The Research On Synthesis,structure And Properties Of Rare Earth Complexes Constructed With Schiff Base

In recent years,the research of rare earth complexes has achieved many important achievements in magnetism and near-infrared luminescence.In particular,single-molecule magnets have become one of the hot topics in molecular magnetic materials due to their rich physical properties.In this thesis,thirteen rare earth complexes are prepared with bis(2-hydroxy-3-methoxybenzylidene)-propane-1,2-diamine Schiff base ligand,[(2-hydroxy-5-methyl)benzaldehyde]-[(2-hydroxy-3-methoxy)benzohydrazide]Schiff base ligand and bis(2-hydroxy-5-methylbenzylidene)-propane-1,2-diamine Schiff base ligand as main ligands and?-diketone(Hacac=acetylacetone,Hdbm=dibenzoylmethane)as co-ligands.At the same time,the crystal structures,PXRD,infrared spectra,thermogravimetric analysis,UV-Vis spectra,near-infrared luminescence properties and magnetic properties of these complexes are analyzed.The research works of this paper are as follow:(1)Seven non-centrosymmetric rare earth complexes are constructed by bis(2-hydroxy-3-methoxybenzylidene)-propane-1,2-diamine Schiff base ligand(H₂L1)and dibenzoylmethane(Hdbm)co-ligand:[Y₂(dbm)₄(L1)(CH₃OH)](1)[Eu₂(dbm)₄(L1)(CH₃OH)](2)[Tb₂(dbm)₄(L1)(CH₃OH)](3)[Dy₂(dbm)₄(L1)(CH₃OH)](4)[Ho₂(dbm)₄(L1)(CH₃OH)](5)[Er₂(dbm)₄(L1)(CH₃OH)](6)[Yb₂(dbm)₄(L1)(CH₃OH)](7).The analysis of single crystal structure shows that complexes 1-7 belong to the triclinic crystal system and P?space group.Complexes 1-7 are binuclear structures and consist of two asymmetric units.The central RE³⁺ions are all in eight coordination mode.All complexes consist of two RE³⁺ions,one L1^2-,four dbm^-and one CH₃OH.The near-infrared luminescence tests of complexes 5-7 show that three complexes exhibit near-infrared luminescence properties.Complex 5 shows characteristic emission peaks of Ho³⁺ions at 974 nm and 1180 nm,which are ⁵F₅?⁵I₇transition and ⁵F₅?⁵I₆transition,respectively.Complex 6 exhibits a characteristic emission peak of Er³⁺ion at 1540 nm,which is ⁴I_13/2?⁴I_15/2transition.Complex 7 exhibits a characteristic emission peak of Yb³⁺ion with a maximum at 973 nm,which is ²F_5/2?²F_7/2transition.The fluorescence lifetime and quantum yield of complex 7 are 4.99?s and0.25%,respectively.The magnetic study of complex 4 shows a typical single-molecule magnet behavior under an external dc field of 3000 Oe.The effective energy barrier(U_eff=28 K)and the pre-exponential factor(?₀=3.39×10^-7 s)are calculated.(2)Five centrosymmetric tetranuclear rare earth complexes are constructed by[(2-hydroxy-5-methyl)benzaldehyde]-[(2-hydroxy-3-methoxy)benzohydrazide]Schiff base ligand and acetylacetone(Hacac)co-ligand:[Y₄(acac)₄(L2)₄(2H₂O)](8)[Dy₄(acac)₄(L2)₄(2H₂O)]·6CH₃CH₂OH(9)[Ho₄(acac)₄(L2)₄(2H₂O)](10)[Er₄(acac)₄(L2)₄(2H₂O)](11)[Yb₄(acac)₄(L2)₄(2H₂O)](12).The analysis of single crystal structure shows that complexes 8-12 belong to the triclinic crystal system and P?space group.Complexes 8-12 are tetranuclear structures and the central RE³⁺ions are all in eight coordination mode.All complexes consist of four RE³⁺ions,four L2^2-,four acac^-and two water molecules.Compared with other complexes,there are six uncoordinated solvent molecules ethanol in the structure of complex 9.The near-infrared luminescence tests of complexes 11-12 show that two complexes exhibit near-infrared luminescence properties.Complex 11 exhibits a characteristic emission peak of Er³⁺ion at 1540 nm,which is ⁴I_13/2?⁴I_15/2transition.Complex 12exhibits a characteristic emission peak of Yb³⁺ion at 973 nm,which is ²F_5/2?²F_7/2transition.The magnetic study of complex 9 shows a typical single-molecule magnet behavior under an external dc field of 3000 Oe.The effective energy barrier(U_eff=32 K)and the pre-exponential factor(?₀=4.02×10^-7 s)are calculated.(3)One non-centrosymmetric rare earth complex is constructed by bis(2-hydroxy-5-methylbenzaldehyde)-propane-1,2-diamine Schiff base ligand and dibenzoylmethane(Hdbm)co-ligand:[Dy₂(dbm)₄(L3)(CH₃OH)]·CH₃CN(13).The crystal structure test result shows that complex 13 belongs to the triclinic crystal system and P?space group.The structure consists of two Dy³⁺ions,one L3^2-,four dbm^-and two solvent molecules(CH₃OH and CH₃CN).The methanol molecule takes part in coordination.The acetonitrile is a free solvent molecule and does not take part in coordination.Dy1 and Dy2 adopt different geometries.The Dy1 center is eight-coordinate,which is described as a distorted square antiprism geometry(D_4d).The Dy2 center is seven-coordinate,which is described as a distorted single-cap octahedron geometry(C_3v).