Synthesis,Structure And Magnetic Studies Of Complexes Based On The Schiff-base Derived From 2-Hydroxy-1-naphthaldehyde

In the recent rapid development of digitization,the application of magnetic materials in spintronic devices,high-density information storage and quantum computing is becoming wider and wider.Single-molecule magnet,one important magnetic material,is also drawing much attention.To develop single-molecule magnets is still a challenging task.In this research work,in-situ reactions of three different alcohol-amines with 2-hydroxy-1-naphthaldehyde in the presence of metal ions gave four series of complexes,the structures and magnetic properties of which were were explored.The main research works are as shown below.The first chapter highlights the background of this work,focusing on the characteristics and properties of single-molecule magnets,and current research progress.In the second chapter,two kinds of rare earth dysprosium complexes of Schiff base with different coordination numbers,[Dy(H₃L¹)₂Cl₂]Cl?Et OH(1)and[Dy(H₃L¹)2Cl₂H₂O]Cl?2H₂O(2),were obtained from the in-situ reactions of 2-hydroxy-1-naphthaldehyde,1,3-diamino-2-propanediol and rare earth dysprosium metal salts under different solvothermal conditions.Their compositions and structures were determined by elemental analysis,infrared spectroscopy,thermogravimetry and X-ray single crystal diffraction.Their magnetic properties were investigated.Single crystal structure tests showed that they are both mononuclear complexes.The Dy(III)ion in complex(1)is a six-coordinated in D_4d configuration,in which the four hydroxyl oxygen atoms of the two Schiff base ligands form the equatorial plane with the two axial positions occupied by two chloride ions.However,the Dy(III)ion in complex(2)is a seven-coordinated in D_5h configuration,in which the equatorial positions are occupied by four hydroxyl oxygen atoms from two Schiff base ligands and one water molecule with the two axial sites occupied by two chloride ions.The difference between the two complexes is that complex(2)has one coordinated water molecule in the equatorial positions more than than that in complex(1).Magnetic studies revealed that complexes(1)and(2)are both field-induced single-ion magnets.However,their magnetic properties are significantly different.The ac magnetic susceptibilities of complex(1)were measured at 0-1000 Hz with an optimal external field of 1200 Oe,which gave an energy barrier of 43.86 K.The ac magnetic susceptibilities of complex(2)were colleceted under an optimal external field of 1000 Oe,which gave an energy barrier of 21.57 K.Clearly,the magnetic difference between the two complexes is caused by the different coordination configurations of their metal ions.It was shown in the third chapter that the reactions of 2-hydroxy-1-naphthaldehyde with3-amino-1,2 propanediol or 2-amino-2-methyl-1,3-propanediol in the presence of Dysprosium salt under solvothermal conditions gave two complexes which are single-molecule magnets.The crystal structures of complexes(3)and(4)were determined by X-ray single crystal diffraction analyses,which showed that they have the formula of[Dy₂(HL²)2(NO₃)₂(Me OH)₂]?2Me OH(3)and[Dy₆(?₃-OH)₂(L³)₂(HL³)₂(H₂L³)₂Cl₂(Et OH)₂]Cl₂?3Et OH?CH₃CN(4).They were further characterized by infrared spectroscopy,elemental analysis and thermogravimetry.The single crystal structural analysis showed that complex(3)has a binuclear structure in which the two metal ions are both eight-coordinated in bicapped triangular prisms.Complex(4)presents a hexanuclear structure in which all of the metal ions are eight-coordinated bicapped triangular prisms.Their magnetic susceptibilities were measured in a temperature range of 2 K-300 K under a magnetic field of 1000 Oe.These magnetic data and the corresponding silmulations showed that the two metal ions in complex(3)are antiferromagnetically interacted,while complex(4)has a dominant ferromagnetic interaction between its metal ions with also possible existence of ferromagnetic interactions between some of it metal ions.Both dynamic magnetic measurents and theoretical calculations revealed that complexes(3)and(4)are single-molecule magnets under zero dc fields with energy barrier of 34 K and 40 K,respectively.Their relaxation mechanisms are presumably due to Orbach processes.It wa shown in the fourth chapter that the in-situ reactions of Dysprosium salt with2-hydroxy-1-naphthaldehyde and 3-amino-1,2 propanediol or 1,3-diamino-2-propanediol under different solvothermal conditions gave a planar tetranuclear complex[Dy₄(L³)₂(L⁴)₄(NO₃)₂(Et OH)₂]?2Et OH?0.5Me OH?0.5CH₃CN?H₂O(5)and a butterfly-like tetranuclear complex[Dy₄(?₄-O)(HL²)₄(H₂L²)₂]?4H₂O?2Et OH?1.5CH₃CN(6).Their crystal structures were determined by single crystal X-ray diffractometry.Their crystalline samples show nice stabilities in alkaline solution,as well as in the solvents such as H₂O,Me OH,Et OH,DMF,CH₂Cl₂,CCl₄.Their magnetic investigations indicated that complexes(5)and(6)exhibit single-molecule magnet behavior under zero external fields with their energy barriers of 1.2 K and 3.68 K,respectively.It is rarely seen for this kind of complexes which show slow magnetic relxation and are rather stable in alkanline solution and normal solvents.It was shown in chapter 5 the solvothernmal in-situ reactions of 3-amino-1,2-propanediol,2-hydroxy-1-naphthaldehyde,lanthanide and Ni(II)ions in presence of triethylamine gave two types of 3d-4f heteronuclear clusters[Ln Ni₄(L²)₂(HL²)(H₂L²)(CH₃COO)₂(CH₃CH₂OH)₂]·3H₂O(Ln=Dy,7;Gd,8;Y,9)and[Ln₂Ni₈(L²)₄(HL²)₂(CH₃COO)₄(CH₃O)₂(CH₃OH)₂(H₂O)₂]·4H₂O(Ln=Dy,10;Gd,11;Y,12).The variable-temperature magnetic susceptibility tests revealed dominant ferromagnetic interactions between the metal ions in complexes(7)?(12).Complex(7)exhibits single molecule magnet behavior,while no slow magnetic relaxation was found in complexes(8)?(12).It shows that the the topologies of these complexes have a great influence on their magnetic properties.The diiferent topologies might adjust the symmetries of the complexes and also the anisotropies of the metal ions,thereby achieving the purpose of regulating the single-molecule magnet behaviors.It will show some significant guidance for the synthesis of single-molecule magnets.