Self-assemble And Magnetic Studies Of The Mixed-valence [Mn3] Clusters

A Single-Molecule Magnet (SMM) has distinctive, molecular originatedmagnetic nature: first of all, its large reverse energy barrier preserves themagnetization from magneton relaxation below a certain temperature, and secondly,the Quantum-tunneling Magnetization effect (QTM), which could be determined byM-H curves, provide an excellent model for quantum state investigations. Suchproperties allow the SMMs not only great potentials to extremely increasemagnetic information storage density, but also possibilities to constructquantum-two-state-system based quantum computing units as the result of QTM,respectively. Therefore, since the advent of the SMM [Mn12O12(O2CMe)16(H2O)4]2MeCO2H H2O (Mn12Ac) in1991, preparation and characterization of novelmagnetic compounds have attracted attentions from scientists in the fields such asbiochemistry and material chemistry. Specially, the preparation of magneticcompounds has displayed fundamental but important function in the studies of suchfields.With deeply understanding the structure-property relationships of magneticmetal cluster, such “serendipitous” and inchoate all-assembling strategies are whollyinadequate to meet the demand of novel magnetic complex preparation. However,during the decade, a Bottom-up strategy has successfully applied in CrystalEngineering, especially in preparations of Metal-Organic Frameworks (MOF),Polyoxometallates (POM), and Zeolites. The kernel of the strategy is employing the“building blocks”(or Secondary Building Units, SBUs) to process partiallycontrolled assembly. This process includes two parts: selection of precursors orcoordinating structure units as building blocks, and the reaction of building blocksand bridging ligands to yield complexes with expected topologic structures. As fornovel magnetic complex preparation, the application of the Bottom-up strategy couldbe able to guarantee the existence of the kernel structure; on the other hand, such strategy could reduce the structure-organizing limit to prompt the possibilities ofdesigned synthesis. Specifically, the Bottom-up strategy might simplify the structureof multiple complexes, to reinforce understandings of structure-magnetic exchangerelations; it might combine high ground spins and large axis anisotropies byintroducing various building blocks to build new SMMs with enhanced property; itmight realize the combination of magnetic and multifunctional properties, toconstitute novel multi-response magnetic complexes; it might be expected thatstructure-induced magnetism shifts could result in new coupled properties.In this dissertation, the linear high spin [Mn3] structure was chosen to constructnovel high-spin magnetic complexes through modification of serinol ligand andintroduction of bridging units. Further structural analysis and magneticmeasurements have proved the structure and property stabilities of selected [Mn3]unit.The first chapter has reviewed some representative results of the SMMs, andintroduced magnetic theory and supermolecular isomerism generated by buildingunits.In the second chapter, fluorene modified serinol ligand was employed to expandthe structure of [Mn3] SBU, and novel0-D and1-D magnetic complexes weresuccessfully achieved. The magnetic characterization data has showed once again thestructural and magnetic stability, as well as self-assemble variability of linear [Mn3]unit.In Chapter Three, through introduction of various groups to serinol ligands andthe assistance of proper bridging ligands, we have obtained [Mn3] based2-Dself-assemble structures. However, surprisingly, the secondary self-assemble of the2-D structure, from sheet to nanotube, has been achieved straightforwardly bymodulating weak interactions between2-D layers.