| Co-Investigator(Kenkyū-buntansha) |
TAJIMA Hiroyuki Tokyo Univ., Institute for Solid State Phys., Asso. Prof., 物性研究所, 助教授 (60207032)
NAITO Toshio Hokkaido Univ., Grad. School of Sci., Asso. Prof., 大学院・理学研究科, 助教授 (20227713)
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| Research Abstract |
Phthalocyanine (Pc) complexes with axial CN ligands were utilized for development of novel conductors based on the originally devised stepwise stacking. When the central metal ion is nonmagnetic Co^<III> normal conductors can be obtained, while when it is magnetic Fe^<III> magnetic conductors can be obtained.
Electrochemical oxidation of [Co^<III>(Pc)(CN)_2]^- yields the neutral radical species in which the Pc ligand becomes open-shell structure. The crystal constructed solely with this species was not highly conducting while co-crystallization with solvent molecules improved the conductivity due to the efficient π-π stacking. Various stacking structures depending on the solvent species have been obtained. The neutral radical crystals are semiconductors due to the electron correlation effect, while crystallization with the anion (partially oxidized salt) gage metallic conductors. Their formation depends on the cationic species, and six partially oxidized salts with various π-π stacking
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structures have been obtained. Among them the crystal with double two-dimensional sheeto structure has been found to maintain metallic character at low temperatures under high pressure.
Electrochemical oxidation of [Co^<III>(Pc)(CN)_2]^- gave isomorphous crystals with the Co salts. For the one-dimensional system, the physical properties of the Co and Fe salts were investigated in detail. Electronic structure was found to be identical based on the thermoelectric power and optical reflectance measurements. On the other hand, the electrical conductivity was found to be dramatically different from each other , the resistivity is almost constant for the Co salt, while it shows insulating behavior at low temperature for the Fe salt. This is due to the existence of periodically arranged magnetic moments at the center of the Pc rings. As an important consequence, we have found that the resistivity decreases by applying external magnetic field. It is unusual that such a one-dimensional system shows "giant negative magnetoresistance". Less
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