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

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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.