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Charge Density Study of a Spin Crossover Complex, trans-[Fe(abpt)2(NCS)2], a Mixed High Spin and Low Spin State
No full text多相晶體trans-[Fe(abpt)2(NCS)2] phase D之晶體結構中，存在兩個不對稱相關的單核分子；兩分子個別以鐵為對置中心，其一Fe原子會隨溫度降低而有自高自旋 (S=2)到低自旋狀態 (S=0)的自旋轉換現象(Tc=162 K)；另一Fe'原子則在量測的溫度範圍維持者高自旋的順磁狀態。兩個單核分子主要的差別在於配位基abpt(abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole)上的平面度；介於未配位的吡啶(pyridine)和疊氮基(triazole)之間的雙面角(dihedral angle)在低溫結構(90 K)分別為6.2度(Fe)及20.1度(Fe')。
由於兩個分子在低溫下的電子組態十分不同，我們利用X-ray單晶繞射技術及DFT理論計算來研究其電子密度的分布。經過電子密度拓樸分析研究，我們可以觀察到在兩個分子間，中心金屬d電子軌域分佈的不同；Fe由於處在低自旋狀態所以在二次電子微分(Laplacian)圖中呈現非球性對稱分佈，Fe'則處於高自旋狀態所以二次電子微分(Laplacian)圖呈現較為球形對稱分佈。理論計算的結果相當符合實驗所得到的結果。
為了瞭解兩分子在低溫下呈現不同磁性及結構的成因，我們利用DFT理論計算的方式觀察其在熱力學上的不同；更進一步的，我們可以粗估其自旋轉換發生的溫度(spin-flip temperature)。由於配位基abpt的平面度在兩分子中存在一定的差異，我們試圖以費米孔洞分析去了解兩分子中兩芳香環上π電子共振的不同。此外，我們可以觀察雙面角的改變對中心金屬和配位氮距離影響。最後，我們利用ADF程式模擬出低自旋-低自旋(LS-LS)的結構，試圖以能量及結構上的觀點去了解磁性轉換的關係。A polymorph D of the complex trans-[Fe(abpt)2(NCS)2], (abpt = 4-amino-3,5 bis(pyridine-2-yl)-1,2,4-triazole)was synthesized and structurally characterized. There are two unique mononuclear molecules in the crystal lattice, one (Fe) undergoes a gradual thermal spin transition from high spin (HS) to low spin (LS) state around 162 K, while the other (Fe') remains in HS at the temperature range of 300-2K. The main difference in these two molecules is the planarity of the abpt ligand; the dihedral angle between the triazole ring and the uncoordinated pyridine ring is 6.2 and 20.1º for Fe and Fe' complex respectively.
In order to understand the differences in electronic density distribution between these HS and LS states, trans-[Fe(abpt)2(NCS)2] polymorph D is chosen to be the ideal case to investigate the charge density using single crystal X-ray diffraction at 90 K. The electron density can also be calculated by DFT calculation. Through the topological analysis on charge density derived from both experimental measurement and quantum calculation, we are able to demonstrate the apparent differences in the environment of metal ion in two states. Furthermore, the d-orbital populations at HS (Fe) and LS (Fe') states can also be derived. The agreement between the experiment and theory is reasonably good. The relationship between the planarity of the ligand, abpt, and the π electron conjugation is depicted in terms of Fermi-hole distribution.
