Synthesis and Structural Characterization of Transition Metal-Substituted Polyoxoanions and Investigation of Their Unique Magnetic Properties

我们建议合成由众多顺磁性过渡金属中心(如Mn2+、Cu2+、Co2+、Fe3+)取代的新型多氧钨酸盐分子。我们的重点是过渡金属离子与‘超空位’和不稳定的多氧阴离子配体[a-H_2P_2W_(12)O_(48)]12-的相互作用。通过X射线衍射、单晶SQUID磁测量、热容测量、变频高场EPR和核磁共振、光学光谱等手段，结合理论计算对材料进行了表征。这是第一次旨在详细了解这种相互作用的研究。我们期望发现具有同样新颖的磁性的新型聚氧阴离子结构。过渡金属与缺位多金属氧酸盐的相互作用允许结合磁性金属离子簇。聚氧阴离子与几个顺磁性过渡金属离子在附近表现出交换耦合，可能导致大的自旋基态。在这种化合物中，多金属氧酸盐基质可被认为是包裹并因此隔离过渡金属的磁团簇的抗磁性主体。

We propose to synthesize novel polyoxotungstate molecules substituted by numerous paramagnetic transition metal centers (e.g. Mn2+, Cu2+, Co2+, Fe3+). Our focus is on the interaction of transition metal ions with the 'super-lacunary' and labile polyoxoanion ligand [a-H2P2W12O48]12-. The materials will be characterized by x-ray diffraction, single crystal SQUID magnetometry, heat capacity measurements, variable frequency-high-field EPR and NMR, and optical spectroscopy, combined with theoretical calculations. This is the first study aimed at a detailed understanding of this kind of interaction. We expect to discover fundamentally novel polyoxoanion structures with equally novel magnetic properties. Interaction of transition metals with lacunary polyoxometalates allows to incorporate clusters of magnetic metal ions. Polyoxoanions with several paramagnetic transition metal ions in close proximity exhibit exchange-coupling, possibly leading to large spin ground states. In such compounds the polyoxometalate matrix may be considered a diamagnetic host encapsulating and thereby isolating magnetic clusters of transition metals.