https://scholars.lib.ntu.edu.tw/handle/123456789/178156
標題: | 偶氮三唑為橋基之鐵二價一維、二維、三維結構與磁性研究 Structural and magnetic studies of atr (trans-4,4 -azo-1,2,4-triazole)-based 1-D、2-D、3-D frameworks |
作者: | 何維倫 Ho, Wei-Lun |
關鍵字: | 自旋交叉;spin crossover | 公開日期: | 2006 | 摘要: | 利用相同試劑不同反應條件得到一維及三維的錯合物討論結構與磁性表現。一雙牙基配基atr(trans-4,4`-azo-1,2,4-triazole)在不同條件下與鐵(Ⅱ)形成一維或三維錯合物,在一維結構中金屬鐵以兩個配位水和兩個單配位atr及兩個橋配位atr均以對位形式形成六配位錯合物,分子式為[Fe(atr)2(μ-atr)(H2O)2](BF4)2.4H2O,三維結構中以六個橋配位的atr配基形成六配位錯合物分子式為[Fe(μ-atr)3](BF4)2.2H2O,一維錯合物經加熱之後經由固態反應轉變為三維錯合物,原本的順磁性一維錯合物轉變為具有自旋交叉的三維錯合物,並利用一維及三維單晶結構可以解釋轉變的行徑。 三維自旋交叉錯合物是一相互連扣的結構,結構中具有三角形的通道其中容納了陰離子及結晶水,除了在高低溫時分別測得高低自旋對的結構外,由磁性測量可知結晶水脫去前後Tc相差了5K,可得知溶劑的存在與否對磁性上反轉溫度也有些微的影響;另外比較不同陰離子對磁性的影響時,可發現當陰離子為BF4-時自旋轉換溫度Tc為285K,相較於陰離子為ClO4-的自旋交叉錯合物Tc=265K高出20K,兩個化合物結構中唯一差別只有陰離子尺寸大小不同,但此差異使得磁性表現不同:ClO4-變溫磁性具明顯兩階段式磁性變化,BF4-則幾乎為連續性的磁性變化,本文中將探討結構與磁性的關係並以X光吸收光譜為輔助工具。 另外以甲基加成之atr二維鐵(Ⅱ)錯合物,鐵以兩個橋配位dmatr及兩個橋配位4,4-bipyridine及兩個NCS-以對位形式形成六配位錯合物,分子式為Fe(μ-dmatr)( μ-4,4-bipyridine)(NCS)2,由差是熱分析的結果可知在190~170K有一個結構相變,室溫時Z=1(鐵在反轉中心上)低於120K之結構Z=2(鐵不在反轉中心上),此二維錯合物具有微弱的鐵磁作用。 New iron(Ⅱ) coordination polymers, 1-D {[Fe(atr)2(μ-atr)(H2O)2] (BF4)2.4H2O}n (atr = trans-4,4’-azo-1,2,4-triazole), 2-D {Fe(μ-admtr) (μ-4,4’-bipyridine) (NCS)2}n (admtr= trans-4,4’-azo-3,5-dimethyl- 1,2,4-triazole) and 3-D {[Fe(μ-atr)3](BF4)2.2H2O}n have been synthesized and characterized. The crystal structure of 1-D and 3-D compounds have similar formula ,but contain two types of coordination: In 1-D compound the coordination of Fe contains two water, two terminal atr ligands ,and one bridging atr ligand, while in 3-D compound the metal coordination contains three bridging atr ligands between iron centers, resulting in a interpenetrated structure. Powder X-ray Diffraction of dehydrated 1-D compounds shows that it actually turns into 3-D structure, which is confirmed by the corresponding magnetic behavior being changed from paramagnetic to a spin crossover at 290K. We can also presume that the path of structural transformation from the 1-D and 3-D crystal structure. In another 2-D structure, the Fe coordination contains one methyl-substituted atr bridging ligand, one 4-4’-bipyridine bridging ligand ,and two NCS anions. The 2-D compound shows a structural phase transition at 105K. At room temperature, the iron is at the center of inversion (Z=1, in P-1), while at 120K, it is not (Z=2, in P-1) with c-axis doubled. The SQUID measurement indicates that there is a weak ferromagnetic interaction below 50K. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/51861 | 其他識別: | zh-TW |
顯示於: | 化學系 |
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