3d-4f And4f Clusters: Synthesis And Studies Of Their Magnetic Properties

Since the dodecanuclear manganese cluster was obtained as the firstsingle-molecule magnet （SMM）, SMMs and SCMs （single-chain magnets） have beenof increasing interest, mainly because of their potential applications in high-densitymagnetic memories, quantum computing and molecular spintronics. Over the lasttwo decades, a great number of transition-metal molecular magnets have beensynthesized and their magnetic properties have been widely studied.3In recent years,3d-4f and4f coordination compounds have attracted more and more attention in thefield of molecular magnetism due to their significant magnetic anisotropy from theunquenched orbital angular momentum. In order to investigate the effects of bridgingligands on magnetic behaviors, it is necessary and challenging to explore newsingle-molecule magnets. In the first chapter of five, the concepts, research methods,histories and new developments of single-molecule magnets are introduced. At theend of this chapter, we pointed out the importance of the search project.In the second charpter, we have shown that the Schiff-base ligands with differentnumbers of hydroxyl can provide access to two unusual polynuclear3d-4f compounds[Na₂Fe^III6Dy^III2（N₃）4（HL）4（CH₃O）4（PhCO₂）6（CH₃OH）2]（CH₃OH）3（CH₃CN）₂（1） and[Na₂Fe^III6Dy^III2（N₃）4（L’）4（CH₃O）4（PhCO₂）6（H₂O）2]（H₂O）2（2）, of which the[Na₂Fe^III6Dy^III2] cores form a couple of cis, trans-isomers. Furthermore, thetrans-[Na₂Fe^III6Dy^III₂] cluster in compound [Na₂Fe^III6Dy^III2（N₃）4（L’）4（CH₃O）4-（ButCO₂）6]（CH3CN）（3） acts as network nodes in the formation of a2D rhombic grid-like layered structure, when the pivalates take the place of bulkier benzoates. Inorder to investigate the magnetic behaviour of3d-4f systems, compounds[Na2Fe^III6Y^III2（N3）4（L’）4（CH₃O）4（PhCO2）6（H₂O）₂]（H₂O）（4） and [Na2Fe^III6Gd^III2-（N3）4（L’）4（CH₃O）4（PhCO₂）6（CH₃OH）2]（H₂O）6（5） which differ in the lanthanide havealso been prepared. The magnetic properties of these compounds are dominated byantiferromagnetic interactions from [NaFe^III3] units, and the interactions between Ln^III-Fe^IIIand Ln^III-Ln^IIIalso make some contributions. To some extent, this researchopens up a promising pathway to investigate the effect of organic ligands on thestructure of polynuclear polymer. Though all the compounds are not SMMsthemselves, the successful synthesis of the compounds may suggest new methods toconstruct novel3d-4f magnetic materials.In the third chapter, three fluoride-bridged lanthanide compounds[Dy^IIIF（oda）（H₂O）₃]（6）,[Tb^III2F2（oda）2（H₂O）₂]（7） and [Dy^III2F2（oda）2（H₂O）2]（8） havebeen obtained. The magnetic measurements show that the complexes6,7and8exhibit intramolecular ferromagnetic interactions, while only antiferromagneticinteractions are observed in hydroxyl-bridged compounds [Tb^III2（OH）2（oda）2（H₂O）4]（9） and [Dy^III₂（OH）₂（oda）₂（H₂O）₄]（10）. Among these compounds6and8showfrequency-dependent ac-susceptibility indicative of slow magnetic relaxation.Because the structures of Dy2cores are very similar in compounds8and10, thesesignificant disparities are most likely due to the differences of bridging ligands for therespective dinuclear cores. The bridging F-ions not only promote magnetic exchangeinteractions, but also induce slow magnetic relaxation. We believe that the successfulsynthesis of the three fluoride-bridged coordination compoundes may open up newopportunities to construct SMMs based on fluoride ligand.In the fourth chapter, three MeQ-bridged lanthanide compounds[Gd^III2（MeQ）4（NO₃）6]（11）,[Dy^III2（MeQ）₄（NO₃）₆]（12）,[Gd^III2（MeQ）₄Cl₆]（EtOH）₂（13）and [Dy^III₂（MeQ）4Cl6]（EtOH）₂（14） have been obtained. The magnetic measurementsshow that the complexes exhibit intramolecular antiferromagnetic interactions.Compounds12and14show frequency-dependent ac-susceptibility indicative of slowmagnetic relaxation, but the values of energy barrier are distinct. Because the bridging ligands are very similar in compounds12and14, these significant disparities are mostlikely due to the differences of terminal ligands for the respective dinuclear cores.Although the terminal ligands can not promote magnetic exchange interactionsbetween the lanthanide ions, they can induce slow magnetic relaxation. We believethat the successful synthesis of these compoundes may open up new opportunities toconstruct SMMs.