四-/五-/六配位雙亞硝基鐵錯合物之光譜鑑定及 氧化還原探討

Spectroscopic Characteristics of {Fe(NO)2}9/10 Four-/Five-/Six-Coordinate Dinitrosyl Iron Complexes (DNICs) and Insight into Redox Sibling of [{Fe(NO)2}9-L]+, [{Fe(NO)2}10-L] and [{Fe(NO)2}10-L−]− DNICs

施偉志(Wei-Chih Shih)

指導教授 ： 廖文峯

國立清華大學/理學院/化學系/博士(2015年)

摘要

相較於具有電子自旋光譜訊號為g = 2.03之四面體結構{Fe(NO)2}9雙亞硝基鐵錯合物[(L)2Fe(NO)2]− (L= RS, NR)，五、六配位之{Fe(NO)2}9 雙亞硝基鐵錯合物[(iPrPDI)Fe(NO)2][BF4] (3-iPrPDI)、[(PyImiS)Fe(NO)2] (5-PyImiS)及 [(TPA)Fe(NO)2][BF4] (1-TPA)其訊號偏移至g = 2.015～2.018。 Fe K-edge X光吸收光譜之結果可知其1s→ 3d 軌域躍遷能量：7113.4～7113.6 eV皆坐落於四配位的{Fe(NO)2}9 (7113.4–7113.8 eV)之範圍內，顯示鐵金屬的躍遷能量會隨著配位環境不同而改變。一般而言，以雙亞硝基鐵錯合物之鐵為主體的氧化反應，可在紅外線吸收光譜觀察到平均約為 ΔvNO 100～146 cm-1的位移，然而在{Fe(NO)2}10 2-iPrPDI 氧化生成{Fe(NO)2}9 3-iPrPDI時，因為從四配位變為五配位導致紅外線光譜的位移僅有85 cm-1。五、六配位的雙亞硝基鐵錯合物之IR ΔNO 分別約為70 cm-1 和100 cm-1，然而四配位雙亞硝基鐵錯合物僅約ΔNO 40~60 cm-1。因此，結合電子自旋光譜和紅外線吸收光譜可以協助判斷雙亞硝基鐵錯合物之配位數。[Et4N][(NO)2Fe(MeDAB)] (9-DAB)、[Et4N][(NO)2Fe(MeDAB)] (9-MeDAB)和[Et4N][(NO)2Fe(BIAN)] (9-BIAN)可由[(NO)2Fe(MeDAB)] (6-DAB)、[(NO)2Fe(MeDAB)] (6-MeDAB)及[(NO)2Fe(BIAN)] (6-BIAN)的還原生成。由於還原並非發生於鐵原子上，因此其紅外線光譜的位移僅約為 82 cm-1。一般而言，配位基α-diimine被還原生成自由基之電子自旋光譜訊號為 g = 2.0023～2.013，然而 9-DAB, 9-MeDAB和 9-BIAN所得到電子自旋光譜訊號為 g = 1.998，顯示此還原反應並非單純發生在配位基上。6-DAB、 6-MeDAB 和 6-BIAN的氧化所獲得之紅外線光譜的位移(ΔNO ≈ 80 cm-1)和電子自旋光譜訊號 (g ≈ 2.020)與2-iPrPDI氧化生成3-iPrPDI的反應具有類似的紅外線光譜位移和電子自旋光譜，因此推測10-DAB, 10-MeDAB和10-BIAN為五配位雙亞硝基鐵錯合物。

