Syntheses,Physical Properties And Surface Deposition Of Molecule-based Magnets

This dissertation focuses on structures and physical properties of molecule-based magnets,such as single-molecule magnets(SMMs)and spin-crossover(SCO)complexes,for the purpose of the synthesis of high-performance SMMs,investigation of dynamic relaxation of magnetization behavior,the assembly of new single-molecule toroics(SMTs)and SCO compounds.Several significant results have been obtained including the synthesis of lanthanide-based SMMs with high effective energy barrier(Ueff),modulation of dynamic relaxation of magnetization behavior via counter anions,functionalization of SMTs protype and the assembly of SCO metallomesogen.Furthermore,the deposition of molecule-based magnets by chemical complementarity has been accomplished for investigating molecule-substrate interactions.The details are as follows:1.Through ligand self-condensation,we synthesized two hexagonal bipyramidal configuration mononuclear Dy complexes.The coordination environment of Dy3+is made of equatorial six neutral nitrogen atoms and axial two Ph3SiOH anions.Magnetic measurements reveal that both complexes are SMMs with high Ueff under zero dc field,however,fast quantum tunneling of magnetization(QTM)relaxation pathway could not be avoided at low temperature.The Magneto-structural correlations prove that distinct counter anions result different CShM compared to ideal D6h symmetry,this may be the reason for different QTM rates.2.Using a dihydrazone ligand,we isolated four binuclear Dy complexes.By changing counter anions,the coordination environment of Dy3+undergoes slight changes.These changes result different dynamic relaxation of magnetization:complex Dy2-Cl exhibits SMMs behavior under zero dc field;complex Dy2-NO3 and complex Dy2-CF3SO3 are SMMs under 600 Oe and 500 Oe optimal dc field;complex Dy2-ClO4 displays only slow relaxation of magnetization even under optimal dc field.The Magneto-structural correlations show that short Dy-O distances and linear O-Dy-O angles create an axial ligand field in which Dy complexes exhibit magnetic anisotropy and SMMs properties.3.We functionalized 2-hydroxy-3-methoxybenzohydrazide ligand by introducing functional group and synthesized eight trinuclear Dy complexes.Dc susceptibility measurements reveal diamagnetic behavior under 2 K and ac susceptibility measurement prove SMMs behavior under zero dc field.Calculation of magnetic anisotropy axis reveal the magnetic moment in a toroidal arrangement.Furthermore,two complexes terminated by C=C bond were chemically grafted on Si(100)surface via hydrosilylation reaction.The different length of linker between complex molecule and substrate modulates molecule-substrate interactions,also affect electronic structure and properties of molecule on substrate surface.4.A Schiff-based ligand was chemically tailored by introducing long alkyl chains with terminal C=C bond.Utilization of this ligand,we synthesized a mononuclear Fe(II)complex.Two-step SCO behavior was confirmed via variable-temperature susceptibility measurement,which originates from the changes of Fe2+ coordination environment and the conformational isomerization of long alkyl chains,respectively.DSC,PXRD and POM measurements suggest crystal-liquid crystal(LC)-liquid phase transition at high temperature and the liquid crystal phase was maintained until room temperature when cooling.In addition,complex molecule was successfully anchored on Si(100)surface via hydrosilylation reaction.A Fe(III)complex was observed on substrate surface by XPS studies.