Synthesis,characterization And Magnetic Properties Of Reduced Salicylaldehyde Schiff Base Transition And Rare Earth Metal Complexes

In recent years,with the rapid development of information technology,the recording and storage of voice,image and digital information is particularly important.Single-molecule magnets are small in size,light in weight,easy to process and have various structures,which are conducive to the storage of magnetic information.Compared with traditional magnetic materials,nano-sized magnets have stronger information storage capacity and achieve high-density information storage.The preparation of single-molecule magnets has become a research hotspot for researchers,but the blocking temperature and low effective barrier are the great challenges for researchers in the preparation of single-molecule magnets.In order to obtain single-molecule magnets with high energy barrier,high spin ground state and significant magnetic anisotropy are essential factors for single-molecule magnets.The ground state spin of transition metals is relatively high,but their magnetic anisotropy is weak.Rare earth metal ions have high magnetic anisotropy,but their radius is large and 4f electrons are shielded by outer electrons,resulting in weak interaction between ions.Therefore,the combination of rare earth and transition metal can make the complexes not only have high ground spin value,but also have significant magnetic anisotropy.Salicylaldehyde Schiff base polydentate ligands containing N and O atoms have strong coordination ability with transition metals and rare earth metals.Reduction of Schiff base can enhance its stability and flexibility.Therefore,a series of reductive Schiff base transition-rare earth metal Heteropolynuclear complexes have been designed and synthesized in this paper.They not only combine the characteristics of large atomic magnetic moment of transition metals,but also retain the remarkable anisotropy of rare earth metals.Their advantages and disadvantages have changed the way of magnetic exchange,thus obtaining single-molecule magnets with good properties.They have wide application prospects in the field of magnetic research.This paper is divided into four parts:1.Schiff bases and their complexes are briefly summarized,and the applications of their complexes are introduced.Single-molecule magnets are briefly summarized,and their research progress in magnetic properties is introduced.Transition metal single-molecule magnets,rare-earth metal single-molecule magnets and transition-rare-earth mixed metal single-molecule magnets are briefly introduced.2.In this paper,N,N'-bis(2-hydroxy-3-methoxybenzaldehyde ethylenediamine)(H₂L')was synthesized by mixing 3-methylsalicylaldehyde with ethylenediamine,and its carbon-nitrogen double bond was reduced to carbon-nitrogen single bond by sodium borohydride in ice bath.The reduced Schiff base ligand N,N'-bis(2-hydroxy-3-methoxyphenylene methylene)ethane-1,2-ethylenediamine(H₂L)was synthesized.The two ligands were characterized by NMR.3.Seven kinds of reductive salicylaldehyde Schiff base transition complexes and rare earth metal Heteropolynuclear complexes[Ni₂Ln₂L₂(?³-O)₂(NO₃)₄]were synthesized by reaction of reductive Schiff base ligands with transition metals Ni(II)and rare earth metals Ln(III)(Ln=Er,Tm,Dy,Ho,Yb,Tb,Gd).The crystal structure and coordination modes of central metals were described in detail by X-ray single crystal diffraction.The complexes were characterized by infrared spectroscopy,ultraviolet spectroscopy and differential thermal analysis.4.The magnetic properties of some reductive Schiff base transition-rare earth Heteropolynuclear complexes were tested,including temperature-dependent susceptibility(MT),magnetic induction and magnetic field intensity.The results show that ferromagnetic coupling exists in complexes 1-4 and antiferromagnetic coupling exists in complexes 5.The conclusion is further confirmed by Curie-Weiss fitting.