關鍵字

雙亞硝基鐵錯合物 ； 電子自旋光譜 ； 電子結構

並列摘要

Compared to the tetrahedral {Fe(NO)2}9 dinitrosyliron complexes (DNICs) [(L)2Fe(NO)2]− displaying EPR signal g = 2.03, the newly synthesized six-/five-coordinate {Fe(NO)2}9 DNICs [(TPA)Fe(NO)2][BF4] (1-TPA), [(iPrPDI)Fe(NO)2][BF4] (3-iPrPDI) and [(PyImiS)Fe(NO)2] (5-PyImiS) exhibit the distinct EPR signal g = 2.015–2.018. The Fe K-edge pre-edge energy (7113.4–7113.6 eV) derived from the 1s→3d transition in the octahedral and square-pyramidal environment of the Fe center, falling within the range of 7113.4–7113.8 eV for the tetrahedral {Fe(NO)2}9 DNICs, implicates that the iron cores of DNICs 1-TPA, 3-iPrPDI and 5-PyImiS are tailored to minimize the electronic changes accompanying changes in coordination geometry. 3-iPrPDI was synthesized from oxidation of 2-iPrPDI, the average shift ΔvNO 85 cm-1 is less than that of Fe-based oxidation of {Fe(NO)2}10 (ΔvNO 100-146 cm-1) due to the change in coordination number. Five-/six-coordinated DNICs display the larger separation of NO stretching frequencies (101 cm-1 (1-TPA), ΔNO = 73 cm-1 (3-iPrPDI) and 72 cm-1 (5-PyImiS), respectively) than those of classical tetrahedral DNICs (ΔNO ≈ 45-60 cm-1). Combination of IR and EPR was demonstrated to serve as an efficient tool to characterize and discriminate four-/five-/six-coordinated DNICs.
The characteristic crystal structures revealed that the one electron reduction of Fe(NO)2}10 complexes [(NO)2Fe(MeDAB)] (6-DAB), [(NO)2Fe(MeDAB)] (6-MeDAB) and [(NO)2Fe(BIAN)] (6-BIAN) to yield [Et4N][(NO)2Fe(MeDAB)] (9-DAB), [Et4N][(NO)2Fe(MeDAB)] (9-MeDAB) and [Et4N][(NO)2Fe(BIAN)] (9-BIAN) occurred on α-diimine. The average shift ΔvNO ≈ 82 cm-1 was observed from the reduced reaction, and 9-DAB, 9-MeDAB and 9-BIAN displayed almost similar characteristic vNO (~ 1640 and 1590 cm-1). EPR measurements of 9-DAB, 9-MeDAB and 9-BIAN showed the EPR g value at 1.998 that deviates from typical mono-anionic α-diimine radical at g = 2.0023–2.013. X-ray structures of [K-(THF)3][(NO)2Fe(DAB)] (7-DAB), [K-(THF)3][(NO)2Fe(MeDAB)] (7-MeDAB) and [K-(THF)3][(NO)2Fe(BIAN)] (7-BIAN) display the interaction of K+ and the high nucleophilicity of NO. Addition of 18-crown-6-ether into solution of 7-DAB, 7-MeDAB and 7-BIAN led to the formation of [K-18-crown-6-ether][(NO)2Fe(DAB)] (8-DAB), [K-18-crown-6-ether] [(NO)2Fe(MeDAB)] (8-MeDAB) and [K-18-crown-6-ether-(THF)2][(NO)2Fe(BIAN)] (8-BIAN), respectively. Oxidation of 6-DAB, 6-MeDAB and 6-BIAN producing five-coordinate [(NO)2Fe(MeDAB)(CH3CN)][BF4] (10-DAB), [(NO)2Fe(MeDAB)(CH3CN)][BF4] (10-MeDAB) and [(NO)2Fe(BIAN)(CH3CN)][BF4] (10-BIAN) show the average shift ≈ 80 cm-1 to higher wavenumber (separation of NO stretching frequencies (vNO = 77 cm-1) and EPR g = 2.020 for 10-DAB (ΔvNO = 82 cm-1 and g = 2.019 for 10-MeDAB; 80 cm-1 and g = 2.019 for 10-BIAN).
Reaction of 9-DAB (9-MeDAB and 9-BIAN) and HBF4 yield one-electron oxidized product 6-DAB, 6-MeDAB and 6-BIAN, respectively. Five-coordinated DNICs (10-DAB, 10-MeDAB and 10-BIAN) were synthesized from treatment of 6-DAB, 6-MeDAB and 6-BIAN with HBF4 in CH3CN solution.

並列關鍵字

Dinitrosyl Iron Complexes ； Electronic paramagnetic Resonance ； Electronic Structure

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