Funded Projects

Start of funding 01.07.2003

Synthesis of Single Molecule Magnets incorporating ferric wheels

Thomas Gottschalk
Friedrich-Alexander-University of Erlangen-Nuremberg
Institut für Organische Chemie I

Prof. J. Fraser Stoddart
University of California, Los Angeles (UCLA)
Department of Chemistry and Biochemistry

Since the discovery, that paramagnetic molecular clusters can act as nanoscale magnets below a critical temperature, the synthesis of polyoxometalates have become the focus of intense research activities. Such single-molecule magnets (SMMs) can be regarded as ideal model systems for the infinite-size version of the linear Heisenberg chain and are promising new materials for data storage and quantum computing. They exhibit magnetization hysteresis, quantum tunnelling of magnetization, and most interestingly, allow to demonstrate an exciting effect: cooling by magnetisation. Over the past years, considerable progress has been made towards the predictability of ordered supramolecular assemblies on the basis of coordinative metal/ligand bonds. A particular symmetric class of compounds with SMM-properties are the so-called ferric wheels and ferric stars, prepared in our laboratory. Further more, we have synthesized a series of carbohydrate dendrimers incorporating ferrocene cores. A detailed analysis of the resulting molecular assemblies revealed that the ß-D-glucopyranose branches surrounding the electronegative core have profound influence on its redox response. The procedures developed for the synthesis of the ferric wheels and the ß-D-glucopyranose branches should allow the convergent synthesis of carbohydrate-contaning metalla-dendrimers incorporating the ferric wheel.

Final report:
In a collaborative effort between the groups of R. W. Saalfrank (FAU Erlangen) and J. Fraser Stoddart, funded by BaCaTec, a series of novel compounds was synthesized (see figure). The novel complexes consist of a carbohydrate periphery and six metal centers. Six indium ions are bridged and held together by ethanolate arms of a diethanolamine motif in the six ligands. Applications and further developments will point toward analogous iron(III) complexes that could lead toward novel, biocompatible single-molecule magnets and novel pharmaceuticals for iron overload/deficiency-related illnesses.

Suggested reading:
R. W. Saalfrank, E. Uller, B. Demleitner, I. Bernt, in Structure and Bonding, Vol. 96 (Ed.: M. Fujita), Springer, Berlin, 2000, p. 149