lifetime?1298.45 ?s?mixed lanthanide coordination polymer {[Gd0.92Eu0.04Tb0.04?dpob??H₂O?₂]·0.5H₂O}n was prepared with careful adjustment of the relative concentration of the lanthanide ions,which has white-light emitting by varying excitation wavelength and CIE coordinate is?0.33,0.34?.The introduction of 4–?3?,5?-dicarboxylphenoxy?phthalic acid?H4dcppa?containing four carboxyl groups in the reaction system leads to form five new three-dimensional lanthanide coordination polymers formulated as {[Eu?Hdcppa??H₂O?₂]·H₂O}n?20?,[Eu1.5?dcppa??HCOO?0.5?H₂O?₂]n?21?,{[Ln2K2?dcppa?₂?H₂O?6]·5H₂O}n?Ln = Eu?22?,Tb?23?,Gd?24??.Coordination polymers 20 and 21 display “Chinese knots” and “dragon boats” like 3D networks,respectively.Coordination polymer 22 exhibits 1D channels?1.664 × 0.836 nm?and open Lewis basic oxygen atoms on the pore surface,which can serve as the luminescent probe for Fe³⁺ and Cu²⁺ with fast response time?8 min?and high sensitivity?Ksv = 4.3/5.2 × 104 L/mol?among 15 kinds of metal ions.The interaction between Fe³⁺ or Cu²⁺ and oxygen atoms changes the electron energy level of H4 dcppa ligand and results the inefficient energy transfer between ligand and Eu³⁺,leading to immediate photoluminescence quenching.The energy transfer mechanism of lanthanide coordination polymers is also studied.The energy can transfer from qlc– to phen ligand and sensitize luminescence of Eu³⁺ ions;Semi rigid V-type 3–?2?,3?-dicarboxylphenoxy?benzonic acid can be partially sensitized luminescence of lanthanide ions(Eu³⁺,Sm³⁺ > Tb_<sup>3+);semi-rigid V-type 4–?3?,5?-dicarboxylphenoxy?phthalic acid can effectively transfer energy to Eu³⁺ and Tb_<sup>3+ ions.The number of ligands containing in the lanthanide coordination polymers are increased with the increasing the number of carboxylic groups.The ligands could tightly wrap the metal centre and shield the energy loss caused by non radiative transitions.There are strong electrons donating group in H3 dpob and H4 dcppa ligands,which benefit for energy transfer process caused by the increase of density of electron.