| This paper mainly studies the synthesis conditions,crystal structure and related properties of lead halide complexes.The experimental process is mainly based on the water bath method and the solvothermal method,and the solution after the reaction can be statically precipitated at room temperature.The synthesized samples were characterized by powder XRD,UV-vis-NIR,infrared analysis,thermogravimetric analysis and fluorescence analysis.The main research contents of this paper are as follows:1 The series of Pb(2,2'-bipy)X2(X=I,Br,Cl,SCN):These four complexes are of the same configuration and they are one-dimensional chain structures.In the UV-visible near-infrared diffuse reflection test,it was found that the boundary absorption wavelength of this series of complexes decreases with the increase of halogen electronegativity,and it also shows the band gaps of the complexes are bigger with bigger electronegativity of halogen,as Pb(2,2'-bipy)I2<Pb(2,2'-bipy)Br2<Pb(2,2'-bipy)(SCN)2<Pb(2,2'-bipy)Cl2.By thermogravimetric analysis,the most stable of the four compounds was Pb(2,2'-bipy)I2(220?).In the fluorescence analysis,the maximum emission wavelengths of the four complexes are the same,but the intensity is largely different.The order of luminescence intensity is Pb(2,2'-bipy)I2?Pb(2,2'-bipy)Br2?Pb(2,2'-bipy)(SCN)2,Pb(2,2'-bipy)Cl2.Pb(2,2'-bipy)I2 has the best luminescence properties,and Pb(2,2'-bipy)(SCN)2,Pb(2,2'-bipy)Cl2 is very weak.It was found by thermogravimetric analysis and fluorescence analysis that Pb(2,2'-bipy)I2 in the four complexes has higher thermal stability and better luminescent properties.2 The series of Pb(1,10-phen)X2?Pb(1,10-phen)2X2(X=I,SCN):The preliminary conclusions obtained in Series 1 are further validated here.By changing ligands,2,2'-bipy is replaced by 1,10-phen with stronger rigidity.There are 4 complexes were synthetized,as Pb(1,10-phen)I2,Pb(1,10-phen)2I2,Pb(1,10-phen)(SCN)2 and Pb(1,10-phen)2(SCN)1.5.The band gap of them were 2.51e V?2.36e V?2.91e V?2.86e V,respectively;the highest stable temperatures of the four complexes were 330?,230?,270?and 230?,respectively;as for the aspect of luminescent properties,luminescent intensity of Pb(1,10-phen)I2 were much higher than Pb(1,10-phen)(SCN)2.The results show that 1,10-phen is better than2,2'-bipy in the aspect of optimizing the thermal stability and luminescent properties of lead halide complexes by the ligand part.In addition,it was found that a ligand 1,10-phen wound separate from the structure of complexes Pb(1,10-phen)2I2 when the temperature is higher than 230?.Then Pb(1,10-phen)2I2 transformed into Pb(1,10-phen)I2.Because both Pb(1,10-phen)I2 and Pb(1,10-phen)2I2 showed different emissive colors,the ratiometric mode was suitable for naked-eye recognition in the practical industrial processes.Heating Pb(1,10-phen)2I2in the range of 230°C-270°C revealed that its emission wavelength would gradually shift from 592 nm to 546 nm,and the higher the temperature,the faster the transfer.When T>330°C,the structure of Pb(1,10-phen)I2 will be further decomposed to cause fluorescence quenching.The method of judging temperature by the colorimetric signal is easy and convenient.And this detection temperature zone belongs to the high temperature zone commonly used in industry,and thus this complex is considered to have potential industrial application value.3 Other lead-complex:Pb X2(DMF)(X=I,Br),Pb2(2,2'-dithbipy)(SCN)2 and Cd(NO3)2(2,2'-bipy)2·2[Pb(NO3)2(2,2'-bipy)].Pb I2(DMF)and Pb Br2(DMF)are isomorphic,both them crystalize in monoclinic P2(1)/n with one-dimensional chain structure.In the structure of them,each long chain is based on a lead halide.The oxygen atoms in the DMF molecule are coordinated with the central element lead on both sides of the long chain.Due to solvent coordination,these two complexes were unstable in the air for a long time and its very easy to decompose into a mixture of lead halide and DMF.The band gaps of Pb I2(DMF)and Pb Br2(DMF)were 2.32 e V and 3.32 e V,respectively,by UV-visible near-infrared diffuse reflection.Pb2(2,2'-dithbipy)(SCN)2 crystalized in orthorhombic space group Pbca(No.61),with a one-dimensional chain structure in space and the crystal is yellow.Its unit cell parameters are:a=11.0277(5)?,b=14.2896(7)?,c=21.5806(10)?.This complex were stable in air,with band gap of 2.84 e V by UV-visible near-infrared diffuse reflection.The highest stable temperature was 230°C by thermogravimetric analysis.Cd(NO3)2(2,2'-bipy)2·2[Pb(NO3)2(2,2'-bipy)]crystalized in monoclinic space group C2/c(No.15).Its unit cell parameters are:a=17.6531(13)?,b=9.5942(7)?,c=29.793(3)?,?=105.619(2)?,Z=8.The complex possesses a bimetallic center,and the lead atoms and the cadmium atoms were connected by a nitrate,wherein the cadmium is an eight-coordinated and the lead is a seven-coordinate,belonging to a multi-metal complex.This complex had a zero-dimensional structure.Intermolecular connections by van der Waals forces.The band gap was 3.56 e V by UV-visible diffuse reflection,and the thermogravimetric analysis showed that the stable maximum temperature was 215°C. |
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