Hybrid Organic/Inorganic Magnets
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Hybrid
Organic/Inorganic Magnets
Kunio Awaga, Eugenio Coronado, and Marc Drillon Introduction The construction of more and more complex systems starting from elemental molecular units used as building blocks is propelling several disciplines of burgeoning interest, such as supramolecular chemistry, molecular electronics, and molecular magnetism. In the particular context of magnetic molecular materials, an attractive possibility for adding complexity to the material is to use a hybrid approach in which an organic component is combined with an inorganic one. Both purely organic and purely inorganic approaches (see the articles in this issue by Veciana and Iwamura and by Miller, respectively) have been used extensively to obtain molecule-based magnets. The combination of these two kinds of magnetic molecular components has also been successfully explored to design polymeric magnets of different dimensionalities (the metal-radical approach).1 In this last case, both components play a magnetic role. A step forward in achieving multifunctionality is to design hybrid molecular materials formed by two independent molecular networks, such as anion/cation salts or host/guest solids, whereby each network furnishes distinct physical properties to the solid. This novel class of materials is interesting because it can give rise to the development of materials in which two properties in the same crystal lattice coexist, or materials that exhibit improved properties over those of the individual networks, or to new, unexpected properties due to the mutual interactions between them. One can imagine, for example, the combination of an extended inorganic magnetic layer opening the pathway to cooperative magnetism, with an organic or organometallic molecule that acts as a structural component controlling the interlayer separation. If the molecule in-
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serted between the layers has unpaired electrons, a hybrid compound is produced that combines cooperative magnetism and paramagnetism. Other suitable combinations, such as electronic conductivity and magnetism, or nonlinear optics and magnetism, can also be achieved by wisely choosing the constituent molecules. In this article, we report some relevant examples that illustrate the potential of this hybrid approach in the context of molecule-based magnetic materials.
Magnetic Multilayers Among the molecule-based magnets, those exhibiting inorganic layered structures are especially noteworthy, as they can be used to create new multilayered magnetic phases in which the network structure as well as the interlayer separation can be chemically controlled at the molecular level. Two illustrative examples are the series of layered hydroxide compounds M2(OH)3X·zH2O (MII Fe, Co, Ni, and Cu),2,3 and the series of bimetallic oxalate complexes [cat] [MIIMIII(ox)3] (MII Mn, Fe, Co, Cu, and Zn; MIII Cr, Fe, and Ru).4 The former series has positively charged magnetic sheets formed by layers, each with a triangular network of metal ions that are interleaved by an anion X, which can be either
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