Development of Molecule-Based Magnets Tunable by Means of Supramolecular Chemistry

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Supramolecular techniques such as host-guest complex formation have been used to tune molecule-based magnetic materials. We have developed two nano-porous magnetic materials, whose magnetic properties were changed by inclusion of small diamagnetic molecules.The first are low-temperature magnets derived from iron(II), dicyanamide anion, and pyrimidine, which have guest molecules incorporated in the clearance of the 3-D framework. The T_c ranges from 3.4 K to 5.6 K, depending on the guest molecules. They are characterized as canted antiferromagnets below T_c. The critical temperature, critical field, and spontaneous magnetization are Modulated by the guest inclusion.The second are hexanuclear wheel-shaped copper(II) complexes, whose crystals have a channel structure in a direction perpendicular to the molecular plane. The ferromagnetic interaction, which is ascribed to intermolecular contacts between the radical substituents, was remarkably enhanced by guest inclusion within a channel. The effect of water is especially noticeable ; the magnetic properties returned to the empty one by removal of water. This system is a rare example of realizing the regulation of magnetic properties by means of host-guest chemistry.We also prepared metal-radical hybrid magnets using bridging ligands as supramolecular synthons. Novel paramagnetic chelating ligands (4ImNNH, pzNN, pzIN, pzbisNN, and pzbisIN) were developed and applied to the synthesis of mononuclear, triangular, and linear polynuclear complexes. We have exploited potential utility of the smallest bridging paramagnetic ligands (HIN and HNN) and clarified that the choice of small ligands was a promising strategy to bestow strong exchange interaction in metal-radical solids.