Physics Colloquium

The vast structural diversity of polyoxomolybdates and their ability to incorporate a large number of 3d or 4f metal cations opens synthetic routes to new magnetic molecules in which the diamagnetic molybdate framework acts as an efficient mediator of magnetic superexchange. Interactions between the magnetic centers are confined to the molecular spin arrays that frequently adopt higher symmetry elements of the nano-sized polyoxometalate host structure, resulting in unprecedented spin geometries and unexpected new magnetic features: Keplerate-type polyoxomolybdate structures of icosahedral symmetry, for example, can incorporate up to thirty quasi-classical or quantum spin centers. Such magnetically functionalized derivatives display highly symmetrical geometrical spin frustration, metamagnetic transitions that hitherto have been observed for Kagome lattices, or high-spin ground states. Moreover, sequential replacement of individual magnetic constituents of polyoxomolybdate cluster structures allows tuning of the system’s magnetic properties to a degree not possible for coordination-based magnetic molecules. Leaving the molecular boundaries, the linking of polyoxomolybdate-based magnetic molecules to networks of different dimensionalities, resulting in the gradual introduction of magnetic inter-cluster interactions, enables us to study the interplay of breaking the symmetry of intra-cluster exchange and the onset of cooperative phenomena. Finally, a glimpse on current development of novel polyoxomolybdate building blocks will illustrate what magnetic systems might be accessible in the near future.