Syntheses,Structures And Luminescent Properties Of Coordination Polymers Based On The Azolate–carboxylic Acid

Coordination polymers(CPs)have attracted much attention as a new type of material which show the potential applications in many aspects.For example,gas storage and separation,molecular sensing,medical applications,heterogeneous catalysis,magnetic,optical and membrane separation and so on.Luminescence and sensing properties are of great importance.Lanthanide coordination polymers(Ln CPs)have special spectral properties,including long fluorescence lifetime,large Stokes shift,narrow characteristic peaks and high color purity.Based on Eu(III)and Tb(III)ions can respectively emit red and green color in the visible region with excellent luminescent properties,by selecting the appropriate organic ligands and using the "antenna effect",energy transfer is realized from the ligands to Ln(III)ions and sensitized luminescence of Ln(III)ions.Consequently,white light emission can be achieved.Except directly synthesizing Ln CPs,by post-synthetic modification,different Ln(III)ions are encapsulated in transition or main group metal coordination polymers so tunable luminescence and white light emission can also be realized.In addition,fluorescence sensing based on luminescent CPs also exibits good prospects because of its advantages such as fast response time,high sensitivity,good reproducibility and low cost.However,it is still a challenging task to design and synthesize CPs with novel structure and excellent properties.We construct CPs by using azolate–carboxylic acid ligands containing N-and O-electron donors.The ligands have π-π conjugated system with luminescent rigid skeleton as well as carboxyl and azole groups providing the connection sites.Under hydrothermal conditions,we select 5-(1H-tetrazol-5-yl)isophthalic acid(H3TZI),1-(triazol-1-yl)-2,4,6-benzene tricarboxylic acid(H3TZBT)and 3,5-bis(3’,5’-dicarboxylphenyl)-1H-1,2,4-triazole(H4L)ligands reacting with different metal ions to construct CPs.Their fluorescence and sensing properties were also studied.The research results of this paper include the following aspects:1.By using H3 TZI ligand and Ln(NO3)3,five isostructured CPs were prepared [Ln(TZI)(H2O)5]n(1-5)(Ln = Nd 1,Eu 2,Gd 3,Tb 4,Sm 5),exbiting 1D double chain.At the same time,a series of doped compounds 6-12 were synthesized by adjusting the ratio of Ln(III)ions,and the fluorescent properties of these compounds were studied.2.Compounds 2 and 4 emit red and green light,respectively.Based on the red,green and blue three primary colors can be doped to obtain white light,taking into account compound 3 emits blue-green light,it can be used as the parent skeleton doped with Eu(III)ion.By adjusting the ratio of Gd(III)/Eu(III)ions in the reactants,white light emitting material [Eu0.10Gd0.90(TZI)(H2O)5]n 6 was successfully obtained.In addition,the different ratio of Eu(III)/Tb(III)ions can also be doped into the Gd(III)framework,white light materials([Eu0.25Gd0.70Tb0.05(TZI)(H2O)5]n 8,[Eu0.20Gd0.70Tb0.10(TZI)(H2O)5]n 9,[Eu0.25Gd0.60Tb0.15(TZI)(H2O)5]n 10,[Eu0.20Gd0.55Tb0.25(TZI)(H2O)5]n 11 and [Eu0.25Gd0.50Tb0.25(TZI)(H2O)5]n 12)were also achieved by selecting the appropriate excitation wavelength.[Eu0.15Gd0.70Tb0.15(TZI)(H2O)5]n 7 emitted tunable colors from yellow to blue and white light emission.3.By using H3 TZI ligand and the main group or transition metal ions Pb(II)/Zn(II),three different CPs were synthesized,[Pb2(TZI)(μ3-OH)(H2O)·(H2O)]n 13,[Pb(HTZI)(phen)·(H2O)]n 14 and [Zn2(TZI)(μ3-OH)(H2O)2·(1/2H2O)]n 15.The coordination modes of H3 TZI ligand in 13-15 were first reported.Fluorescence properties were well studied.Compound 13 has stability and suitable channels which can encapsulate Ln(III)ions in different ratios,thus tunable colors and white light emission were achieved.In addition,13 can be used as a potential CHCl3 small molecule fluorescent probe.4.By using H3 TZBT ligand and Zn(II)ions without adding and adding phen auxiliary ligands,two new CPs were prepared,[Zn2(TZBT)(trz)·3.5H2O]n 16 and [Zn2(TZBT)(phen)(μ2-OH)·4H2O]n 17.These two compounds have good stability and suitable pores which can encapsulate Ln(III)ions.By adjusting the ratio of Ln(III)ions and selecting the appropriate excitation wavelength,the tunable light and white light emission can be realized.In addition,the two compounds have an intensive sensitization of Tb(III)ion than other Ln(III)ions(Eu3+,Dy3+ and Sm3+),which can be used as a potential Tb(III)ion fluorescent probe.Compounds 16 and 17 could be used for the detection of acetone molecules.The transition metal CP sensors are very convenient because they must not be evacuated to remove coordinated solvent molecules before utilization,which are different from Ln CP sensors.Therefore,utilizing ligand based luminescence is a strategy to construct CP sensors for direct use.5.By using H4 L ligand and d10-metal ions Zn(II)/Cd(II),two new CPs were synthesized,[Zn(H2L)(H2O)2·H2O]n 18 and [Cd(H2L)(H2O)2·H2O]n 19.In the compounds,H4 L ligand is not completely deprotonated,forming H2L2-ligand.Each H2L2-ligand bridged three different metal ions by carboxylate oxygen atoms,forming a two-dimensional layered structure.The adjacent 2D layers are extended to 3D supramolecular structure through hydrogen bonding interactions.The solid fluorescence emission spectra showed that compounds 18-19 have good fluorescence properties and the luminescence mechanism is probably the intermolecular energy transfer.