- 學位論文
四螯合配位基bpt-雙核系列金屬錯合物的結構及磁性探討
Structural and Magnetic Properties of Dinuclear Metal Complexes with a Tetradentate bpt- Ligand
摘要
利用四螯合配位基bpt( bpt = 3,5-bis(pyridin-2-yl)-1,2,4-triazole )以特殊的溶劑熱單一步驟合成法，成功合成出雙配位基跨接的雙核錯合物[Fe2(μ-bpt)2(NCS)2(X)2] ( X = CH3OH (1-1)；py (1-2) )、一維曲折型鏈狀雙核錯合物{FeII(μ-bpt)(NCS)}2(μ-X) . yMeOH] n ( X = 4,4’-bipy，y = 1 (2-1)，y = 0 (2-2)；pyrazine，y = 0 (2-3) ) 及一維螺旋鏈狀錯合物 [MII(μ-bpt)(μ- COOC5H4N).1/2 H2O]n ( M = Fe (3-1)；Mn (3-2) )。 錯合物(1-1)的X-ray單晶結構解析Fe-N鍵長是2.292(3) Å、2.094(3) Å，錯合物(1-2)為2.110(2) Å及2.321(2) Å，均為典型高自旋態；量測變溫磁化率數值，知道兩錯合物在60-400 K溫度範圍內穩定存在高自旋態。有趣的是，在低溫時錯合物(1-2)高自旋態可被808 nm.雷射光源反激發至低自旋態，具有逆光激發電子自旋捕捉性質( reverse-LIESST )。 而一維雙核錯合物{FeII(μ-bpt)(NCS)}2(μ-X).yMeOH] n 具有不一樣的自旋交叉轉換特性，錯合物(2-1)與(2-3)的溫度轉換點在130 K，而錯合物(2-2)在156 K。此系列錯合物的FeII配位中心，在赤道平面上被兩個四螯配位基"bpt"鉗合成雙核結構，軸向上以4，4’–聯吡啶( 4,4’-bipy )及吡嗪( pyrazine )跨接雙核結構而形成一維雙核曲折型鏈狀結構，結構中因為兩個FeII配位中心間有i對稱中心存在，所以最小不對稱單元中只有一個FeII存在，當溫度低於溫度轉換點時，Fe配位中心會從高自旋態轉變為低自旋態，錯合物(2-3)的自旋態為 [LS-LS]，而錯合物(2-1)(2-2)為[HS-LS]。當溫度低於25 K時，適當波長的雷射光源( 532 nm., power 10 mW cm-2 )可將低自旋態激發至高自旋態，具光激發電子自旋捕捉性質( LIESST )，透過X-光單晶繞射 、磁性及光譜量測( XANES 、IR 及SQUID )，可以更了解此激發自旋捕捉現象。 一維螺旋錯合物[MII(μ-bpt)(μ- COOC5H4N).H2O]n (M=Mn, Fe)的結晶空間群為I 41/a，金屬間以橋接配位基bpt及尼古丁酸( isonicotinic acid )串接起來，沿著41軸無限延伸成為一維螺旋鏈，兩金屬錯合物為共構物( iso-structure )。Fe(II)核由bpt上的四個氮原子及尼古丁酸的兩個氧原子配位成[FeN4O2]八面體配位中心，300 K時的Fe-N及Fe-O鍵長顯示Fe(II)為典型高自旋態，磁性量測顯示Fe(II)核間存在鐵磁作用力，且水分子與一維鏈間的氫鍵作用力扮演著重要角色。反觀同結構Mn(II)錯合物的磁性表現則為典型的順磁性，低溫時有反鐵磁作用力存在，論文中對其結構及磁性也會進行探討。
並列摘要
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. Based 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. The 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. Additional 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.