Study On [Mo (CN) ₇ ^{4 -} Molecular Magnetic Materials

The study of cyano-bridged paramagnetic compounds based on 4d/5d transition metals is an emerging research topic in the field of molecular magnetism. An ess ential driving force for the interest in this area is the fact that heavier metal ions introduce important attributes to the physical properties of paramagnetic compounds. Among the attractive characteristics of heavier elements vis-a-vis magnetism are the diffuse nature of their d orbitals, their strong magnetic anisotropy owing to enhanced spin-orbit coupling, and their diverse structural and redoxproperties. Cyanide also has significant advantages to construct molecular magnets as a bridging ligand. This thesis focuses on the research of molecular magnetism based on the [Mo(CN)7]4-building blocks, hoping to get more compounds of interesting magnetic properties. Through wide attempts, the main results obtained are as following.First, aiming at the existing problems of the formly obtained results of our group, we performed more careful studies on two compounds formly obtained, [Mn(LN5C10)]2[Mo(CN7]·2H20 (1) and [MnⅡ(LN5C6)H2O]2][MoⅢ(CN)7]·5H2O·CH3CN (2). Both compounds are rare one-dimensional (1D) complex based on the [MoⅢ(CN)7]4- building block. Since low-dimensional compounds based on the [MoⅢ(CN)7]4- unit are very rare due to the instability of the [Moin(CN)7]4- unit and its tendency to form high dimensional compounds, these two compounds are of great interest for the study of low-dimensional magnetic materials. For compound 1, we performed the reaction in a more rigid oxygen-free atmosphere and synthesized the pure material by an improved method. Detailed characterizations, including the new magnetic measurement, were performed on the new material. The new results confirmed that compound 1 exhibits a spin-glass like long-range ferrimagnetic ordering with the Tc of 5.6 K. In addition, clear hysteresis loop was observed at 1.8 K. For compound 2 with a one-dimensional helical chain structure, we obtained big single crystals by improved synthetic method. With these single crystals, we performed detailed anisotropic magnetic measurement on this compound. We found that the slow magnetic relaxation was only observed when the field is along the chain direction.As the blocking temperature is below 1.8 K, we also measured its magnetic properteis at very low temperatures down to 0.5 K, which further proved the single-chain magnetic behavior of compound 2. According to the ac data below 2 K, the magnetic relaxation energy barrier is found to be 19.2 K.In addttion, by using some bidentate ligands such as pypz-1, pypz-5, pyim, as second ligand, we successfully synthesized three 3D compounds based on the [MoⅢ(CN)7]4- unit, namely [Mn2(pypz-5)][Mo(CN)7]·H2O·CH3CN (3), [Mn2(pypz-1)][Mo(CN)7]·H2O·CH3CN (4), [Mn2(pyim)][Mo(CN)7]·H2O·CH3CN (5). X-ray single crystal diffraction measurements show that these three compounds are isomorphous with three dimensional structures. Magnetic characterization revealed that they are magnets of long-range magnetic ordering with the critical temperatures at above 60 K.