The difference of ~0.2Ǻ in Fe–N distance is often observed between HS and LS states. The significant difference in the intra-ligand dihedral angle in this case is also highly correlated with the magnetic behaviour. A few models based on such consideration are calculated to rationalize the HS-LS transition. The energies of HS-HS; HS-LS and LS-LS pairs are computed accordingly; the absence of LS-LS case in this compound can be realized. The spin-flip temperature can be predicted.目錄
中文摘要 Ⅰ
英文摘要 Ⅱ
目錄 Ⅲ
表目錄 Ⅴ
圖目錄 Ⅶ
第一章. 序 論 1
第二章. 原 理 5
2-1. X-ray單晶繞射 5
2-2. 多極模型與靜電荷分析 7
2-2-1. 單極精算 7
2-2-2. 多極精算 8
2-2-3. 淨電荷分析 9
2-3. 量子理論計算原理 10
2-3-1. HF-SCF簡介 10
2-3-2. Ab initio Calculation by Density Functional Theory 12
2-3-3. 量子化學計算中的基底函數組 15
2-3-4. 費米孔洞函數(Fermi-hole distribution)16
2-4. 拓樸學分析原理 17
2-4-1. Atoms in Molecules Theory 17
2-4-2. 臨界點的定義 19
2-4-3. 原子空間和鍵結路徑(atomic basin & bond path) 21
2-4-4. vs. 化學鍵 22
第三章. 自旋交叉錯合物[Fe(abpt)2(NCS)2] phase D的結構探討 24
3-1. 實驗方法 24
3-1-1. 合成與養晶 24
3-1-2. X-ray繞射實驗 24
3-1-3. 吸收校正 25
3-1-4. 變溫磁性量測 28
3-2. 結構解析 29
3-2-1. 室溫及低溫結構討論 29
3-2-2. [Fe(abpt)2(NCS)2] polymorph A、B、C、D結構之比較 37
3-3. 量子理論計算 39
3-3-1基底函數之選擇 40
3-3-2. trans-[Fe(abpt)2(NCS)2]的單點計算及幾何優選
及[HS-HS]、[HS-LS]、[LS-LS]相對能量及結構比較 41
3-3-3. 配位基雙面角的改變對[Fe(abpt)2(NCS)2]磁性改變影響和[HS-HS]、[HS-LS]、[LS-LS]相對能量及結構比較 42
3-3-4. 變溫紅外線光譜研究實驗數據與理論計算比較之研究 45
3-3-5. 理論計算觀察Entropy在室溫及低溫隨自旋轉換變化 48
第四章. 自旋交叉錯合物[Fe(abpt)2(NCS)2]的電荷密度分析 52
4-1. 多極模型精算 52
4-2. 拓樸學分析 53
4-2-1. 剩餘電子密度 53
4-2-2. Fe-N鍵結電子密度拓樸學分析 55
4-2-3. 淨電荷分佈和d-軌域電子分佈(d-orbital population) 58
4-2-4. 電子密度分佈之理論計算 61
4-3. 費米孔洞分析(Fermi-hole Distribution Analysis) 65
第五章. 結論 69
參考文獻 70
附錄 7
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The "tz'u" of Ouyang Hsiu
No full textOuyang Hsiu is well-known as a historian and a prose writer. His accomplishment as a "shih" poet has also been noted and confirmed. His "tz'u", however, remains relatively neglected. The object of this thesis is to introduce the "tz'u" of Ouyang Hsiu, to examine the qualities of these works, and to evaluate their significance in the history of "tz'u" development. Since biographical information on Ouyang Hsiu is readily available in English, I have provided in the introduction only a brief summary of Ouyang's life and his various achievements. Apart from 54 poems which are also attributed to other Sung poets, the authenticity of 73 "tz'u" (about one-third of his total corpus) in Ouyang's collection has been a question of doubt and heated dispute. In Chapter I, the different editions of Ouyang Hsiu's "tz'u" are mentioned and compared. The historical, literary and biographical factors which surround the suspicion of fabrication are presented and analysed. Chapter II is a selection of 43 "tz'u" by Ouyang Hsiu, translated and followed by annotations. This selection presents a spectrum of the various styles of Ouyang Hsiu's "tz'u". It is intended to give the readers a personal experience of the poet's works before their discussion. Chapter III is the critical study. Since much work has been done in English on the subject of "tz'u" as a genre, I have only given cursory-information on the background of "tz'u" and its development prior to Ouyang's time. The poems are classified into four major groups for discussion: "tz'u" which are typical of the "tz'u" tradition; "tz'u" which are written mainly for self-expression; "tz'u" composed strictly for entertainment; and, lastly, the 73 "tz'u" of doubtful authorship. In each case, I have contrasted Ouyang's "tz'u" with the works of other poets. I have also compared his "tz'u" with his "shih" and prose works. If the beauty of a poem is better felt by reliving the poet's creative experience than by tearing its ingredients apart for inspection, this is particularly the case with Ouyang's works. Since he excels more in artistic expression than technical innovations, I have concentrated this study mainly on interpreting his works and relating my own feelings about them. But I have also included a general survey of the technical aspects of his "tz'u".Arts, Faculty ofAsian Studies, Department ofGraduat
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