| Summary: | 博士 === 國立臺灣大學 === 化學研究所 === 104 === Metal strings have attracted much attention of physicists and chemists because of their potential applications for the devices of nanoelectronics. Heteronuclear metal strings have their special properties of electronic conduction. In this work, the syntheses, crystal structures, and magnetic properties of seven trinuclear, heterometal string complexes stabilized by four dipyridylamide (dpa) ligands are reported. All compounds exhibit an approximate D4 symmetry and a linear metal framework helically wrapped by four syn-syn-type ligands. The center metal ions bond with the amide part of dpa in square-planar environment, and the outer metal ions bond with Cl and pyridine part of dpa in square-pyramidal environment. Compounds MnMMn(dpa)4Cl2 (M = Ni for 3, M = Pd for 4, M = Pt for 5) and FeMFe(dpa)4Cl2 (M = Ni for 6, M = Pd for 7, M = Pt for 8) show antiferromagnetic interaction between the terminal metal ions, and the 2J value increases with increasing atomic number of the central metal ion. This trend is the exact reverse of the trend observed for the CuMCu(dpa)4Cl2 (M = Cu3+, Pd2+, Pt2+) analogs. This observation may be explainable by the different magnetic coupling mechanisms between two series of compounds.
Co2+ has the higher stability at the terminal position in metal string than Co2+. In the reaction of CoPtCo(dpa)4Cl2 (1) and 20 eq Cu(OA)2, Co2+ can be replaced by Cu2+, and CoPtCu(dpa)4Cl2 (9) can be obtained. Compound 9 has the metal disorder in the structure. From NMR and Mass spectra, the unsymmetric metal arrangement and the components of compound 9 can be confirmed. Compound 9 shows antiferromagnetic interaction between the terminal Co2+ and Cu2+ at low temperature (4─150 K) and shows the spin crossover of Co2+ at high temperature (150─300 K).
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