Credit: © 2008 Wiley

The properties of nanoscale single-molecule magnets (SMMs) can be fine-tuned by structural and chemical modification. Now, by encapsulating SMMs in a polyoxometalate (POM) framework, a team from the University of Glasgow led by Leroy Cronin and Mark Murrie, and co-workers from Scotland, Germany and Japan, have shown1 that manganese-based SMMs can be effectively isolated and stabilized. Furthermore, their physical properties can be modified through variations in the POM ligand.

Two different SMMs were synthesized, each consisting of a central mixed-valence hexanuclear manganese unit that forms a number of co-ordination bonds with two identical polytungstate POM ligands. The two complexes differed only in the heteroatom — either silicon or germanium — included within oxo-anion building blocks of the POM ligands. In each case, the sandwiched central core adopted a stable and well-defined geometry, arranging into a double cubane structure — two cubes attached by a single shared face. Interestingly, even though the core unit of both SMMs is chemically equivalent, large geometrical differences were observed depending on the heteroatom present in the POM ligands.

The magnetic susceptibility properties of the structures were found to differ in a way that was consistent with the geometrical differences induced by the respective heteroatoms of the POMs. The SMM characteristics of the germanium-containing complex were further confirmed by demonstrating their temperature- and sweep-rate-dependent magnetic hysteresis.