Synthesis, Self-Assemble And Magnetic Characterizations Of High-spin1,3-Propanediol-Mn Compounds

Polynuclear manganese compounds have been of great interest for their closerelevance to various research areas such as bioinorganic chemistry and molecularnanoscience. The former, bioinorganic chemistry, Mn clusters have been componentsin some important enzymes related to energy transformation processes, such asphotosystem II （PS II） in green plants. The latter has attracted much attention sincethe first discovery of Single–Molecule Magnets （SMMs）.As for an SMM or a Single–Chain Magnet （SCM）, in which there is a significantreversal barrier to the magnetization relaxation and quantum tunneling, it is extremelydesirable of high–spin mixed–valence Mn clusters, benefiting from their large spins（from MnII） and anisotropy （from Jahn–Teller distortion of MnIII）, combined withtheir coordination adjustability. However, the “serendipitous” strategy by ordinarilymixing chelating ligands and Mn salts or precursors, from which there has been seriesof polynuclear Mn clusters reported with aesthetically pleasing structures andinteresting magnetic properties, is very limited to shepherd preparation and propertyexpansion of new high–spin Mn compounds.Upon the development of Crystal Engineering,“bottom–up” approach has beenbroadly employed in preparative researches of Metal–Organic Frameworks （MOFs）,polyoxometallates （POM）, and zeolites. Such approach is focused on the self–assemble of so–called Secondary Building Units （SBUs）, which are smallcoordination sub–units able to construct high dimensional compounds via one–pot orstepwise reactions. For a magnetic SBU, three points are requisite,1) structuralstability, that is, the magnetic SBU should certainly and rapidly generate in acoordinating process, especially in one–pot preparation,2) continuing reactivity, in which vacant coordination sites should be included, and3) the most important, minorproperty sensitivity to coordination structural shifts, when being applied in thesynthesis of high–spin Mn clusters. Lack of property tolerance might be one reasonthat the “bottom–up” approach is hardly employed in the synthesis of molecular–based magnets.There are many high–spin Mn clusters reported in the presence of1,3–propanediol ligands. By close structural analysis, we have discovered the firstappropriate high–spin SBU: the supertetrahedral [Mn10]. Furthermore, introducingweak interaction centers via ligand modifications, another high–spin SBU, linear[Mn₃] has been isolated, and its structural stability and magnetic reliability have beenrevealed. The maintained structure as well as ferromagnetically coupling natureamong all compounds obtained, without exception, indicates extraordinary potentialapplication of [Mn₃] as a high–spin SBU.In Chapter One, prominent results in molecule–based magnets are brieflyreviewed; molecular magnetism and basic principles of magnetic fitting are alsoconcisely introduced.In Chapter Two, ligand modification effects in1,3–propanediol–Mn chemistry isconcerned, and the process from supertetrahedral [Mn10] to linear [Mn₃] is described.In Chapter Three and Four, self–assembles of [Mn₃] SBUs to construct highdimensional aggregates under manifold weak interactions such as π–π stacking,hydrogen bond, steric repulsion and electronic interactions, have been successfullyachieved.In Chapter Five, carboxylate co–ligands and heteroatomic DyIIIions have beenused to investigate the stabilities and organizations of [Mn₃] SBUs in competingcoordination conditions. As a result, two chains were obtained with a novel helicalaggregation and an SCM behavior, respectively. The intrinsic ferromagnetic couplingwas vanished despite the maintenance of the quasi–linear structure. It might beresulted from the different magnetic superexchange pathways and/or variousinterrelated magnetic orbitals, respectively.