Molecule-based Magnets: New Materials, Chemistry, and Physics for this Millennium

Joel S. Miller (University of Utah)

Molecule-based materials exhibiting the technologically important property of bulk magnetism have been prepared and studied in collaboration with many research groups worldwide frequently exhibit supramolecular extended 3-D structures. These magnets are prepared via conventional organic synthetic chemistry methodologies, but unlike classical inorganic-based magnets do not require high-temperature metallurgical processing. Furthermore, these magnets are frequently soluble in conventional solvents (e. g., toluene, dichloromethane, acetonitrile, THF) and have saturation magnetizations more than twice that of iron metal on a mole basis, as well as in some cases coercive fields exceeding that of all commercial magnets (e.g., Co5Sm). Also several magnets with critical temperatures (Tc) exceeding room temperature have been prepared. In addition to an overview of magnetic behavior, numerous examples of structurally characterized magnets made from molecules will be presented. Our group has discovered 7 families of molecule-based magnets, mostly organic-based, and have significantly contributed to an eighth family based upon the Prussian blue structure. Four examples magnetically order above room temperature and as high at 127 oC. These will include [MIII(C5Me5)2][A], [MnIII(porphyrin)][A] (A = cyanocarbon etc. electron acceptors) as well as M[TCNE]x, which for M = V is a room temperature magnet that can be fabricated as a thin film magnet via Chemical Vapor Deposition (CVD) techniques. A newer class of magnets of [Ru2(O2CR)4]3[M(CN)6] (M = Cr, Fe; R = Me, t-Bu) composition will also be discussed. For R = Me an interpenetrating, cubic (3-D) lattice forms and the magnet exhibits anomalous hysteresis, saturation magnetization, out-of-phase, c"(T), AC susceptibility, and zero field cooled-field temperature-dependent magnetization data. This is in contrast to R = t-Bu, which forms a layered (2-D) lattice. Additionally, new magnets possessing the nominal Prussian blue composition, M'[M(CN)6]x and (Cation)yM'[M(CN)6], will be described.

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