Design,Synthesis,Structures And Performance Study Of Rare Earth And Rare Earth-transition Metal Clusters

Rare earth-based metal clusters have attracted extensive research interest due to their rich topological structures and their unique physical and chemical properties in fluorescence,magnetism,catalysis,gas adsorption separation,high-density data storage,etc.Among them,the potential application of rare earth-based clusters in photoluminescence and magnetic refrigeration has attracted special attention.However,the assembly process of rare earth metal clusters is extremely complicated.Rational design and synthesis of rare earth-based clusters with good photoluminescence and magnetic refrigeration effects are still a great challenge.This paper designed from the perspective of structure-activity relationship and synthesized a series of rare earth-based metal clusters based on synergistic effect of ligand-controlled metal ion hydrolysis and template anion groups.Their synthetic structures and properties are discussed in detail in this paper,and the results are as follows:1.Using calixarene to construct ligand-protected rare earth clusters for stable photoluminescence.In order to solve the problems of weak light absorption and poor stability in rare earth luminescence.In this work,we obtained two types of 4-tertbutylthiacalix[4]arene(H4TC4A)capping-protected hourglass-shaped lanthanum oxygen clusters,{[Ln4(μ4-OH)(TC4A)2(DMF)6(CH3OH)3(HCOO)Cl2]}-xCH3OH(Ln=Eu(1),Tb(2);x=0～1)and ｛[Ln9(μ5-OH)2(μ3-OH)8(OCH3)(TC4A)2(H2O)24Cl9]｝·xDMF(Ln=Gd(3),Tb(4),Dy(5);x=2～6),by hydrothermal and room temperature solvent evaporation methods.Among them,nonanuclear core cluster 3-5 are the largest homometallic lanthanide cluster supported by H4TC4A ligands.By comparing 2 and 4,we find that several critical luminescent properties(such as quantum efficiency and luminescent stabilities)depends directly on the cluster core structure.With the square-planar[Ln4(μ4-OH)]cluster cores,2 demonstrate high quantum yield(-65%)and excellent luminescent stability against moisture,high temperature,and UV-radiation.A white light-emitting diode(LED)with ultrahigh color quality is successfully fabricated by mixing 2 with commercial phosphors.These results imply that high quality phosphors might be achieved by exploiting the double thiacalix[4]arene-capping strategy with an emphasis on the cluster core structure.2.Ultrastable photoluminescence enabled by Rare earth cluster chains based on double thiacalix[4]arene capped nodesIn our previous work,the tetranuclear rare earth clusters(SBUs)coordinated with 4-tert-butylthiacalix[4]arene have been selected to have stable luminescence characteristics.In order to further improve its luminous stability,a series of 1D-MOF phosphors,{Ln4(μ4-OH)(TC4A)2(H2O)2(OCH3)(HCOH)(HCOO)2}(Ln=Sm(1),Eu(2),Tb(3),Dy(4)),based ondouble p-tertbutylthiacalix[4]arene(H4TC4A)-capped SBUs,were prepared and characterized.The SBUs are connected equatorially by formate bridges to obtain zigzag 1D-MOF chains,which further interact with each other via hydrogen bonding to form aquasi-2D structure.Because of the strong TC4A coordination and the highly stable extended frameworks,the 1D-MOF phosphor demonstrates excellent long-term luminescent stability against moisture,elevated temperature,and UV exposure.By using 3 as the green phosphor,a whiteLED device was constructed and demonstrates stable operation during the long-term test.By exploiting the coordination chemistry of 4-tert-butylthiacalix[4]arene(H4TC4A),our work provides a new alternative for achieving structurally stable lanthanide complexes for improving luminescent stability.3.Using calixarene ligands to construct high nuclear 3d-4f clustersThe formation of high nuclearity 3d-4f clusters through the coordination assembly of metal ions controlled by calixarenes still faces great challenges.In this work,we designed and synthesized a series of 3d-4f clusters assembled by H4TC4A ligands,{GdNi12},{Gd2Ni28},{Gd4Ni24} and {GdsNi26} through simple solvothermal method.Among them,{Gd2Ni28},{Gd4Ni24} and {GdsNi2} all exhibit similar obliquely symmetrical bowl configurations,and can be regarded as being formed by further temperature-driven assembly of {GdNi12} cluster molecules.These bowl-packed clusters are novel in structure and are the clusters with the highest nuclearity among the 3d-4f coordinated by H4TC4A reported so far.In addition,{GdNii2} structurally exhibits a large number of regular tetrahedral and octahedral channels packed by {GdNi,2} cluster molecules.Magnetic tests show that{GdNi12} has an antiferromagnetic interaction.Our work has greatly enriched the coordination chemistry of calixarenes,especially providing a reference for the design,synthesis and performance of high-nuclearity 3d-4f metal clusters.4.Construction of high-nuclear wheel-shaped {Gd44Ni22} clusters with large magnetocaloric effect by multi-ligand strategyMultinuclear 3d-4f nano-clusters,consisting of a large number of metal ions,are interesting both structurally and functionally.The Gd(Ⅲ)containing clusters,in particular,attract great research attention because of their significant magnetocaloric effect.Here,we report the synthesis of a gigantic 3d-4f wheel-like cluster,{Gd44Ni22},achieved through self-assembly by using the "mixed-ligands" strategy.Magnetic characterizations reveal that the {Gd44Ni22)cluster exhibits large magnetocaloric effect(MCE),with an isothermal magnetic entropy change of 44.9 J·kg-1·K-1 at 2.0 K for ΔH=7 T,which is one of the largest among all highnuclearity Ni-Gd clusters.Our work provides a reference for the design and synthesis of high-nuclearity 3d-Gd clusters with large magnetocaloric effects.5.Nested high-nuclearity {Gd22Ni22} clusters based on microstructural regulation for enhanced magnetocaloric effectStructural designing and functional application of atomically precise nanoscale inorganic clusters are the subject of immense interest.In this work,we elaborately designed and constructed a double-shell 3d-4f cluster,{Gd22Ni22｝,by microstructural tuning of recently reported {Gd23Ni20} cluster.Magnetic studies revealed that the{Gd22Ni22} cluster exhibits larger enhanced magnetic refrigeration effect(MCE)(46.0 J·kg-1·K-1 at 2.0 K for ΔH=7 T)than {Gd23Ni20} cluster(38.15 J kg-1 K-1 atΔH=7.0 T for 2.0 K)because of the weak magnetic interaction after structural adjustment.This work provides valuable reference for the design of materials with large magnetocaloric effect.6.Controlled self-assembly of rare earth ions by polyhydroxy acid ligands to form high-symmetry high-nucleus clustersIn this work,we obtained a series of 4f metal clusters including {Dy12},{Ce12},{Dy60} and {Ce80} by simple solvothermal and room temperature evaporation methods using polyhydroxy acid ligands with similar configurations.Among them,the {Dy12} and {Ce12} clusters have similar ring configurations and are the building blocks of the spherical configuration {Dy60} and {Ce80} clusters.On this basis,it is reasonable to speculate that the spherical high-symmetry clusters may undergo the assembly process of {Ln4}-{Ln12}-{Ln60}/{Ln80}.Furthermore,magnetic tests on{Dy12} and {Dy60} revealed similar antiferromagnetic interactions in both cluster molecules.This work reveals the assembly process of highly symmetrical clusters and provides a reference for the design and synthesis of functional clusters.