Synthesis,Structures And Luminescent/Magnetic Properties Of Dinuclear Rare Earth Complexes

In recent years,rare-earth elements have been widely used in optical,magnetic,catalytic,adsorption,superconductivity and other research fields due to their unique physical and chemical properties.In particular,the near-infrared fluorescence and magnetization dynamics of rare earth complexes have become the research focus of current researchers.With these in mind,a family of new dinuclear complexes were constructed by using N'-(2-hydroxy-5-methylphenyl)-pyrazine-2-carbohydrazide Schiff base ligand H2L and five slightly different ?-diketonate co-ligands.The crystal structures,powder X-ray diffraction,thermogravimetry,UV-Vis absorption and photoluminescence of the complexes have been carried out,furthermore,modulation of near-infrared luminescence and magnetization dynamics properties have been discussed in depth.1.A family of new dinulear rare earth complexes as the simplest entity carrying intramolecular magnetic interactions,[RE2(dbm)2(L)2(CH3OH)2](RE=Y(1),Tb(2),Dy(3),Ho(4),Er(5),Yb(6),Lu(7)),[RE2(acac)2(L)2(EtOH)2](RE=Dy(8),Er(9)),[Dy2(TTA)2(L)2(CH3OH)2]·2CH2Cl2(10),[Dy2(tfa)2(L)2(CH3OH)2](11)?[Dy2(beac)2(L)2(CH3OH)2](12)(H2L=N'(2-hydroxy-5-methylphenyl)-pyrazine-2-carbohydrazide,Hdbm=1,3-diphenyl-1,3-propanedione,Hacac=acetylacetone,HTTA=2-thenoyltrifluoroacetone,Htfa=trifluoroacetylacetone,Hbeac=1-phenyl-1,3-butanedione),were constructed successfully by the reaction of Schiff base ligand H2L and five different ?-diketonate salts.2.Single-crystal X-ray diffraction analysis confirms that complexes 1-12 are all centrosymmetric dinuclear complexes.Complexes 1-7 all are isomorphous,crystallizing in an orthorhombic crystal system Pbcn,and the RE(?)ions own geometric configuration of distorted triangular dodecahedron;complexes 8-11 all crystallize in the triclinic crystal system Pi,RE(?)ions demonstrate distorted square antiprism geometry for complexes 8-9,both central Dy(?)ions adopt distorted biaugmented trigonal prism geometry for complexes 10-11;and complexes 12 crystallizes in the monoclinic crystal system P21/n,Dy3+ owns geometric configuration of distorted square antiprism.3.The measurement of near-infrared luminescence indicates that complexes 5,6 and 9 all show characteristic emission peaks of corresponding rare earth ions in the NIR region and the complexes of Yb(?)are found to be well-matched to the energy level of ligands as compared to the Er(?)complexes,exhibiting high intensity of the emission peaks.Complexes 5 and 9 have potential applications in modern telecommunication networks,while complex 6 can be used in solar photovoltaic cells or optical applications.4.The test for magnetic properties show that no magnetic relaxation process are available for 3 and 8 when there is the dc magnetic field of 0 Oe,however,both complexes 10 and 11 possess typical slow magnetic relaxations,a hallmark of SMMs behaviors,their effective energy barriers are 102 K and 140 K,respectively.The application of optimum dc field may remove the ground state degeneracy and fully or partly suppress the quantum tunneling process in RE-SMMs.For complex 3,the plots of ln? versus 1/T can be fitted by the Arrhenius law,receiving two effective energy barriers of 29 K and 44 K for the low temperature relaxation and high temperature relaxation,respectively(Hdc=3000 Oe).For complexes 8,10 and 11,the effective barrier:Ueff=61 K(8,Hdc=1500 Oe),Ueff=112 K(10,Hdc=2000 Oe)and Ueff=152 K(11,Hdc=1500 Oe).5.Magneto-structural correlations show that the substituent group CF3 of auxiliary ligand may create great changes to the magnetic properties of the four Dy2 complexes;the more appropriate deviation of configuration can make SMMs with fascinating magnetic properties;the relatively small Dy…Dy distances and Dy-O-Dy angles can engender great energy barrier.