Syntheses,Structures And Properties Of Carboxylate-controlling Dawson-type Lanthanide-substituted Phosphotungstates

In this dissertation,based on the principle of molecular design and self-assembly,we have synthesized thirteen novel organic–inorganic hybrid carboxylated rare-earth-substituted monolacunary Dawson-type phosphotungstates by reaction of K₁₂[H₂P₂W₁₂O₄₈]·24H₂O({P₂W₁₂}),rare-earth ions,organoamine components and carboxylic acid ligands under hydrothermal conditions.All the compounds have been characterized by IR spectra,elemental analyses,X-ray single-crystal diffraction and thermogravimatric analyses.Magnetic and photoluminescence properties of some carboxylated rare-earth-substituted monolacunary Dawson-type phosphotungstates have been studied.The introduction of different carboxylic acid ligands（2-picolinic acid or oxalate）has led to the formation of different rare-earth substituted Dawson-type phosphotungstates,which indicates that carboxylic acid ligands play an importantly tunable role in the structural construction of rare-earth substituted Dawson-type phosphotungstates.This dissertation can be divided into four sections to introduce my work during the master study:Section Ⅰ.The main developments of Dawson-type polyoxotungstates and their derivatives have mainly been summarized.Section Ⅱ.The related physical measurements and reagents have been given.Section Ⅲ.Eight novel rare-earth-substituted monolacunary Dawson-type phosphotungstates decorated by 2-picolinic acid have been synthesized:[Hdap]₄[Gd（H₂O）（Hpic）₃][Gd（Hpic）₂(α₂-P₂W₁₇O₆₁)]·21H₂O（1）[Hdap]₄[Tb（H₂O）（Hpic）₃][Tb（Hpic）₂(α₂-P₂W₁₇O₆₁)]·21H₂O（2）[Hdap]₄[Dy（H₂O）（Hpic）₃][Dy（Hpic）₂(α₂-P₂W₁₇O₆₁)]·21H₂O（3）[Hdap]₄[Ho（H₂O）（Hpic）₃][Ho（Hpic）₂(α₂-P₂W₁₇O₆₁)]·21H₂O（4）[Hdap]₄[Er（H₂O）（Hpic）₃][Er（Hpic）₂(α₂-P₂W₁₇O₆₁)]·21H₂O（5）[Hdap]₄[Tm（H₂O）（Hpic）₃][Tm（Hpic）₂(α₂-P₂W₁₇O₆₁)]·21H₂O（6）[Hdap]₄[Yb（H₂O）（Hpic）₃][Yb（Hpic）₂(α₂-P₂W₁₇O₆₁)]·21H₂O（7）[Hdap]₄[Y（H₂O）（Hpic）₃][Y（Hpic）₂(α₂-P₂W₁₇O₆₁)]·21H₂O（8）Compounds 1–8 were made by reaction of the{P₂W₁₂}precursor,rare-earth ions,2-picolinic acid and1,2-diaminopropane at the pH region of 5–6 under hydrothermal conditions.Their polyoxoanionic framework{[RE（H₂O）（Hpic）₃][RE（Hpic）₂(α₂-P₂W₁₇O₆₁)]}^4-can be considered that a dual-Hpic decorated[RE1（Hpic）₂]³⁺cation is embedded into the vacancy on the polar position of mono-lacunary[α₂-P₂W₁₇O₆₁]^10-fragment and a tri-Hpic decorated[RE₂（H₂O）（Hpic）₃]³⁺cation grafts to the equatorial position of[α₂-P₂W₁₇O₆₁]^10-fragment through a W–O–RE linker.Each RE³⁺ion is combined with the N and O atoms on the Hpic ligands in the five-membered ring fashion and adopts the eight-coordinate highly distorted square antiprism geometry.The solid-state UV–Vis photoluminescence properties for 2,3,5 and the solid-state NIR photoluminescence properties for 5 and 7 have been studied at room temperature,and their emission spectra mainly reveal the characteristic emission bands of Tb³⁺,Dy³⁺,Er³⁺and Yb³⁺ions.Additionally,the results of magnetic susceptibility measurements demonstrate that 3 displays the single-molecule magnet behavior.Section Ⅳ.Five unique oxalate-bridging rare-earth-substituted monolacunary Dawson-type phosphotungstate dimers have been prepared under hydrothermal conditions:[H₂dap]8[Ho₂（H₂ox）₂（ox）(α₂-P₂W₁₇O₆₁)₂]·25H₂O（9）[H₂dap]8[Er₂（H₂ox）₂（ox）(α₂-P₂W₁₇O₆₁)₂]·25H₂O（10）[H₂dap]8[Tm₂（H₂ox）₂（ox）(α₂-P₂W₁₇O₆₁)₂]·25H₂O（11）[H₂dap]8[Yb₂（H₂ox）₂（ox）(α₂-P₂W₁₇O₆₁)₂]·25H₂O（12）[H₂dap]₈[Y₂（H₂ox）₂（ox）(α₂-P₂W₁₇O₆₁)₂]·25H₂O（13）9–13 are isostructural and their polyoxoanionic skeleton[RE₂（H₂ox）₂（ox）(α₂-P₂W₁₇O₆₁)₂]^16-is constructed from two[RE（H₂ox）(α₂-P₂W₁₇O₆₁)]^7-subunits through an oxalate bridge.Every[RE（H₂ox）(α₂-P₂W₁₇O₆₁)]^7-subunit can be viewed that a[RE（H₂ox）]³⁺cation is encapsulate into the vacancy of a[α₂-P₂W₁₇O₆₁]^10-fragment.Magnetic susceptibility properties for 9 and 10 have been studied and both show the antiferromagnetic interactions between adjacent rare-earth ions.Moreover,the solid-state UV–Vis and NIR photoluminescence properties for 10,12 and Yb³⁺–Er³⁺codoped samples have been investigated and their emission spectra reveal the characteristic emission bands of rare earth ions.In addition,the doping ratio of Yb³⁺/Er³⁺can control the emission intensity and emission color of Yb³⁺–Er³⁺codoped samples.