Syntheses,Structures And Properties Of Multi-nuclear Rare-Earth Substituted Seleno/Tellurotungstates

In this dissertation,by the one-step self-assembly strategy,sodium tungstate,heteroatom salts with lone pair-electron effect,rare-earth ions and organic components were used as the starting materials in the conventional aqueous solution to successfully synthesize three series of novel multi-rare-earth substituted selenotungstoates/tellurotungstates through controlling the molar ratios of reactants,adjusting the pH of the solution and reaction temperature,etc.These multi-rare-earth substituted selenotungstoates/tellurotungstates have been structurally characterized by elemental analyses,single crystal X-ray diffraction,IR spectra and thermogravimetric analyses.Magnetic properties and solid-state photoluminescence properties of some typical compounds have been investigated in detail.This work not only enriches the synthetic strategy of preparing novel multi-rare-earth substituted polyoxometalates,but also expands the research fields of polyoxometalate properties.This dissertation is divided into three sections to describe the work during my master’s degree:In the first section,five tartaric-acid-bridging multi-nuclear rare-earth substituted selenotungstoate derivatives[H2N(CH3)2]13H{[W3O6(H2tart)2][RE2(H2O)6][SeW9O33]2}[W2O5(OH)2]{[W3O6(H2tart)][RE2(H2O)6][SeW9O33]2}·31H2O[RE = Eu3+(1),Tb3+(2),Dy3+(3),Ho3+(4),Y3+(5)](H4tart = tartaric acid)have been synthesized by reaction of Na2WO4·2H2O,dimethylamine hydrochloride,RE(NO3)3 6H2O,Na2SeO3 and D-tartaric acid in acidic aqueous media.The tetrameric polyoxoanion of 1-5 consists of one{[W3O6(H2tart)2][RE2(H2O)6][SeW9O33]2}4-unit,one {[W3O6(H2tart)][RE2(H2O)6][SeW9O33]2}4-unit and a di-nuclear tungsten-oxo([W2O5(OH)2]} cluster.The {[W3O6(H2tart)2][RE2(H2O)6][SeW9O33]2}4-unit contains a tungsten-oxo[W3O6(H2tart)2]6-cluster decorated by tartaric-acid ligands,two trivacant Keggin-type[SeW9O33]8-fragments and two rare-earth ions.The {[W3O6(H2tart)][RE2(H2O)6][SeW9 O33]2}4-unit comprises a tungsten-oxo[W3O6(H2tart)2]6-cluster decorated by tartaric acid,two trivacant Keggin-type[SeW9O33]8-and two rare-earth ions.The thermogravimetric results of 1-5 show that they behave as a two-step weight loss.In addition,the visible fluorescent properties of 1-4 have been studied and their emission spectra show the characteristic emission peaks of Eu3+,Tb3+,Dy3+ and Ho3+ ions,respectively.Their fluorescence lifetime curves have been also collected under their corresponding emission and excitation wavelengths.Moreover,the magnetic properties of 2,3 and 4 have been preliminaryly studied,and the alternating-current susceptibility measurements suggest the slow magnetic relaxation and the possible single-molecule magnetic behavior in 3.In the second section,based on the first section in which tartaric acid was replaced by flexible DL-malic acid,five malic-acid-bridging multi-nuclear rare-earth-substituted selenotungstate derivatives[H2N(CH3)2]16H2{[W6RE4SeO16(H2O)10(Mal)2][SeW9O33]4}·44H2O[RE = Sm3+(6)、Gd3+(7)、Ho3+(9)、Er3+(10)]and[H2N(CH3)2]16Na2{[W6Tb4SeO16(H2O)10(Mal)2][SeW9O33]4}·44H2O(8)(H2Mal = Malic acid)have been successfully synthesized.The polyoxoanions of 6-10 are isostructural and their polyoxoanionic skeletons {[W6RE4SeO16(H2O)10(Mal)2][SeW9O33]4}18-are constructed from two {[W3RE2O16(H2O)5][SeW9O33]2}24-subunits through two malic acid bridges.Every {[W3RE2O16(H2O)51[SeW9O33]2}24-subunit can be viewed as a tungsten-oxo[W3Ln2O16]8-cluster encapsulating into the vacancy of two[SeW9O33]8-fragments.At the same time,the Se atom play the role of connecting two crystallograhic rare earth ions in this structure.The thermogravimetric results of 6-10 show that they behave as a two-step weight loss.Furthermore,the fluorescent properties of 6,8,9 and 10 have been measured and their fluorescence spectra all exhibit the characteristic emission peaks of rare-earth ions.Their fluorescence lifetime decay curves have been also collected under their corresponding emission and excitation wavelengths and conform to the double exponential function.In addition,the magnetic properties of 6,9 and 10 have also been explored.In the third section,four organotin-rare-earth substituted tellurotungstate derivatives[H2N(CH3)2]8 H6[RE(OH)(TeW7O28)RESn2(CH3)4(W5O18)]2·18H2O[RE = Er3+(11),Yb3+(12),Ho3+(13),Y3+(14)]have been synthesized.The tetrameric polyoxoanions of 11-14 are formed by two symmetrical units{[(TeW7O28)RESn2(CH3)4(W5O18)]}7-linked via rare-earth cations.The tetrameric polyoxoanion simultaneously contains mono-vacant Lindqvist isopolyoxotungstate building blocks and five-vacant Keggin tellurotungstate building blocks.The thermogravimetric results of 11-14 show that they behave as a two-step weight loss.The thermal decomposition process of 11 has been comprehensively studied by TG analyses,variable-temperature infrared spectroscopy and variable-temperature photoluminescence as well as variable-temperature powder X-ray diffraction.In addition,the solid-state near-infrared photoluminescence behaviors of 11 and 13 as well as the solid-state visible photoluminescence behaviors have been examined under ambient temperature and all exhibit the characteristic emission peaks of rare-earth ions.Their fluorescence lifetime decay curves have been also collected under their corresponding emission and excitation wavelengths and abide by the double exponential function.