Regulating The Structures,Luminescent Properties And Magnetic Properties Of Rare-earth Complexes By β-diketonate Coligands

Rare-earth complexes have attracted a great deal of research interest in recent years due to their potential applications in magnetism,luminescence,catalysis,gas separation and so on.Among them,the magnetic research is the most extensive,there has been a series of reports of single-molecule magnets（SMMs）and molecular magnet coolers（MMCs）.In order to deeply understand the relationship between the structures and luminescent properties,magnetic properties of rare-earth complexes,we chose a Schiff base ligand（H₂L=N’-（2-hydroxybenzylidene）-2-（hydroxyimino）-propanohydrazide）andβ-diketones as coligands to construct eleven binuclear complexes.The luminescent properties and magnetic properties of these complexes were studied.The main results are as follows:1.Eleven rare-earth complexes,[RE₂（dbm）₂L₂（DMF）₂]·2CH₃OH（RE=Y（1）,Nd（2）,Dy（6）,Er（7））,[RE₂（dbm）₂L₂（CH₃OH）₂]·nCH₃OH（RE=Eu（3,n=2）,Gd（4,n=2）,Tb（5,n=1）,Yb（8,n=0））and[RE₂（acac）₂L₂（CH₃OH）₂]（RE=Dy（9）,Er（10）,Yb（11））havebeensynthesizedthroughtheligand（H₂L=N’-（2-hydroxybenzylidene）-2-（hydroxyimino）-propanohydrazide）andtwoβ-diketones coligands（Hdbm=1,3-diphenyl-1,3-propanedione and Hacac=acetylacetone）.2.X-ray single crystal diffraction data show that the complexes are binuclear structures.The rare-earth ions are located in eight-coordinated environment.Among them,complexes 1,6 and 7 are crystallize in the monoclinic space group P2₁,complex 2 crystallize in the monoclinic space group P2₁/c,complexes 3-5 crystallize in the monoclinic space group P2₁/n,while complexes 8-11 crystallize in the triclinic space group Pī.According to single-crystal X-ray diffraction data and symmetry measurement value calculated by SHAPE 2.0,complexes have two configurations,including triangular dodecahedrom（3-5,8-11）and biaugmented trigonal prism（1,2,6,7）.3.The luminescence spectra of the complexes in methanol solution show that complexes 3,5 and 6 exhibit the typical emissions of the RE（Ⅲ）ions,while complex1 exhibits emission peak similar to that of the H₂L ligand.And for complexes 2,7,8and 11,all of them show near-infrared fluorescent characteristic peaks.4.Magnetic studies reveal that complex 4 can act as cryogenic magnetic refrigerant with the maximum magnetic entropy change（-ΔS_m）of 25.79 J kg^-11 K^-11 at 7T and 2 K.Complex 9 shows slow magnetic relaxation behavior with energy barrier of 23.78 K and the pre-exponential factor of 1.74×10^–66 s,while complex 6 does not exhibit excellent SMM behavior.The distinct magnetic relaxation behaviors of the two Dy₂ complexes originated from the different coordination environment around the Dy（Ⅲ）ions.These results mean that a series of complexes with different structures can be synthesized,and then the luminescent properties and magnetic properties of rare-earth complexes can be finely tuned by alteringβ-diketonate ligands.