Structure and Magnetic Properties of Pentanuclear Metal Cluster and 1D chain Metal Complexes with a tetradentate bpt- Ligand
Date Issued
2010
Date
2010
Author(s)
Huang, Hsin-Chia
Abstract
With a tetra-dentate ligand abpt ( abpt = 4-amino-3,5 -di-2-pyridyl-1,2,4triazole ), the pentanuclear metal cluster complexes[{FeⅡ(μ4-bpt)3}2FeⅡ3(μ3-O)][(ClO4)2] (1) and the one-dimensional zigzag type complexes {[FeⅡ(μ4-bpt)(abpt)](ClO4)}n (2) （bpt = 3,5-di-2-pyridyl-1,2,4triazole）; have been synthesized by one-pot solvo-thermal method, and both exhibit spin crossover property.
The resulting trigonal-bipyramidal (TBP) cluster complexe (1), consisting of three Fe(II) center in the equatorial positions and two Fe(II) centers in the axial positions respectively, and both exhibit different properties. Among them, the equatorial position Fe(II) metal centers remain high spin in all temperature range; but the equatorial ones show spin-crossover property while changing the temperature. Our combined susceptibility and crystallographic measurements have demonstrated that spin crossover in (1) is kinetically slow, with the compound becoming trapped in a metastable mixed-spin state when cooled from room temperature at “normal” rates. And in approximately 100 % yield by rapidly quenching the sample to 5K, where the Fe(II) metal centers at axial positions reveal metastable high spin state (HS-2q), which convert slowly to a second, thermodynamically stable LS-2q phase upon annealing while warming up to about 150K. Slower cooling from room temperature affords the thermodynamic LS state directly.
The crystal structure of (2) has been derived in the different spin states: the high-temperature state (300K), below the incomplete spin transition low-temperature state (25K), and both are monoclinic space group P21/c. The FeII metal center is octahedrally coordinated by a bidentate ligand abpt and two bis-bidentate bpt- ligand, and the infinite one-dimensional zig-zag chain along the c axis is linked by bis-bidentate ligand bpt-. The results of temperature-dependent magnetic susceptibility measurements (5~300 K), and the single crystal X-ray diffraction studies (300K and 25 K) have exhibited that (2) undergoes the thermally induced spin transition HS→LS (SCO). The χMT(T) dependence shows in the range 110~75K gradual SCO. Below 75K the transition is finished and 60% of the HS fraction is present in the sample. The HS→LS transition is accompanied by a shortening of the Fe-N bonds of 0.1 Å. The LIESST phenomenon is observed with 532nm laser at 5K for (2), and the electronic configuration changes are characterized by XAS and SQUID.
Subjects
spin crossover
inorganic metal complex
metal cluster
Type
thesis
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