Structural and Magnetic Properties of Dinuclear Metal Complexes with a Tetradentate bpt- Ligand
Date Issued
2009
Date
2009
Author(s)
Chen, Szu-Miao
Abstract
With a tetra-dentate ligand bpt ( = 3,5-bis(pyrid-2-yl)-1,2,4-triazole ), the dinuclear double bridging complexes [Fe2(μ-bpt)2(NCS)2(X)2] ( X = CH3OH (1-1)；py (1-2) ); the spin crossover one-dimensional ladder type dinuclear complexes {FeII(μ-bpt)(NCS)}2(μ-X)?yMeOH] n ( X = 4,4’-bpy, y = 1 (2-1)，y = 0 (2-2)；pyrazine，y = 0 (2-3) ) have been synthesized by one-pot solvo-thermal method. In addition, a couple of one dimensional helical two metal complexes, [MII(μ-bpt)(μ- COOC5H4N)?1/2 H2O]n ( M = Fe (3-1)；Mn (3-2) ) have also been synthesized.ased on the Fe-N bond lengths and the magnetic measurements of complexes (1-1) and (1-2), the Fe(II) in these complexes are at high spin (HS) state at 300 K. The temperature dependent magnetic susceptibility measurement reveals that two complexes steady stay at HS state. Interestingly, the complex (1-2) has a light induced spin transition from HS to LS at 14K using 808 nm radiation, which exhibits a reverse-Light Induced Electronic Spin State Trapping ( reverse-LIESST ) phenomenon.he one-dimensional dinuclear complexes {FeII(μ-bpt)(NCS)}2(μ-X)?yMeOH]n exhibit an abrupt spin transition at 130 K for (2-1) and (2-3), but at 156 K for (2-2). Two FeII centers are chelated by two tetradentate bpt- ligands equatorially, the one-dimensional dinuclear zigzag chain is linked by axially bridged ligand pyrazine(2-3) or 4,4’-bipy( (2-1) and (2-2) ). Due to the center of symmetry, there is only one unique Fe site in the structure. As the temperature is lowering below the spin transition temperature, the spin state of Fe centers of di-nuclear species could induce various changes in spin state. For example, a [LS–LS] pair for (2-3) and [HS-LS] for (2-1) (2-2) dinuclear complexes will be resulted. The LIESST phenomenon is observed with proper light irradiation at T ≤ 25 K for these complexes. All the structural and electronic configuration changes are characterized by XRD, XANES, IR spectra and SQUID. The LIESST process is also monitored in the same way.dditional one dimensional helical complexes, [MII(μ-bpt)(μ- COOC5H4N)?1/2 H2O]n ( M=Mn, Fe ), are crystallized in a tetragonal space group I41/a with the metal centers linked each other with one bpt- and one isonicotinic acid, which forms an infinite helical chain along a screw axis 41. It is iso-structure for both metal ions, the metal ion is octahedrally coordinated by four nitrogen atoms of bpt- and two oxygen atoms of isonicotinic acid, [FeN4O2]. The bond lengths of Fe-N and Fe-O at 300 K indicate that FeII is at its high spin state. However, this Fe chain complex displays a distinct ferromagnetic interaction between the FeII centers. The hydrogen bonds between water molecules and the ligands of the chain may play important role on the inter-chain interactions. On the contrary, the Mn(II) complex displays a typical paramagnetic character through the structure is exactly the same as that of Fe one. Detail structure descriptions of the chain complexes will be given. The comparison on the magnetic properties of these two metal chain complexes will be discussed.
Subjects
spin crossover
magnetic coupling
dinuclear
Type
thesis
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