Syntheses,Structure And Magnetic Properties Of Lanthanide-Based Single-Molecule Magnets Constructed From Alkylol-Amines-Based Schiff-base Ligands

The study of single-molecule magnets(SMMs)continues to fascinate the scientific community because of their unique and intriguing properties and potential applications in high-density information storage,quantum computing,and molecular spintronics.In the past decades,the lanthanide-SMMs have promoted agrowing realization that single-ion anisotropy is the crucial factor when designing SMMs.Lanthanide ions have been recognized as highly promising candidates for the development of higher-barrier SMMs because of the significant single-ion anisotropy originated from the strong spin-orbit coupling and crystal field effect.This work explores the synthesis,crystal structure and magnetic properties of 3d-4f and 4f complexes constructing from a series of Schiff-base ligands.We focus on the magnetic properties,mechanism and ab initio calculations of SMMs.The whole thesis includes eight chapters:Chapter 1 introduces the research overview and background of single-molecule magnets,mainly introduces the current progress,organic ligand,synthesis methods,status and trends of the research of 3d SMMs,3d-4f SMMs and 4f-SMMs at present.Chapter 2 explores the structures and magnetic properties of a serial defect-dicubane NiⅡ2LnⅢ2 clusters constructed from Schiff-base ligands of 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propane diol,which forms in situ.NiⅡ located in the central plane of the defect-dicubane,and plays an effective role in regulating the magnetic coupling.Magnetic analyses indicate that NiⅡDyⅢ2 and NiⅡ2TbⅢ2 complexes exhibit typical single-molecule magnet behavior and display different anisotropy barrier.Ab initio calculations are performed on these complexes and determines the low lying electronic structure of each LnⅢ(Ln = Dy,Tb)ion and the magnetic interactions.It finds that there is a strong correlation between the energy gap of the ground and the first excited doublets of single LnⅢ(Ln = Dy,Tb)ion and the intramolecular exchange couplings with the experimentally observed anisotropy barrier,which provides a hint in preparing the single-molecule magnets with high Ueff.Chapter 3 describes the structures and magnetic properties of a serial CoⅢ2LnⅢ4 clusters with butterfly shaped configuration constructed from Schiff-base ligands of 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propane diol,which forms in situ.Trivalent cobalt ion as diamagnetic ion locating in cluster center,CoⅢ2DyⅢ4 clusters exhibits single-molecule magnets behavior and its effective energy barrier is mainly determined by the magnetic anisotropy of dysprosium ion.Ab initio calculations are used in the study of the electronic structure of two different rare earth dysprosium ion independent units,attaining the dysprosium ion spin state energy and determining the easy magnetization axis direction.The exchange coupling constant between rare earth ions and possible ways of relaxation are obtained by using of magnetic coupling pathways corresponding Hamiltonian operator.Chapter 4 studies the crystal structures and magnetic properties of a serial 3D chiral metal-organic frameworks based on Dy2Cu10 secondary building units andμ3-NO3-as 3-connected vertices,constructed from Schiff-base ligand of 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propane diol.The metal-organic framework which is based on Dy2Cu10 secondary building units,formed by the nitrate(which is used as the connecting body)and with the topological structure of qtz is first discovered.Organic Schiff-base ligand of 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propane diol in situ show various different coordination modes and play a decisive role in the formation of high heteronuclear secondary building units.The complex which containing Dy2Cu10 secondary building units exhibit slow magnetic relaxation behavior,and it is a rare example of 3d-4f heteronuclear metal-organic frameworks with single-molecule magnetic behavior.Chapter 5 researches the crystal structures and magnetic properties of a serial hexanuclear rare clusters with chair conformation constructed from Schiff-base ligand 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propane diol and pivalate ligands.Magnetic characterization shows Dy6 exhibits a clear slow magnetic relaxation behavior and strong ferromagnetic coupling between the DyⅢions.This work represents a successful rational design of Dy3 triangles trapped in a Schiff-base ligand showing slow magnetic relaxation.In future,it should be develop more simple models to explain and predict the presence of significant single-ion anisotropy,based on the shape variation of the f-electron charge cloud.Chapter 6 studies the crystal structures and magnetic properties of two novel Ln10 clusters constructed from Schiff-base ligand of 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propane diol.The anions(nitrate and acetate)play an important role in the formation of high nuclear clusters,and rare earth ions linked by a nitrate-bridging with μ5-η2:η2:η3 mode.Magnetic characterization shows Dy10 exhibits obviously slow magnetic relaxation behavior,antiferromagnetic coupling between the Dy ions intraclusters.The magnetic susceptibility studies reveal that Dy10 exhibits single-molecule magnetic behavior and weak antiferromagnetic coupling between the DyⅢ ions.In chapter 7,a series of Ln4 clusters,have been synthesized by the reaction of Ln(NO)3 and a Shiff-base ligand 2-{[2-(2-hydroxy-ethoxy)-ethylimino]-methyl}-6-methoxyphenol)formed in situ.These complexes display similar structure with an overall metal core comprising two edge-sharing triangular Ln3 units linked by a μ4-NO3-bridge.The magnetic susceptibility studies reveal that the LnⅢ ions are very weakly coupled in complexes,only Dy4 exhibits slow magnetiv relaxation behavior with an anisotropic barrier of 25 K.This is an interesting example of single-molecule magnets bridging by naitrate group.The successful synthesis of these complexes may imply a new opportunity to develop novel nitrate-bridged lanthanide single-molecule magnets for magnetic dynamic studies.Finally,a brief conclusion of the work is given.