Synthesis And Property Of Functional Mn₁₂ Single Molecule Magnets And Layered MPS₃ Magnetic Materials

Generally, the traditional magnetic materials are some transition metals, rare earth metals and other inorganic materials consisting of inorganic elements. In the past decades molecule-based magnetic materials has been attracted much attention due to its superior properties to inorganic materials such as easily controlling or modifying structure, good processiblity and so on. Among the molecule-based magnetic materials, single-molecule magnets (SMMs) is considered to be a intersection of molecule-based ferromagnets and nano-magnetic materials.It is the first true single-dispersed nano-magnets that does not derive from the long-range ordered magnetic interaction among the spins. The wide and deep study on SMM will help to understand that how does the quantum mechanics behavior of SMM work at macro-scale to explain its macroscopic magnetic property. It is a promising functional materials that will be applied in high-density information storage devices and future quantum computer. On the other hand, the layered transition metal phosphorus trisulfides and the corresponding intercalation compounds attracted wide attention because of the unique magnetic properties. Searching for new layered MPS3 solids, high-Tc magnetic intercalation compounds and multifunctional intercalation compounds is also a challenging research work that needs to be further attempted. This paper focuses on the design, synthesis and magnetic properties of Mn12 SMM and MPS3-based magnets, respectively.The thesis is composed of two sections. One part (Chapters II and III) probes into the functionazation and polymerization of Mn12 cluster as single molecule magnets. The other part (Chapter IV to VI) is focused on the synthesis of new layered MPS3 compounds and the corresponding intercalation compounds.Chapter I briefly summarizes the development of single-molecule magnets and the intercalation compounds. The attention is focused on Mn12 clusters as single-molecule magnet and layered MPS3-based intercalation compounds. And then the design strategies and main contents for this thesis are outlined.In Chapter II, four aromatic monomers (M1-M4) and corresponding conjugated oligomers (01-04) with alkyl-chain carboxylic group have been synthesized. Via the exchange of M1-M4 and 01-04 with Mn12-Ac a series of new Mn12 clusters (Mn12-M1—Mn12-M4 and Mn12-O1—Mn12-O4) are obtained for the first time. Their structure is characterized by TEM, SEM, IR and elemental analysis. The long bar-shape of the Mn12 compounds is observed with TEM measurement, which is much different from the round-ball shape of Mn12Ac, suggesting that the 8 axial positions of Mn12 core are occupied by the conjugated small molecules or oligomers. Their photophysical properties and electrochemical properties are studied. It is found that the Mn12 clusters modified by conjugated molecules show almost same UV-vis absorption and emission spectra to the corresponding monomers (M1-M4) and oligomers (01-04), indicating that the introduction of Mn12 core does not affect the photophysical properties of the conjugated molecules. The magnetic properties are also primarily studied by SQUID. Among them four Mn12 Clusters (Mn12-M3, Mn12-M4, Mn12-02 and Mn12-O4) show the distinct ladder-type hysteresis loop at 2 K similar to that of Mn12-Ac cluster, suggesting that they are typical of single molecule magnets. However, Mn12-O1 cluster shows an obvious hysteresis loop at 2 K but no ladder-type hysteresis is observed. As for Mn12-O3 cluster, no hysteresis loop at 2 K is observed, indicating that single molecule magnetic properties does not exist. This indicates that the structural change of the conjugated molecules can influence the magnetic properties of Mn12 cluster.In Chapter III two main-chain polyflurorene-based conjugated polymers (P1 and P2) with pendent alkyl carboxylic are designed and synthesized initially. And then two corresponding Mn12 cluster containing conjugated polymers are obtained via the exchange of P1 and P2 with Mn12-Ac. TEM characterization indicates that Mn12 core is wrapped by polymer chain. Their photophysical properties and electrochemical properties are studied. It is found that the main-chain conjugated polymers and the corresponding Mn12 clusters show almost same UV-vis absorption and emission