| Summary: | 博士 === 國立清華大學 === 化學系 === 103 === 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.
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