The investigation of structures and processes at the nanometer scale is a research domain of steadily increasing importance, with relevance to both basic sciences as well as technological applications. A particularly active area of nanoscience deals with the design, synthesis, investigation, and modeling of magnetic particles of nanometer scale. The interest in these kinds of materials spans such diverse areas as quantum physics, magnetochemistry, and biology. Physicists try to confirm basic concepts of quantum theory and explore the border between classical and quantum physics, chemists set out to synthezise and study new nanoscale magnetic materials, and biologists are interested in metal storage, biomineralization, and the role of magnetic minerals in magnetotactic bacteria. It is however still difficult to control the size and exact composition of such nanometer scale magnetic particles. An extremely promising approach to overcome these difficulties is the synthesis of discrete molecular clusters of exchange-coupled transition metal ions. Such efforts have, over the last few years, lead to several molecule-based magnets. These molecular magnetic materials possess many properties normally associated with organic polymeric compounds, such as low specific density or optical transparency, but combined with the magnetic properties of classical bulk magnets. Molecular magnetism is therefore one of the most challenging research areas in the development of new technologies in electronics.
The general search for new compounds with interesting magnetic properties has prompted chemists to combine different spin carriers within the same molecular entity. Purely organic magnetic materials have been prepared from macrocyclic and dendritic polyradicals, nitroxides, nitronyl nitroxides, and semiquinone radicals. Most of the work has however been devoted to metal complexes with o-semiquinonate, imino nitroxide, and nitronyl nitroxide radical ligands so far. The whole subject has been intensively reviewed in the recent years.