Ln/Cd Metal-organic Luminescent Materials Based On Nitrogen Containing Heterocyclic Ring Carboxylic Acid Ligands

Because lanthanide compounds possess the excellent spectral properties and the transition metal Cd2+ ions with a 3d10 electronic configuration also can have good luminescent properties through energy transfer between organic ligands and Cd2+cation,in our work,nine types of Ln/Cd metal-organic luminescent materials have been prepared from nitrogen containing heterocyclic ring carboxylic acid ligands and lanthanide salts or cadmium salts by hydrothermal or solvent-thermal methods.The structures of these compounds were confirmed by X-ray single crystal diffraction and X-ray powder diffraction analysis.The compounds were characterized by TGA,IR,XPS,fluorescence spectra and UV-vis spectra.At the same,luminescent sensing for Fe3+ ion,Cr2O72-anion and organic solvent molecules have been investigated.In addition,the mechanism of luminescence quenching has been discussed.The innovative features of our current work are described as follows:(1)Three series of lanthanide-organic frameworks la-le,2a-2c and 3 with Lewis basic imidazole and pyridyl sites have been constructed from pyridyl-carboxyl and imidazole-carboxyl bifunctional ligands and lanthanide salts.The structures of la-1e and 3 can be described as 3D open-frameworks based on lanthanide carboxylate([Ln(COO)3]n)with uncoordinated Lewis basic pyridyl and imidazole sites hung in the channels.The compounds 2a-2c possess 2D layered structures constructed from lanthanide carboxylates with uncoordinated Lewis basic pyridyl sites above or below the layers.Compounds la-lc,2a-2c all exhibit characteristic fluorescence emission of lanthanide ions.The luminescent investigations show that compound lc displays interesting NIR luminescence property.Compound la exhibits a good potential as a luminescent sensor material for multi-responsive Fe3+ ions and Cr2O72-anions.Compound 2a has a good quenching response to metal ions Fe3+,Cr2O72-,N3-and alcohol solvent such as MtOH,EtOH.So compounds la and 2a possess potential as a luminescent sensor.The lanthanide-organic frameworks with Lewis basic imidazole and pyridyl sites provide a new strategy for the construction of novel fluorescent probes.(2)Six kinds of cadmium-organic compounds with 2D layer and 3D frameworks were synthesized by using pyridyl-carboxyl and imidazole-carboxyl bifunctional ligands and cadmium salts.Compound 4 is a 3D open cadmium-organic framework with dia topology based on 4-(pyridin-3-yl)benzoic acid.When 3-(pyridin-4-yl)benzoic acid is used as ligand,different two-dimensional layered compounds 5-7 can be obtained by adjusting different reaction conditions.The structure of compound 5 exhibits a 2-fold interpenetrating structure.Using different ligand,two 3D Cd-organic open frameworks 8 and 9 with a 5-fold interpenetrating dia topology were constructed.The difference in structure lies in the link modest the ligand.The compounds 5 and 7 have good thermal stability and can keep the stable structures at 400?.It is found that the Fe3+ has obvious quenching effect on the fluorescence of compounds 4,8.So compounds 4 and 8 possess potential as a luminescent sensor for the Fe3+.In addition,the fluorescence of compound 4 can be quenched by anions such as Cr2O72-anions,while small solvent molecules such as acetone and propylenediamine can obviously quench the luminescence of compound 8.The results show that these cadmium compounds have good luminescence properties,and 4,8 have potential fluorescence probe properties.