四螯合配位基bpt-之五核及一維鏈金屬錯合物結構及磁性探討

Structure and Magnetic Properties of Pentanuclear Metal Cluster and 1D chain Metal Complexes with a tetradentate bpt- Ligand

黃信嘉(Hsin-Chia Huang)

指導教授 ： 王瑜

國立臺灣大學/理學院/化學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.00500

摘要

利用溶劑熱（solvo-thermal method）單一步驟合成法，以4-amino-3,5 -di-2-pyridyl-1,2,4triazole（abpt）做為主要配位基與亞鐵金屬在高溫高壓下進行反應，成功合成出兩類亞鐵自旋交叉錯合物，分別是五核亞鐵金屬簇錯合物[{FeⅡ(μ4-bpt)3}2FeⅡ3(μ3-O)][(ClO4)2] (1) （bpt = 3,5-di-2-pyridyl-4-H-1,2,4triazole）與一維鋸齒（Zig-Zag）鏈狀錯合物{[FeⅡ(μ4-bpt)(abpt)](ClO4)}n (2)。
五核亞鐵金屬簇錯合物(1)是由赤道面（equatorial）的三個亞鐵與軸位置（axial）兩個亞鐵所組成的三角雙椎構形（trigonal bipyramidal, TBP），其中，赤道面三個亞鐵在任何溫度條件下皆呈現高自旋態，而軸位置兩個亞鐵室溫時為高自旋態（HS-1）且具有自旋交叉性質，經由變溫磁化率數值，知道軸位置亞鐵具有動力學上緩慢（kinetically slow）之自旋交叉性質；以一般的速度（2K/min）從室溫降溫，會被捕捉在介穩混自旋態（metastable mixed-spin state），在略低於轉換溫度發生退火（annealing）之現象，緩慢轉變為熱力學穩定之低自旋態；但快速降溫至5K，可得到接近100%之高自旋態（HS-2q），並且經由升溫在150K得到熱緩解低自旋態（LS-2q）。由300K室溫單晶結構，錯合物(1)單晶為單斜晶系(Monoclinic)，空間群為C2/c，其軸位置的平均Fe(ax)-N鍵長為2.206 Å，為典型高自旋態；25K淬冷(quench)態單晶結構解析，平均Fe(ax)-N鍵長為2.196 Å，與室溫高自旋態相近，為典型高自旋態鐵氮鍵長；而150K熱緩解單晶結構解析，仍為單斜晶系，空間群變為P21/c，平均Fe(ax)-N鍵長為1.993 Å，為典型低自旋態鐵氮鍵長。
錯合物(2)的單晶屬於單斜晶系，空間群為P21/c，金屬間以四螯合配位基bpt-串接，沿著c軸無限延伸成為一維鋸齒鏈。亞鐵核分別由配位基bpt-的四個氮原子及abpt的兩個氮原子配位形成[FeN6]八面體配位環境，室溫的平均Fe-N鍵長2.19 Å，為典型高自旋態鐵氮鍵長。由磁性量測，(2)具有不完全（incomplete）自旋交叉性質，轉換點溫度Tc為97K，由磁性數據推算，在低於轉變溫度，約40%轉換為低自旋態。超低溫25K單晶結構，單晶為單斜晶系，空間群為P21/c，而平均Fe-N鍵長2.09 Å，介於典型高低自旋態鐵氮鍵長之間，與磁性量測之部分結果吻合。當溫度5K時，使用適當波長的雷射光源（532nm）可將亞鐵配位中心由低自旋態激發至高自旋態，具有光激發電子自旋捕捉性質（LIESST），透過磁性及光譜量測（XANES），可以了解激發自旋捕捉現象。

關鍵字

自旋交叉 ； 無機金屬撮合物 ； 金屬簇

並列摘要

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.

並列關鍵字

spin crossover ； inorganic metal complex ； metal cluster

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