spectra, indicating that the photophysical properties of the conjugated polymers are almost not influenced by the introduction of Mn12 core. Magnetic measurement for Mn12-P1 and Mn12-P2 shows an obvious hysteresis loop at 2 K, but no ladder-type hysteresis is observed.In this chapter another polymer (P3) polyethylene glycol containing a carboxylic acid at the endis is prepared via "Click Reaction". With exchange of Mn12-Ac with P3 a Mn12 cliuster (Mn12-P3) is obtained. It has good solubility in common organic solvents. TEM images show the long-strip shape for it. At the same time, we also synthesize polythiophene (P4) with catboxylic group at the end of mian-chain, in which a carboxylic acid group directly linked conjugated main-chain. The corresponding Mn12 cluster (Mn12-P4) is also obtained by the exchange of P4 with Mn12-Ac. TEM images show the irregular cubic shape for it. Optical performance show that the introduction of Mn12 core into ploythiophene lead to the "red-shift" of UV absorption and photofluorescence emission. We studied the magnetic properties of them with SQUID technology. Similar to Mn12-P1 and Mn12-P2, the hysteresis loops at 2 K is observed, but the ladder-type hysteresis behavior disappear. Their magnetic properties also need further study.In Chapter IV, we have synthesized a series of layered NixMn1-xPS3 (x= 0.15, 0.25,0.50,0.75,1) compounds by high temperature solid state reaction. Through the ion-exchange two series of intercalation compounds (NixMn1-x-yPS3(bipy)4y and NixMn1-x-yPS3(Et4N)2y) are obtained and characterized by XRD, IR and elemental analysis. The magnetic properties are studied by SQUID. It is found that all the NixMn1-xPS3 compounds exhibite anti-ferromagnetic phase transition at low temperature. But the ratio of Mn and Ni can greatly influence the magnetic properties of NixMn1-xPS3. If the content of Mn and Ni is almost equal or so, the Neel temperature of NixMn1-xPS3 greatly decreases, which may be attributed to the difference of the electronic structure and ion radius between Mn and Ni ions that results in the disorder of structure and reduces the magnetic interaction of the spins. In addition, it is found that all the full intercalation compounds exhibit the paramagnetism. The possible reason is that the disordered structure of NixMn1-xPS3 and the "magnetic dilution" of intralayered Mn2+ion vacancies by the ion-exchange greatly reduce the magnetic interaction of the metal spins in NixMn1-xPS3 slab.In Chapter V we synthesize a series of layered MnPSxSe3_x (x= 0.4,0.6,0.8,1.2, 1.8 and 2.4) compounds by high temperature solid state reaction. Via the ion-exchange method two kinds of intercalation compounds is synthesized. One is Mn1-yPSxSe3-x(bipy)4y intercalation compounds and the other is Mn1-yPSxSe3-x(Et4N)2y intercalation compounds. Their structure is characterized by XRD, IR and elemental analysis. The magnetic properties are studied by SQUID. It is found that all layered MnPSxSe3-x compounds exhibit antiferromagnetic phase transition at low temperature and the Neel temperature is affected by the content of sulfur. In addition, the ratio of sulfur and selenium greatly influences the magnetic properties of the intercalation compounds. When the content of S and Se is much difference, the intercalation compounds show obvious ferromagnetic phase transition at low temperature. If the content of S and Se is almost equal or so, the intercalation compounds become paramagnets.In Chapter VI, three intercalation compounds based on the cationic complex [M(DETA)]2n+(M= Cu2+, Co3+, Ni2+) into the layered MnPS3 have been obtained. The structure of the intercalation compounds are characterized by XRD, IR and elemental analysis and the magnetic properties is studied. Compared the lattice expansion of intercalates with pristine MnPS3, it can be inferred the coordination geometry of the cationic complexes at the inrerlayered space of MnPS3 is different between Cu(DETA)22+ and M(DETA)2n+(M= Ni2+ and Co3+). The magnetic measurement confirms that the intercalates Mno.88PS3[Cu(DETA)2]0.12·H20 and Mno.74PS3[Co(DETA)2]0.17·0.5H2O exhibit bulk spontaneous magnetization at low temperature that is different from the magnetic behavior of Mno.79PS3[Ni(DETA)2]0.21. This indicates that the intercalation of cationic complexes with different spin metal ion can influence the magnetic properties of the layered MnPS3 slab.