Synthesis And Properties Of Lanthanide/Transition Metal-organic Frameworks Based On Niobium Substituted Dawson-type Phosphotungstates

Polyoxometalates(POMs),as a very important part of metal oxides clusters,have a widely range of potential application in many fields such as magnetism,photochemistry and electrochemistry.As an inorganic building unit,the self-assembly of polyoxometalates cluster not only enriches the structure of the compounds but also obtains hybrid compounds with excellent properties.Among them,the synthesis of POM-based rare earth metal-organic frameworks is a challenging topic by the introduction of rare earth metals with excellent photoelectric properties.Polyoxoniobates(PONs),as a member of the polyoxometalates family,were.obtained relatively limited because of their chemical inertness and easy hydrolysis.In this article,18 new POM-based rare earth/transition metal-organic frameworks 1-18 were synthesized and characterized by IR,UV spectroscopy,elemental analysis,XRPD and single-crystal X-ray diffraction analysis,where POM building block is niobium-substituted Dawson-type heteropolytungstate and the organic ligand is nitrogen-containing organic compounds.The photochemistry,electrochemical and magnetic properties of compounds were also investigated.This paper is divided into three chapters which were introduced as follows:1.Four POM-based rare earth metal-organic frameworks 1-4 were synthesized based on 3,5-pyridinedicarboxylic acid ligand,K8H[P2W15Nb3O62]·12H2O and Ln3+(Ln = Sm,Gd,Sm,Pr).K2H2[Sm3(3,5-pydc)2(H2O)12.5(P2W15Nb3O62)]·15H2O(1)KH6[Gd2(3,5-pydc)2(H2O)8(P2W15Nb3O62)]·17H2O(2)KH6[Sm2(3,5-pydc)2(H2O)8(P2W15Nb3O62)]·17H2O(3)KH6[Pr2(3,5-pydc)2(H2O)8(P2W15Nb3O62)]·17H2O(4)Singel-crystal X-ray diffraction analysis reveal that the compounds 1-4 exhibit a 3D porous structures,while[P2W,5Nb3O62]9-are bounded by a supramolecular interaction with Ln-pydc coordination cation units.The fluorescence emission spectra of compounds 1 and 3 show the emission peaks of the corresponding rare earth ions at room temperature.In compound 4,there is an antiferromagnetic interaction between the metals.The band gap values(Eg)of compounds 1-4 are 3.03,3.05,3.00 and 3.06 eV,respectively,indicate that compounds 1-4 have the properties of broad band semiconductors materials.Photocatalytic measurement shows that 1-4 can effectively accelerate the photodegradation of RhB.The results showed that compounds 1-4 have good adsorption properties for methylene blue.In particular,the adsorption rate of compounds 1-4 are 94.1%、91.2%、96.2%and 71.9%.2.Seven POM-based rare earth metal-organic frameworks 5-8 were synthesized based on 2,6-pyridinedicarboxylic acid liangd,K8H[P2W15Nb3O62]·12H2O,K7[P2W17NbO62]·8H2O and Ln(NO3)3(Ln = Sm,Dy,Eu,Nd).The UV-Vis,magnetic properties,electrochemical analysis and fluorescence characteristics of the corresponding compounds were studied.H3[Sm4(2,6-pydc)3(H2O)18(P2W15Nb3062)]·15H2O(5)H3[Dy4(2,6-pydc)3(H2O)18(P2W15Nb3062)]·15H2O(6)H3[Eu4(2,6-pydc)3(H2O)I8(P2W15Nb3O62)]·15H2O(7)H[Sm4(2,6-pydc)3(H2O)18(P2W17NbO62)]·15H2O(8)H[Dy4(2,6-pydc)3(H2O)18[P2W17NbO62)]·15H2O(9)H[Nd4(2,6-pydc)3(H2O)18(P2W17NbO62)]·15H2O(10)H[Eu4(2,6-pydc)3(H2O)18(P2W17NbO62)]·15H2O(11)Compounds 5-11 are basically isostructural and feature a 3D POM-based metal-organic framework containing 3D porous,which formed through the coordination interaction of Ln3+,2,6-pydc2-,[P2W15Nb3o62]9-and[p2W17Nbo62]7-as tetradentate ligands.The fluorescence emission spectra of compounds 5,7,8 and 11 at room temperature show the characteristic emission peaks of the corresponding rare earth ions.The magnetic behavior of 6 and 9 suggest the presence of ferro-magnetic coupling interactions.The optical properties indicate the energy bands(Eg)of compounds 5-11 are 3.09,3.22,3.20,3.30,3.13,3.13 and 3.12 eV,respectively,implying that compounds 5-11 have semiconducting properties.Compound 11 exhibits good catalytic performance for photocatalytic hydrogen evolution.The UV-Vis spectra,magnetic properties and electrochemical behavior for compounds 5-11 have been studied.The photocatalytic H2 evolution activity of 11 is investigated and the rate of H2 is 0.033 μmol ·h-1g-1.Photocatalytic measurement shows that 5-11 can effectively accelerate the photodegradation of RhB.In the presence of compound 11,the decolorization rate of RhB solution can achieve 61.5%.The results showed that compounds 5-11 have good adsorption properties for MB.In particular,the adsorption rate of compounds 5-11 are 92.2%、90.1%、86.9%、90.5%、88.3%、93.8%and 87.5%。3.Six POM-based rare earth metal-organic frameworks 12-17 were synthesized based on dpdo ligand,K8H[P2W15Nb3O62]·12H2O,K7[P2W17NbO62]·8H2O,Ln(NO3)3(Ln = Eu,Gd,Pr)and Cu(NO3)2.H7[Cu(dpdo)2(H2O)12(P2 W15Nb3O62)]·15H2O(12)H3[Gd2(dpdo)2(H2O)10(P2W15Nb3O62)]·14H2O(13)H3[Cu2(dpdo)5(H2O)5(P2W17Nb062)]·10H2O(14)H[Eu2(dpdo)2(H2O)10(P2W17NbO62)]· 14H2O(15)H[Gd2(dpdo)2(H2O)10(P2W17Nb062)]·14H2O(16)H[Pr2(dpdo)2(H2O)10(P2W17Nb062)]·14H2O(17)Compounds 12,15-17 are basically isostructural and feature a 1D POM-based metal-organic framework,which formed through the coordination interaction of Nb/W mixed-addendum polyoxometalate and dpdo units as ligands.The luminescent properties of compound 15 was investigated at room temperature and shows five characteristic emission peaks of Eu3+.The UV-Vis spectra,magnetic properties and electrochemical behavior for compounds 12-17 have been studied.4.In addition,one POM-based transition metal-organic frameworks 18 was synthesized by the reaction of nitrogen-containing organic ligand and[P2W15Nb3O62]9-:14[Co(L’)(XL)(H2O)10(P2W15Nb3O62XL")]·6H2O(18)Organic ligands of the compund have been broken into three components(L:C26H22N2O4Cl2,L’:C19H7N202Cl,L":C12H12N2).